Transcript Ethernet Topology, Physical Layer

Ethernet Standards
• 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
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Thick coaxial – thicknet – 10Base5
Thin coaxial – thinnet- cheapernet –10Base2
UTP XBaseT
Fibre XBaseF
Broadband version XBroad36
Ethernet Standards
• Other specifications
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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
• Result
– Shift in Ethernet shared access – to switched
Ethernet
– Subsequent – Fast Ethernet – 100BASE-T
(1995)
– High bit rate interconnectivity requirement
• Gigabit Ethernet 109 bits per second
– (Ethernet frame format maintained)
Network Connection
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Network Interface Card – NIC
Attachment Unit Interface – AUI
Medium Attachment Unit – MAU
PHY + MAC – HW
LLC - SW
Network Connection
• MAU – Transceiver
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Transmit data
Receive data
Loopback
Collision detection
SQE test
Jabber protection
10BASE5 Thicknet
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Early 80s standard
Tapped Bus topology – 50 ohm coax cable
Maximum 500 m segment length
100/200 users per segment
Max 4 repeaters
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
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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-FL
• Runs over 2 strands of single/multimode
fibre
• Fibre distance between MAU – 2000m
• Point-to-point links
Functions of a NIC
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Physical Addressing
Encoding Data
Access to Physical Medium
Connection to Physical Medium
Framing - encapsulate & decapsulate data
Create and Check CRC - error detection
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
• Methods
– Static
– Configurable
– Dynamic
Types of addresses
• Broadcast
• Multicast
• Unicast
Ethernet Frame Format
Frame
Header
Frame
Data Area
Preamble/
SYNCH
Dest.
Address
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6
Header
Source Frame
Address Type
6
2
Data in Frame
CRC
46-1500
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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