- The document discusses different types of computer networks at the data link layer, including broadcast networks where all stations share a channel and point-to-point networks where pairs of hosts are directly connected. It focuses on wired local area networks (LANs). - Common LAN technologies discussed include Ethernet, Token Ring, FDDI, and ATM LAN. Ethernet standards including Fast Ethernet and Gigabit Ethernet are explained in detail, covering their goals, frame formats, addressing, and implementations of half-duplex and full-duplex modes. - Ten-Gigabit Ethernet is also summarized, with the goals of upgrading the data rate to 10Gbps while maintaining compatibility with previous Ethernet standards.

1. Underlying Technologies
ET3003 Computer Networks
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Tutun Juhana
Telecommunication Engineering
School of Electrical Engineering & Informatics
Institut Teknologi Bandung

2. Two types of networks
at the data link layer
– Broadcast Networks: All stations share a single
communication channel
– Point-to-Point Networks: Pairs of hosts (or routers)
are directly connected
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Broadcast Network Point-to-Point Network
• Typically, local area networks (LANs) are broadcast and wide area
networks (WANs) are point-to-point

3. WIRED LOCAL AREA NETWORKS
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4. • A local area network (LAN) is a computer
network that is designed for a limited
geographic area such as a building or a
campus
• Most LANs today are also linked to a wide
area network (WAN) or the Internet
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5. FDDI
Fiber Distributed Data Interface
Token Ring
Token Bus
ATM LAN
IEEE Standard Project 802, designed to
regulate the manufacturing and
interconnectivity between different LANs
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6. IEEE Standards
• Project 802 is a way of specifying
functions of the physical layer and the data
link layer of major LAN protocols
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7. The Ethernet
• Robert Melancton
"Bob" Metcalfe
(born April 7,1946)
is an electrical
engineer from the
United States who
co-invented
Ethernet
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8. Frame Format
‘Length” used by
IEEE standard to
define the number of
bytes in the data field
“Type” used by
original Ethernet to
define upper-layer
protocol using the
frame
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9. Frame Length
• The minimum length restriction is required for the correct operation of CSMA/CD
• If the upper-layer packet is less than 46 bytes, padding is added to make up the
difference
Reason for the maximum length restriction:
1. To reduce the size of the buffer (memory was very expensive when Ethernet was
designed)
2. It prevents one station from monopolizing the shared medium
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10. Addressing
• Each station on an Ethernet network has its own
network interface card (NIC)
• The NIC provides the station with a 6-byte
physical address
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11. • Ethernet Address
– The address normally is referred to as the
data link address, physical address, or MAC
address
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12. 12
Example:
• 00-14-22 OUI for Dell
• 00-04-DC for Nortel
• 00-40-96 for Cisco
• 00-30-BD for Belkin

13. • The address is sent left-to-right, byte by byte
• For each byte, it is sent right-to-left, bit by bit
• Example
– Show how the address 47:20:1B:2E:08:EE is sent out
on line
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14. Unicast, Multicast, and Broadcast Addresses
• A source address is always a unicast
address
– the frame comes from only one station
• The destination address can be unicast,
multicast, or broadcast
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15. • The broadcast address is a special case of
the multicast address; the recipients are all
the stations on the LAN
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16. • Define the type of the following destination
addresses
– 4A:30:10:21:10:1A
– 47:20:1B:2E:08:EE
– FF:FF:FF:FF:FF:FF
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17. Ethernet Evolution
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18. STANDARD ETHERNET
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19. Access Method: CSMA/CD
• The IEEE 802.3 standard defines carrier
sense multiple access with collision
detection (CSMA/CD) as the access
method for traditional Ethernet
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20. • Stations on a traditional Ethernet can be
connected together using a physical bus or star
topology, but the logical topology is always a bus
Physical star, logically bus topology
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Physical bus topology
• The medium (channel) is shared between stations and only one station at
a time can use it
• All stations receive a frame sent by a station (broadcasting)
• The real destination keeps the frame while the rest drop it

21. • How can we be
sure that two
stations are not
using the medium at
the same time?
• If they do, their
frames will collide
with each other
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22. 22

23. • To minimize the chance of collision and,
therefore, increase the performance, the
CSMA method was developed
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24. • Carrier sense multiple access (CSMA)
requires that each station first listen to the
medium (or check the state of the
medium) before sending
– sense before transmit, or
– listen before talk
• CSMA can reduce the possibility of
collision, but it cannot eliminate it
– The possibility of collision still exists because
of propagation delay 24

25. Space/time model of a collision in CSMA
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26. Collision of the first bit in CSMA/CD
• A transmits for the duration t4 - t1; C transmits for the duration t3 - t2
 for the protocol to work, the length of any frame divided by the bit
rate in this protocol must be more than either of these durations
• Before sending the last bit of the frame, the sending station must
detect a collision, if any, and abort the transmission  because, once
the entire frame is sent, station does not keep a copy of the frame and
does not monitor the line for collision detection 26

27. Minimum Frame Size
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The worst collision on a shared bus
http://cnp3book.info.ucl.ac.be/lan/lan/

28. • The frame transmission time Tfr must be at
least two times the maximum propagation
time Tp
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29. • Example
– In the standard Ethernet, if the maximum
propagation time is 25.6 μs, what is the
minimum size of the frame?
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30. CSMA/CD flow diagram
The station transmits
and receives
continuously and
simultaneously
(using two different
ports)
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31. Implementation
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32. FAST ETHERNET
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33. • IEEE created Fast Ethernet under the name 802.3u
• Fast Ethernet is backward-compatible with Standard
Ethernet, but 10 times faster (100 Mbps)
• The goals of Fast Ethernet:
1. Upgrade the data rate to 100 Mbps
2. Make it compatible with Standard Ethernet
3. Keep the same 48-bit address.
4. Keep the same frame format.
5. Keep the same minimum and maximum frame lengths
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34. MAC Sublayer
• Keep only the star topology
– There are two choices: half duplex and full duplex
– In the half-duplex approach, the stations are
connected via a hub
– in the full-duplex approach, the connection is made
via a switch with buffers at each port
• The access method is the same (CSMA/CD) for
the half-duplex approach
• For full-duplex there is no need for CSMA/CD
– The implementations keep CSMA/CD for backward
compatibility with Standard Ethernet
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35. Autonegotiation
• Autonegotiation allows two
devices to negotiate the mode
or data rate of operation
• It was designed particularly for
the following purposes:
– To allow incompatible devices to
connect to one another
– To allow one device to have
multiple capabilities
– To allow a station to check a
hub’s capabilities.
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36. Implementation
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37. GIGABIT ETHERNET
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38. • Gigabit Ethernet (IEEE 802.3z)
• The goals of the Gigabit Ethernet:
1. Upgrade the data rate to 1 Gbps
2. Make it compatible with Standard or Fast Ethernet
3. Use the same 48-bit address
4. Use the same frame format
5. Keep the same minimum and maximum frame
lengths.
6. To support autonegotiation as defined in Fast
Ethernet
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39. MAC Sublayer
• A main consideration: keep the MAC
sublayer untouched  To achieve a data
rate of 1 Gbps, this was no longer possible
• Gigabit Ethernet has two distinctive
approaches for medium access
1. Half-duplex
2. Full-duplex
• Almost all implementations of Gigabit
Ethernet follow the full-duplex approach
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40. Full-Duplex Mode
• There is a central switch connected to all
computers or other switches
– Each switch has buffers for each input port in which
data are stored until they are transmitted
• There is no collision in this mode  CSMA/CD
is not used
• The maximum length of the cable is determined
by the signal attenuation in the cable, not by the
collision detection process
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41. Half-Duplex Mode
• A switch can be replaced by a hub  a
collision might occur  CSMA/CD is used
 the maximum length of the network is
totally dependent on the minimum frame
size
• Three solutions have been defined:
1. Traditional
2. Carrier extension
3. Frame bursting
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42. • Traditional approach
– Keep the minimum frame length 512 bits
– The maximum network length only 25 m
(because the length of a bit is 1/100 shorter
than in standard Ethernet)
• It may not even be long enough to connect the
computers in one single office
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43. • Carrier Extension
– Increase the minimum frame length  512 bytes (4096 bits) 
8 times longer
– It forces a station to add extension bits (padding) to any frame
that is less than 4096 bits
– The maximum length of the network can be increased 8 times
to a length of 200 m
– This allows a length of 100 m from the hub to the station
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Frame RRRRRRRRRRRRR
Carrier Extension
512 bytes

44. Carrier Extension is very inefficient if we
have a series of short frames to send (each
frame carries redundant data)
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45. • Frame Bursting
– To improve efficiency, frame bursting was proposed
– Instead of adding an extension to each frame,
multiple frames are sent
• To make these multiple frames look like one frame, padding
is added between the frames (96 bits) so that the channel is
not idle  The method deceives other stations into thinking
that a very large frame has been transmitted
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Frame Extension Frame Frame Frame
512 bytes
Frame burst
Maximum frame burst is 8192 bytes

46. Gigabit Ethernet Implementation
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47. TEN-GIGABIT ETHERNET
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48. • Ten-Gigabit Ethernet standard : IEEE802.3ae
• The goals :
1. Upgrade the data rate to 10 Gbps.
2. Make it compatible with Standard, Fast, and Gigabit Ethernet.
3. Use the same 48-bit address.
4. Use the same frame format.
5. Keep the same minimum and maximum frame lengths.
6. Allow the interconnection of existing LANs into a metropolitan
area network (MAN) or a wide area network (WAN)
7. Make Ethernet compatible with technologies such as Frame
Relay and ATM.
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49. Implementation
• Ten-Gigabit Ethernet operates only in full
duplex mode  no need for contention 
CSMA/CD is not used
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