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

LANsAdvantagesShare resources (H/W: high quality printers, modems, tape backup, plotters, mass storage) (S/W: commercial apps, in-house apps, data sets) (Comms: email, messaging, web, print jobs, DB records

Mix and match of vendor equipment (MAC / PC / Sun...)

Transfer rates / low error rates

Can be privately owned and maintained: provide services to employees it deems is best

4

DisadvantagesDepreciation of equipment (lease)

Can be expensive- eg. Network server, NOS, cabling, hubs / switches, network-based apps, security, support and maintenance

Interoperability can be an issue as well (my print server and WinXP/Linux and MAC)

Licensing of S/W can become complex

Well trained staff required – LAN does not manage and diagnose itself

Only as strong as it s weakest link

Bus / Tree Topology

5

Bus / Tree Topology

6

Bus / Tree Topology

7

Bus / Tree Topology

8

Star-wired Bus Topology

9

Star-wired Bus Topology

10

Star-wired Ring Topology

11

Star-wired Ring Topology

12

Wireless Topology - BSS

13

Wireless Topology - ESS

14

Wireless Topology – Ad Hoc

15

LAN Topologies

16

CSMA/CD

17

CSMA/CAWireless - 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 pollMidlength IFS used by access device when it is issuing polls to user devicesLong 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)

21

IEEE 802.5 (Token Ring)

22

Ethernet

23

FDDI (Fibre Distributed Data Interface)

24