3c ethernet

Networking Fundamentals
WIRED LANs: ETHERNET

13.2
IEEE STANDARDSIEEE STANDARDS
• In 1985In 1985(80)(80), the Computer Society of the IEEE, the Computer Society of the IEEE
started a project, called Project 802, to setstarted a project, called Project 802, to set
standards to enable intercommunication amongstandards to enable intercommunication among
equipment from a variety of manufacturers.equipment from a variety of manufacturers.
• Project 802 is a way of specifying functions of theProject 802 is a way of specifying functions of the
physical layer and the data link layer of major LANphysical layer and the data link layer of major LAN
protocolsprotocols (PANs/MANs also)(PANs/MANs also)..

IEEE 802 Standards
The 802 working groups. The important ones are
marked with *. The ones marked with  are
hibernating. The one marked with † gave up.

13.5
HDLC frame compared with LLC and MAC frames

13.6
STANDARD ETHERNETSTANDARD ETHERNET
• The original Ethernet was created in 1976 atThe original Ethernet was created in 1976 at
Xerox’s Palo Alto Research Center (PARC).Xerox’s Palo Alto Research Center (PARC).
• Since then, it has gone through four generations.Since then, it has gone through four generations.
• We now briefly discuss theWe now briefly discuss the Standard (orStandard (or
traditional) Ethernettraditional) Ethernet..

13.7
Ethernet evolution through four generations

13.9
Minimum and maximum lengths
Reason for Min frame length already see (CSMA/CD). Max for saving on
Memory cost and preventing a station from monopolising the channel.

13.10
Example of an Ethernet address in hexadecimal notation

Ethernet (?) network card showing its MAC address

13.12
Unicast and multicast addresses
The broadcast destination address is a
special case of the multicast address in
which all 48 bits are 1s.

13.13
Define the type of the following destination addresses:
a. 4A:30:10:21:10:1A b. 47:20:1B:2E:08:EE
c. FF:FF:FF:FF:FF:FF
Solution
To find the type of the address, we need to look at the
second hexadecimal digit from the left. If it is even, the
address is unicast. If it is odd, the address is multicast. If
all digits are F’s, the address is broadcast. Therefore, we
have the following:
a. This is a unicast address because A in binary is 1010.
b. This is a multicast address because 7 in binary is 0111.
c. This is a broadcast address because all digits are F’s.
Example 1

13.14
Show how the address 47:20:1B:2E:08:EE is sent out on
line.
Solution
Address in binary is 0100 0111 0010 0000 0001 1011
0010 1110 0000 1000 1110 1110
The address is sent left-to-right, byte by byte; for each
byte, it is sent right-to-left, bit by bit, ie. The bit which
defines uni/multicast arrives first as shown below:
Example 2

Some Information
• Access Method : 1 persistent CSMA/CD
• Slot Time : Equal to round trip time plus time to send
jam sequence, defined in bits. Seen it is equal to 512
bits. For Standard Ethernet it is 51.2 μs.
• Slot Time and Maximum Network Length : Propagation
speed = 2 x 108
m/s
Max length = Propagation speed x Tp (= Slot Time/2)
= 2 x 108
m/s x 51.2 x 10-6
/2 s
= 5120 m
In actuality due to repeater delays and time for jam
sequences the practical max is 2500 m.
13.15

13.16
Physical Layer implementations : Categories of Standard Ethernet

13.17
Encoding in Standard Ethernet – Manchester (self-synchronous)

13.18
10Base5 implementation
Transceiver also responsible for detecting collisions

13.19
10Base2 implementation
Transceiver part of NIC, connected via tees. Much cheaper

13.20
10Base-T implementation
Two pair twisted cable for trans/receive, therefore collisions
in hub. Length defined as 100 m due to attenuation.

13.23
Summary of Standard Ethernet implementations

13.24
CHANGES IN THE STANDARDCHANGES IN THE STANDARD
The 10-Mbps Standard Ethernet has gone throughThe 10-Mbps Standard Ethernet has gone through
several changes before moving to the higher dataseveral changes before moving to the higher data
rates. These changes actually opened the road to therates. These changes actually opened the road to the
evolution of the Ethernet to become compatible withevolution of the Ethernet to become compatible with
other high-data-rate LANs. Some of the changes :other high-data-rate LANs. Some of the changes :
• Bridged EthernetBridged Ethernet
• Switched EthernetSwitched Ethernet
• Full Duplex EthernetFull Duplex Ethernet

13.25
Sharing bandwidth – Unbridged Network

13.26
A network with and without a bridge – Gain more BW

13.27
Collision domains in an unbridged network and a bridged network - Reduced

13.28
Switched Ethernet – a n-port bridge, even better!

13.29
Full-duplex switched Ethernet – even even better, no collisions so no CSMA/CD

13.30
FAST ETHERNETFAST ETHERNET
• Fast Ethernet was designed to compete with LANFast Ethernet was designed to compete with LAN
protocols such as FDDI or Fiber Channel.protocols such as FDDI or Fiber Channel.
• IEEE created Fast Ethernet under the nameIEEE created Fast Ethernet under the name
802.3u.802.3u.
• Fast Ethernet is backward-compatible withFast Ethernet is backward-compatible with
Standard Ethernet, but it can transmit data 10Standard Ethernet, but it can transmit data 10
times faster at a rate of 100 Mbps.times faster at a rate of 100 Mbps.

13.31
Fast Ethernet topology
If hub used instead of switch - half duplex approach.

13.32
Fast Ethernet implementations

13.33
Encoding for Fast Ethernet implementation
Manchester baud
rate twice the data
rate, hence use
other line codes.
To reduce cost of new cat 5. Have
100 x 6/8 = 75 Mbaud available,
ie. 25 Mbaud /wire.
0 1 0 0 1 1 1 0
X – for Block Coding.

13.34
Block coding is normally referred to as
mB/nB coding;
it replaces each m-bit group with an
n-bit group. As No. of contiguous 0s or
1s is restricted, aids in synchronization.
Note

13.36
Multilinetransition: MLT-3 scheme
Waveform periodic with baud rate 1/4th
the data rate.

4.37
In mBnL schemes, a pattern of m data
elements is encoded as a pattern of n
signal elements in which 2m
≤ Ln
.
Note

4.38
Multilevel: 8B6T scheme (28
=256 data : 36
=478 signal)

13.39
Summary of Fast Ethernet implementations
3
2000 m

13.40
GIGABIT ETHERNETGIGABIT ETHERNET
• The need for an even higher data rate resulted in theThe need for an even higher data rate resulted in the
design of the Gigabit Ethernet protocol (1000design of the Gigabit Ethernet protocol (1000
Mbps).Mbps).
• The IEEE committee calls the standard 802.3z.The IEEE committee calls the standard 802.3z.

13.41
In the full-duplex mode of Gigabit
Ethernet, there is no collision;
the maximum length of the cable is
determined by the signal attenuation
in the cable.
Note

13.42
Topologies of Gigabit Ethernet

13.43
Gigabit Ethernet implementations

13.44
Encoding in Gigabit Ethernet implementations

4.45
Multilevel: 4D-PAM5 scheme
4D - 4 wires: Data rate to 1/4; 8 bits, 4 levels: Signal rate 1/2; thus net 1/8

13.46
Summary of Gigabit Ethernet implementations

13.48
Summary of Ten-Gigabit Ethernet implementations
Physical layer coding has not been specified by the official standards body.

3c ethernet

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