Ethernet Standards Ethernet concepts origin DIX consortium – Mbps Ethernet 1 st 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 –1 st version of Ethernet standard

Ethernet Standards IEEE – 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 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 10 9 bits per second –(Ethernet frame format maintained)

First Generation Ethernet 10Mbps

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 is a DEC NIC board ex 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

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