Local Area Networks:Ethernet

IEEE Background

Institution of Electrical and Electronic Engineering (IEEE)

A professional non-profit organization Project group 802 under IEEE

Entrusted with the task of setting standards relating to physical and logical links of nodes in a network

Standard mostly applies to the Physical and Data Link layers

Example IEEE 802.3 standard for the Ethernet bus network

IEEE 802 Focus

OSI Reference Data Link layer Physical layer

Areas of applications Network cards and cables WAN connectivity etc.

Different subgroups under 802 that focus on different activities of the LAN

IEEE 802 Subgroups and their Responsibilities 802.1

Internetworking 802.2

Logical Link Control (LLC) 802.3

CSMA/CD 802.4

Token Bus LAN

IEEE 802 Subgroups and their Responsibilities (Cont.) 802.5

Token Ring LAN 802.6

Metropolitan Area Network 802.7

Broadband Technical Advisory Group 802.8

Fiber-Optic Technical Advisory Group

IEEE 802 Subgroups and their Responsibilities (Cont.) 802.9

Integrated Voice/Data Networks 802.10

Network Security 802.11

Wireless Networks 802.12

Demand Priority Access LANs Ex: 100BaseVG-AnyLAN

A Perspective of IEEE 802 Standards in Network Communication

LogicalLink

Control(LLC)

MediaAccessControl(MAC)

802.2

802.3802.4802.5802.12

802.1 appliesto both.

802 Layers - Physical

Encoding/decoding Preamble generation/removal Bit transmission/reception Transmission medium and topology

Logical Link Control Flow control, Error control,& part of the framing Transmission of link level PDUs between two

stations Must support multiaccess, shared medium Relieved of some link access details by MAC layer LLC defines PDU similar to HDLC Addressing involves specifying source and

destination LLC users Referred to as service access points (SAP) Typically higher level protocol

Three generations of Ethernet

802.3 MAC frame

Preamble: Provides an alert & a timing pulse

SFD: Signals the beginning of the frame,& also warns the stations that

this is the last the chance for synchronization. Last 2 bits alerts

the receiver that next field is the destination address

DA & SA : Physical address of receiver & sender

Length or type: Define the upper layer protocol using the MAC frame

IEEE use as length field to define the number of bytes

in the data field

Minimum and maximum length

If 18 bytes of header and trailer(6 SA + 6 DA + 2 Length + 4 CRC)

Then Minimum length of data from the upper layer is 64-18= 46 bytes

If the upper-layer packet is less than 46 bytes, padding is added to make up the difference

Ethernet addresses in hexadecimal notation

Unicast and multicast addresses

Source address is always a unicast address

Destination address can be unicast, multicast ,or broadcast

LSB of the 1st byte defines the type of address

Broadcast DA is a special case of the multicast address in which all bits are 1s

Access method: standard ethernet uses 1-persistent CSMA/CD

SLOT TIME: round trip time + time required to send the jam sequence

Defined in bits,time required to send 512 bits

Depends on the data rate For 10-Mbps ethernet it is 51.2 μs

Physical layer

PLS

Manchester encoding

Categories of traditional Ethernet

10Base5,thick Ethernet, thicknet, Max length 500 m (coaxial cable)

10 base2,Thin coaxial cable,185 m, bus topology

10base-T,twisted pair Ethernet, physical star topology,100 m max length

10base-F,fiber,2000m,star topology

Connection of a station to the medium using 10Base5

Connection of stations to the medium using 10Base2

Connection of stations to the medium using 10Base-T

Connection of stations to the medium using 10Base-FL

Sharing bandwidth

A network with and without a bridge

Collision domains in a nonbridged and bridged network

Switched Ethernet

Full-duplex switched Ethernet

Fast EthernetFast Ethernet

MAC Sublayer

Physical Layer

Physical Layer Implementation

IEEE 802.3u

Fast Ethernet physical layer

Goal of Fast Ethernet

Upgrade the data rate to 100 Mbps Compatible with standard Ethernet Same 48-bit address Same frame format Same Min & Max frame lenths

MAC sublayer

For full-duplex no need of CSMA/CD Autonegotiation

- Allows station or a hub a range of capabilities- Allow to negotiate the mode or data rate of operation

MII

Fast Ethernet implementations

100Base-TX implementation

Encoding and decoding in 100Base-TX

Four Binary/Five binary coding scheme

Multiline Transmission(three levels)

Use 2 pairs of twisted pair cable

Use MLT-3,as it has good bandwidth performance

MLT-3 signal

100Base-FX implementation

2 pair fiber cable, 100 m,4B/5B block coding,NRZ-I line coding

Encoding and decoding in 100Base-FX

100Base-T4 implementation

Cat 4 UTP,4 pair of wires,100 Mbps

* Data elements are encoded as six signal elements

Using four wires in 100Base-T4

Gigabit EthernetGigabit Ethernet

MAC Sublayer

Physical Layer

Physical Layer Implementation

Physical layer in Gigabit Ethernet

Three Methods for Gigabit ethernet Traditional: 512 bits,length of bit is

1/100 shorter,slot time=.512microsec

Carrier extension: Min length of a frame is 512 bytes

Frame bursting:

Gigabit Ethernet implementations

2 wire Short,longwave(sx,Lx), STP CX,NRZ line encoding

4 wire use Twiste pair category 5 4D-PAMS line encoding

Block coding is 8B/10B

1000Base-X implementation

Encoding in 1000Base-X

1000Base-T implementation

Encoding in 1000Base-T

Ethernet Protocol Standards

10 Mbps IEEE 802.3

100 Mbps IEEE 802.3u

1 Gbps IEEE 802.3ab Uses all 4 pairs of the RJ-45 cable (

www.techfest.com/networking/lan/ethernet1.htm )

10 Gbps IEEE 820.3ae