This document provides an overview of local area networks (LANs), including their components, topologies, and standards. It discusses the IEEE 802 project and standards for Ethernet (IEEE 802.3), Token Bus (IEEE 802.4), and Token Ring (IEEE 802.5). The key topics covered include the characteristics of LANs, common network topologies like star, bus, ring and their advantages/disadvantages, and the access methods used in Ethernet and Token Ring specifications.

1. 05/23/13 TJ 2013 - Data Comm. 1
CHAPTER TEN (10)CHAPTER TEN (10)
LOCAL AREA NETWORK

2. 05/23/13 TJ 2013 - Data Comm. 2
Learning ObjectivesLearning Objectives
 After completing this chapter you will be able to:-
– Components of LAN
- Topology
– Describe Project 802.
– Explain IEEE 802.3 (Ethernet), IEEE 802.4 (Token Bus),
IEEE 802.5 (Token Ring) network data transports and
media specifications.
– Understand the access methods used in Ethernet and
Token Ring.

3. 05/23/13 TJ 2013 - Data Comm. 3
Chapter OutlineChapter Outline
Introduction
Topology
Project 802
Ethernet
Fast Ethernet
Token Bus
Token Ring

4. 05/23/13 TJ 2013 - Data Comm. 4
IntroductionIntroduction
Computer Network – a set of devices (nodes)
connected by communication links creating data
routes where we share and exchange information.
Categories of Network:
 Local Area Network (LAN)
 Metropolitan Area Network (MAN)
 Wide Area Network (WAN)
 Internetworks (internet)

5. 05/23/13 TJ 2013 - Data Comm. 5
MANMAN
Designed to extend over an entire city.
It may be a single network (cable television
network) or it may be a means of connecting
a number of LANs into larger network so
that resources may be shared LAN-to-LAN
or device-to-device.
Example: (Telekom, ASTRO)

6. 05/23/13 TJ 2013 - Data Comm. 6
MANMAN

7. 05/23/13 TJ 2013 - Data Comm. 7
WANWAN
Provides long-distance transmission of data,
voice, image, and video information over
large geographical areas that may comprise
a country, a continent, or even the whole
world.
WAN that is wholly owned by a single
company is often referred to as an
enterprise network.

8. 05/23/13 TJ 2013 - Data Comm. 8
WANWAN

9. 05/23/13 TJ 2013 - Data Comm. 9
internet vs. Internetinternet vs. Internet
internet ~ two or more networks connected
by the use of internetworking devices such
as routers or gateways.
Internet ~ specific worldwide network using
TCP/IP protocol suite.

10. 05/23/13 TJ 2013 - Data Comm. 10
Internetwork (internet)Internetwork (internet)

11. 05/23/13 TJ 2013 - Data Comm. 11
LANLAN
 A local area network (LAN) is a data communication system
that allows a number of independent devices to
communicate directly with each other in a limited
geographic area.
 It is usually privately owned within a single office, building
or campus of up to a few kilometers in size.
 It is widely used to connect personal computers and
workstations in home, company offices and factories to
share resources and exchange information.
 The resources to be shared can include hardware (e.g.
printers), software (e.g. application program) or data.

12. 05/23/13 TJ 2013 - Data Comm. 12

13. 05/23/13 TJ 2013 - Data Comm. 13
CharacteristicsCharacteristics
 LANs are distinguished from other types of networks
by their size, transmission technology and topology.
 They are restricted in size, which means that the
worst-case transmission time is bounded and known in
advance.
 Traditionally, LANs have data rates in the 4 to 100
Mbps range, however, newer LANs may operate at
higher speeds, up to gigabits/second.
 Various topologies are possible for broadcast LANs,
and the most common are bus, star and ring.

14. 05/23/13 TJ 2013 - Data Comm. 14
TopologyTopology
Topology ~ refers to the way network is laid
out, either physically or logically.
Two or more devices connect to a link; two
or more links form a topology.
The topology of a network is the geometric
representation of the relationship of all links
and linking devices (nodes) to each other.
i.e. mesh, star, bus, ring, tree, hybrid

15. 05/23/13 TJ 2013 - Data Comm. 15
Mesh TopologyMesh Topology
 Every device has a dedicated point-to-
point link to every other device.
 Dedicated means that the link carries
traffic only between the two devices it
connects.
 A fully connected mesh network has
n(n-1)/2 physical channels to link n
devices.
 To accommodate that many links,
every device on the network must
have n –1 input/output ports.
 I.e. telephone network

16. 05/23/13 TJ 2013 - Data Comm. 16
Mesh Topology (example)Mesh Topology (example)
 The Big Pond Company has a fully
connected mesh network consisting
of 5 devices. Calculate the total
number of cable links needed and the
number of ports for each device.
 Solution:
– # of links = n(n-1)/2 = 5(4)/2 = 10 links
– # of ports per device = n-1 = 5-1 = 4 ports

17. 05/23/13 TJ 2013 - Data Comm. 17
Mesh Topology AdvantageMesh Topology Advantage
 Eliminating traffic problems ~ each connection can
carry its own data load.
 Robust ~ if one link fails, it does not anticipate the
entire system.
 Privacy or security ~ when every message sent
travels along a dedicated link, only the intended
recipient sees it.
 Fault identification & isolation easy ~ traffic can be
routed to avoid links with suspected problems.

18. 05/23/13 TJ 2013 - Data Comm. 18
Mesh Topology DisadvantageMesh Topology Disadvantage
The amount cabling and I/O ports required ~
every device must be connected to every
other device.
Installation and reconfiguration are difficult.
Need a lot of space since bulk of wiring
required.
Expensive ~ the hardware required to
connect each link (I/O ports and cable) are
expensive.

19. 05/23/13 TJ 2013 - Data Comm. 19
Star TopologyStar Topology
 Each device has a dedicated
point-to-point link only to a
central controller/ concentrator,
usually called a hub.
 The controller acts as an
exchange; if one device wants
to send data to another, it sends
data to the controller, which then
relays the data to the other
connected device.
 Star topology does not allow
direct traffic between devices.
 I.e. 10BaseT

20. 05/23/13 TJ 2013 - Data Comm. 20
Star Topology AdvantageStar Topology Advantage
 Less expensive than a mesh topology ~ each
device needs only one link and one I/O port to
connect it to any number of others.
 Easy to install and reconfigure ~ involve only one
connection between that device and the hub.
 Robustness ~ if one link fails, only that link is
affected; all other links remain active.
 Easy fault identification & isolation ~ hub can be
used to monitor link problems and bypass
defective links.

21. 05/23/13 TJ 2013 - Data Comm. 21
Bus TopologyBus Topology
 Multipoint configuration, where one
long cable acts as a backbone to link
all the devices in the network.
 Backbone ~ the major transmission
path in a network.
 Nodes are connected to the bus cable
by drop lines and taps.
 A tap is a connector that either splices
into the main cable or punctures the
sheathing of a cable to create a
contact with the metallic core.
 The end of the bus cable, must be
terminated with a resistive load or
terminating resistors.
 I.e. 10Base2

22. 05/23/13 TJ 2013 - Data Comm. 22
Bus Topology AdvantageBus Topology Advantage
Ease of installation ~ backbone cable can be
laid along the most efficient path, then
connected to the nodes by drop lines of
various lengths.
Cheap ~ Less cabling is needed than mesh
and star topology

23. 05/23/13 TJ 2013 - Data Comm. 23
Bus Topology DisadvantageBus Topology Disadvantage
Difficult reconfiguration ~ difficult to add new
device since require modification or
replacement of the backbone.
fault isolation is difficult ~ a fault or break in
the bus cable stops all transmission.

24. 05/23/13 TJ 2013 - Data Comm. 24
Ring TopologyRing Topology
 Each device has a dedicated point-
to-point line configuration only with
the two devices on either side of it.
 A signal is passed along the ring in
one direction, from one device to
device, until it reaches its
destination.
 Each device in the ring
incorporates a repeater; when a
device receives a signal intended
for another device, its repeater
regenerates the bits and passes
them along.
 I.e. Token Ring (IEEE 802.5)

25. 05/23/13 TJ 2013 - Data Comm. 25
Ring Topology AdvantageRing Topology Advantage
Easy to install and reconfigure ~ each
device is linked only to its neighbors. To add
or delete a device requires moving only two
connections.
Easy fault identification & isolation ~ a
device capable of issuing an alarm to alert
the network operator to the problem and its
location.

26. 05/23/13 TJ 2013 - Data Comm. 26
Ring Topology DisadvantageRing Topology Disadvantage
Unidirectional traffic ~ a break in the ring
(disable station) can disable the entire
network.
Note: this weakness can be solved by using
a dual ring or a switch capable of closing off
the break.
– I.e. FDDI (using dual ring)

27. 05/23/13 TJ 2013 - Data Comm. 27
Wireless TopologyWireless Topology
 There’s no topology
for wireless network.
 Nodes can be
everywhere but it
must be in the range
that can be access
between the access
point.
 Example: IEEE
802.11

28. 05/23/13 TJ 2013 - Data Comm. 28
Project 802Project 802
 In 1985, the Computer Society of the IEEE started
a project, called Project 802, to set standards to
enable intercommunication between equipment
from a variety of manufacturers.
 It covers the first two layers of the OSI model and
part of the third level.
 Project 802 has split the data link layer into two
different sublayers:
– Logical link control (LLC)
– Media access control (MAC)

29. 05/23/13 TJ 2013 - Data Comm. 29
Project 802 & OSI ModelProject 802 & OSI Model

30. 05/23/13 TJ 2013 - Data Comm. 30
Logical Link Control (LLC)Logical Link Control (LLC)
IEEE 802.2 LLC is the upper sublayer of the
data link layer.
The functions include the logical address,
control information, and data.

31. 05/23/13 TJ 2013 - Data Comm. 31
Medium Access Control (MAC)Medium Access Control (MAC)
MAC is the lower layer of the DLL layer.
MAC sublayer resolves the contention for
the shared media.
It contains the synchronization, flag, flow,
and error control specifications necessary to
move information from one place to another,
as well as the physical address of the next
station to receive and route a packet.

32. 05/23/13 TJ 2013 - Data Comm. 32
ArchitectureArchitecture
IEEE 802 are subdivided into several
functions, identified by:
– a number
• 802.1 ~ internetworking
• 802.2 ~ LLC
– The MAC module
• 802.3 ~ CSMA/CD (Ethernet)
• 802.4 ~ Token Bus
• 802.5 ~ Token Ring
• Others (802.6 ~ DQDB, 802.11 ~ Polling)

33. 05/23/13 TJ 2013 - Data Comm. 33
Project 802 ArchitectureProject 802 Architecture

34. 05/23/13 TJ 2013 - Data Comm. 34
IEEE 802.1~ InternetworkingIEEE 802.1~ Internetworking
The section of project 802 devoted to
internetworking issues in LANs and MANs.
It seeks to resolve the incompatibilities
between network architectures without
requiring modifications in existing
addressing, access, and error recovery
mechanisms, among others.

35. 05/23/13 TJ 2013 - Data Comm. 35
802.2 ~LLC802.2 ~LLC
IEEE 802.2 LLC is the upper sublayer of the
data link layer.
The functions include the logical address,
control information, and data.

36. 05/23/13 TJ 2013 - Data Comm. 36
IEEE 802.3IEEE 802.3
It supports a LAN standard originally
developed by Xerox and later extended by a
joint venture between Digital Equipment
Corporation, Intel Corporation and Xerox.
This was called Ethernet and the access
method used is CSMA/CD.
IEEE 802.3 therefore is known as Ethernet
or CSMA/CD.

37. 05/23/13 TJ 2013 - Data Comm. 37
IEEE 802.3 CategoriesIEEE 802.3 Categories
 IEEE 802.3 defines two categories:
– Baseband ~ base specifies digital signal
– Broadband ~ broad specifies analog signal
 IEEE divides the baseband category into several
different standards:
– 1Base5, 10Base5, 10Base2, 10BaseT, 100BaseT
 IEEE defines only one specification for the
broadband catergory:
– 10Broad36

38. 05/23/13 TJ 2013 - Data Comm. 38
IEEE 802.3 CategoriesIEEE 802.3 Categories
 1Base5, 10Base2, 100BaseT, 10Broad36
 The first number (1,10,100) indicates the data rate
in Mbps.
 The base or broad indicates type of signal.
 The last number or letter (1,2,5,T) indicates the
maximum cable length or the type of cable.
 The maximum cable length restriction can be
changed using network devices such as repeaters
or bridges.

39. 05/23/13 TJ 2013 - Data Comm. 39
IEEE 802.3 Access MechanismIEEE 802.3 Access Mechanism
 Whenever multiple users have unregulated access to a
single line, there is a danger of signals overlapping and
destroying each other.
 Such overlaps, which turn the signals into unusable
noise, are called collisions.
 As traffic increases on a multiple-access link, so do
collisions.
 A LAN therefore needs a mechanism to coordinate
traffic, minimize the number of collision occur, and
maximize the number of frames that are delivered
successfully.

40. 05/23/13 TJ 2013 - Data Comm. 40
IEEE 802.3 Access MechanismIEEE 802.3 Access Mechanism

41. 05/23/13 TJ 2013 - Data Comm. 41
IEEE 802.3 Access MechanismIEEE 802.3 Access Mechanism
 The access mechanism
used in an Ethernet is called
Carrier Sense Multiple
Access with Collision
Detection (CSMA/CD).
 CSMA/CD is the result of an
evolution from Multiple
Access (MA) to Carrier
Sense Multiple Access
(CSMA), and finally to
CSMA/CD.

42. 05/23/13 TJ 2013 - Data Comm. 42
Multiple Access (MA)Multiple Access (MA)
 The original design was MA method in which every
workstation had equal access to a link.
 There was no provision for traffic coordination.
 Access to the line was open to any node at any time.
 Any station wishing to transmit did so, then relied on
acknowledgements to verify that the transmitted frame
had not been destroyed by other traffic on the line.
 The examples of algorithms for allocating a multiple
access channel is ALOHA.

43. 05/23/13 TJ 2013 - Data Comm. 43
CSMACSMA
 In Carrier Sense Multiple Access (CSMA) system, any
workstation wishing to transmit must first listen for existing
traffic on the line.
 Carrier Sense ~ a device listens by checking for a voltage.
 If no voltage is detected, the line is considered idle and the
transmission is initiated.
 CSMA cuts down on the number of collisions but does not
eliminate them.
 Collisions can still occur, if another station has transmitted
too recently for its signal to have reached the listening
station, the listener assumes the line is idle and introduces
its own signal onto the line.

44. 05/23/13 TJ 2013 - Data Comm. 44
CSMA/CDCSMA/CD
In CSMA/CD the station wishing to transmit first
listens to make certain the link is free, then
transmits data, then listens again.
During the data transmission, the station
checks the line for the extremely high voltages
that indicate a collision.
If a collision is detected, the station quits the
current transmission and waits a predetermined
amount of time for the line to clear, then sends
its data again.

45. 05/23/13 TJ 2013 - Data Comm. 45
IEEE 802.3 Frame FormatIEEE 802.3 Frame Format
IEEE 802.3 specifies one type of frame
containing seven fields:
– Preamble ~ alert the receiving system of incoming frame
and synchronize input timing
– Start Frame Delimiter (SFD) ~ starts signal the
beginning of the frame
– Destination Address (DA) ~ physical address
– Source Address (SA) ~ physical address
– Length/type of PDU
– 802.2 frame/PDU/Data and padding/payload
– CRC ~ error detection

46. 05/23/13 TJ 2013 - Data Comm. 46
MAC Frame FormatMAC Frame Format

47. 05/23/13 TJ 2013 - Data Comm. 47
ImplementationImplementation
 Although the Project 802 standard focuses on the data link
layer of the OSI model, it also defines some physical
specifications for each of the protocols defined in the MAC
layer.
 In the 802.3 standard, IEEE defines the types of cable,
connections, and signals that are to be used in each
Ethernet implementations.
 All Ethernet LANs are configured as logical buses, although
they may be physically implemented in bus or star
topologies.
 Each frame is transmitted to every station on the link but
read only by the station to which it is addressed.

48. 05/23/13 TJ 2013 - Data Comm. 48
10BASE5: Thick Ethernet10BASE5: Thick Ethernet
 The 1st
of the physical standards defined in the IEEE 802.3 model
is called 10Base5 or Thick Ethernet or Thicknet.
 The name derives from the size of the cable, which is roughly the
size of garden hose and too stiff to bend with your hands.
 It’s a bus topology LAN that uses baseband signalling and has a
maximum segment length of 500 meters.
 Using networking devices such as repeaters or bridges the total
length of the bus should not exceed 2500 meters (5 segments) to
reduce collisions.

49. 05/23/13 TJ 2013 - Data Comm. 49
10BASE5 (cont…)10BASE5 (cont…)
The standard demands that each separated
from each neighbor by 2.5 meters (200 stations
per segment and 1000 stations total)
The physical connectors and cables utilized by
10Base5 include coaxial cable, network
interface cards, transceivers, and attachment
unit interface (AUI) cables and terminators.
Coaxial cable
– RG-8 (Radio Government) cable is a thick coaxial
cable that provides the backbone.

50. 05/23/13 TJ 2013 - Data Comm. 50
10BASE5: Thick Ethernet10BASE5: Thick Ethernet

51. 05/23/13 TJ 2013 - Data Comm. 51
10BASE5 (cont…)10BASE5 (cont…)
Transceiver
– Each station is attached by an AUI cable to an
intermediary device called medium interface unit
(MAU) or transceiver (transmitter-receiver).
– It performs the CSMA/CD function of checking for
voltages and collisions on the line and may contain
a small buffer.
– It also serves as the connector that attaches a
station to the thick coaxial cable itself via a tap.

52. 05/23/13 TJ 2013 - Data Comm. 52
10BASE5 (cont…)10BASE5 (cont…)

53. 05/23/13 TJ 2013 - Data Comm. 53
10BASE5 (cont…)10BASE5 (cont…)
 AUI Cables
– Each station is linked to its corresponding transceiver by an
attachment unit interface (AUI), also called a transceiver
cable.
– An AUI is a 15-wire cable with plugs that performs the
physical layer interface functions between the station and the
transceiver.
– Each end of an AUI terminates in a DB-15 (15 pin) connector.
– One connector plugs into a port on the NIC, the other into a
port on the transceiver.
– AUIs are restricted to a maximum length of 50 meters,
allowing for some flexibility in placement stations relative to
the 10Base5 backbone cable.

54. 05/23/13 TJ 2013 - Data Comm. 54
10BASE5 (cont…)10BASE5 (cont…)
 Transceiver Tap
– Each transceiver contains a connecting mechanism called a
tap because it allows the transceiver to tap into the line at any
point.
– The tap is a thick cable-sized well with a metal spike in the
center.
– The spike is attached to wires inside the transceiver.
– When the cable is pressed into the well, the spike pierces the
jacket and sheathing the layers and makes an electrical
connection between the transceiver and the cable.
– This kind of connector is often called the vampire tap because
it bites the cable.

55. 05/23/13 TJ 2013 - Data Comm. 55
10BASE5 (cont…)10BASE5 (cont…)
Terminator
– Terminators are required for bus topologies where
one main cable acts as a backbone with branches
to several devices.
– Located at the end in bus cabling.
– If the main cable is left unterminated, any signal
transmitted over the line echoes back and interferes
with the original signal.
– A terminator absorbs the wave at the end and
eliminates echo-back.

56. 05/23/13 TJ 2013 - Data Comm. 56
10BASE5 (cont…)10BASE5 (cont…)

57. 05/23/13 TJ 2013 - Data Comm. 57
10Base2: Thin Ethernet10Base2: Thin Ethernet
 The 2nd
Ethernet implementation defined by the IEEE
802 series called 10Base2, thin Ethernet, thinnet,
cheapnet, cheapernet, thinwire Ethernet.
 It provides an inexpensive alternative to 10Base5
Ethernet, with the same data rate.
 Like 10Base5, 10Base2 is also bus topology LAN.
 The advantages of thinnet are reduced cost and ease
of installation. (The cable is lighter weight and more
flexible than that used in Thicknet)
 The disadvantages are shorter range (185 meters) and
smaller capacity (30 stations/segment).

58. 05/23/13 TJ 2013 - Data Comm. 58
10Base2 (cont…)10Base2 (cont…)
The connectors and cables utilized are NICs,
thin coaxial cable, BNC-T connectors and
terminators.
NIC
– The NICs in a thinnet system provide all of the same
functionality as those in the thicknet system, plus
the functions of the transceivers.
– It does not only provide the station with an address
but also checks for voltages on the link.

59. 05/23/13 TJ 2013 - Data Comm. 59
10Base2 (cont…)10Base2 (cont…)

60. 05/23/13 TJ 2013 - Data Comm. 60
10Base2 (cont…)10Base2 (cont…)
 Thin coaxial cable
– The cable required to implement the 10Base2 standard is
RG-58.
– These cables are relatively easy to install and move around.
 BNC-T
– The BNC-T connector is a T-shaped device with three ports:
one for the NIC and one each for the input and output ends of
the cable.
 Terminator
– 50-ohm is used to absorbs the wave at the end and
eliminates the echo-back.

61. 05/23/13 TJ 2013 - Data Comm. 61
10BaseT: Twisted Pair Ethernet10BaseT: Twisted Pair Ethernet
 The most popular standard defined in the IEEE 802.3
series.
 Physically a star-topology LAN, but logically is a bus-
topology.
 It uses unshielded twisted pair cable (UTP CAT-3 or
CAT-5)
 It supports data rate of 10Mbps and has a maximum
length (hub to station) of 100 meters.

62. 05/23/13 TJ 2013 - Data Comm. 62
10BaseT (cont…)10BaseT (cont…)
 It places all of its networking operations in an intelligent
hub with a port for each station.
 Stations are linked into the hub by four-pair RJ-45
cable (8-wire UTP) terminating at each end in a male-
type connector much like telephone jack.
 The hub sends out any transmitted frame to all of its
connected stations.
 Logic in the NIC assures that the only station to open
and read a given frame is the station to which that
frame is addressed.

63. 05/23/13 TJ 2013 - Data Comm. 63
10BaseT (cont…)10BaseT (cont…)

64. 05/23/13 TJ 2013 - Data Comm. 64
Other Ethernet NetworksOther Ethernet Networks
During the last decade, there has been an
evolution in Ethernet Networks.
Several new schemes have been devised to
improve the performance and the speed of
Ethernet LANS.
Some of the efforts are:
– Switched Ethernet
– Fast Ethernet
– Gigabit Ethernet

65. 05/23/13 TJ 2013 - Data Comm. 65
Switched EthernetSwitched Ethernet
 An attempt to improve the performance of 10BaseT
Ethernet.
 10BaseT is a shared media network, which means that the
entire media is involved in each transmission.
 This is because the topology, though physically a star, is
logically a bus.
 When a station sends a frame to a hub, the frame is sent
out all ports (interfaces) and every station will receive it.
 In this situation, only one station can send a frame at any
time.
 If two stations try to send frames simultaneously, there is a
collision.

66. 05/23/13 TJ 2013 - Data Comm. 66
10BaseT Example10BaseT Example
Station A is sending a frame to station E. The frame is
received by the hub and is sent to every station. All of
the cabling in the system involved in this transmission.
Another way to think about this is that one transmission
uses the entire capacity of 10Mbps; if one station uses
it, no other station can.
A
E
DC
F
B

67. 05/23/13 TJ 2013 - Data Comm. 67
Switched Ethernet (cont…)Switched Ethernet (cont…)
 If we replace the hub with a switch, a device that can
recognize the destination address and can route the frame
to the port to which the destination station is connected, the
rest of the media are not involved in the transmission
process.
 This means that the switch can receive another frame from
another station at the same time and can route this frame to
its own final destination.
 In this way, theoretically, there is no collision.
 Using a switch, instead of hub, we can theoretically
increase the capacity of a network with N devices to N x 10
Mbps because the two pairs of UTP for full-duplex
communications.

68. 05/23/13 TJ 2013 - Data Comm. 68
Switched Ethernet ExampleSwitched Ethernet Example
Station A is sending a frame to station E. The frame is
received by the hub and sent to station E. Only station
E receives the frame, so the rest of the media is free
for another transmission. Station B can also send a
frame to station D without any collision.
A
E
DC
F
B

69. 05/23/13 TJ 2013 - Data Comm. 69
Fast Ethernet (IEEE 802.3u)Fast Ethernet (IEEE 802.3u)
Fast Ethernet is a version of Ethernet operates
at 100 Mbps data rate.
There is no change in the frame format and the
access method (CSMA/CD).
The only two changes in the MAC layer are the
data rate and the collision domain.
The data rate is increased by a factor of 10; the
collision domain is decreased by a factor of 10.

70. 05/23/13 TJ 2013 - Data Comm. 70
Fast Ethernet (cont…)Fast Ethernet (cont…)
In the physical layer, the specification
developed for Fast Ethernet is a star topology
similar to 10Base-T; however, to match the
physical layer to different resources available,
IEEE has designed two categories of Fast
Ethernet:
– 100Base-X (2 cables between the station to hub)
• 100Base-TX (2 pairs of UTP or STP)
• 100Base-FX (2 optical fibers)
– 100Base-T4 (4 pairs of UTP)

71. 05/23/13 TJ 2013 - Data Comm. 71
100Base-TX100Base-TX
It uses two category 5 UTP or STP cables to
connect a station to the hub.
One pair is used to carry frames from the
station to the hub and the other to carry from
the hub to the station (1 pair for transmission, 1
pair for reception).
The distance between the station and the hub
(or switch) should be less than 100 meters.

72. 05/23/13 TJ 2013 - Data Comm. 72
100Base-FX100Base-FX
It uses two optical fibers (either multimode fiber
or single mode fiber), one to carry frames from
the station to the hub, and the other from the
hub to the station (1 for transmission, 1 for
reception).
The distance between the station and the hub
should be less than 412 meters for multimode
half duplex, 2 km for multimode full duplex and
20 km for single mode fiber.

73. 05/23/13 TJ 2013 - Data Comm. 73
100Base-T4100Base-T4
It uses 4 pairs of UTP between the station to
the hub (2 pairs for transmission and two pairs
for reception).
A length of 4-pair UTP must not more than 100
meters between the NIC in the station and the
port in the 100Base-T4 hub.
The physical layer implementation for 100base-
T4 varies significantly from the physical layer
definition of 10baseT.

74. 05/23/13 TJ 2013 - Data Comm. 74
100Base-T4 (cont…)100Base-T4 (cont…)
It achieves its speed by dividing a 100 Mbps
data stream into three 33 Mbps streams.
These 3 streams are sent over 3 pairs of UTP.
A 4th
pair is used for collision detection.
No data is sent on the 4th
pair; instead, a hub
uses it to signal a station when a collision
occurs.

75. 05/23/13 TJ 2013 - Data Comm. 75
Gigabit EthernetGigabit Ethernet
 The migration from 10 Mbps to 100 Mbps encouraged
the IEEE 802.3 committee to design gigabit Ethernet,
which has data rate of 1000 Mbps or 1 Gbps.
 The MAC layer and the access method remain the
same, but the collision domain is reduced.
 The physical layer ~ the transmission media and the
encoding system, however, changes.
 It is mainly designed to use optical fiber, although the
protocol does not eliminate the use of twisted pair
cables.

76. 05/23/13 TJ 2013 - Data Comm. 76
Gigabit Ethernet (cont…)Gigabit Ethernet (cont…)
It usually serves as a backbone to connect Fast
Ethernet networks.
Four implementation has been designed for
Gigabit Ethernet:
– 1000Base-LX (multimode FO, max 550 meters)
– 1000Base-SX (multi, max 550 m or single, 5 km)
– 1000Base-CX (STP, max 25 meters)
– 1000Base-T (UTP, max 25 meters)

77. 05/23/13 TJ 2013 - Data Comm. 77
TOKEN BUS (IEEE 802.4)TOKEN BUS (IEEE 802.4)
 It combines features of Ethernet and Token Ring.
 It combines the physical configuration of Ethernet (a bus
topology) and the collision free (predictable delay) feature
of Token Ring.
 Token Bus is a physical bus that operates as a logical ring
using tokens.
 Stations are logically organized into a ring.
 A token is passed among stations, if a station wants to
send data, it must wait and capture token.
 Token bus is limited to factory automation and process
control and has no commercial application in data
communication.

78. 05/23/13 TJ 2013 - Data Comm. 78
Token Ring (IEEE 802.5)Token Ring (IEEE 802.5)
A LAN using a ring topology and token-passing
method.
A control station creates a special entity on the
network called a token and passes it around the
network ring.
A token is a simple placeholder frame that is
passed from station to station around the ring.
A station may send data only when it has
possession of the token.

79. 05/23/13 TJ 2013 - Data Comm. 79
Token Ring: Access MethodToken Ring: Access Method
 Token Ring use the access method called token
passing.
 Token passing is an example of deterministic protocol.
 It solves collision problem in CSMA/CD.
 2 types of token
- Free token (no data)
- Busy token (with data)
 Token moves in one way circling the ring and only one
token at a time.

80. 05/23/13 TJ 2013 - Data Comm. 80
A token is passed from NIC to NIC in sequence until
it encounters a station with data to send.
When the token reaches a station on the network that
has something to transmit, it “captures” (keep the token
in its network board) the token, changes the status of
the token to busy.
It then sends data frame.
This data frame proceeds around the ring, being
regenerated by each station.
Token Ring: Access Method (cont…)Token Ring: Access Method (cont…)

81. 05/23/13 TJ 2013 - Data Comm. 81
Token Ring: Access MethodToken Ring: Access Method
 Each intermediate station examines the destination
address, finds that the frame is addressed to
another station, and relays it to its neighbor.
 The intended recipient recognizes its own address,
copies the message, checks for errors, and
changes four bits in the last byte of the frame to
indicate address recognized and frame copied.
 The full packet then continues around the ring until
it returns to the station that sent it.

82. 05/23/13 TJ 2013 - Data Comm. 82
The sender receives the frame and recognizes
itself in the source address field.
It then examines the address-recognized bits.
If they are set, it knows the frame was
received.
The sender then discards the used data and
releases the token back to the ring.
Token Ring: Access MethodToken Ring: Access Method

83. 05/23/13 TJ 2013 - Data Comm. 83
Token Ring: Access MethodToken Ring: Access Method

84. 05/23/13 TJ 2013 - Data Comm. 84
ExerciseExercise
 Complete the figure below with 10BaseT configuration.

85. 05/23/13 TJ 2013 - Data Comm. 85
SolutionSolution

86. 05/23/13 TJ 2013 - Data Comm. 86
ReviewReview
Introduction
Topology
Project 802
Ethernet
Fast Ethernet
Token Bus
Token Ring