Transcript Ethernet Topology, Physical Layer

Ethernet Standards
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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
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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
• 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
DB 15 female
Attachment Unit Interface
DB 15 male
Physical Medium Attachment
Medium Attachment Unit
Medium independent interface
medium
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
• PLS resides in DTE
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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
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Max length 50m
15 pin connectors
Female on the DTE side
Male on the MAU side
Network Connection
• MAU – Transceiver
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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
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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
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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-T Twisted Pair
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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
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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
Frame
Header
Frame
Data Area
Preamble/
SYNCH
Dest.
Address
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6
Header
Source Frame
Address Type
6
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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
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