Ch 13. Wired LANs: Ethernet

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Oct 26, 2013 (3 years and 9 months ago)

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Ch 13. Wired LANs: Ethernet

13.1 IEEE Standards


Project 802 launched in 1985


To set standards to enable intercommunication
among equipment from a variety of
manufacturers


Data Link Layers


Framing


Logical Link Control (LLC)




Medium Access Control (MAC)





CSMA/CD for Ethernet LAN


Token passing for Token Ring and Token Bus LAN



flow and error control

13.2 Standard Ethernet


Ethernet


Originally developed at Xerox’s Palo Alto Research
Center (1976)


Generations


Standard Ethernet: up to 10 Mbps


Fast Ethernet: up to 100 Mbps


Gigabit Ethernet: up to 1
Gbps


Ten Gigabit Ethernet: up to 10
Gbps



Frame Format


802.3 MAC frame format

Frame Length









Minimum length is required for
collision detection


Maximum length is for
small buffer size

and
preventing monopoly of shared medium

Physical Address


Addressing


6
-
byte physical address, in hexadecimal notation






Usually dedicated to network interface card (NIC)


Support
unicast
, multicast, and broadcast


Refer to the textbook

Multiple Access


Access method


1
-
persistent CSMA/CD


Slot
-
time = round
-
trip time + time to send the
jamming


Defined in bits: 512 bits (= 51.2 us over 10
-
Mbps Ethernet)


To detect collision on time, a station should be able to detect
a collision before it sends out the minimum
-
size frame (512
bits)


Maximum network length


= propagation speed x slot time / 2


= (2x10
8
m/s) x (51.2 us) / 2 = 5120m


Time for sending the jamming signal and others (e.g.,
repeater) reduces it to
2500m

Coding


Now, we move from MAC to PHY


Manchester encoding and decoding







Help synchronization owing to the transition in the
middle


Requires doubled signal rate of the original

Cables for Ethernet


Implementations

13.3 Changes in the Standard


Bridged Ethernet


Connect two or more Ethernet networks by

bridge






Bridge acts as a station in each separate network,
and prevents signals from propagating across
networks


Effects of bridge


Raising the bandwidth


Separating collision domains

domain

domain


Switched Ethernet


Multi
-
port bridge allows the bandwidth is shared
only between the station and the switch

Layer 2 switch or
switching hub


Full
-
Duplex Ethernet


Increase the capacity of each domain from 10
Mbps up to 20 Mbps

13.4 Fast Ethernet


IEEE 802.3u


Upgrade the data rate to 100 Mbps


Make it compatible with Standard Ethernet


Keep the same 48
-
bit address


Keep the same frame format


Keep the same min. and max. frame lengths


MAC


CSMA/CD


Autonegotiation


PHY


Point
-
to
-
point or start topologies only (no bus
topo
.)


Implementation

13.5 Gigabit Ethernet


IEEE 802.3z


Upgrade the data rate to 1
Gbps


Make it compatible with Standard or Fast Ethernet


Use the same 48
-
bit address


Use the same frame format


Keep the same min. and max. frame lengths


Support
autoconfiguration

as defined in Fast
Ethernet

Modes of Gigabit Ethernet


Full
-
duplex mode with switch


mostly used


Half
-
duplex mode with hub


Traditional: 512
-
bit min. frame



slot time = 0.512us


max. network length =
25m


Carrier extension: 512
-
byte

min. frame



slot time = 4.098us


max. network length =
200m


Frame bursting: combine multiple short frames as
a single frame


Topologies


Point
-
to
-
point, star,

two stars, and

hierarchy of stars



Implementation


Homework


Exercise in Chapter 13


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