Ethernet Standards • Ethernet concepts origin • DIX consortium – 1979 • 10Mbps 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
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Ethernet Standards Ethernet concepts origin DIX consortium – 1979 10Mbps Ethernet 1 st Blue book – 1980 IEEE group takes over – Project 802 –802.1 – High.
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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
• 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)