Ethernet Standards

• Ethernet concepts origin• DIX consortium – 1979• 10Mbps Ethernet 1st Blue book – 1980• IEEE group takes over – Project 802

– 802.1 – High Level Interface –HLI –• Focused on high level inter-network protocols & management

– 802.2 – Logic Link Control

– 802.3 – Data Link & Medium Access Control • DLMAC

Ethernet Standards

• 1982 – DLMAC – 3 groups– 802.3 – CSMA/CD – driven by DIX– 802.4 – Token Bus – burroughs, concorde, – 802.5 – Token – Ring - IBM

• 1982 – DIX & IEEE merges– 1st version of 802.3 Ethernet standard

Ethernet Standards

• IEEE 802.3 – series of specifications for 10Mbps– Thick coaxial – thicknet – 10Base5– Thin coaxial – thinnet- cheapernet –10Base2– UTP XBaseT– Fibre XBaseF – Broadband version XBroad36

Ethernet Standards

• Other specifications– 100 Mbs – fast Ethernet– 1000 Mbps – gigabit Ethernet– Switched Ethernet– Proposal for 100MBps – 1982– IEEE 802 focused on 1- 20 MBps– ANSI took up 100 Mbps - led to FDDI

Ethernet Popularity

• Low network management requirements

• Open standards– Reasonable prices– Easy to license– 1990 – 10Mpbs Ethernet on UTP

• 10BASE-T – inexpensive twisted pair

• Massive surge in Ethernet installations

Ethernet Popularity

– Coincides with distributed high-performance computing to the desktop

• Result– Large networks – many systems– More network aware applications– Massive increase in BW needs

Ethernet Popularity

• Result– Need for higher bit rates – fast Ethernet (1995 –

100BaseT)– Shift in Ethernet shared access – to switched

Ethernet– High bit rate interconnectivity requirement

• Gigabit Ethernet 109 bits per second

– (Ethernet frame format maintained)

First Generation Ethernet 10Mbps

Logic Link Control

Medium Access Control

Physical Layer Signalling

Physical Medium Attachment

medium

Medium independent interface

Medium Attachment Unit

DB 15 male

DB 15 female

Attachment Unit Interface

Network Connection

• Network Interface Card – NIC

• Attachment Unit Interface – AUI

• Medium Attachment Unit – MAU

• PHY + MAC – HW

• LLC - SW

Network Connection

• PLS resides in DTE – Data o/p– Data I/p– Carries Sense– Error Sense

• MAC – Data output in NRZ format

Network Connection

• MAC – Data output in NRZ format

• PLS Manchester encoding – differential

• AUI cable – 3 different signal pairs– DO– DI– CI (control input)

Network Connection

• AUI cable – 3 different signal pairs– Max length 50m– 15 pin connectors– Female on the DTE side– Male on the MAU side

Network Connection

• MAU – Transceiver– Transmit data– Receive data– Loopback– Collision detection– SQE test– Jabber protection

Bus Technologies

– 10BASE5 – Thicknet – coaxial– 10BASE2 – Thinnet, coaxial – cheapernet– 10BASE-T – Twisted Pair

10BASE5 Thicknet

• Early 80s standard

• Tapped Bus topology – 50 ohm coax cable

• Maximum 500 m segment length

• 100 users per segment

• Max 4 repeaters

10BASE5 Thicknet

• Transceivers separated by 2.5m

• AUI- NIC to transceiver max 50 m

10BASE5 Thicknet

10BASE2 Thinnet

• 1989 standard BNC ( British Navel Connector)

• Less expensive cable – flexible – to the desktop

• Max segment size 185m, max nodes 30

• Max length with repeaters – 925 m

• Min distance between MAU = 0.5m

10BASE-T Twisted Pair

• Uses standard voice grade telephone cable

• 1990 – IEEE 802.3i UTP standard

• 4 twisted pairs

• Star topology – logically bus

• Hub – repeater at the centre– Signal restoration– Repeated incoming signal in all output ports

10BASE-T Twisted Pair

• Advantages of star

• Cable distance 100m to repeater

• MAUs can be connected via AUI

• MAU & AUI can be part of DTE or repeater

10BASE-FL

• Runs over 2 strands of single/multimode fibre

• Fibre distance between MAU – 2000m

• Point-to-point links

Functions of a NIC

• Create and Check CRC - error detection• Physical Addressing• Medium Access• Framing - encapsulate & decapsulate data• Encoding Data• Connection to Physical Medium• Transceiver - translates signal to medium specific

signal

Physical MAC addresses

• Unique Addresses

• assigned by the IEEE

• 48 bit address in two parts– First 24 bits specify the vendor (block number)

• ex. AA-00-00 is a DEC NIC board

• ex. 08-20-00 is SUN

– Next 24 bits are a unique serial number

MAC addressing

• Static– Most common– Vendor guaranteed uniqueness

• Configurable– SW assigned MAC address

• Dynamic– Random pick and check for uniqueness

Types of addresses

• Broadcast

• Multicast

• Unicast

Broadcast addresses

• A MAC address of all one’s

• All NIC’s on a network accept broadcast addressed messages

Multicast addresses

• A specific MAC address that only certain NIC are programmed to accept– the first bit of the destination address is set to 1

Unicast addresses

• A unique MAC address assigned to each NIC which is used to send messages to that specific host.– the first bit of the destination address is set to 0

Ethernet II Frame Format

FrameHeader

FrameData Area

8 6 6 2 46-1500 4

Preamble/ SYNCH

Dest. Address

Source Address

Frame Type CRC Data in Frame

Header

Ethernet Operation

• Broadcast/half duplex network– On a bus topology

• Listen first then transmit if clear

• What to do if you collide– Backoff and try again

CSMA/CD

• LAN transmissions operate on the idea of a bit period

• For 10baseT this is 100ns (10,000,000 bits/sec)

• 3 times to keep track of– Slot time– Interframe gap– Jam period

Timings

• Slot time – min time transmitter needs to access media to transmit smallest frame– All nodes must listen for 1 slot time before

transmitting– 512 bit periods or 51.2 µsec

• Interframe Gap (dead time) – space between transmissions of 96 bit periods or 9.6 µsec

Timings

• On collision

• All stations involved stop transmitting and transmit 32 bit time (3.2 µsec) jam signal

• All attached stations hear the jam signal

• Back-off algorithm used to determine when another attempt will be made– This is done up to 16 times

Ethernet Operations

• Min frame size: 64 bytes (72 counting preamble and SFD)

• 64 bytes incl CRC, control, addresses and data fields (64 x 8 x 100ns = 51.2 µsec)

• Max size is 1526 bytes