Session 5
Objectives:
By the end of this session, the student will be able to:
•State the definition of a Local Area Network
•List the primary function, activities and application areas of a LAN
•Cite the advantages and disadvantages of local are networks
•Identify the physical and logical topologies of local area networks
•Cite the characteristics of wireless local area networks and their medium access control
protocols
•Specify the different medium access control techniques
LANs
3
LANs
Advantages
Share resources (H/W: high quality
printers, modems, tape backup, plotters,
mass storage) (S/W: commercial apps, inhouse apps, data sets) (Comms: email,
messaging, web, print jobs, DB records
Mix and match of vendor equipment
(MAC / PC / Sun...)
Disadvantages
Depreciation of equipment (lease)
Can be expensive- eg. Network server,
NOS, cabling, hubs / switches, networkbased apps, security, support and
maintenance
Interoperability can be an issue as well (my
print server and WinXP/Linux and MAC)
Transfer rates / low error rates
Licensing of S/W can become complex
Can be privately owned and maintained:
provide services to employees it deems is
best
Well trained staff required – LAN does not
manage and diagnose itself
Only as strong as it s weakest link
4
Bus / Tree Topology
5
Bus / Tree Topology
6
Bus / Tree Topology
7
Bus / Tree Topology
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Star-wired Bus Topology
9
Star-wired Bus Topology
10
Star-wired Ring Topology
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Star-wired Ring Topology
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Wireless Topology - BSS
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Wireless Topology - ESS
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Wireless Topology – Ad Hoc
15
LAN Topologies
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CSMA/CD
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CSMA/CA
Wireless - CSMA/CA
Carrier Sense Multiple Access with Collision Avoidance
IFS – Interframe Space, a period of time. 3 types:
Short IFS: used by devices that require an immediate response such as an
acknowledgement, a clear to send or response to poll
Midlength IFS used by access device when it is issuing polls to user devices
Long IFS the minimum delay a device can wait while contending for access to
network.
Allows higher priority devices to transmit first
IF Medium Idle
•device wait IFS
•if medium still idle then transmits
IF Medium busy
•wait for medium to go idle
•Wait IFS
•if still idle, calculate a random Back off factor (multiple of IFS)
•when back off counter reaches zero transmit packet.
18
Token Ring
19
IEEE 802
20
IEEE 802.3 (CSMA/CD)
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IEEE 802.5 (Token Ring)
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Ethernet
23
FDDI (Fibre Distributed Data Interface)
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