DCN286Introduction to Data Communication

Technology

Session 7

Review1) Which type of cabling is the most appropriate choice for Ethernet connectivity from a switch to a workstation?

a) Coax b) UTPc) Fibre-optic d) RJ-11

2) Comparing switches, hubs, repeaters and bridges, which of these devices typically have multiple ports that provide a convenient connection point for end-user computers (Select the two best answers)?

a) Repeater b) Switchc) Bridge d) Hub

3) For which of the following do you need a cross-over cable?a) Connecting a switch to a switch b) Connecting a switch to a routerc) Connecting a workstation to a hub d) Connecting a workstation to a

switch

4) What data-transmission method does a WAN use?a) Parallel b) Serialc) Single d) None of the answers

are correct

5) Which of the following best describes a DCE device?a) User device at the end of a network b) Equipment that serves as the datac) Physical devices such as protocol source or destination

translators and multiplexers d) Device that provides the clocking rate

for a serial connection

Objectives

Ethernet NamingEthernet StandardsEthernet FramesMAC AddressesCSMA/CDFull Duplex, Half Duplex, Collision DomainsDeterministic and Nondeterministic Media Access10Mbps Ethernet10BASE-T Ethernet100Mbps EthernetGigabit Ethernet

Note:Hubs are represented by the symbol:

Switches are represented by the symbol:

Ethernet Names consist of three parts:

Speed – Transmission Type – Cabling

Speed – measured in Mbps10 – 10Mbps100 – 100Mbps1000 – 1Gbps

Transmission TypeBASE – baseband transmissionBROAD – broadband transmission

Cabling – type of cableT – UTPF – Fibre# - coaxial, provides maximum length in 100m (2, 5,

etc)4

Ethernet Naming

Transmission Type

BASE – baseband transmissionUses a single frequency for transmitting data

BROAD – broadband transmissionUses a range of frequencies for transmitting data

E.g. FM radio is BROADBAND, a range of 200kHz is used, with the station's defined frequency in the middle.

Station: 97.5MHz (“97.5 on your FM dial” as the announcer would say) uses a range of frequencies from 97.4MHz to 97.6MHz

10BROAD36, 10BASE5, 100BASE-FX, 10BASE-T? 5

Ethernet Naming

IEEE Ethernet StandardsOriginated by Xerox in 1970s

DIX EthernetXerox teamed up with Intel and Digital Equipment Corp (DEC) to release products and establish proprietary standards.

DIXv2Second release of DIX (version 2) publish in 1980. The basis for 10BASE5

IEEE took over Ethernet standards from the original companies in February 1980 (giving the committee its name: 802)

6

Ethernet Standards

IEEE802 created several sub-committees for different LAN standards:IEEE802.1 – LAN management and control functions

IEEE802.2 – standards that apply to several types of LANs

IEEE802.3 – Ethernet standards10BASE5 – 198010BASE2 – 198510BASE-T – 1990Fast Ethernet (100Mbps) – 1995Gigabit Ethernet - 1Gbps 199810Gigabit Ethernet – 10Gbps - 2002

IEEE802.4 – Token Bus LANs

IEEE802.5 – Token Ring LANs7

Ethernet Standards

IEEE802.1 – LAN Management and control functionsManagement and control functions that could be used by any IEEE802 LAN – e.g. Spanning Tree Protocol

IEEE802.2 – Standards that apply to several types of LANsStandardize features that encompassed three early LANs defined by 802.3, 802.4, 802.5.

They determined that the LAN types needed to control the LAN using a set of logic and rules.

The standard was named Logical Link Control - LLC

8

Ethernet Standards

Ethernet LAN Physical Layer

9

Ethernet Standards - OSI Model

Data LinkLayer

PhysicalLayer

ISO LayersE

ther

net

IEEE 802.2 (Logical Link Control - LLC)

IEEE 802.3 (Media Access Control – MAC andphysical details including cabling details)

10B

AS

E2

802.

3 -

10B

AS

E5

10B

AS

E-T

10B

AS

E-F

802.

3u -

100

BA

SE

-TX

100B

AS

E-F

X

100B

AS

E-T

4

802.

3ab

- 10

00B

AS

E-T

802.

3z -

100

0BA

SE

-X

NetworkAccessLayer

TCP/IPLayers

LLC

MAC

MAC SublayerThe MAC sublayer performs functions that the OSI Physical Layer cannot (by definition within standards):

Physical Layer cannot communicate with upper layer protocols. MAC sublayer can

Physical Layer cannot identify other computers. MAC sublayer defines physical addresses (MAC addresses)

Physical layer defines how to send bits, but cannot interpret their meaning – MAC sublayer standard defines framing

Physical Layer cannot manage the process of which device can send, and at what time. MAC Sublayer defines CSMA/CD

10

Ethernet Standards

MAC Sublayer defines framing. Why?

AAAAAAAAAAAAAAAB0004AC5824185004A0C82008004510028B77A40004006B08E0A0000648ECC3987AF17001790B288C4C1A71588501016D026780000DE04

11

Ethernet Framing

ETHERNET FRAME

Network

Transport

Application

Fields of the Ethernet Frame

Three styles of Ethernet Frames:

DIX

IEEE 802.3 (Original)

IEEE 802.3 (1997)12

Ethernet Framing

Preamble8

Destination6

Source6

Type2

Data and Pad46 - 1500

FCS4

Preamble7

SFD1

Destination6

Source6

Length2

Data and Pad46 - 1500

FCS4

Preamble7

SFD1

Destination6

Source6

Length/

Type2

Data and Pad46 - 1500

FCS4

Fields of the Ethernet Frame

PreambleSynchronization (7 bytes of 10101010)Start Frame Delimiter (SFD)Signifies that the next byte begins the Destination MAC field (1 byte = 10101011)DestinationPhysical address of recipient of this frameSourcePhysical address of sender of this frameLengthDefines the length of the frame's next data field (if present, Type is NOT present)

13

Ethernet Framing

Preamble7

SFD1

Destination6

Source6

Length/

Type2

Data and Pad46 - 1500

FCS4

Fields of the Ethernet Frame

TypeDefines the type of protocol listed inside the frame (if present, Length is NOT present)Data and PadData from the higher layer protocols (Network, Transport, Application). Data field must be at least 46 bytesFrame Check Sequence (FCS)An error detection scheme. Uses CRC-32. Treats the message as if it is one large number. Performs division on 'number' using “generating polynomial”. The remainder (32 bits) is the FCS. The receiver performs the same calculation (including FCS) – if result is zero, no bits have been corrupted.

14

Ethernet Framing

Preamble7

SFD1

Destination6

Source6

Length/

Type2

Data and Pad46 - 1500

FCS4

Fields of the Ethernet Frame

Length / TypeHow do you know if it is a Type field or a Length field?Type Protocols are numbers > 0600

16, whereas Lengths are

less than 060016

CRC-32How reliable is it?Single bit errors = 100%Double bit errors = 100%Odd number of bits in error = 100%Error burst length < r + 1 = 100%Error burst length = r + 1 = 1 – (½) (r – 1) = 99.999999953%Error burst length > r + 1 = 1 – (½)r = 99.999999976%

15

Ethernet Framing

Preamble7

SFD1

Destination6

Source6

Length/

Type2

Data and Pad46 - 1500

FCS4

Structure of MAC addressEach MAC address is split into two parts:

OUI – Organization Unique Identifier – 24 bits (3 bytes) that identify the manufacturer of the NIC card

Vendor Assigned – 24 bits that uniquely identify a card within the OUI

The MAC address is permanently assigned to a card and is burned into the hardware (also referred to as a BIA – Burned-In Address).

All BIA assigned to a NIC must use the 24 bits assigned to the vendor

All BIAs within the OUI must be unique 16

MAC Addresses

Interpreting OUI with Protocol Analyzer (Wireshark)

17

MAC Addresses

Carrier Sense Multiple Access with Collision DetectionAs the Ethernet network is a broadcast network, it is possible for two hosts to transmit at the same time. CSMA/CD resolves the problem:

1) Host listens for any other stations transmitting2) If no Host is transmitting, send a message3) Listen as you transmit for a corrupted message (collision)4) Try to resend the message

What are the ramifications of this type media access?

18

CSMA/CD

Carrier Sense Multiple Access with Collision Detection

1) Carrier Sense – listen for another station transmitting

2) Multiple Access – Two stations simultaneous transmit their messages (both did not hear a carrier)

3) Collision Detection – The signals collide, corrupting what each sending host hears compared to what they are sending

4) Transmitting hosts send a jamming signal (32 bits: 01010101010101010101010101010101)

5) Transmitting hosts each set a semi-random timer

6) When timer expires, repeat from step 119

CSMA/CD

Half DuplexBy nature of the CSMA/CD protocol, it is Half Duplex

Full DuplexWhen using a switch, the frames that enter the switch are buffered when more than 1 frame is destined for a port

20

Full Duplex, Half Duplex, Collision Domains

HostC

HostB

HostA

HostDMessageB

MessageC

Turning on Full Duplex, disables CSMA/CD

Collision DomainsThe devices and ports that will experience collisions

21

Full Duplex, Half Duplex, Collision Domains

Nondeterministic Media AccessCSMA/CD is nondeterministic – there is no way to determine the number of times a device will access the LAN or how much bandwidth will be used. If an unlucky host keeps colliding with other hosts, it may be a few seconds before it can send a message.

As access is more of a probability, CSMA/CD is sometimes referred to as Probabilistic

Deterministic Media AccessToken Ring is deterministic – we can predict access to the media as the use of the token ensures equal or near equal access to the media.

Works like First Nations “Circle Talk”.22

Deterministic & Nondeterministic Media Access

10BASE5AUI (Attachment Unit Interface) and coaxial wiring

10BASE2BNC (same as CATV) and coaxial wiring

10BASE-TRJ45 and UTP wiring

23

10Mbps Ethernet

www.wikipedia.org

All three 10Mbps Ethernet standardssupport any of the three Ethernet Frame standards:DIXIEEE802.3 (original)IEEE802.3 (1997)

Use logical bus topologyAsynchronous Transmission (no electrical signals are present when no data is being sent – the media is idle)The preamble and SFD is how the NIC cards synchronize

themselves with the incoming messageUse CSMA/CDHalf duplex

24

10Mbps Ethernet

10BASE-TPhysical star topology (10BASE5, 10BASE2 are physical bus topology)Support for Full Duplex after 1997 (IEEE802.3x), with the following restrictionsEthernet switches/bridges must be used (no hubs or repeaters)Only two Ethernet interfaces can be in the same collision domainFull Duplex Doubles the bandwidth (10Mbps each direction = 20Mbps)Wiring types:Cat3 UTP (installed for telephones, so piggyback on installed infrastructure)Cat5 UTPCat5e UTPHow do you wire a straight-through cable?How do you wire a crossover cable?

25

10Mbps Ethernet

Design – Hubs, CSMA/CD and Half DuplexWhat is the 5-4-3 Rule?Propagation delay is reason for limiting Hubs/RepeatersDoes this satisfy the 5-4-3 Rule?What is the Collision Domain?

26

10BASE-T Ethernet

Does this satisfy the 5-4-3 Rule?

27

10BASE-T Ethernet

Does this satisfy the 5-4-3 Rule?

28

10BASE-T Ethernet

Design – Using Switches5-4-3 Rule applies to each Collision DomainDoes this satisfy the 5-4-3 Rule?What is the Collision Domain?

29

10BASE-T Ethernet

100BASE-TX and 10BASE-T EthernetSame Cat5/Cat5e cabling, with same 100m restrictionSupports CSMA/CD, half duplexSupport auto negotiationEthernet frame is the sameUses same pinouts on RJ-45 connectorCan disable CSMA/CD to use Full-duplex – same conditions as IEEE802.3x.

100BASE-TXUses synchronous transmission – always transmitting bitsUses an 'idle frame' to indicate that no data is being sentListens for idle frames when determining when to send data

30

100Mbps Ethernet

100BASE-FXWas preceded by FDDI (Fibre Distributed Data Interface)Did not catch on as much as 100BASE-TX:Companies had already bought the infrastructure for FDDIOther Companies opted for ATM (Asynchronous Transfer Mode) running up to 622MbpsIntroduction of 1000BASE-X doomed 100BASE-FX

31

100Mbps Ethernet

1000BASE-XCovers three Gigabit Ethernet Standards:1000BASE-X (fibre)1000BASE-SX (short distance, fibre)1000BASE-LX (long distance, fibre)

1000BASE-SXMulti-mode fibre (laser transmitter)220m limit (can be extended to 500m)

1000BASE-LXSingle-mode fibre5000m limit

1000BASE-TCat 5e UTP copper cable, all 4 pairs used100m limit 32

Gigabit Ethernet

Advantages of 1000BASE-SX/1000BASE-LX over 1000BASE-TNoise immunityNo grounding or potential electrical problemsVarious options for different types of cables, connectors, price pointsGreater cabling distances

However, fibre is still more expensive than copper:

Cable Length (type) Cost ($2007)1000BASE-SX 33' (patch) $1651000BASE-LX 33' (patch) $3541000BASE-T 1000' (bulk) $260

33

Gigabit Ethernet