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Ethernet Reference GuideYour everyday Ethernet testing reference tool

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Following its introduction in the early 1970s, the Ethernet protocol for data networking has been characterized by ever-increasingpopularity and adaptation. In recent years, Ethernet has become the predominant network access protocol, now used in over 95%of all local-area networks.

With the advent of Gigabit Ethernet and 10 Gigabit Ethernet, this technology has matured and made its way from local-areanetworks to metropolitan-area networks, and now wide-area networks, challenging traditional transport protocols such asSONET/SDH and ATM.

This guide provides a detailed overview of Ethernet technology. It presents common Ethernet implementations in service-provider networks, the testing requirements to ensure reliable service, as well as installation and maintenance techniques.

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Table of Contents

Symbols Used in Illustrations ................................................3

1. Introduction ............................................................................................51.1 What is Ethernet? ..................................................................................51.2 Some History............................................................................................61.3 Ethernet in Carrier Networks ................................................................71.4 Ethernet Naming and Standards ........................................................8

1.4.1 802.3 Naming Convention ..................................................81.4.2 Evolution of Ethernet Standards ........................................9

2. Ethernet Nuts and Bolts ......................................................132.1 Ethernet Logical Specifications ........................................................132.2 Basic Ethernet 2 Frame ......................................................................14

2.2.1 Ethernet vs. 802.3 Frame Format ....................................152.2.2 Preamble and Start-of-Frame............................................152.2.3 Destination and Source Addresses ................................162.2.4 Type/Length ..........................................................................182.2.5 802.3 Logical Link Control Header ................................192.2.6 Snap Header ........................................................................20

2.3 Data Field................................................................................................212.3.1 Ethernet ..................................................................................212.3.2 IEEE 802.3............................................................................21

2.4 Frame Check Sequence ....................................................................222.5 Interframe Gap ......................................................................................222.6 Ethernet Frame Format Extensions ..................................................22

2.7 Ethernet Frame Tag ..............................................................................232.8 VLAN Tagging........................................................................................232.9 Traffic Priority ........................................................................................252.10 Frame Bursting ......................................................................................262.11 Jumbo Frames........................................................................................262.12 Ethernet Media Access Control ........................................................26

2.12.1 Half-Duplex Ethernet and CSMA/CD ............................262.12.2 Carrier Sense........................................................................272.12.3 Multiple Access ....................................................................272.12.4 Collision Detection ..............................................................27

2.13 CSMA/CD Transmission Flow ..........................................................282.13.1 Full-Duplex Ethernet ............................................................282.13.2 Flow Control..........................................................................282.13.3 Pause Frame Format ..........................................................292.13.4 Auto-Negotiation ..................................................................292.13.5 Link Aggregation ..................................................................30

2.14 10 Gigabit Ethernet..............................................................................312.14.1 Physical-Layer Specifications............................................31

3. Ethernet Applications..................................................................363.1 Ethernet in Local-Area Networks (LANs)........................................363.2 Ethernet in Access Networks ............................................................393.3 Ethernet in Metro Networks ..............................................................413.4 Ethernet in Wide-Area or Long-Haul Networks ............................413.5 Ethernet Service Types........................................................................41

3.5.1 E-Line Variants ......................................................................443.5.2 E-LAN Variants......................................................................45

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3.6 Ethernet Infrastructures ......................................................................453.6.1 Native Ethernet ....................................................................463.6.2 SONET/SDH........................................................................463.6.3 Native Ethernet vs. SONET/SDH: Pros and Cons ........463.6.4 Resilient Packet Ring (RPR) ............................................473.6.5 ATM ........................................................................................483.6.6 IP/MPLS ................................................................................48

4. Introduction to Installation and Provisioning............................................524.1 Quality and Performance ....................................................................524.2 Ethernet Performance Verification ....................................................52

4.2.1 Test Configurations..............................................................534.2.2 RFC 2544 tests ..................................................................55

4.3 Fiber Characterization..........................................................................614.4 BERT over Ethernet ............................................................................62

4.4.1 GigE and 10 GigE BERT over Dark Fiber and PONs ......634.4.2 GigE and 10 GigE BERT over a DWDM Network ......63

4.5 Ethernet Service Acceptance Testing ............................................64

5. Commissioning Ethernet for Voice-over-IP and Video-over-IP Deployment ................................665.1 Essential Testing Techniques ............................................................665.2 Simulating the Customer’s Network ................................................665.3 Simulating Real-World Traffic Patterns ............................................675.4 Performing Unidirectional Testing ....................................................68

6. Monitoring Ethernet Networks ....................................716.1 Ethernet Quality-of-Service Assurance............................................71

6.1.1 Performances and Traffic Monitoring ..............................716.2 Remote Testing for Ethernet in the First Mile Deployments ..........72

6.2.1 Access Line Management Using the 802.3ah Standard ............................................73

6.2.2 Demarcation Devices ..........................................................746.2.3 Ethernet Test-Heads ............................................................746.2.4 Management Software........................................................76

7. Glossary ..................................................................................................78

8. Acronyms Index ..............................................................................92



Symbols Used in Illustrations

Router DWDM Filter

ATM or Ethernet Switch Multilayer Switch

Workgroup Switch Metro DWDM Add/Drop Multiplexer

SONET/SDH Add-Drop Multiplexer (ADM) DWDM Ringor Multiservice Provisioning Platform (MSPP)


Introduction



1. Introduction

1.1 What is Ethernet?Since its invention in the 1970s, Ethernet has gradually become the world’smost widely used network technology. In local-area networks (LANs),Ethernet has largely replaced all other LAN standards such as Token Ring,ARCNET (Attached Resource Computer network), and FDDI (FiberDistributed Data Interface). More recently, Ethernet has moved intometropolitan and wide-area networks (MANs and WANs) as well.

Ethernet is a frame1-based computer networking technology that has beenstandardized by the Institute of Electrical and Electronics Engineers

(IEEE, pronounced “I-triple-E”). The Ethernet standards define cabling and signaling standards for the physical layer of the Open SystemsInterconnection2 (OSI) model, as well as frame formats and protocols for the data-link layer. Although Ethernet has become closely associated with Internet Protocol (IP), it can carry almost any other networking protocol used within LANs.

In a LAN, Ethernet carries frames of data between desktop computers, servers, printers and other devices located within a small area, usually insidea single building. Devices on a LAN are interconnected using coaxial cable, special categories of twisted-pair wiring, fiber-optic cable or wireless(radio or infrared) connections. The most popular Ethernet LAN standard (10Base-T) supports a data transmission rate of 10 Mb/s. Newer versionscalled Fast Ethernet and Gigabit Ethernet support data rates of 100 Mb/s and 1 Gb/s, respectively.

In a MAN or WAN, fiber-optic cables carry Ethernet frames over greater distances and at speeds up to 10 Gb/s.

Virtual LANs (VLANs) are used to provide a secure virtual network to each customer, allowing geographically dispersed users to communicate asif they were in the same building (see Figure 1.2). Initially, the VLAN was created to segregate a single LAN domain into multiple virtual LANs.It was intended to limit the spread of broadcasts between VLANs.

1 A frame is a unit of data that is transmitted between network points; it includes a data payload as well as addressing and protocol control information.2 The Open Systems Interconnection (OSI) Reference Model is a seven-layered description of how messages should be transmitted between any two points in a telecommunication network.

BusinessLAN

Central OfficePoint of Presence (POP)

Home

WAN MAN Access

Hundreds orthousands of km

Ten orhundreds of km

Several km

Figure 1.1 – LAN, Access, MAN and WAN networks



1.2 Some HistoryEthernet was invented at the Xerox Palo AltoResearch Center in the 1970s by Dr. Robert M.Metcalfe. Originally known as experimentalEthernet, it was designed to supportresearch on the “office of the future,” whichincluded one of the world's first personalworkstations, the Xerox Alto. Ethernet thenran at approximately 3 Mb/s over tapped, half-inch-thick coaxial cable. Figure 1.2shows a drawing used by Dr. Metcalfe topresent Ethernet to the National ComputerConference in June 1976.

Ether refers to luminiferous ether, postulated in the nineteenth century as an all-pervading,infinitely elastic, massless medium of propagation of electromagnetic waves. Ethernet was so-named to describe the way that cabling could similarly carry datathroughout the network.

The first formal specification for Ethernet was published in 1980 by DEC-Intel-Xerox (DIX).A second version of the DIX standard was published two years later, and became knownas Ethernet 2. In 1983, the IEEE published its version of the LAN standard entitled IEEE802.3 Carrier-Sense Multiple-Access with Collision Detection (CSMA/CD) AccessMethod and Physical-Layer Specifications. Standard 802.3 was based on Ethernet 2, the most significant difference being an altered frame format, and was designed to provideinteroperability between the two frame types on a single LAN.

Store

Store

OC-48 OC-48

OC-3

DWDMCustomer C

Customer C

Customer C

Customer CCustomer C

Customer ACustomer A

Customer A

Customer A

Customer A

Customer BCustomer B

Customer B


Figure 1.2 — Ethernet VLANs provide secure virtual networks to individual customers across a MAN

Figure 1.3 — Drawing used by Dr. Metcalfe to present Ethernet



IEEE 802.3 was also known as thicknet, since it specified 10 mm coaxial cable to connect devices in a bus topology. In 1985, the IEEE publishedthe 802.3a (thinnet) standard, which made it possible to use less expensive 5 mm coaxial cable, resulting in an immediate increase in popularity.

Since 1985, all Ethernet LAN equipment is built according to the IEEE 802.3 standard, although the vast majority of Ethernet frames sent still usethe DIX Ethernet 2 format. The differences between Ethernet 2 and IEEE 802.3 are subtle and are transparently managed by network equipment;the frame type is not a concern during practical use or testing.

1.3 Ethernet in Carrier NetworksEthernet is now the most widely deployed accesstechnology in carrier networks. In new installations,Ethernet access lines are outselling all other forms ofaccess combined. Ethernet is also carried throughoutMANs and WANs, either in its pure (native) form orcombined with other technologies.

What makes Ethernet so attractive? Why is it eitherreplacing, or being used in combination with, othertransport protocols and infrastructures such as ATM,frame relay, SONET/SDH, and CWDM/DWDM?

One reason is that the recent Ethernet standards, suchas Gigabit Ethernet (GigE), 10 Gigabit Ethernet (10 GigE) and the new IEEE 802.3ah standard forEthernet in the first mile, as well as emergingtechnologies such as the multiprotocol label switching(MPLS) and resilient packet ring (RPR), are helping to make Ethernet a reliable and economically viablecarrier-class transport technology.

Metro NetworkGigabit Ethernet

10/100Base-T

Access Network


10/100Base-T Access Network

Figure 1.4 — Ethernet is used throughout carrier networks



Due to economies of scale, Ethernet equipment has historically been more cost-effective than competing technologies. Manufacturers are nowoffering economic solutions for Ethernet switching and routing, virtual LAN (VLAN) services, MPLS, and IP forwarding, as well as traffic-management features that allow service providers to fulfill various service agreements. Ethernet services require less time for commissioning andprovisioning than legacy services, and can even be provisioned remotely, resulting in additional savings for service providers. Since almost all LANsuse Ethernet, they can easily be integrated with Ethernet-based carrier networks since Ethernet equipment performs bit-rate conversion andstatistical multiplexing.

Ethernet is flexible in that it can be used with many different infrastructures and protocols. Ethernet services can be offered over existing ATMarchitectures. In next-generation SONET/SDH networks, Ethernet frames can be encapsulated into Generic Framing Procedure (GFP) frames andtransported through SONET/SDH channels. Ethernet can also be transmitted in its native format over dark fiber or on a DWDM wavelength, or using free-space optics (FSO).

Other advantages of Ethernet include dynamic bandwidth commissioning (ability to increment bandwidth to subscribers on an as-needed basis)and a wide range of services based on Ethernet standards for wide-area networking (virtual private LAN, E-Line services, etc.). Ethernet serviceswill be described in detail in Chapter 3.

1.4 Ethernet Naming and Standards1.4.1 802.3 Naming Convention

Different physical implementations of Ethernet (rate, medium, etc.) follow a standard namingconvention developed within IEEE 802.3. Figure 1.5 illustrates the name format using10Base-T as an example. The first section refers to the speed of the transmission, the secondrefers to type of transmission, and the third refers to the type of medium used (T designatesan electrical medium, whereas X designates an optical medium).

Baseband signaling simply means that transmitted signals use the whole available bandwidthand are not modulated onto other carrier frequencies or time-lotted to share the bandwidth;i.e., one-at-a-time transmission. Baseband is the only standard used in Ethernet today.

LAN Speed, in Mb/s Physical Media Type

Base = Baseband

Base10 T

Figure 1.5 — 802.3 naming convention



1.4.2 Evolution of Ethernet Standards

Since the initial Ethernet standards were defined, newer IEEE 802.3x standards have evolved that have enhanced Ethernet’s performance andversatility. These are summarized in Table 1.1.

The 10Base-T standard represented a major advance as it allowed the use of inexpensive Category 3 unshielded twisted-pair (UTP) cable insteadof coaxial cable. It also allowed the devices to be connected in the shape of a star, rather than a bus topology making it much easier to install,manage, and troubleshoot the network. Some of these early rates and cabling standards are no longer in common use.

The 100Base-T standard increased data rates by a factor of 10 and was hence known as Fast Ethernet. Performance was again improved by afactor of 10 with the release of the 1000Base-T Gigabit Ethernet standard. Originally only available when using optical fiber or short-haul shieldedtwisted-pair (STP) cable, Gigabit Ethernet can now be carried over inexpensive Category 5/Category 5e UTP cable.

With the recent introduction of 10 Gigabit Ethernet, integration of LAN and WAN applications is greatly simplified. 10 GigE supports two physicalinterfaces at different rates: one for LANs at 10 times the rate of GigE (LAN PHY), and one at 9.585 Gb/s (WAN PHY); these are the same ratesas SONET/SDH-based transmission systems. The WAN rate, and its related frame enhancements, allow Ethernet traffic to be transparently carriedover OC-192 SONET or STM-64 SDH networks.

In 2004, the IEEE approved the 802.3ah specification for Ethernet in the first mile. This new standard has the largest scope of any IEEE 802.3standard and will give service providers a variety of flexible and cost-effective solutions for delivering Ethernet services in access networks.



Year Name EEE Speed Description Used?1983 10Base-5

(Thick Ethernet or Thicknet) 802.3 10 Mb/s 50 Ω; 10 mm coaxial cable; bus topology Not common

1985 10Base-2(Thin Ethernet or Thinnet) 802.3a 10 Mb/s 50 Ω; 5 mm coaxial RG58 cable; bus topology Not common

1990 10Base-T 802.3i 10 Mb/s 100 Ω Category 3 UTP; two-pair cable; Yesstar topology; 100 m link (switch to host)

1993 10Base-F (FL, FB, and FP) 802.3j 10 Mb/s 850 nm light over two multimode fibers Yes(Ethernet over Fiber)

1995 100Base-T(Fast Ethernet)

• 100Base-T4 802.3u 100 Mb/s 100 Ω; Category 3 UTP, four-pair cable No

• 100Base-TX 802.3u 100 Mb/s 100 Ω; Category 5 UTP, two-pair cable; Most common100 m link length (switch to host)

• 100Base-FX 802.3u 100 Mb/s 1300 nm light over two multimode fibers Yes

1997 Full-Duplex Ethernet 802.3x 10 and All applications(FDX) 100 Mb/s

1997 100Base-T2 802.3y 100 Mb/s 100 Ω; Category 3 UTP; two-pair cable No

1998 Virtual LANs (VLANs) 802.3ac Extensions to support VLAN tagging Yes

Table 1.1 — Main Ethernet standards



Year Name EEE Speed Description Used?1998 1000Base-X

(Gigabit Ethernet or GigE)

• 1000Base-SX 802.3z 1 Gb/s 850 nm light over multimode fiber Yes

• 1000Base-LX/HX 802.3z 1 Gb/s 1300 nm light over multimode or singlemode fiber Yes

• 1000Base-CX 802.3z 1 Gb/s Short-haul copper STP cable; 100 m link Yeslength (switch to host)

1999 1000Base-T 802.3ab 1 Gb/s 100 Ω; Category 5/5e UTP; four-pair cable Yes(Gigabit Ethernet or GigE)

2002 10 Gigabit Ethernet 802.3ae 10 Gb/s 850 nm over multimode fiber; 1310 nm and Yes(10 GigE) 1550 nm over singlemode fiber. Full-duplex

mode only. Includes a WAN physical interface (PHY) to simplify interfacing to a SONET/SDH or G.709 OTN network.

2004 Ethernet in the First Mile 802.3ah 1 Gb/s Support for various access technologies: Yes

• Point-to-point copper• Point-to-point fiber• Point-to-multipoint fiber (EPON)Support for operation, administration, and maintenance (OAM) in access networks including:• Remote failure indication• Remote loopback indication• Link monitoring

Table 1.1 — Main Ethernet standards (continued)


Ethernet Nuts and Bolts



2. Ethernet Nuts and BoltsEthernet is a packet-based technology; i.e., fixed amounts of data are encapsulated into Ethernet frames. In addition to the data payload, eachframe also contains information about the source of the packet, its destination address, the type of data in the payload, and other useful informationrequired for transmission. The focus of this chapter will be the basic frame structure of Ethernet, as well as the applications some special frameextensions provide.

As introduced in Chapter 1, there are two frame formats used in Ethernet networks: the original and more common Ethernet 2 format, and theIEEE 802.3 variation. Both frame types will be described, as these can be used in combination on any given network. Except for some specificapplications, network equipment is typically transparent to the type of frame transmitted.

2.1 Ethernet Logical SpecificationsThe most commonly deployed Ethernet connections today run at 10, 100, and 1000 Mb/s. The logical specifications are similar with the exceptionof the connectors and cable category requirements shown in the table in the previous chapter:

Media Access: CSMA/CD (HDX/Shared)Frame Format: 802.3/EthernetMAC Address: 6 bytesMin. Frame Size: 64 bytesMax. Frame Size: 1518 bytes



2.2 Basic Ethernet 2 FrameThe original Ethernet frame as developed by Xerox was updated to the Ethernet 2 frame, now in common use.

Type DATA Unit FCSDestinationAddress

SourceAddressPreamble

10101...

8 6 6 2 46-1500 4

Destination/Source addresses

I/G U/L 46 bits

Ethernet Encapsulation (RFC 894) Frame Format

6-byte address

I/G = Individual/Group Address 0 = Individual Address 1 = Group AdressU/L = Universal/Local Address 0 = Universally Administered 1 = Locally Administered

Ethernet Protocol TypesValue Description(hexadecimal)0800 IPv40801 X.75 Internet0802 NBS Internet0803 ECMA Internet0805 X.25 Level 30806 Arp (for IP and for CHAOS)0BAD Banyan Systems Inc.6001 DEC MOP Dump/Load Assistance6002 DEC MOP Remote Console6003 DEC DECnet Phase IV6004 DEC LAT6005 DEC DECnet Diagnostics6010-6014 3Com Corporation7000-7002 Ungermann-Bass download7034 Cabletron8035 Reverse ARP8046-8047 AT&T8088-808A Xyplex809B Kinetics Ethertalk - Appletalk over Ethern80C0-80C3 Digital Communication Associates80D5 IBM SNA Services over Ethernet80F3-80F5 Kinetics80F7 Apollo Computer80FF-8103 Wellfleet Communications8137-8138 Novell86DD IPv6

CRC-32Frame CheckSequence

Bytes

Transmission Parameters

Parameters ValuesInter Frame Gap (10Base-T) 9.6 msInter Frame Gap (100Base-TX) 0.96 msMax Frame Size 1518 bytesMin Frame Size 64 bytesAddress Size 48 bits

Figure 2.1 — Ethernet frame format and common parameters



2.2.1 Ethernet vs. 802.3 Frame Format

As shown in the figures below, Ethernet frames differ slightly from IEEE 802.3frames.

2.2.2 Preamble and Start-of-Frame:

Because there is no synchronous clocking mechanism between Ethernet devices, components in the network require time to detect the presenceof a signal: a transmitted frame carries leading preamble bits (or bytes) to enable synchronization to take place before the actual frame begins;two consecutive 1s mark the start-of-frame.

The preamble takes the form of alternate 1s and 0s: 7 bytes of 10101010, while the start-of-frame (SOF) is indicated by one preamble-like bytewith two 1s at the end —10101011.

Type DATA FCSDestinationAddress

SourceAddress

Preamble Length DATA FCSDestinationAddress

SourceAddress

SOF

802.2Header

Ethernet

IEEE 802.3

7 1

PreambleSOF

7 1

6 6 2 46-1500 4

6 6 2 46-1500 4

The field lengths are in bytes

Figure 2.2 — Ethernet and 802.3 frame format



2.2.3 Destination and Source Addresses

Known as MAC addresses (short for media access control), these arehardware addresses that uniquely identify each node on a network.

Source Address: The source address is always a unicast (single-node) address.

Destination Address: The destination address can be unicast, multicast (group of nodes), or broadcast (all nodes).

Each address is associated with a user (host) device, more specifically with an interface on that device. It consists of a 6-byte (48-bit) field, whichmust contain a globally unique number.

The address is divided into two sections—the first (sometimes known as the organizationally unique identifier or OUI) is allocated to networkinterface card (NIC) manufacturers by the IEEE; the other section is like a serial number allocated to each NIC by the manufacturer himself. Shownbelow is a typical MAC address in its various formats.


SourceAddress


SourceAddress

SOF

802.2Header

Ethernet

IEEE 802.3

7 1

PreambleSOF

7 1

6 6 2 46-1500 4

6 6 2 46-1500 4


Figure 2.3 — Destination and source address location



The IEEE manufacturer number allocation forms the most significant part of the MAC address; and this, combined with the serial number, providesa globally unique address for every manufactured NIC.

Various formats exist to represent MAC addresses, but they all break down into a binary number. Although the IEEE OUI is assumed to be 24 bitslong, the two most significant bits have another purpose:

bit 47 — when set to 0, indicates an individual address; when set to 1, indicates a group (multicast) address.

bit 46 — when set to 0, indicates the universally administered global addressing IEEE scheme; when set to 1, indicates a locallyadministered addressing scheme.

0000 1000 0000 0000 0000 1100 1001 1110 0001 0111 1000 1010 Binary

0 8 0 0 0 c 9 e 1 7 8 a Hex

08 — 00 — 0c — 9e — 17 — 8a

08 : 00 : 0c : 9e : 17 : 8a

08 . 00 . 0c . 9e . 17 . 8a

0800 . 00c 9e . 178a

SometimesWritten

IEEE Assigned Manufacturer Assigned

Figure 2.4 — Sample MAC address in three common formats



A MAC address of FF-FF-FF-FF-FF-FF (all ones) is reserved for use as a broadcast address.

Unfortunately, the MAC system is based on what is known as a flat addressing scheme, asopposed to a hierarchical scheme. For example, a flat scheme would be the equivalent of a streetfull of houses with names instead of numbered addresses; the only way of locating a specific housewould be to inspect them all individually. With a hierarchical scheme, on the other hand, thesequential numbered addresses make it much easier and quicker to locate the position of a specificdestination. This is why MAC addressing is only used in confined (local) areas.

Here is the address shown above in context of the destination address. Both Ethernet and 802.3use a similar address format.

2.2.4 Type/Length

This is the major difference between the two Ethernet standards. Where Ethernet 2 uses a TYPE field, 802.3 specifies a LENGTH field, followedby a special data header known as the 802.2 logical link control layer (LLC).

These fields are used to identify the Layer 3 protocol that the data payload isencoded with. This allows routers to correctly forward the traffic to the relatedLayer 3 device. The following diagram shows the values these fields containwhen indicating the Ethernet payload is encoded with Internet Protocol (IP) atLayer 3.

DestinationAddress

SourceAddress

00-80-0c-9e-17-8a

A B

6 6

A: Address specified by IEEEB: Address specified by manufacturer

Preamble Type DATA FCSDestinationAddress

SourceAddress

Ethernet

8 6 6 2 46-1500 4


SourceAddress

SOF

802.2Header

IEEE 802.3

7 1 6 6 2 46-1500 4


Figure 2.6 — Type/length fields

Figure 2.5 — IEEE and manufacturer MAC address division



Ethernet TYPE field — identifies the protocol type of the data field forforwarding to the appropriate higher-layer protocol.

802.3 LENGTH field — indicates the length of data (minus padding) in thedata field.

2.2.5 802.3 Logical Link Control Header (LLC)

The IEEE, having written their 802.3 specification according to a LENGTHfield, were faced with finding another way to represent the function of theTYPE field. They did this by creating another protocol (LLC) that ‘sits’ directlyabove the MAC layer (but still within the Layer 2 data-link layer).

At the LLC level, Ethernet functionality is not evident, so this protocol, definedin the 802.2 specification, can function on other LAN types as well (e.g., tokenring, FDDI, etc.), forming a common layer between them.

This 802.2 specification is known as the logical link control (LLC) layer.

IP

08-00 06

Ethernet 802.3/802.2

00-03-01-xx-xx-xxOr FF:FF:FF:FF:FF:FF

Type Snap

Coax, UTP/STP, Fiber Optics

Network Layer

Data-Link Layer

Physical Layer

Figure 2.7 — Type and snap fields defining IP Layer 3 payload


SourceAddress

SOF

802.2Header

DSAP SSAP Control

1

7 1 6 6 2 46-1500 4

1 1-2

IEEE 802.3

LLC (802.2)

Figure 2.8 — Logical link layer header location


LLC consists of the following:

Destination or Source Service Access Points (DSAP/SSAP) is the equivalent of the Ethernet 2 TYPE field – A range of numbers,specified by the IEEE 802.2 sub-committee, to identify the higher-layer protocols requiring the data field contents. Only seven bits areused for protocol identification, which means there are a total of 128 numbers. Of these 128, 64 are allocated to ISO protocols and 64 to proprietary protocols. The most significant DSAP bit is used to indicate individual or group addressing, while the most significantSSAP bit indicates whether the PDU is a command or a response.

The Control Field consists of 1 byte (optionally 2 bytes) and could carry 802.2 control information such as type of service(connectionless/connection-oriented) etc. Currently it is unused and set to 03hex.

Padding is used to ensure minimum frame length.

2.2.6 SNAP Header

The TYPE field of Ethernet 2 can contain more than 1500 unique data typevalues, whereas the SSAP fields in the LLC header can only contain 128. To enable compatibility between Ethernet 2 and the 802.3 frame, the SNAPheader variant was added to the 802.2 LLC standard.

In a SNAP frame, the 802.2 header has both DSAP and SSAP set to 0xAA,and the first 5 bytes of the data field are used to give the protocol ID – out ofthe 5 bytes, the last two specify the value of the TYPE field, using the Ethernet2 standard; the first three bytes specify an OUI (like in MAC addressing) butare typically set to zero.

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SourceAddress

SOF

802.2Header

OUI Type

3

7 1 6 6 2 46-1500 4

2

IEEE 802.3

LLC (802.2)

Figure 2.9 — Snap header location



2.3 Data Field2.3.1 Ethernet

Once physical-layer and link-layer processing is complete, the data containedin the frame is sent to an upper-layer protocol, which is identified in the Typefield. Although Ethernet Version 2 does not specify any padding (in contrastto IEEE 802.3), Ethernet expects at least 46 bytes of data. Any padding hasto be removed by the higher-layer protocol and this contravenes the principlesof the OSI model.

2.3.2 IEEE 802.3

In comparison, according to the IEEE 802.3 standard, once physical-layer and link-layer processing is complete, the data is also sent to an upper-layer protocol, but it is defined within the data portion of the frame, if at all. If data in the frame is insufficient to fill the frame to its minimum64-byte size, padding bytes are inserted to ensure at least a 64-byte frame. This padding is removed before the data is presented to the higher- layer protocol, thus meeting the OSI model requirements.


SourceAddress


SourceAddress

SOF

802.2Header

Ethernet

IEEE 802.3

7 1

PreambleSOF

7 1

6 6 2 46-1500 4

6 6 2 46-1500 4


Figure 2.10 — Data field location



2.4 Frame Check Sequence (FCS)This sequence contains a four-byte cyclic redundancy check (CRC) value,which is created by the sending device and is recalculated by the receivingdevice to check for damaged frames. If the CRC values do not match, an erroris detected and the frame is discarded.

There is no error correction in Ethernet — higher-layer protocols areresponsible for detecting the loss of frames and initiating retransmission.

2.5 Interframe GapEthernet devices must allow a minimum idle period between transmission of frames known as the interframe gap (IFG) or interpacket gap (IPG).It provides a brief recovery time between frames to allow devices to prepare for reception of the next frame. The minimum interframe gap isspecified according to the time it takes to transmit 96 bits (12 bytes), which is 9.6 µs for 10 Mb/s Ethernet, 960 ns for 100 Mb/s Ethernet, and 96 ns for 1 Gb/s Ethernet.

2.6 Ethernet Frame Format ExtensionsThe original Ethernet standards defined the minimum frame size as 64 bytes and the maximum as 1518 bytes. These numbers include all bytesfrom the Destination MAC Address field through the Frame Check Sequence field. The Preamble and Start Frame Delimiter fields are not includedwhen quoting the size of a frame.

In 1998, the IEEE 802.3Q standard extended the allowable frame sizes to permit traffic to be segregated into different broadcast domains withinLANs. The minimum frame size was brought down to 68 bytes, while the maximum was increased to 1522 bytes, allowing VLAN frame tags to beinserted into the standard frame format and thus accommodating emerging needs.This change was adopted to allow traffic to be segregated intodifferent broadcast domains within LANs. In wide-area networks VLANs are used by service providers to separate and prioritize customer traffic.


SourceAddress


SourceAddress

SOF

802.2Header

Ethernet

IEEE 802.3

7 1

PreambleSOF

7 1

6 6 2 46-1500 4

6 6 2 46-1500 4


Figure 2.11 — Frame check sequence location


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2.7 Ethernet Frame Tag

The Tag Protocol Identifier (TPID) – 2 bytes –indicates that a tag header comes next.

The Tag Control Field (TCI) – 2 bytes – is furthersubdivided into a 3-bit User Priority field that isdefined in 802.1Q, a 1-bit canonical formatindicator (CFI) that is used in Ethernet to show thatthere is a routing information field after the lengthfield, and the 12-bit VLAN identifier (VID).

2.8 VLAN TaggingVLAN tagging, detailed in 802.1Q, permits various virtual LANs to be created — segregating customer traffic over common Ethernet network links.

Virtual LANs (VLANs) allow a network administrator to group devices together into broadcast domains that are logical rather than physical. Thisrequires an additional identification (tag header) for the VLAN at the data-link layer.

As a 12-bit field, the VLAN ID allows 4096 possible VLANs. ID=0 is reserved to identify priority frames (no VLAN specified), and ID=FFF is simplyreserved (not to be used).

In the diagram above, two switches are connected to each other; as they are both aware of 802.1Q, the VLANs can understand the tag header.This link between them is called a trunk link and uses explicit tagging; i.e., packets sent on this link have the tag header added. Connecting devicesthat do not need to be VLAN are connected via access links. As these devices do not understand the tag header, it is not sent; this is called implicit tagging.

It is possible to have a device that is VLAN-aware and can be connected directly to a trunk link. It is also possible to have both “aware” and “notaware” devices on the same link; this is called a hybrid link.

DestinationMAC

Address

Ethernet Frame Tag

Preamble

7 1 6 6 2 2 2 0 0 4

Tag Protocol ID User Priority CFI VLAN ID

ETHERNET FRAME TAG TCI

StartFrame

Delimiter

DestinationMAC

Address

Length/Type= 802.1 QTag Type

TagControl

Information

Length/Type

MAC ClientData

PadFrameCheck

Sequence

Figure 2.12 — Ethernet frame tag location and VLAN ID



In 802.1Q, devices in the network can be assigned toa VLAN either through the port they are connected to,their MAC address or the protocol type they are using.In all cases, the bridge/switch needs to have a filterdatabase that identifies who is on which VLAN. The MAC address option is the most administration-intensive, as the allocations have to be done manuallyfor every device. The entries in the database can bestatic or dynamic.

Generic Attribute Registration Protocol (GVRP)is used to dynamically update port-to-VLANassignment and to communicate between VLAN-aware bridges or switches.

Group Multicast Registration Protocol (GMRP)is used to send multicasts on a single VLANwithout affecting other VLANs. For each VLAN, a spanning tree algorithm must be calculated.

Switch Switch

VLAN Aware

Trunk Link

Host Host

Virtual LAN 1 Virtual LAN 2 Virtual LAN 3

Workstation Workstation

Figure 2.13 — Example of virtual LAN



2.9 Traffic PriorityIn addition to specifying a method to delineate virtual LANs, the frame tag also allows traffic priority to be specified. This is outlined in the 802.1pstandard, which defines a way for MAC devices (such as switches) to interoperate. The 802.1p standard primarily relies on traffic buffering toassist priority data flow. 802.1p allows the device doing the buffering to determine which packet to transmit first. It is commonly used inapplications where two traffic streams use the same port, or if two connected LANs are running at different speeds.

Potentially, depending on the protocol used on the WAN and the extent to which 802.1p-compliant devices have been deployed, a consistent levelof service can be ensured over a WAN from one Ethernet LAN to another Ethernet LAN.

The User Priority value is a 3-bit field that provides eight priority levels (0 through 7), with 0 representing the lowest priority (best effort) and 7 representing the highest priority (reserved).

These eight priority levels map to the prioritization schemes used by many protocols (such as ATM) that operate at Layer 2 (the data-link layer) ofthe OSI model.

The priorities that are available are shown in Figure 2.14 (left). Using these priority levels, it is possible, in a VLAN-aware device, to assign a traffic class on the basis of protocol type,source or destination MAC address or port number. There are also suggestions forproviding the same choice for higher layers such as applications, but this is not currentlyimplemented in the standard. With this system, it is possible to make prioritizing policydecisions across the network and implement them in VLAN-aware networking devices.

Priority Binary Traffic Types 7 111 Network Control 6 110 Interactive Voice 5 101 Interactive Multimedia 4 100 Controlled Load Applications (Streaming Multimedia) 3 011 Excellent Effort 2 010 Spare 1 001 Background 0 000 Best Effort (Default)

Tag Protocol ID User Priority CFI VLAN ID

ETHERNET FRAME TAG TCI

Figure 2.14 — Traffic priority and related types



2.10 Frame BurstingThe 802.3z (1 Gigabit Ethernet) standard introduced burst mode operation. This optionally allows a station to transmit a series of frames (up to65,536 bit times or 8192 byte times) without relinquishing control of the transmission medium. Burst mode is only specified for Gigabit and higherEthernet speeds and applies to half-duplex mode only. It is designed to improve short frame transmission.

The first frame of a burst is transmitted normally and may have an extension field. Following frames in the burst do not require the extension fieldbecause if a collision occurs, only the first frame in the burst is affected.

2.11 Jumbo FramesIn 1998, Alteon Networks, Inc. proposed that the maximum size of the MAC Client Data field be increased from 1500 bytes to 9000 bytes. This way, larger frames could use network bandwidth more efficiently while reducing the number of frames that have to be processed. Although this initiative was not adopted by the IEEE 802.3 Working Group, it was adopted by a number of network element manufacturers who continue to support this functionality.

The Jumbo Frame specification restricts the use of jumbo frames to full-duplex Ethernet links, and defines a link-negotiation protocol that allows a station to determine whether or not the station at the other end of the segment is capable of supporting jumbo frames.

2.12 Ethernet Media Access ControlThere are two media access control protocols defined for Ethernet: half-duplex, and full-duplex.

2.12.1 Half-Duplex Ethernet and Carrier-Sense Multiple-Access/Collision Detection (CSMA/CD)

In half-duplex Ethernet, devices both transmit and receive, but the cabling structure in the device is common to both the transmitter and thereceiver, so it cannot transmit its own data and receive incoming data at the same time; i.e., it cannot talk and listen at the same time. This meansthat only one device can successfully send output onto the media at any given moment. The technique used to control traffic flow on a half-duplexnetwork is called Carrier-Sense Multiple-Access/Collision Detection (CSMA/CD). The basic components of this method are the following:



2.12.2 Carrier Sense (CS)

Since only one device at a time can successfully send output, the Carrier Sense component refers to the “sensing” operation that occurs when adevice listens for a signal. It must ascertain that no other device is transmitting before it starts sending its own transmission. The device does thisby detecting or sensing a carrier signal, hence the term Carrier Sense (CS).

2.12.3 Multiple Access (MA)

This component refers to how many devices have access to the medium.Since there is no organized access system — no hierarchy or preference interms of order of transmission — multiple devices have equal-opportunityaccess, hence Multiple Access (MA).

2.12.4 Collision Detection (CD)

This component refers to the signal collision that occurs when twodevices try to access the medium simultaneously (at times, this isinevitable). In such case, the collision can be recognized by the receivingfunction of the NICs and, as each individual transmission will now becorrupted, the devices stop transmitting. They have detected a collision,hence Collision Detection (CD).

Listen (Carrier Sense)

Transmit (Access)CS

?

Any Device Listen — Transmit(Multiple Access)

MA? ?

Device Listen — Transmit at sametime (Collision Detect)

CD? ?

Figure 2.15 — Illustration of CSMA/CD



Devices detecting a collision will generate a predetermined jamming signal to tell all other devices that a collision has occurred and will thenwithdraw for a while (referred to as a Backoff Strategy, in which the specific withdrawal time period is governed by a randomly generated number),before going back to the Carrier Sense phase and trying again.

2.13 CSMA/CD Transmission Flow2.13.1 Full-Duplex Ethernet

In full-duplex Ethernet, devices at each end of a link can send and receive data simultaneously. One advantage of this approach is that the full-duplex link can theoretically provide twice the bandwidthof normal (half-duplex) Ethernet. The full-duplex mode of operation requires that each end of the linkconnect only to a single device, such as a workstation or a switched hub port.

A device at the end of a full-duplex Ethernet link does not have to listen for other transmissions or forcollisions when sending data. Therefore, there is no need to adhere to the original Ethernet mediumaccess control system (CSMA/CD);

The 10Base-T, 100Base-TX, and 100Base-FX and 1000Base-T/X signaling systems support full-duplexoperation; they have transmission and reception signal paths that can be simultaneously active.

2.13.2 Flow Control (802.3x)

Flow control is a mechanism created by the IEEE to define a standard to manage the flow of data between two Ethernet devices operating in full-duplex mode. Flow control is supported on 10, 100, GigE and 10 GigE links. Using flow control, a device that can no longer process frames asthey arrive sends a pause message to its link partner to temporarily reduce the amount of data transmitted. Otherwise, buffer overflow occurs, datais lost and retransmission is required.

Data StationReady to Send

Wait According toBackoff Strategy

Transmit DataSense Channel

TransmitJam Signal

TransmissionComplete

SenseChannel

New Attempt

Channel Busy

Channel Free

No collision Detected

CollisionDetected

Figure 2.16 — CSMA/CD algorythm



Flow control is defined for neighboring devices on a point-to-point link; i.e., flow control is not implemented end to end. If a receiving stationbecomes congested, it sends a pause frame to the transmitting station specifying the amount of time for which the transmitting station should stopsending packets. The transmitting station waits for the specified time before sending additional packets. This effectively reduces throughputbetween the two devices and results in much less retransmission, as the packet loss that occurs from lack of flow control is no longer an issue.

A second form of flow control, called XON/XOFF, toggles traffic flow by sending one pause frame to stop traffic flow and a second to request aresumption of traffic (typically when the receiving buffer has emptied).

2.13.3 Pause Frame Format

The pause frame is a standard Ethernet frame that is sent where the type fieldis specified as 8808. The pause time is specified in the data payload asshown below.

2.13.4 Auto-Negotiation

There is an optional part of Ethernet allowing two devices to negotiate thebest possible connection between them. Auto-negotiation devices exchangeinformation about their range of link speeds, possible modes of operation

(full-duplex or half-duplex), and whether they support flow control. For 1000Base-T links, auto-negotiation also includes master clock support. Flow control can be implemented symmetrically or asymmetrically (if one device has manually configured and/or fixed transmission settings).

On copper connections, the auto-negotiation process takes place using a modified version of the normal link pulse (NLP) signals used to verifylink integrity, called the fast link pulse (FLP) signals. It should be noted that NLPs and FLPs are specified only for twisted-pair media using eight-pin connectors, such as 100Base-TX over unshielded twisted-pair wire.

Optical links use a special order-set control symbol instead of FLPs to carry auto-negotiation information.

Preamble DATA FCSDestinationAddress

SourceAddress

0100 0-0xFFFF PAD (0x0000)

802.3xOpCode

PauseTime

8808PreambleSOF

Figure 2.17 — Pause frame format and location



Devices on a network that are capable of auto-negotiation find their highest-performance mode of operation based on a set of negotiation rules,shown in the table below.

Auto-Negotiation Priority Rules

A 1000Base-TB 100Base-TX full-duplexC 100Base-T4D 100Base-TXE 10Base-T full-duplexF 10Base-T

The negotiation process works its way from F to A until the highest value match is achieved. Switches and hosts can override auto-negotiationwith manual settings. 10 GigE does not support auto-negotiation.

2.13.5 Link Aggregation

Link aggregation (or trunking) is another Ethernet feature only applicable to the full-duplex operation. It provides increased link availability andbandwidth between two Ethernet stations by allowing multiple physical links to be combined as a single "logical" link. The link-aggregationspecification is specified in 802.3ad.

Prior to link aggregation, it was difficult if not impossible to have multiple links between two Ethernet stations; the spanning tree protocol (STP)algorithm used in Ethernet bridging (802.1D) disables parallel paths to prevent loops in the network.



Link aggregation allows multiple links between any two Ethernet stations if they consist of two switches, a switch and a server, or a switch and anend-user station. The following advantages are provided:

• Bandwidth can be increased by combining available lines (for example, two 10 Mb/s links can result in a 20 Mb/s link)• Load balancing can be performed by distributing traffic across the multiple links. One line can be dedicated to high-priority traffic, if required.• Redundancy is provided by the multiple links

Link aggregation operates by adding a new layer of function between the Ethernet MACs and the higher-layer protocols above. The link-aggregation function is completely transparent to all higher-layer protocols and functions, including the spanning tree algorithm, VLANs,SNMP and routers.

Aggregation can only be performed if:

• Links are point-to-point (no multipoint permitted)• Links must operate in full-duplex mode• Links being aggregated run at the same data rate (e.g. 10 Mb/s, 100 Mb/s, or 1 Gb/s)

2.14 10 Gigabit Ethernet (10 GigE)10 Gigabit Ethernet is a departure from standard 10/100/1000 Mb/s Ethernet in that it is optimized for both LAN and WAN applications. Since most 10 Gb/s WAN links today are SONET/SDH-based, the 10 GigE specification has a second physical-layer specification allowing it toeasily interact with existing SONET/SDH network elements. 10 GigE maintains the standard 802.3 Ethernet frame size and format, so that Layer 3and higher protocols are preserved. It operates over point-to-point links in full-duplex mode only.

2.14.1 Physical-Layer Specifications

LAN PHY runs at 10.000 Gb/s and is designed to directly aggregate and carry GigE traffic. This interface comes in two different versions:a serial version using 64B/66B encoding, operating at a line rate of 10.313 Gb/s (data rate of 10.000 Gb/s), and a wide wave-divisionmultiplexing (WWDM) version, 10Base-LX4, using 8B/10B encoding on four channels, each running at 3.125 Gb/s, which results in a linerate of 12.500 Gb/s (again at a data rate of 10.000 Gb/s).



WAN PHY runs at a data rate compatible with SONET OC-192c/SDH STM-64c (9.5846 Gb/s). The WAN PHY is designed to supportconnections with SONET/SDH circuit-switched networks. It adds a WAN interface sublayer (WIS) to the LAN PHY. The WIS takes thedata payload and encapsulates it with its embedded SONET/SDH frame into a simplified SONET OC-192c/SDH STM-64c(concatenated) frame. Because of the SONET/SDH overhead and the 64B/66B encoding, the actual data rate supported is lower thanthe LAN PHY, so the WIS has a mechanism to pad and buffer data to the 10 Gb/s MAC data rate.

WAN PHY is designed to bridge asynchronous data media and synchronous TDM transport networks, which allows 10 GigE to betransparently carried across today’s TDM infrastructure. It is 100% compatible with current DWDM networks carrying OC-192/STM-64and 100% compatible with OTN (DigiWrapper) networks carrying OC-192/STM-64.

However, it should be understood that this WAN interface is not true SONET. The "S" in SONET (or SDH) stands for synchronous; thatis, all points on the network are synchronized to an accurate central master clock. Ethernet is an asynchronous system in which eachreceiving device derives clock and data from the incoming stream and re-times the outgoing characters with a local clock. The 10 GigabitEthernet output from a device with a WAN PHY does not connect directly to a SONET/SDH ring as it requires an access device.

WAN PHY has some SONET/SDH features, but does not support the full SONET/SDH standard:

• Supports only the SONET/SDH overhead features required for fault isolation• Ignores line and section DCC• Ignores local and express orderwire• Supports pointer processing to allow carriage over future OC-768/STM-256 backbones

Telco-like features supported on 10 GigE WAN PHY:

• WAN PHY has facility-loopback capabilities• WAN PHY has threshold for severely errored seconds• WAN PHY has embedded test pattern generation/detection capabilities (PRBS-31)



DWDM Optical Network

Location AData

Center

RoutingSwitch

RoutingSwitch

RoutingSwitch

Transponder

10 GEWAN PHY

Location C

RemoteServers

Location B

10 GEWAN PHY

Transponder

Transponder

10 GEWAN PHY

Figure 2.18 — 10 GigE WAN PHY applications: ITU-T grid compatibility



DWDM Optical Network

Location A

RoutingSwitch

10 GEWAN PHY

10 GEWAN PHY

OC-766 MuxOC-766 Mux

OC-766 Mux

National

Backbone

Figure 2.19 — 10 GigE WAN PHY applications: OTN and OC-768 compatibility

OC-48

OC-48Access Routers

Access Routers

Access Routers

Access Routers10 GigE LAN link

10 GigE WAN linkEdge Routers

Edge Routers

DWDM

GigE link

10-100 M Ethernet link

Figure 2.20 — Typical 10 GigE WAN and LAN PHY applications


Ethernet Applications


3. Ethernet ApplicationsEthernet is widely used in local-area networks (LANs) as well as in different types of carrier networks — access networks, metropolitan-areanetworks (MANs) and long-haul or wide-area networks (WANs).

3.1 Ethernet in Local-Area Networks (LANs)A LAN is a network of computers and associated devices within a small geographical area, usually within a building or group of buildings. Devices on the LAN can be connected using coaxial cables, twisted pairs of copper wiring or fiber-optic cables, or even wireless radio or infrared connections.

Ethernet is by far the most popular LAN technology.Common Ethernet standards are 10Base-T (10 Mb/sover twisted pairs), 100Base-T or Fast Ethernet(100 Mb/s over twisted pairs), and 1000Base-T(Gigabit Ethernet using four pairs of Category 5 orCategory 5e balanced copper wiring).

Figure 3.1 shows a typical corporate LAN with aclient/server architecture. Some small networks,such as home-office networks, do not include aserver but use a peer-to-peer architecture instead.

Several common network components are requiredto build a corporate LAN; these include repeaters,hubs, switches, and routers:

BackupWAN WANRouter

Corporate LAN

Firewall

Switch

File/Print Server E-mail Server

Application Server

Hub (48 port)

Workstations

Workstations

Shared Laser Printer


Workstations


Hub

Hub

Hub Hub

Figure 3.1 — A typical office LAN topology




A Repeater joins two network segments together to overcome cable-length limitations. The roleof this element is to simply regenerate signals. A maximum of four repeaters are allowed betweenany two terminating clients (computers).

A Hub is a multiport repeater that joins devices to a common backplane. Within the hub, the datagoes through a repeater process.

Hubs can have differentinterfaces for different cabletypes; they can offer rateconversion and, if software isadded to them, they can becomemanaged devices. If hubs areconnected to each other toincrease the number of availableports, they must also follow thefour-consecutive-repeater limit.

Hub

Host

Workstation

Figure 3.2 — A typical office LAN topology using a 10Base-T hub

Workstation

Workstation Workstation

Hub Hub

HubHub

Shared backplane in each hubHub Uplink

Host

Host

Host

Host

Figure 3.3 — LAN using multiple hubs to add users to a common network



All devices connected to a hub (or via interconnected hubs) are capable of colliding with each other so they are in the same collision domain(CD), allowing only one device to transmit at a time. CSMA/CD is a very efficient media access scheme under light to moderate traffic loads.As the traffic volume gets heavier, however, a significant amount of network transmission time becomes consumed by collisions, and networksneed to be segmented (using a switch) to restore traffic efficiency.

The use of hubs is declining because switches are now just as inexpensive andthey offer a much more efficient way of constructing the LAN.

Switches and Bridges

A bridge divides a network into two segments. It restricts traffic to asingle segment unless the device needs to access a device on the othersegment (known as bridging). A hub cannot segment a network sincesegmenting is performed using MAC addresses, which are notunderstood by hubs; they are simply Layer 1 (repeater) devices. A strategically placed bridge can significantly reduce collisions bysegmenting workgroup traffic flow.

A switch is a multisegment bridge. Each segment is connected to a port,which can be bridged to any other segment (port). Switches have a largebandwidth backplane, allowing devices on two segments to betemporarily connected at what is called wire-speed, while simultaneouslyenabling similar bridging between other device pairs.

If every client on a network is interconnected through a switch, collisionsdo not occur and maximum possible throughput is enjoyed by all clients.Switches allow multiple hosts to transmit at the same time, withoutcontention for bandwidth. Switches can be VLAN tag-aware, permitting

Switch

Workstation

Host

Host

Host

High Speed, HighBandwidth Backplane

Figure 3.4 — A typical office LAN topology using a Layer 2 switch



the formation of virtual LANs.

There are various types of switching techniques:

• Cut-Through – The frame is forwarded on-the-fly. This is fast, but no FCS check is possible and the communicating devices mustuse the same LAN format.

• Modified Cut-Through – Stores the frame for 64 bytes before forwarding. Same drawbacks as the cut-through technique and slightlyslower, but eliminates short frames (runts).

• Store and Forward – Slowest of the three types because itstores the complete frame beforeforwarding it. This allows for a fullcheck and also permits the removal ofthe data field for insertion into a differentLAN frame type; e.g., Ethernet to tokenring.

A Router is a multilayer switch used to direct Layer 3 (commonly InternetProtocol, or IP) traffic. By examining the IP address, a switch determinesthe corresponding MAC address so that the Layer 3 traffic can becorrectly forwarded through a Layer 2 Ethernet network. Addressresolution protocol (ARP) is the standard mechanism used to correlateMAC and IP addresses in routers.

3.2 Ethernet in Access NetworksPersonal computers and LANs are usually connected to the outside world via

Optical WDM cross-connect mesh

Multiple regionaland backbone

providers

Long-Haul Networks (WANs)

Metropolitan Networks (MANs)

Inter-metroconnecton

SONET

Intra-metroconnection

Residential x-DSL orcable modem networks

PSTN/cellular Regional ISP Corporateenterprise clients

IP Router

ATMSwitch

EthernetLAN

FrameRealyESCONFiberChannel Gigabit

Ethernet

Long-Haul/metro

Intra-metroconnection

Figure 3.5 — Interconnection of access networks, MANs and WANs


an access network (see figure below). An access network, commonly referred to as the first mile or the last mile depending on the context, coversa relatively small geographic area and connects subscribers, such as corporations, government offices, educational institutions and residentialcustomers, to a metropolitan-area network (MAN). MANs in close proximity may be directly interconnected. Long-distance connections betweenMANs are provided by long-haul telecom networks to create wide-area networks (WANs).

Access networks use a variety of media such as twisted pairs of copper wire, hybrid fiber coax (HFC) or, optical fiber in FTTx and passive opticalnetworks (PONs). Access rates range from sub-rate channels such as DS1, DS3, OC-3, OC-12, Fast Ethernet and Gigabit Ethernet, to full-wavelength capacities such as OC-48 and OC-192.

Access networks use a variety of protocols including ATM, frame relay, SONET/SDH, Ethernet and MPLS. Ethernet services can be delivered overany of these access technologies, but the most cost-effective and simple method is to deploy Ethernet services directly over Ethernet access lines.

Ethernet access networks typically run at 1000Mb/s (Gigabit Ethernet, or GigE). Traffic isdelivered to the customer from the tributary sideof an access router or Layer 2 switch. Rate limitingis commonly used to limit the bandwidth to thecustomer, which can be provided in increments assmall as 1 Mb/s. Using identifiers in Ethernet dataframes called virtual private LAN (VLAN) tags (seeChapter 2), service providers can separate trafficto offer a secure virtual network to each customerover a common backbone.


Store

Store

OC-48 OC-48

OC-3

DWDMCustomer C

Customer C

Customer C

Customer CCustomer C

Customer ACustomer A

Customer A

Customer A

Customer A


Customer B


Figure 3.6 — VLANs provide secure virtual networks to individual customers across a MAN



3.3 Ethernet in Metro NetworksMANs cover geographic areas up to several hundred kilometers and typically serve concentrated metropolitan areas. They interconnect manyaccess networks and provide connection points to WANs. Many current and emerging MAN technologies support Ethernet services.

These networks use a wide variety of networking protocols and channel speeds. SONET/SDH is presently the most common technology withpoint-to-point or add/drop multiplexer (ADM) ring topologies. In some new MAN installations, 10 Gigabit Ethernet (10 GigE) is challengingSONET/SDH with its lower cost and simpler maintenance requirements.

3.4 Ethernet in Wide-Area or Long-Haul NetworksA WAN is a network that covers a large geographical area using long-haul networks that can extend over thousands of kilometers to connect manydifferent MANs. Most WAN links are SONET/SDH-based and many use DWDM. With the introduction of 10 Gigabit Ethernet, carriers can nowuse one wavelength on a long-haul DWDM system to transmit Ethernet in its native format, further simplifying the deployment of Ethernet services(see Chapter 2).

3.5 Ethernet Service TypesThe two basic Ethernet service types defined by the Metro Ethernet Forum (MEF) are:

Ethernet Line (E-Line) for point-to-point connectivity. E-Line services are used to create Ethernet private line services, Ethernet-based Internet access services, and point-to-point Ethernet VPNs.

Ethernet LAN (E-LAN) for multipoint-to-multipoint (any-to-any) connectivity. E-LAN services are designed for multipoint Ethernet VPNs and native Ethernet transparent LAN services.



Service type Connectivity Use

Ethernet Line (E-Line) Point-to-point (one-to-one) • Ethernet private line (EPL) services• Ethernet-based Internet access services• Point-to-point Ethernet virtual private networks (VPNs)

Ethernet LAN (E-LAN) Multipoint-to-multipoint (any to any) • Multipoint Ethernet VPNs• Native Ethernet transparent LAN services

Figure 3.7 and Figure 3.8 illustrate the two basicservice types and how they are used tointerconnect geographically separated LANs byinterfacing customer edge (CE) equipment to the MAN. Note that each customer requires onlyone CE, regardless of the number of Ethernetvirtual connections (EVCs) involved. It would evenbe possible to make a multipoint-to-multipointconnection and several point-to-point connections tothe same CE. In all cases, the Ethernet service ensuresthat frames are delivered to the correct destination.

Table 3.1 — Basic Ethernet service types

IP Video

IP Video

IP Voice

Data

Data

IP Voice

IP PBX

Servers

CE

CE

CE

MAN

Point-to-PointEthernet Virtual Connections

(EVCs)

Figure 3.7 — Ethernet line (E-Line) service



Both of the basic Ethernet service types allowconnectivity services that are either private or virtual. Ina private service, a specific amount of bandwidth isdedicated to the subscriber whether they are using itor not. A private service does not use dedicatedphysical connections (such as a TDM circuit), but isinstead a dedicated-bandwidth service implementedover a public network infrastructure. Customerseparation is ensured through packet encapsulationand logical connections.

In contrast, a virtual service allows bandwidth to beshared among different subscribers with connectionsto the network. Virtual services are less costly thanprivate services because they allow the serviceprovider to accept more traffic by dynamicallyreassigning idle capacity. To maximize the use ofinfrastructure, the service provider can oversubscribe,since it is unlikely that all subscribers will requiremaximum capacity at the same time.

The combination of private and virtual E-Line and E-LAN service types results in the four basic Ethernetservices described below:

IP Voice

Data

Data

IP Voice

Data

IP Voice

IP PBX

Servers

CE

CECE

CE

MAN

Multipoint-to-MultipointEthernet Virtual Connection

(EVC)

Figure 3.8 — Ethernet LAN (E-LAN) service


3.5.1 E-Line Variants

Ethernet Private Lines

This service consists of a point-to-point connection that uses dedicated bandwidth, be it virtually concatenated SONET/SDH channels orreserved packet bandwidth in a packet-switched network.

The customer’s Ethernet frames stay strictly separated from others’ at the Ethernet layer, and the customer will always have the contractedbandwidth rate available (also known as CIR, the committed information rate). In this regard, the Ethernet private line is much like legacy TDM-based private lines, yet offers the benefit of a native Ethernet interface to the customer and to the network operator’s edge equipment.

Like typical TDM private lines, the Ethernet private line can be deployed to support a number of different carrier services such as EthernetInternet, network services access or LAN-to-LAN interconnect, in which the customer owns one or both (in the case of LAN-to-LAN) ends ofthe connection. The Ethernet private line is the simplest E-Line service to deploy. Carriers typically provide these services from a multiserviceprovisioning platform (MSPP), which acts as the demarcation between the customer’s network and the carrier’s SONET/SDH transport network.

Ethernet Virtual Private Line

For the Ethernet virtual private line, the rules are slightly different. In this service, the customer still gets point-to-point connectivity, but overshared bandwidth instead of dedicated. The shared bandwidth can be a TDM channel in the transport network or the switched-fabricbandwidth of switches and routers in the packet network. The service can either be offered as best-effort or with service-level agreementsspecifying committed information rates (CIR) and other critical network parameters such as latency. This service is quite similar to frame relayand its model of creating networks using permanent virtual circuits (PVCs).

The MEF defines Ethernet virtual private line service as a point-to-point Ethernet virtual connection (EVC) between two subscribers. Multiple EVCs can be combined to provide hub-and-spoke architectures in which multiple remote offices all require access to a head office,or multiple customers all require access to managed services from an operator’s point of presence (POP).




3.5.2 E-LAN Variants

Ethernet Private LAN

The Ethernet Private LAN (EPLan) service provides multipoint connectivity over dedicated bandwidth; i.e., it may connect two or moresubscribers. Subscriber data sent from one customer site can be received at one or more of the other customer sites. Each site is connectedto a multipoint-to-multipoint EVC and uses dedicated resources so different customers’ Ethernet frames are not multiplexed together. As newsites are added, they are connected to the same multipoint EVC, thus simplifying provisioning and service activation. From a subscriberstandpoint, an EPLan makes multiple LAN sites look like a single, really big LAN.

Ethernet Virtual Private LAN

The Ethernet Virtual Private LAN (EVPLan) has gone by many names over the past two years, from Virtual Private LAN Service (VPLS) toTransparent LAN Service (TLS), to Virtual Private Switched Network (VPSN). Regardless of how it is termed, the EVPLan is a network serviceproviding Layer 2 multipoint connectivity between Ethernet edge devices. Customer separation is accomplished via encapsulation using VLANtags or other encapsulation technologies such as MPLS.

The EVPLan is a cost-effective service for the carrier, as it can leverage shared transmission bandwidth in the network. However, because itis a multipoint service, it can be complex to administer. The operator must implement protection, bandwidth profiles, congestion management,buffering, etc.; these are much more complex to implement in EVPLans when compared to point-to-point services.

3.6 Ethernet InfrastructuresMany means are available to carry Ethernet in carrier networks, each with their own advantages and disadvantages. The method used depends onmany factors, including the reliability and manageability of legacy services and the risks involved in implementing new technologies that may notbe entirely proven and standardized. Some carriers incorporate Ethernet services into existing optical WDM/SONET/SDH infrastructures whileothers opt for emerging packet-based technologies such as IP/MPLS.



3.6.1 Native Ethernet

The most straightforward way of carrying Ethernet is to use native Ethernet over dark fiber or on a DWDM wavelength. In a MAN, Ethernet switchesare used to direct traffic over the network. This solution is particularly suitable to Ethernet virtual private line and virtual private LAN services.However, it is not easy to provide the dedicated bandwidth necessary for Ethernet private line or private LAN services.

Since native Ethernet systems cannot guarantee sub-50 ms protection to redirect traffic around an outage, and since a native Ethernet networkdoes not provide operations, administration and maintenance (OAM), the services are offered as “best-effort”; that is, there is no guarantee of QoS.

3.6.2 SONET/SDH

In past years, many carriers overbuilt their SONET-based infrastructure, and much of this capacity is still underutilized. For this reason, many of theservice providers in North America are seeking to capitalize on it by deploying Ethernet and other data services over their existing SONET networks.

In next-generation SONET/SDH networks, Ethernet frames are encapsulated one at a time into GFP frames, which are then mapped into a SONETchannel using virtual concatenation (VCAT).

SONET/SDH networks are most often used for Ethernet private lines today, but will be evolving to support Ethernet virtual private lines andEthernet virtual private LANs through integrated Ethernet switching or RPR technology.

3.6.3 Native Ethernet vs. SONET/SDH: Pros and Cons

SONET and SDH were created to transmit TDM circuits carrying mostly voice. Ethernet, on the other hand, was created to transmit frames ofdata. Because of this difference, the type of traffic being transported influences the choice of technology. Table 3.2 summarizes these differencesaccording to five important criteria.



Criteria SONET Native Ethernet

Redundancy Provided by automatic protection switching Provided by spanning tree algorithm (minute range).(APS) capability (50 ms). A fast-spanning tree algorithm has brought this time down to

< 1 minute, now averaging in the 30-second range.

Intervendor If both vendors are GR-253-compliant, both vendors If both vendors are IEEE 802.3-compliant, both vendorsOperability can interoperate. OAM&P issues are created. can interoperate. OAM&P issues are created.

Maintenance Loopback capability for out-of-service tests. No loopback in Ethernet. Switch and router information canChallenges be obtained through remote monitoring (RMON) statistics.

Provisioning Provisioning of SONET network elements is done through Provisioning of Ethernet switches and routers is done Challenges line interface commands or an element management through line interface commands or an element management

system (EMS). system (EMS).

Fault Detection B1, B2, B3 detection. Frame check sequence (FCS) errors and link status.Will provide threshold crossing as per GR-253 PM. Programmable SNMP traps can be sent upon threshold crossing.Sectionalization in terms of section, line and path. Sectionalization in terms of inter-switch link span.

3.6.4 Resilient Packet Ring (RPR)

Resilient packet ring (RPR) is a technology that combines packet-switched networks with dual rings and supports sub-50 ms ring-based recoveryon packet-switched networks. RPR can run over SONET/SDH or native Ethernet transport networks and supports a significant degree ofbandwidth efficiency on rings through the implementation of bandwidth sharing, spatial reuse, and statistical multiplexing.

Table 3.2 — Comparison of SONET/SDH and native Ethernet



3.6.5 ATM

Ethernet can be carried over existing ATM networks by using the information in each Ethernet frame to map the frame to an appropriate ATM virtualcircuit and service class. Ethernet services can thus be provided over ATM with the same QoS and resiliency as ATM. This method allowsconsiderable flexibility in service topology, including point-to-point and multipoint-to-multipoint services and optimal levels of oversubscription.Greenfield deployments, however, are more likely to use IP/MPLS, rather than ATM, due to advantages in cost and scalability.

3.6.6 IP/MPLS

The first Ethernet-based carrier services were less expensive and more flexible than leased lines or frame relay services, and they also offered fullsupport for VLANs. However, they were not carrier class and lacked the reliability, scalability and security of traditional TDM and ATM services. In addition, the IP routers used to provide Ethernet IP services could not perform longest prefix match lookups at wire speed, resulting in lowerperformance.

Multiprotocol label switching (MPLS) is a control-plane packet-forwarding technology that is rapidly being adopted to overcome these drawbacksand make Ethernet “carrier class” – allowing Ethernet to transmit voice and other delay-sensitive applications. MPLS also makes the entire networkeasier to provision and engineer. As the name implies, MPLS technologies are applicable to multiple network layer protocol including IP, ATM andframe relay.

MPLS helps move traffic faster by building virtual circuits, or tunnels, called label-switched paths (LSPs) across the network (see Figure 3.9) andby using simple labels to make data-forwarding decisions. The ingress-edge label-switching router (LSR) analyzes the Layer 3 header of eachpacket to determine the destination address and assigns a label to the packet. The LSRs in the core only inspect the label in order to forward thepacket to the next hop in the LSP. At each hop, the LSR strips off the existing label and applies a new label, which tells the next hop how to forwardthe packet. The LSR at the egress edge removes the label and forwards the packet normally.

Label-switched paths (LSPs) can be established for virtual private networks to guarantee a certain level of performance or to route around networkcongestion. LSPs are similar to circuit-switched paths in ATM or frame relay networks, except that they are not dependent on a particular Layer 2 technology.



MPLS also provides other benefits, such as virtual private networking (VPN) to create IP tunnels through the network; traffic engineering (TE) toprovide traffic prioritization for different classes of traffic; quality of service (QoS); and bandwidth management. Another feature is fast rerouting,which allows traffic to be quickly transferred to a pre-established backup tunnel. This is similar to SONET’s protection switching.

Pseudo-wires, which emulate a native serviceover a packet-switched network (PSN) arespecified in the MPLS standards as a techniqueto carry TDM traffic and legacy access protocolssuch as ATM and frame relay over MPLS networksalongside Ethernet traffic. MPLS can be used withnative Ethernet over xWDM (dark fiber), over next-generation SONET/SDH networks usingGFP/LCAS/VCAT, or directly over SONET using 10 GigE WAN technology to connect toSONET/SDH ADMs, over RPR and ATM.

MPLS provides the assurance that carriers need to migrate all their transport services to a converged IP/MPLS core network (see Figure 3.10). This would eliminate the need for separate networks for each type of Layer 2 protocol.

Ingress-edge label-switched router

(LSR) labelsthe packets

Core LSR switches the packet using label-swapping

Label-switchedpath (LSP)

Egress-edge LSRremoves thelabels anddelivers the

packets

Figure 3.9 — MPLS network connecting two premises



Frame Relay

ATM

Ethernet

SONET

MPLS-BasedPacketized

MAN

IP/MPLSCore

OpticalOC-nOC-nOC-n

OC-nPort

UniversalPort

CirtualCircuits

Access Metro Core

Figure 3.10 — Convergence of services to an IP/MPLS core network


Introduction to Installation and Provisioning


4. Introduction to Installation and Provisioning

4.1 Quality and PerformanceLegacy transport technologies used in carrier networks, such as ATM, were designed to be able to guarantee measurable quality of service. This allowed service providers to establish service-level agreements with their customers.

A service-level agreement (SLA) is a legal contract between a service provider and a customer that specifies a required level of service. SLAs helpservice providers attract and retain customers, but there are also penalties associated with sub-standard service: poor customer satisfaction,increased spending on maintenance and, often, direct financial payouts. SLAs typically specify maximum downtime, mean-time-to-repair (MTTR)when outages occur, and minimum performance criteria.

Unfortunately, Ethernet was not designed with quality of service (QoS) in mind and, originally, offered no means to differentiate between low- andhigh-priority data. This made it difficult to combine different types of services, such as e-mail and voice communication over the same link, whileensuring that transfer rates met pre-established criteria. Service class extensions, such as type of service (ToS) and differentiated services (Diff Serv), have been added to IP, but these are still based on best-effort delivery and simply help to prioritize traffic flow without any SLA-type assurances. Ethernet class of service (CoS) can be supported only through VLANs (802.1p).

Regardless of which technique is used, various factors such as network congestion can affect the actual rate at which the data is transferred. For this reason, specific tests are required to verify Ethernet performance in order to ensure that the SLA requirements are met.

4.2 Ethernet Performance VerificationThe Internet Engineering Task Force (IETF) has put together a test methodology to address the issues of performance verification at the Layer 2and 3 levels. RFC 2544, Benchmarking Methodology for Network-Interconnect Devices, specifies the requirements and procedures for testingthroughput (performance availability), latency (transmission delay), back-to-back frames (link burstability), and frame loss (service integrity).




When these measurements are performed, they provide a baseline for service providers to define SLAs with their customers. They enable serviceproviders to validate the quality of the service delivered and can provide them with a tool to create value-added services that can be measuredand demonstrated to customers. For example, these tests provide performance statistics and commissioning verification for virtual LAN (VLAN),virtual private networks (VPNs) and transparent LAN services (TLS), all of which use Ethernet as an access technology.

The SLA criteria defined in RFC 2544 can be precisely measured using specialized test instruments. The performance verification is usually doneonce the installation is complete. The measurements are taken when the network is out of service to make sure that all parameters are controlled.

4.2.1 Test Configurations

Different configurations are possible for performing the tests. These are explained below.

Dual-test-set configuration

Two test sets are required for local/remote testing, also known as head-to-head testing (see Figure 4.1). This test configuration, also knownas ”master-slave”, is ideal for:

• End-to-end testing• Going through a routed network

This configuration, the user operates one test set, which controls the other by designating one as the local test set and the other as theremote test set. This makes it easy to determine in which direction thetraffic is flowing. The remote test set is controlled via the connectionunder test. During the test, results from both directions are visible onthe local test set.

Networkunder test

Figure 4.1 — Dual-test-set configuration (arrows show direction of traffic)



Dual-port configuration

In some cases, testing can be performed using one test set with two ports (see Figure 4.2). This is ideal for:

• Testing a switch locally• Lab environment• End-to-end testing with high port density

Single-port loopback configuration

The single-port loopback configuration is similar to the dual-port configuration inthat it requires only one test set. The difference is that the traffic does not go fromone port to another but simply loops from the transmit connection of one port tothe receive connection of the same port (see Figure 4.3). It is ideal for:

• DWDM systems• End-to-end testing with end devices that can loop back to the same port,

either with a cable or a software loopback

Note: Many systems (mainly Ethernet switches or routers) will not allow asimple loopback to the same port. This is because switches forward framesaccording to a destination MAC address. Routers work the same way, but usea destination IP address. If such a device is looped back to the same port, it willnot know where to forward the frames and will drop them. A special loopbackdevice that can correctly address the originating test set is required for theseconfigurations.

CustomerNetwork

Port 2

Layer 2 Switch10/100 Mb/s

1000 Mb/s

CustomerNetwork

Port 1

Port 1

Port 2

Port 1

Port 2

Switch A Switch B

Figure 4.2 — Dual-port configuration



4.2.2 RFC 2544 tests

The following sections describe each of the RFC 2544 tests. The test equipmentused should be able to generate and analyze traffic for 10/100/1000Base-T,1000Base-SX, 1000Base-LX and 1000Base-ZX full-duplex networks at all framesizes in order to test transparent connectivity for LAN-to-LAN services delivered viaATM, frame relay, next-generation SONET/SDH, SONET/SDH hybrid multiplexers,switched Ethernet, VLANs, dark fiber, WDM or other means. The instrumentsshould be capable of transmitting at full line rate, in order to allow the provider tocertify that the circuit is efficient and error-free at 100% utilization.

Some test instruments enable automated testing, which helps to ensure repeatableresults. Automation also provides ease of use for technicians in the field byenabling accurate, efficient measurements and providing reports they can give tocustomers for future reference related to their specific SLAs.

Testing can be performed end-to-end or end-to-core, depending on the SLA (see Figure 4.4). Remote testing is also possible.

CustomerNetwork

CustomerNetwork

Port 1TX

Port 2TX

CustomerNetwork

Port 1TX

Port 1TX

Loopback

On the same Port

λ1

Figure 4.3 — Single-port loopback configuration


Throughput

Throughput is the maximum rate at which none ofthe offered frames are dropped by the deviceunder test (DUT) or network under test (NUT).For example, the throughput test can be used tomeasure the rate-limiting capability of a switch.The throughput is essentially equivalent to thebandwidth and can be measured bidirectionallyusing a dual-port loopback configuration orunidirectionally using two test sets (see Figure 4.5).

The throughput test allows vendors to report asingle value, which has proven to be useful in themarketplace. Since even the loss of one frame ina data stream can cause significant delays whilewaiting for the higher-level protocols to time out,it is useful to know the actual maximum data ratethat the device can support. Measurementsshould be taken over an assortment of framesizes. Separate measurements should beperformed for routed and bridged data in thosedevices that can support both. If there is achecksum in the received frame, full checksumprocessing should be done.



10/100Base-T 10/100Base-T

Internet

Gigabit Ethernet

Remote Testing

Figure 4.4 — End-to-end, end-to-core, and remote testing



The following issues will affect throughput test results:

• Single path vs. aggregate – If data always takes the same path through a network,then short-term test results will be consistent. However, if the route is dynamicallychanged by MPLS fast reroute or by another traffic control protocol, then the trafficwill continually experience different environments and short-term test results will varyover time. In this case, a longer-term test is required to assess the worst case.

• Load – The amount of traffic on the network, on the access line, or generated bythe Ethernet tester will determine how traffic reaches the other end. Congestioncan result in dropped or lost frames, high latency, etc.

• Unidirectional vs. bidirectional testing – Bidirectional testing means testing asdata flows from A to B and back to A. As access link bandwidths tend to beasymmetrical (download bandwidth may exceed upload bandwidth, or vice versa),bidirectional testing provides only an overall indication of throughput.Unidirectional testing, first from A to B and then from B to A, allows for themeasurement of upload and download throughput separately.

• Checksum processing required on some protocols – Checksum processing slowsdata transmission and affects throughput, frame loss, etc. It is preferable to use atester that can test with or without checksum processing.

• Packet size – Smaller packets can transmit quicker, but testing with smallerpackets increases the likeliness of losing packets. Larger packets hold a greaterpercentage of payload vs. header. A compromise needs to be reached between allowingroom for other traffic (smaller packets) and the greater efficiency of larger packets.

OC-3STM-1

Dual-Port Configuration

OC-3STM-1

Dual-Test-Set Configuration

Figure 4.5 — Measuring throughput



Throughput test procedure3:

1. Send a specific number of frames at a specific rate through the DUT/NUT and then count the frames that are transmitted by the DUT/NUT.

2. If the count of offered frames is equal to the count of received frames, the rate of the offered stream is raised and the test is rerun.

3. If fewer frames are received than were transmitted, the rate of the offered stream is reduced and the test is rerun.

4. The throughput is the fastest rate at which the count of test frames transmitted by the DUT/NUT is equal to the number of test framessent to it by the test equipment.

Burst (Back-to-Back)

In this test, fixed-length frames are presented at a rate such that there is the minimum legal separation for a given medium between framesover a short to medium period of time, starting from an idle state. The back-to-back value is the number of frames in the longest burst that theDUT/NUT will handle without the loss of any frames.

Burst test procedure:

1. Send a burst of frames with minimum inter-frame gaps to the DUT/NUTand count the number of frames forwarded by the DUT/NUT.

2. If the count of transmitted frames is equal to the number of framesforwarded, the length of the burst is increased and the test is rerun.

3. If the number of forwarded frames is less than the numbertransmitted, the length of the burst is reduced and the test is rerun.

4. The back-to-back value is the number of frames in the longest burstthat the DUT/NUT will handle without the loss of any frames.

5. The trial length must be at least two seconds and should be repeated atleast 50 times, with the average of the recorded values being reported.

STM-1X

# of Bytes

STM-1

# of Bytes

Burst

Burst

Figure 4.6 — Back-to-back test



3 All test procedures are from RFC 2544 (http://www.faqs.org/rfcs/rfc2544.html).

Frame Loss

Frame loss is the percentage of frames that should have been forwarded by a networkdevice under steady state (constant) loads that were not forwarded due to lack ofresources. This measurement can be used in reporting the performance of a networkdevice in an overloaded state. It can be a useful indication of how a device would performunder pathological network conditions such as broadcast storms.

Frame loss test procedure:

......1. Send a specific number of frames at a specific rate through the DUT/NUT to be

...... tested and count the frames that are transmitted by the DUT/NUT.

......2. The frame loss at a particular line rate is calculated using the following equation:

...... Frame loss = x 100%

......3. Separate measurements should be taken for different frame sizes.

STM-1

86 % frames lost at 1000 Mb/s

STM-1

74 % frames lost at 900 Mb/s

.

.

....

Figure 4.7 — Frame loss test Transmitted frames – Received frames

Transmitted frames



Latency

For store-and-forward devices, latency is the time interval between frames (input and output); it starts when the last bit of the input framereaches the input port, and ends when the first bit of the output frame is seen at the output port. Round-trip latency is the time it takes a frameto come back to its starting point. Variability of latency can be a problem. With protocols like VoIP, a variable or long latency can cause degradationin voice quality.

Latency test procedure:

1. Determine the throughput of the DUT/NUT for each frame size.

2. Send a stream of frames at a particular frame size through the DUT/NUT at thedetermined throughput rate to a specific destination.

3. Send a tagged frame after 60 seconds and store timestamp A. Capture tag frame onreception side and store timestamp B.

4. The latency is timestamp B minus timestamp A.

5. The test must be repeated at least 20 times with the reported value being the average ofthe recorded values.

STM-1

Start Time:

Return Time:

Figure 4.8 — Round-trip latency test



4.3 Fiber CharacterizationAs GigE and 10 GigE are now considered alternatives to SONET/SDH in the MAN, fiber characterization is crucial for ensuring optimalperformance. Chromatic dispersion (CD) and polarization mode dispersion (PMD) are forms of optical dispersion that broaden pulses and limitthe transmission speed over long distances. These must be measured in order to ensure high-speed transmission. Specialized PMD and CDoptical measurement instruments perform these tests quickly and with minimal setup (see Figure 4.9 and Figure 4.10).

Figure 4.9 — Chromatic Dispersion Analyzer Figure 4.10 — PMD Analyzer



4.4 BERT over EthernetBecause transparent transport of Ethernet over physical media is becoming a common service, Ethernet is increasingly carried across a variety ofLayer 1 media (e.g., 10Base-FL, 100Base-FX, 1000Base-LX) over longer distances. There is therefore a growing need to certify Ethernet carriageon a bit-per-bit basis. This can be done using bit-error-rate testing (BERT).

BERT uses a pseudo-random binary sequence (PRBS) encapsulated into an Ethernet frame, making it possible to go from a frame-based errormeasurement to a BER measurement. This provides the bit-per-bit error-count accuracy required for the acceptance testing of physical-mediumtransport systems.

BERT over Ethernet should be used when Ethernet is carried transparently over the following Layer 1 media:

• Ethernet over DWDM

• Ethernet over CWDM

• Ethernet over dark fiber

• Ethernet over free-space optics

• Ethernet over wireless LANs

Figure 4.11 — Test set providing BERT over Ethernet. This instrument enables testing of transparent GigabitEthernet circuits running over an xWDM network as if they were SONET/SDH circuits.


www.exfo.com Ethernet Reference Guide EXFO 63

4.4.1 GigE and 10 GigE BERT over Dark Fiber and PONs

Carriers are increasingly using dark fiber and passive optical networks(PONs) to provide point-to-point and point-to-multipoint access links,respectively, using physical-layer fiber transceivers. When Ethernetservices are provided over these links, short light budgets and partialfiber faults will reduce GigE throughput. BERT over Ethernet testingallows providers to verify the ability to fully load the GigE bandwidthwithout any bit errors (see Figure 4.12).

4.4.2 GigE and 10 GigE BERT over a DWDM Network

When GigE is transported transparently across DWDM networks, wavelength crosstalk andtransponder fade-out reduce GigE throughput. Ethernet BERT is required to validate error-free GigE transmission across the DWDM ring (see Figure 4.13).

CPE

GigE

5-10 Km

POP

Figure 4.12 — Testing a GigE fiber point-to-point access link

DWDM Ring

OC-3OC-12Gigabit EthernetESCONOPTeraDWDM RingExtension Rings

CLEC Office

Loop

Figure 4.13 — Testing GigE transmission over a DWDM network



4.5 Ethernet Service Acceptance TestingThe type of testing required for Ethernet service acceptance testing depends on how theservice is carried on the network. Figure 4.14 shows how to test for switched transportor transparent physical transport using either RFC 2544 tests or BERT over Ethernet.

All of the tests that are part of the service-level agreement can be performed on eitherpart of the network (end-to-core) or on all of it (end-to-end). For both switched transportand transparent physical transport, end-to-end measurements can be performed byusing two portable units and testing from one end to the other. Another way of doingthis is to send a technician to one site, and setting up a second test device in thenetwork (e.g., in a central office) to test the other site. This type of testing is useful whentwo technicians cannot be sent at the same time or when the service provider isproviding access to the Internet.

Switch Transport

Service Accepted Service Rejected

Are SLA performance parameters met?

In media 100% error free?

RFC 2544

Yes No NoYes

BERT

Transparent Physical Transport

Is the Ethernet Service delivered via SwitchedTransport or via Transparent Physical Transport?

Figure 4.14 — Flow chart of Ethernet service acceptance testing


Commissioning Ethernet for Voice-over-IPand Video-over-IP Deployment


5. Commissioning Ethernet for Voice-over-IP and Video-over-IP DeploymentAs Ethernet services grow in popularity with enterprises, the rapid deployment of voice and video conferencing over Internet protocol is a toppriority for many service providers. Customers who switch from traditional voice and video-conference services to IP-based solutions, expect bothtoll-quality voice and high-quality video running over their Ethernet access lines. As a result, SLAs for VoIP and video conferencing outline detailedperformance criteria related to quality of service (QoS).

Service providers can confidently commit to these SLAs if the link is thoroughly tested when commissioned. A simple test plan that only validatesthe basic functionality of an Ethernet link (using ping, connectivity verification, etc.) leaves an operator exposed to poor network performance oncelive customer traffic begins. Knowing this problem but lacking test capabilities, some providers over-commission bandwidth to ensure SLAs willbe met. This expensive practice can be avoided by diligently confirming a link’s performance before activating a service.

Delay-sensitive applications such as VoIP and IP video are sensitive to performance parameters such as inter-packet delay (packet jitter) andpacket sequencing (out-of-order packets). Because multimedia traffic coexists with other types of data traffic, bandwidth-demanding applicationssuch as remote backup or FTP can degrade the quality of VoIP and video-conferencing services. This type of problem can be avoided by simulatingreal traffic patterns during commissioning and adjusting network parameters to provide priority for time-sensitive multimedia packets.

5.1 Essential Testing TechniquesWhen performing these tests, the following techniques must be used to ensure accurate results.

5.2 Simulating the Customer’s NetworkTo realistically simulate and analyze the interaction of multiple services being transported over a single link, the test instruments used must be ableto re-create the client’s network environment, both on a LAN and WAN level. To emulate customer premises equipment, parameters such as flowand throughput need to be controlled. To ensure that generated test traffic is carried with the same priority and routing scheme as the customer’sdata, VLAN tagging of test traffic is required.




5.3 Simulating Real-World Traffic PatternsIn order to qualify an Ethernet link carrying various services, multistream test-traffic analysis is required. This functionality allows a deployment teamto simulate normal link traffic by generating unique test streams for each of the multiple services typically sharing an access line. For example, a high-priority stream with variable bandwidth and frequent bursts of data replicates VoIP traffic, while a low-priority, continuous throughput streamsimulates off-site backup applications.

As representative client traffic is fundamental to an accurate test plan, the Ethernet tester used must be able to support a reasonable number ofindependently configurable streams. Normally, a maximum of ten streams is sufficient for commissioning applications. Streams should containframes that replicate the types of data the customer would typically use over the link. The following tables specify various Ethernet frame/payloadqualities that should be used to replicate various media streams.

Predefined type-P packet Description ValuesVoIP G.711 No compression algorithm on the voice channel IP packet size = 140 B

- Voice rate = 64 kb/s Data rate = 64 kb/s- VoIP payload = 100 B Line rate = 80 f/s

VoIP G.723.1 Compression on voice channel to: IP packet size = 64 B- Voice rate = 6.4 kb/s Data rate = 6.4 kb/s- VoIP payload = 24 B Line rate = 33.3 f/s

VoIP G.729 Compression on voice channel to: IP packet size = 50 B- Voice rate = 8 kb/s Data rate = 4 kb/s- VoIP payload = 10 B Line rate = 50 f/s

Table 5.1 — Common VoIP packet definitions as specified by the ITU



Video streaming Video payload size (bytes) Video bandwidth (f/s) Ethernet frame size (bytes)

Business Quality Videoconferencing 915 107 973NetMeeting Video LAN (videoconf) 779 77 837NetMeeting Video DSL (videoconf) 363 65 421NetMeeting Video 28K (videoconf) 288 5 346PictureTel StarCast (stream) 1343 155 1401RealAudio Radio (stream) 681 30 739Media Player 80K (stream) 697 15 755Media Player 20K (stream) 476 7 533Real Video 28K (stream) 384 8 442

When commissioning VoIP or video services, the test set used should be able to configure streams with these parameters.

When stressing a network with multiple streams, detailed measurements are performed on one stream while controlling the priority, bandwidth andcharacteristics of the others. This technique enables realistic network traffic simulation over a wide variety of typical boundary conditions.

5.4 Performing Unidirectional TestingA final key consideration in VoIP pre-deployment testing is the effect of traffic direction. As traffic or bandwidth over an access link tends to beasymmetrical (downloads exceed uploads, or vice versa), quality problems often occur predominantly in one direction. It is for this reason that one-way effects are often experienced in telephone conversations using VoIP — one caller hears echo, dropouts and delay, while the other hearsa perfectly clear conversation.

Table 5.1 — Common packet characteristics for multimedia applications including video



To ensure that unidirectional effects are accounted for, it is important to use atest setup that permits parameter measurement in each directionindependently. Most Ethernet testers can only perform measurements inloopback configuration (see Figure 5.1). This results in upload and downloadtest scores being combined into a single, averaged measurement, making itimpossible to separate upload and download issues.

It should be noted that one parameter — latency — cannot be measuredunidirectionally without sophisticated clock synchronization schemes (involving GPS signals, for example). Latency is typically tested with a loopbackconfiguration. All other performance metrics including throughput, burst, frame loss, and packet jitter should be measured unidirectionally to obtainaccurate test results.

Upload direction

Download direction

Remote (slave) Local (master)

Loopbacktesting

Upload direction

Download direction

Remote (slave) Local (master)

Unidirectionaltesting

Ethernet network

Figure 5.1 — Loopback and unidirectional testing


Monitoring Ethernet Networks



6. Monitoring Ethernet Networks

6.1 Ethernet Quality-of-Service AssuranceBecause SLAs specify minimum performance criteria for Ethernet services, it is important that service providers be able to continually monitorperformance and live traffic on the network. This monitoring helps maintain good quality of service (QoS) for clients of the network.

6.1.1 Performance and Traffic Monitoring

Performance monitoring can be achieved by polling networkelements or probes across the network for their performancestatistics. Simple network management protocol (SNMP) andremote monitoring (RMON) are the standard protocols used togather performance data from measurement probes or networkelements. In Ethernet monitoring applications, probes may consistof specialized hardware or may simply be software agents runningon a network element or a standard PC.

Probes analyze different protocol layers in order to provide aperformance evaluation of the Ethernet network. In activemonitoring applications, probes send synthetic data across thenetwork to provide a basis for performance evaluation. In passiveprobe installations, live traffic is examined without generatingsynthetic test traffic.


10/100Base-T 10/100Base-TAgent

Gigabit Ethernet

Probe

Probe

Agent

Figure 6.1 — Ethernet performance monitoring using external probes and software agents



Statistics and alarms provide a high-level view of the network in order to detect problems. By using probes or protocol analyzers on the problem segment,the service provider will usually be able to identify, troubleshoot and resolve most problems before a customer experiences degraded performance.

By gathering traffic statistics in a database, trending patterns can be provided to network management staff. With this data, the service providercan architect new network installations or proactively groom traffic through optimal routes to provide bandwidth to trouble areas. This approachgenerates additional revenues through customer retention and a reduction in SLA performance-penalty payouts.

6.2 Remote Testing for Ethernet in the First Mile Deployments Until recently, Ethernet deployment and maintenance wereexpensive endeavors compared with traditional alternatives; lackof sufficient remote network management solutions meantfrequent on-location troubleshooting and maintenance.

The recent ratification of the IEEE 802.3ah testing standard onEthernet in the first mile offers significant opportunities forservice provider OPEX reduction and quicker deployment ofEthernet services. This new standard created the operation,administration and maintenance (OAM) sub-layer within theEthernet/data-link layer of the Open Systems Interconnection(OSI) Reference Model (see Figure 6.3).


10/100Base-T 10/100Base-TAgent

Gigabit Ethernet

Probe

Probe

Agent

RMON RMON

Figure 6.2 — Ethernet traffic monitoring using RMON-compliant network elements and external probes



Test solutions based on the 802.3ah guidelines address all of the key challengescommonly encountered with Ethernet service deployment: reliability, performance, QoSassurance and network troubleshooting.

Key to the standard are specifications for remote loopback testing to customerpremises. This single-ended testing technique permits proactive network managementand speeds up restoration of failed services. In addition to loopback testing, 802.3ahalso provides guidelines for remote failure and event notification, link-monitoringstatistics, diagnostics, as well as the ability to collect historical performanceparameters from 802.3ah-compliant elements. Because this standard emulatescommon DS1/3 access maintenance practices, 802.3ah management solutions areeasily integrated into existing operations. As the 802.3ah standard is increasinglyadopted by system, switch and broadband equipment suppliers, remote testing andmonitoring deployment is becoming straightforward and cost-effective.

6.2.1 Access Line Management Using the 802.3ah Standard

Remote testing with 802.3ah involves three key elements:

• A demarcation device located between the provider and customer networks• A remote test-head capable of advanced performance evaluation and

commissioning functions• Management software capable of identifying and cataloging demarcation devices

and their location to simplify test access

ApplicationPresentation

SessionTransportNetworkData Link

LLC — Logical Link ControlOAM — 802.3ah Standard for Ethernet

MPMC — Multipoint MAC ControlMAC — Media Access Control

Physical

Figure 6.3 — Open Systems Interconnection (OSI) Reference Model,showing 802.3ah OAM sub-layer in data-link layer

Figure 6.4 — An Ethernet NIU made by ADC (customer and provider side)



6.2.2 Demarcation Devices

The most common demarcation device is a network interface unit (NIU), which marks the hand-off between client and provider.

Ethernet Layer 2 switches with 802.3ah compatibility may also beused as demarcation devices in some installations, but this isimpractical if a single switch serves multiple clients (as in an officetower) or if the switch is owned by the customer. As low-costdevices, NIUs are most often the service providers’ best choice fordemarcation. A typical NIU installation is shown in Figure 6.5.Several NIUs can be connected to a single, carrier-supplied switchto provide separate demarcations when there are multiplecustomers connected to a single access link.

NIUs are often combined with media converters for optical-to-electricalconversion between the fiber access line and the copper-basedEthernet commonly used in enterprise environments. Advanced NIUscan also perform rate conversion with bandwidth provisioning,allowing providers to remotely alter customer bandwidth on demand.802.3ah-compliant units can be remotely queried for usageinformation and link-performance statistics, and they will broadcastlink failures and events to network management systems.

6.2.3 Ethernet Test-Heads

An Ethernet tester is required for remote 802.3ah link testing.Compliant test sets can activate the loopback mode in the NIU,allowing advanced performance and troubleshooting tests to be

CarrierProvidedSwitch

CustomerProviderSwitch

NIU

ProviderNetwork

CustomerNetwork

MetroNetwork

10/100/1000 Mb/sEthernet Link

10/100/1000 Mb/sEthernet Link Enterprise

X-Based-SX or LXFiber

X-Based-TXUTP Copper

DemarcationPoint

Figure 6.5 — Typical NIU installation on an Ethernet access line

CarrierProvidedSwitch

Customer2NIU

NIU

NIU Customer3

Customer1

GigEAccess Link

DemarcationPoint

10 Mb/s

100 Mb/s

200 Mb/s

Figure 6.6 — Typical NIU installation with multiple customers on a single access link



conducted from a central office or other remote location. Two commonexamples are illustrated in Figure 6.7 and Figure 6.8. Tests commonly performedinclude RFC 2544-compliant performance analysis (throughput, latency, frameloss, burst tolerance), BERT and application-specific tests such as packet jitterfor VoIP and other delay-sensitive applications.

When customers report a problem with an Ethernet service, the cause isoften related to events or constraints within the customer’s network. Remote testing with an NIU allows service providers to quickly segment thenetwork up to the customer premises and subsequently determine if anetwork issue is within the access line (service provider’s responsibility) or related to customer-side problems (no further support required). This technique significantly reduces truck-rolls to customer premises,decreases troubleshooting time and results in faster service restoration.

Remote testing can also be used for commissioning, monitoring and SLAmanagement. Remote bandwidth provisioning is a typical example of theadvantages of an 802.3ah-based Ethernet access network. When acustomer requests additional bandwidth on their access link, the related NIUis remotely accessed by the provider and a message is sent to immediatelyincrease the throughput available to the customer. The NIU is then put intoloopback mode and remote Ethernet performance tests are conducted toensure that the expected bandwidth is available. A series of tests are thenperformed to ensure that revised SLA parameters will be met under variousnetwork conditions. With the new bandwidth assured and commissioned, theNIU is returned to pass-through mode and the customer’s traffic passes overthe upgraded link.

Metro NetworkSONET/SDH/DWDM

NIUCustomerPremises

EthernetSwitch

Ethernet TesterNOCRemote

Management

Figure 6.7 — Remote troubleshooting of performance on a link from a central office withcustomer-site NIU in loopback mode


NIUCustomer

Premises 1(under test)

EthernetSwitch

Ethernet Tester

CustomerPremises 2

Figure 6.8 — In a virtual private LAN a portable Ethernet tester can be used to test fromone customer location to a second site where an NIU is installed



6.2.4 Management Software

If a large number of NIUs are deployed in a provider’s network,management software that can actively catalog their location andstatus in order to facilitate remote testing operations. Automateddiscovery schemes identify active NIUs in real time and retrievecustomer-related information stored in the units. Interoperabilitybetween this database and the Ethernet test set allows for quickloopback activation to any customer on the network.


NIU 1

NIU 2

NIU 3

CustomerA

CustomerB

CustomerB

NOCRemote

Management

Database Customer NIU A 1 B 3 C 2

Central OfficeEthernet tester

With NIU discovery

Figure 6.9 — Automatic NIU discovery facilitates remote testing operations


Glossary


7. GlossaryAAdapter: Also known as a network interface card (NIC). An adapter isa circuit board installed in a computing device to connect it to anetwork. The adapter or NIC performs the hardware functions that arerequired to provide a computing device with physical communicationcapabilities.

Address Resolution Protocol (ARP): A network-layer protocol used inTCP/IP transmission. ARP is used by end stations to determine thephysical address of other stations on the same LAN.

Asynchronous: Said of transmission in which sending and receivingdevices are not synchronized. Data division is indicated by data itself,which carries these signals.

Asynchronous Transfer Mode (ATM): A data networking protocolused for high-bandwidth, low-delay, connection-oriented, packet-likeswitching and multiplexing.

Auto-Negotiation: Algorithm allowing two devices (at each end of a link)to negotiate common data service functions (i.e., transmission rate, half vs.full duplex, etc.)

BBackbone: Part of the network that joins several local-area networks,either inside a building or across a city or country. This is achievedthrough a cable connection between telecommunication or wiringclosets, floor distribution terminals or entrance facilities. In star networks,the backbone cable interconnects hubs and similar devices, as opposedto cables running between hub and station. The backbone is the part ofthe communications network that carries the heaviest traffic.

Backoff Delay: In Ethernet transmission, the backoff delay is the lengthof time that a station waits before retransmitting a frame, after a datacollision is detected. This operation applies to carrier-sense multiple-access networks with collision detect (CSMA/CD; see separate entry).

Baseband: A transmission method in which one single digital signaluses an entire bandwidth. The unmodulated signal is sent directly overthe transmission medium. Baseband is simpler, cheaper and lesssophisticated than broadband. All Ethernet media types are basebandexcept for 10Broad36, which is broadband.




Bandwidth: The range of frequencies required for proper transmissionof a signal. Bandwidth represents the amount of data that can betransmitted through a communications channel in a fixed amount oftime. For digital devices, it is usually expressed in bits (or bytes) persecond, whereas for analog devices, it is expressed in cycles persecond, or in hertz (Hz). The greater the bandwidth, the greater theinformation-carrying capacity and the faster the speed. A continuousfrequency range starting from zero is said to be baseband, while arange starting substantially above zero is considered broadband.

Bit: One binary digit

Bit Error Rate (BER): A measure of data integrity referring to thenumber of digital highs that are interpreted as lows (and vice versa),divided by the total number of bits received. The BER ratio is oftenexpressed as a negative power of ten.

Bridge: Specified in IEEE 802.1D standard, a bridge is a device thatconnects two or more networks at the data-link layer (Layer 2). Bridgesare not part of the collision domain; i.e., they may be used to split anetwork into multiple collision domains.

Broadband: A transmission medium whose bandwidth capacity issufficient to carry multiple voice, video or data channels simultaneously.Each channel is modulated to a different frequency bandwidth andoccupies a different place on the transmission medium; the signals arethen demodulated to their original frequency at the receiving end.10Broad36 is the only broadband Ethernet media type. All otherEthernet media types are considered baseband.

Broadcast: The act of sending a frame to all network stations. Alsodescribes the class of media (designed especially for CSMA/CDEthernet) in which all stations are capable of receiving a signaltransmitted by any other station.

Broadcast Address: A multicast address that identifies all the stationson a network.

Broadcast Domain: A restricted area that allows all connecteddevices to transmit and receive information from each other. Thedevices are interconnected through bridges, allowing them to share thetransmission medium and, consequently, the data.

Byte: A group of 8 bits. Also known as an octet.



C

Carrier Sense: A method of detecting the presence of signal activityon a common channel. With Ethernet, a method of detecting whetheranother station is transmitting.

Carrier-Sense Multiple-Access with Collision Detection (CSMA/CD):A network access method used by Ethernet in which a station listensfor traffic before transmitting. If two stations transmit simultaneously, acollision is detected and both stations wait a brief time beforeattempting to transmit again. So called because it a) allows multiplestations to access the broadcast channel at will, b) avoids contentionvia carrier sense and deference, and c) resolves contention via collisiondetection and retransmission.

Channel: A logical medium in a communication system over whichdata is transmitted.

Chromatic Dispersion (CD): Phenomenon caused by the wavelengthdependence of group velocity in an optical fiber. Since any practicallight source has a certain spectral width, CD results in pulsebroadening.

Coarse Wavelength-Division Multiplexing (CWDM): Method ofcombining multiple signals on laser beams at various wavelengths fortransmission along fiber-optic cables. CWDM uses fewer channelsthan DWDM, but more than standard WDM.

Collision: A meeting of two or more data signals. A collision occurswhen more than one station transmits signals concurrently over aCSMA/CD (Ethernet) transmission medium.

Collision Detect (CD): A method to detects two or more simultaneoustransmissions on a common signal channel.

Collision Domain: A single CSMA/CD network, consisting of an areain a network where data packets can collide. Collisions occur whentwo or more Ethernet stations are within the same collision domain andboth transmit at the same time. Ethernet stations separated by arepeater are in the same collision domain, while stations separated bya bridge are in different collision domains. The concept of collisiondomain applies only to half-duplex Ethernet. Collisions do not occur infull-duplex Ethernet configurations.

Concentrator: LAN device allowing multiple network devices to beconnected to the LAN cabling system through a central point.Sometimes called a hub.

Contention: Interference between colliding transmissions (seecollisions). Normal part of Ethernet CSMA/CD protocol.

Crossover Cable: A twisted-pair patch cable, wired to route thetransmitted signals from one element to the received signals of anotherelement, and vice versa.



Cyclic Redundancy Check (CRC): Error-checking technique usedto ensure the accuracy digital-code transmission over acommunications channel. The transmitted signals are divided intopredetermined lengths which, used as dividends, are divided by afixed divisor. The remainder of the calculation is appended onto andsent with the message. At the receiving end, the computerrecalculates the remainder. If it does not match the transmittedremainder, an error is detected.

D

Data-Link Layer: Layer 2 of the OSI reference model. This layer takesdata from the network layer and passes it on to the physical layer (layer1). The data-link layer is responsible for transmission and reception ofEthernet frames, 48-bit addressing, etc. It includes both the mediaaccess control (MAC) and logical link control (LLC) layers.

Dense Wavelength-Division Multiplexing (DWDM): A technologythat enables a single optical fiber to carry multiple data channels (orwavelengths). Commercial DWDM systems can have as many as 160separate channels.

Destination MAC Address: Address identifying the station or stationson a LAN to which a frame is being sent.

DIX: Acronym identifying the three companies that released the originalEthernet specification in 1980: Digital, Intel, and Xerox.

Duplex: Circuit used to transmit signals simultaneously in both directions.

E

Electronic Industry Association (EIA): An association ofmanufacturers and users that establishes standards and publishes testmethodologies. Formerly known as RMA or RETMA.

Ethernet Version 2: The original Ethernet specification produced byDigital, Intel, and Xerox (DIX) that served as the basis for the IEEE802.3 Ethernet standard.

Excessive Collision Error: Error that causes frame loss. This type oferror occurs when a station receives 16 consecutive collisions whileattempting to transmit a single frame; then the frame is dropped due tothe excessive collisions.



F

Fast Ethernet: Ethernet standard supporting 100 Mb/s operation.

Fast Link Pulse (FLP): A link pulse that encodes information used inthe Auto-Negotiation protocol. Fast link pulses consist of bursts of thenormal link pulses originally used in 10Base-T.

Fiber-to-the-x (FTTx): The x in fiber-to-the-x is a variable indicating the point at which the fiber in a network stops and copper (coaxial or twisted-pair) cabling takes over; e.g., fiber-to-the-home,fiber-to-the-curb, etc. The further the fiber goes, the wider thebandwidth, the quicker the speed, and the more applications andservices can be offered.

Filtering: Process that uses bridges and switches to help reduce thelevel of congestion on a LAN. A filtering bridge or switch forwards apacket from one LAN segment to another only as required. Packetsthat are not forwarded by a bridge or switch are said to be filtered.

Filtering Rate: The maximum number of frames per second that a bridge or switch can continuously receive, parse, and make a forwarding decision on.

Flow Control: The process of controlling data transmission at thesender to avoid overfilling buffers and loss of data at the receiver.

Forwarding: The process of moving frames from one port to another in abridge or switch.

Forwarding Rate: The maximum number of frames per second that canbe forwarded by a bridge or switch, assuming no congestion at theoutput port.

Frame: The sequence of bits that form the unit of data transmission atthe LAN data-link layer or medium access-control layer. In Ethernet, aframe consists of the sequence of bits transmitted by a station from thepreamble through the frame check sequence. Also known as a packet.

Frame Bursting: A technique permitted only in half-duplex GigabitEthernet networks. Frame bursting optionally allows a station totransmit a series of frames without relinquishing control of thetransmission medium. It improves the performance of Gigabit Ethernetwhen transmitting short frames.

Frame Check Sequence (FCS): An encoded value appended to eachframe by a transmitting station to allow transmission errors to bedetected by the receiving station. Implemented as a 32-bit cyclicredundancy check (CRC) code.

Full-Duplex: Data transmission over a circuit capable of transmitting inboth directions simultaneously. For Ethernet, full-duplex operation wasdefined in the IEEE 802.3x standard.



G

Gb/s or Gbps: Gigabits per second. One Gb/s equals one billion bits per second.

Generic Framing Procedure (GFP): Traffic adaptation protocolproviding convergence between packet-switched and transmissionnetworks. GFP elegantly maps packet-based protocols such asEthernet, Fibre Channel, FICON, ESCON, and various forms of digitalvideo into SONET/SDH, typically using virtual concatenation toprovide right-sized pipes for data services.

Giants: Giants are frames that are longer than the maximum Ethernetsize (giant frames > 1518/1522 bytes with bad FCS, whereas oversizeframes > 1518/1522 bytes with good FCS). Giant packets usuallyoccur when you have a jabbering node on your network; i.e., a nodethat is continuously transmitting, or transmitting improperly for shortbursts – probably due to a bad transmitter on the NIC. Giants can alsobe caused by packets being corrupted as they are transmitted, eitherby the addition of garbage signals, or by the corruption of the bits thatindicate frame size.

Gigabit Ethernet (GigE): A version of Ethernet that operates at 1 Gb/s(1000 Mb/s).

Group Address: An address specifying a group of logically relatedstations on a network. Also called a multicast address.

H

Half-Duplex: Data transmission over a circuit capable of transmittingin either direction, but not simultaneously. For Ethernet, the CSMA/CDmethod is a half-duplex protocol.

Headend: The equipment in a cable system which receives the variousprogram source signals, processes them, and retransmits them tosubscribers.

Hub: A device at the center of a star topology network. Hubs can beactive (where they repeat signals set to them) or passive (where theydo not repeat but merely split signals sent through them). Hub mayrefer to a repeater, bridge, switch, router, or any combination of these.

I

IEEE: Institute of Electrical and Electronics Engineers. A professionalorganization and standards body. The IEEE Project 802 is the groupwithin IEEE responsible for LAN technology standards.

IEEE 802.1: The IEEE standards committee defining high-levelinterfaces, network management, internetworking, and other issuescommon across LAN technologies.



IEEE 802.2: The IEEE standards committee defining logical linkcontrol (LLC).

IEEE 802.3: The IEEE standards committee defining Ethernet networks.

Individual Address: A MAC address that identifies a single station.The low-order bit of the first byte (first bit transmitted) of an individualaddress is always 0.

Intelligent Hubs: Wiring concentrators that can be monitored andmanaged by network operators.

Inter-Frame Gap (IFG): The delay or time gap between frames. Alsocalled inter-packet gap.

Internet Protocol (IP): Method or protocol by which data is sent fromone computer to another on the Internet. Each computer on the Internethas at least one IP address that uniquely identifies it from all othercomputers on the Internet. Because of these standardized IPaddresses, the gateway receiving the data can keep track of, recognizeand route messages appropriately.

Inter-Packet Gap (IPG): The delay or time gap between packets. Alsocalled inter-frame gap.

J

Jabber: Term used with Ethernet to describe the act of continuouslysending data. A jabbering station is one whose circuitry or logic has failed,and which has locked up a network channel with its incessant transmission.

Jitter: The slight movement of a transmission signal in time or phasethat can introduce errors and loss of synchronization. More jitter will beencountered with longer cables, cables with higher attenuation, andsignals at higher data rates. Also, called phase jitter, timing distortion,or intersymbol interference.

L

LAN Adapter: see Local-Area Network and Network Interface Card

Link: A transmission path between two points. The link does not includeany of the terminal equipment, work-area cables, or equipment cables.

Link Aggregation: Link Aggregation provides for increased linkavailability and bandwidth between two Ethernet stations by allowingmultiple physical links to be combined to operate as a single logicallink. Defined by the 802.3ad Working Group. Also called trunking.



Link Segment: In Ethernet, a point-to-point segment that connects twoand only two transceivers at its endpoints.

Local-Area Network (LAN): A term used to refer to a form ofnetworking technology that implements a high-speed, relatively shortdistance form of computer communications. Ethernet is one type of LAN.

Logical Link Control (LLC): A protocol defined in the IEEE 802.2standard for data-link-level transmission control. It is the upper sublayerof the IEEE Layer 2 (OSI) protocol that complements the MACprotocol. LLC is independent of any specific LAN technology.

M

MAC Address: The 48-bit address used in Ethernet to identify astation. Generally a unique number that is programmed into a device attime of manufacture.

MAC Frame: Name for the data unit exchanged between peer MediumAccess Control sublayer entities. Also called simply a "frame".

Manageable Hubs: Another definition for intelligent hubs. Each of theports on the managed hub can be configured, monitored, and enabledor disabled by a network operator from a hub management console.

Mb/s or Mbps: Megabits per second. One Mb/s equals one millionbits per second.

Media: Wire, cable, or conductors used for transmission of signals.

Medium Access Control (MAC): A mechanism operating at the datalink layer of local-area networks which manages access to thecommunications channel (medium). It forms the lower layer of the IEEEdata link layer (OSI layer 2) which complements the Logical Link Control (LLC). MAC is a media-specific protocol within the IEEE 802 specifications.

Medium-Dependent Interface (MDI): The connector used to makethe mechanical and electrical interface between a transceiver and amedia segment. An 8-pin RJ-45 connector is the MDI for the 10Base-T,100Base-TX, 100Base-T2, 100Base-T4, and 1000Base-T media systems.

Media-Independent Interface (MII): Used with 100 Mb/s Ethernetsystems to attach MAC level hardware to a variety of physical mediasystems. Similar to the AUI interface used with 10 Mb/s Ethernetsystems. An MII provides a 40-pin connection to outboard transceivers(also called PHY devices).



Metropolitan-Area Network (MAN): A network, often ringed instructure, that covers an entire city and its suburbs. Also known as ametro network.

Multicast: An addressing mode in which a given frame is targeted to agroup of logically related stations.

Multicast Address: An address specifying a group of logically relatedstations on a network. Also called a group address.

N

Network Interface Card (NIC): Also known as an adapter. An NIC iscircuit board installed in a computing device to connect it to a network.The NIC or adapter performs the hardware functions that are required toprovide a computing device with physical communication capabilities.

Node: End point of a network connection. Nodes include any deviceconnected to a network such as file servers, printers, or workstations.

N-Way: Name originally used for the Ethernet Auto-Negotiation algorithm.

O

Octet: Eight bits (also called "byte")

Optical Time-Domain Reflectometry (OTDR): A method forevaluating optical fiber based on detecting and measuringbackscattered (reflected) light. Used to measure fiber length andattenuation, evaluate splice and connector joints, locate faults, andcertify cabling systems.

Open Systems Interconnection (OSI): A communications referencemodel developed by the International Standards Organization (ISO) todefine all of the services a LAN should provide. This model definesseven layers, each of which provides a subset of all of the LANservices. This layered approach allows small groups of related servicesto be implemented in a modular fashion that makes designing networksoftware much more flexible.



P

Packet: Bits grouped serially in a defined format, containing a command or data message sent over a network. Same as a frame.

Packet Jitter: Also known as IP packet delay variation (IPDV). Thisvariation is defined for a selected pair of packets within the continuousstream of packets going from measurement point 1 (MP1) toMeasurement point 2 (MP2). The IPDV is the difference between theone-way delay of the selected packets.

Parallel Detection: An auto-negotiation device's means to establishlinks with non-negotiation, fixed-speed devices.

Passive Optical Network (PON): Network in which fiber-optic cabling(instead of copper) brings signals all or most of the way to the end-user. It is described as passive because no active equipment(electrically powered) is required between the central office (or hub)and the customer premises. Depending on where the PON terminates,the system can be described as an FTTx network, which typically allowsa point-to-point or point-to-multipoint connection from the central officeto the subscriber’s premises; in a point-to-multipoint architecture, a number of subscribers (for example, up to 32) can be connected tojust one of the various feeder fibers located in a fiber distribution hub,dramatically reducing network installation, management andmaintenance costs.

Pause Frames: An optional flow-control technique for full-duplexEthernet networks. One end station may temporarily stop all traffic fromthe other end station by sending a pause frame.

Physical Address: The unique address value associated with a givenstation on the network. An Ethernet physical address is defined to bedistinct from all other physical addresses on the network.

Physical Layer: Layer one of the seven-layer ISO Reference Model forOpen Systems Interconnection. This layer is responsible for thetransmission of signals – electrical, optical, or radio – betweencomputing machines.

Polarization Mode Dispersion: Dispersion of light causing a delaybetween the two principal states of polarization propagating along a fiber or through a device due to the birefringence properties of the material.

Preamble: A sequence of 62 encoded bits transmitted (by a station)before each frame to allow for the synchronization of clocks and otherphysical-layer circuitry at other stations on the channel.

Propagation Delay: The signal transit time through a cable, networksegment, or device.

Protocol: A formal set of rules governing the format, timing,sequencing and error control of data exchange across a network. Many protocols may be required and used on a single network.



R

Registered Jack (RJ): A term from the telephone industry, used forjacks (connectors) that were registered for use with particular types oftelephone services.

Repeater: A device that receives, amplifies (and sometimes reshapes),and retransmits a signal. It is used to boost signal levels and extend thedistance a signal can be transmitted. It can connect two or more LANsegments and physically extend the distance of a LAN. It immediatelycopies all bits arriving on each segment to all other segments, whetheror not they are part of a valid frame.

RJ-45: A USOC code identifying an 8-pin modular plug or jack usedwith unshielded twisted pair cable. Officially, an RJ-45 connector is atelephone connector designed for voice grade circuits only. RJ-45 typeconnectors with better signal handling characteristics are called 8-pinconnectors in most standards documents, though most peoplecontinue to use the RJ-45 name for all 8-pin connectors.

Routers: These are more complex internetworking devices that arealso typically more expensive than bridges. They use Network LayerProtocol Information within each packet to route it from one LAN toanother.

Runt Frame: An Ethernet frame that is less than the minimum length of64 bytes with bad FCS (whereas undersize frames < 64 bytes with

good FCS). In a half-duplex Ethernet environment, runt frames are almostalways caused by collisions. If runt frames occur when collisions are nothigh or in a full-duplex Ethernet environment, then they are probably theresult of underruns or bad software on a network interface card.

S

Segment: On Ethernet, a media segment may be made up of one ormore cable sections joined together to produce a continuous cable forcarrying Ethernet signals.

Shared Ethernet: Same as half-duplex (CSMA/CD) Ethernet.

Simplex Transmission: Data transmission over a circuit capable oftransmitting in one preassigned direction only.

Slot Time: A key parameter for half-duplex Ethernet network operation.Defined as 512 bit times for Ethernet networks operating below 1 Gb/s, and 4096 bit times for Gigabit Ethernet. In order for eachtransmitter to reliably detect collisions, the minimum transmission time fora complete frame must be at least one slot time, whereas the round-trippropagation delay (including both logic delays in all electroniccomponents and the propagation delay in all segments) must be lessthan a slot time.

SNMP: Simple Network Management Protocol



Spanning Tree: A structure that includes all the bridges and stationson an extended LAN in which there is never more than one active pathconnecting any two stations.

Star Topology: A network configuration in which there is a centralpoint to which a group of systems are directly connected. Alltransmissions from one system to another pass through this centralpoint. Ethernet 10Base-T is one example of a media system that usesa star topology. All stations are connected through a central devicecalled a hub.

Station: A unique, addressable device on a network. A station isidentified by a destination address (DA).

Station Address: see MAC Address

STP: Shielded Twisted Pair

Switch: A switch is a multi-port bridge. Each port on the switch is in itsown collision domain.

Synchronous: Transmission in which the data character and bits aretransmitted at a fixed rate with the transmitter and receiver being synchronized.

Synchronous Digital Hierarchy (SDH): Standardized by theInternational Telecommunication Union (ITU-TSS). A protocol fortransmitting information over optical fiber.

Synchronous Optical NETwork (SONET): Standardized by theAmerican National Standards Institute (ANSI). A protocol for backbonenetworks, capable of transmitting at extremely high speeds andaccommodating gigabit-level bandwidth.

Time-Domain Reflectometry (TDR): A technique for measuring cablelengths by timing the period between a test pulse and the reflection ofthe pulse from an impedance discontinuity on the cable. The returnedwaveform reveals many undesired cable conditions, including shorts,opens, and transmission anomalies due to excessive bends orcrushing. The length to any anomaly, including the unterminated cableend, may be computed from the relative time of the wave return andnominal velocity of propagation of the pulse through the cable. Seealso Optical Time-Domain Reflectometry.

U

Unicast Address: An address that is assigned to uniquely identify asingle station on a network.

Unshielded Twisted Pair (UTP): Twisted pair cabling that includes no shielding. UTP most often refers to the 100 Ω Category 3, 4, and 5 cables specified in the TIA/EIA 568-A standard.



V

Virtual Concatenation (VCAT): Process enabling transport pipes to be"right-sized" for various data payloads by allowing SONET/SDHchannels to be multiplexed in arbitrary arrangements. VCAT breaksdown data packets and maps them into the base units of TDM frames.This data is then grouped in multiple data flows of varying size to createlarger, aggregate payloads optimally sized to match availableSONET/SDH pipe capacity. VCAT is applied at the end-points of theconnections, which permits each channel used to be independentlytransmitted through a legacy transport network.

Virtual LAN: A method in which a port or set of ports in a bridge orswitch are grouped together and function as a single "virtual" LAN.

Virtual Private Network (VPN): One or more wide-area network linksover a shared public network, typically over the Internet or an IPbackbone from a network service provider (NSP), that simulates thebehavior of dedicated WAN links over leased lines.

Voice-over-Internet-Protocol (VoIP): Refers to communicationsservices—voice, facsimile and/or voice-messaging applications—thatare transported via the Internet,rather than the public switched telephonenetwork. In an Internet-based telephone call, the voice signals areconverted to digital format and compressed/translated intoInternetprotocol (IP) packets for transmission over the Internet; the process isreversed at the receiving end.

W

Wavelength-Division Multiplexing (WDM): Optical transmissiontechnique that uses different light wavelengths to send data.Combination of two or more optical signals for transmission over acommon optical path.

Wide-Area Network (WAN): A network that links data processing andtelecom equipment over a larger area than a single work site ormetropolitan area. A WAN usually links cities and is based on X.25packet switching.

0-9

10 GigE: 10 Gigabit Ethernet

4B/5B Code: Scheme used to encode data for transmission in which4-bit binary data values are encoded into 5-bit symbols for transmissionacross the network media. 4B/5B is used with Ethernet 100Base-TXand 100-Base-FX media systems.

8B6T: Signal encoding method used with the 100Base-T4 Ethernetmedia system.

8B/10B Code: Scheme used to encode data for transmission in which8-bit binary data values are encoded into 10-bit symbols fortransmission across the network media. 8B/10B is used with1000Base-X Gigabit Ethernet media systems and 10G Base-LX4.



LLC

Logical Link Control (see entry in glossary)

LSP

Label-Switched Path

LSR

Label-Switching Router

M

MAC

Medium Access Control (see entry in glossary)

MAN

Metropolitan-Area Network (see entry in glossary)

Mb/s

Megabits per second. One Mb/s equals one million bits per second.

MDI

Acronyms Index



9. Acronyms IndexAADM Add/Drop Multiplexer

APS Automatic Protection Switching

ARCNET Attached Resource Computer Network

ARP Address Resolution Protocol (see entry in glossary)

ATM Asynchronous Transfer Mode (see entry in glossary)

BBER Bit Error Rate (see entry in glossary)

BERT Bit-Error-Rate Testing

b Bit (one binary digit)

B Byte (group of 8 bits)

CCD 1. Chromatic Dispersion (see entry in glossary)

2. Collision Detect (see entry in glossary)

CE Customer Edge

CIR Committed Information Rate

CoS Class of ServiceCRC Cyclic Redundancy Check (see entry in glossary)

CSMA/CD Carrier-Sense Multiple-Access with Collision Detect (see entry in glossary)

CRC Cyclic Redundancy Check (see entry in glossary)

CWDM Coarse Wavelength-Division Multiplexing (see entry in glossary)

DDIX Digital, Intel, and Xerox (the three companies that

released the original Ethernet specification in 1980)

DUT Device Under Test

DWDM Dense Wavelength-Division Multiplexing (see entry in glossary)

EEIA 1. Electronic Industry Association (formerly RMA

or RETMA). 2. Ethernet Internet Access

E-LAN Ethernet LAN



E-Line Ethernet Line

EMS Element Managing System

EPL Ethernet Private Line

EPLan Ethernet Private LAN

ESCON Enterprise System Connectivity

EVC Ethernet Virtual Connection

EVPL Ethernet Virtual Private Line

EVPLan Ethernet Virtual Private LAN

FFCS Frame Check Sequence (see entry in glossary)

FDDI Fiber-Distributed Data Interface

FDX Full-Duplex Ethernet

FSO Free-Space Optics

FTTx Fiber-to-the-Building, Fiber-to-the-Home, Fiber-to-the-Curb, etc.

GGb/s or Gigabits per second. One Gb/s equals one billion bitsGbps per second.

GFP Generic Framing Procedure (see entry in glossary)

GigE Gigabit Ethernet (operates at 1 Gb/s; i.e., 1000 Mb/s).

HHFC Hybrid Fiber Coax

IIEEE Institute of Electrical and Electronics Engineers

IFG Inter-Frame Gap (see entry in glossary) IP Internet Protocol (see entry in glossary)

IPG Inter-Packet Gap (see entry in glossary)

LLAN Local-Area Network (see entry in glossary)

LLC Logical Link Control (see entry in glossary)

LSP Label-Switched Path

LSR Label-Switching Router



MMAC Medium Access Control (see entry in glossary)

MAN Metropolitan-Area Network (see entry in glossary)

Mb/s or Megabits per second. One Mb/s equals one million bitsMbps per second.

MDI Medium-Dependent Interface (see entry in glossary)

MII Media-Independent Interface (see entry in glossary)

MEF Metro Ethernet Forum

MEN Metropolitan Ethernet Network

MON Metropolitan Optical Network

MPLS Multiprotocol Label Switching

MSPP Multiservice Provisioning Platform

MTTR Mean Time to Repair

NNIC Network Interface Card (see entry in glossary)

NIU Network Interface Unit

NUT Network Under Test

OOAM&P Operation, Administration, Maintenance and Provisioning

OTDR 1. Optical Time-Domain Reflectometry (see entry in glossary) 2. Optical Time-Domain Reflectometer

OSI Open Systems Interconnection (see entry in glossary)

PPHB Per-Hop Behaviour

PMD Polarization Mode Dispersion (see entry in glossary)

PON Passive Optical Network (see entry in glossary)

POTS Plain Old Telephone System

PRBS Pseudo-Random Binary Sequence

PVC Permanent Virtual Circuit

QQoS Quality of Service



RRJ Registered Jack (see entry in glossary)

RMON Remote Monitoring

RPR Resilient Packet Ring

SSDH Synchronous Digital Hierarchy (see entry in glossary)

SLA Service-Level Agreement

SNMP Simple Network Management Protocol

SONET Synchronous Optical NETwork (see entry in glossary)

STP Shielded Twisted Pair

TTDR Time-Domain Reflectometry (see entry in glossary)

TE Traffic Engineering

TLS Transparent LAN Service

ToS Type of Service

UUTP Unshielded Twisted Pair (see entry in glossary)

VVCAT Virtual Concatenation

VLAN Virtual LAN (see entry in glossary)

VoIP Voice-over-Internet-Protocol (see entry in glossary)

VPLS Virtual Private LAN Service

VPN Virtual Private Network (see entry in glossary)

VPSN Virtual Private Switched Network

WWAN Wide-Area Network (see entry in glossary)

WDM Wavelength-Division Multiplexing (see entry in glossary)



Notes


Acknowledgements

This guide would not have been possible without the collaboration and teamwork of EXFO staff; particularly, the technical expertise of Mr. Bruno Giguère, B.Eng., Ethernet Product Manager; Mr. Matthew Demyttenaere, B.Eng., Application Engineer; Mr. Andre Leroux, M.Eng.,Systems Engineer; and Mr. Scott Sumner, M.Eng., Strategic Marketing Manager.

No part of this guide may be reproduced in any form or by any means without the prior written permission of EXFO.

Printed and bound in Canada

ISBN 1-55342-004-7

Legal Deposit—National Library of Canada 2005Legal Deposit—National Library of Quebec 2005

© 2005 EXFO Electro-Optical Engineering Inc., Quebec City, Canada. All Rights Reserved.Ethernet Reference Guide: Your Everyday Ethernet Testing Reference Tool, 1st edition


Unit price: US$19.95

For details on any of our products and services,or to download technical and application notes,visit our website at www.exfo.com.

PBEG

.1AN

05/

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