lan topologies and standards networks and protocols prepared by: tgk first prepared on: last...

LAN Topologies and Standards

Networks and Protocols

Prepared by: TGK First Prepared on: Last Modified on:

Quality checked by: Copyright 2009 Asia Pacific Institute of Information Technology



Slide 2 of 27

Topic & Structure of the lesson

LAN Topologies (Bus, Star, Ring, Mesh, and Tree)Characteristics of TopologiesLAN Standards (IEEE 802.x Series)



Slide 3 of 27

Learning Outcomes

At the end of this module, YOU should be able to:

• Explain the WAN technologies – Cellular Network, Satellite Network, and Wireless Network



Slide 4 of 27

Key Terms you must be able to use

If you have mastered this topic, you should be able to use the following terms correctly in your assignments and exams:

• Bus Topology• Star Topology• Ring Topology• Mesh Topology • Tree Topology• Characteristics of Topologies• LAN Standards



Slide 5 of 27

Main Teaching Points

• Communication pattern

• Expansion of networks

• Physical outlook of networks

• Logical operations of networks

• Network components and connectivity

• Medium access control and techniques

• IEEE 802 standards committee and working groups



Slide 6 of 27

Bus Topology

• Connected in a row along a single cable, trunk, backbone or segment

• Communication on a bus

• Sending the signal

• Signal propagates along cable(s)

• A terminator absorbs the signal at the end

• Only one computer can access wire at any one time

• The more PC’s attached, more traffic generated

• Bus is a PASSIVE topology

• PC only listens for traffic



Slide 7 of 27

• Signal bounce occurs if ends of bus not terminated

• Terminators attached to each end. Every cable end

must be attached to something

• Generally a 50 Ohm resistor is used as terminator

• LAN expansion - bus topology

• Barrel connector

• Repeater - boosts signal (regenerate/amplify)

Bus Topology



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Bus Topology

• Data sent to all computers, but only destination accepts

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Bus Topology

• Terminators absorb ‘free’ signals



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Bus Topology

• Unplugged cable not terminated will take down the

network



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Bus Topology

• Connectors can be used to combine cable segments

• Connectors can be used to combine cable segments

Weakened signal

Regenerated signal

Repeater



Slide 12 of 27

Bus Topology

• CSMA/CD (Contention Method) - Carrier Sense Multiple

Access /Collision Detection:

• also called listen-before talk

• used with bus topology

• part of Ethernet standard 802.3



Slide 13 of 27

Star Topology

• Each segment attached to centralized component, called

a Hub

• If the hub fails, the network goes down

• The hub is the central connector; not the central

controller

• Simple Star topology:



Slide 14 of 27

Star Topology

• Hub is the central point in a Star topology

Hub

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Slide 15 of 27

Ring Topology

• Signal travels around a ring

• Travels in one direction

• Signal boosted (regenerated) by each computer as signal

passes through (computer acts as repeater)

• Generally uses Token Passing

• Simple ring network showing logical ring:



Slide 16 of 27

Ring Topology

• A computer grabs the token and passes it around the

ring:

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Data

Data

• IEEE 802.5 standard for ring access protocol allows priority

levels to be set for tokens and messages. (Problem - one

station with high priority messages can monopolize network)



Slide 17 of 27

Ring Topology

• FDDI - standard for high speed ring LAN, using optic

fiber.

• Also uses token passing protocol. Some differences to

maximize efficiency

• Multiple tokens can be circulated because station

transmits free token immediately after transmits

message



Slide 18 of 27

Mesh Topology

• The advantages of a mesh topology is that the two nodes

are using the entire capacity of the link exclusively

• In terms of robustness, a mesh topology network can

withstand the destruction of anyone of its components

without incapacitating the entire network

• Due to its nature, the mesh network physically prevents

any intrusion on the information sent

• Total number links required:- n(n-1)/2



Slide 19 of 27

Mesh Topology

• Due to its nature, the mesh network physically prevents

any intrusion on the information sent

• Total number links required:- n(n-1)/2

• To connect all its nodes together, a mesh topology

would require n(n-1)/2 wires, or channels



Slide 20 of 27

Mesh Topology

• This number increases exponentially when new nodes

are added to the network

• Each node itself would, then, be equipped with n-1 I/O

ports to connect itself to the network

• The disadvantage of the mesh topology is, simply, the

amount of cabling itself



Slide 21 of 27

Tree Topology

• Addition of new networks to a bus topology would be

hard

• A tree topology, however, is an extension of the bus

• In a tree, the trunk is usually a high capacity device or

connection which facilitates data transmission amongst

the branches



Slide 22 of 27

Tree Topology

• The advantage of a tree topology is usually that the

privacy of transmissions are isolated in a particular

branch

• Also, if a particular branch is incapacitated, the trunk and

the other branches may still function

• The disadvantage is naturally the fault isolation

• Should a transmission fails to be sent, a fault detection

exercise may have to cover the entire distance of the

cabling

• The trunk of the tree must also be properly configured to

be robust



Slide 23 of 27

The physical topology of a network is the layout or actual

appearance of the cabling scheme used on a network

The logical topology of a network describes how the data

flows through the physical topology

Point-to-point (PTP) topology connects two nodes

directly together - Mesh

Multipoint topologies link three or more devices

together through a single communication - Star, Bus,

Ring, Hybrid

Characteristics of Topologies



Slide 24 of 27

LAN Standards

• The IEEE 802 Committee

• IEEE has multiple standards committees

• LAN standards are set by the IEEE 802 Standards

Committee

• Working Groups of the 802 Standards Committee create

individual standards

• 802.3 for Ethernet Standards

• 802.5 for Token-Ring LAN Standards

• 802.11 for Radio and Infrared Wireless LANs

• Are there others not listed above?...



Slide 25 of 27

LAN Standards

• Project 802 produced recommendations covering:

• Topology, speed, and data link protocol (Bus, Ring,

CSMA/CD, Token passing)

• Medium - coax, twisted pair, fiber optic cable

• Addressing: (Local access 16 bit address, Unique

International 48 bit)

• The following diagram illustrates where the IEEE 802.

standards relates to the ISO - Open Systems

Interconnect(OSI) model:



Slide 26 of 27

PHYSICALMEDIA

CSMA/CD

BUS TOPOLOGY RING TOPOLOGY

TOKEN BUS

BASEBAND/BROADBANDCOAX,

UNSHIELDEDTWISTED PAIR

BROADBAND COAX

OPTIC FIBRE

TOKEN RING TOKEN RING

SHIELDEDTWISTED PAIR

OPTIC FIBRE

802.3 802.4 802.5 FDDI (ANSI)

LAN Standards



Slide 27 of 27

Quick Review Question

1. Describe the advantages and disadvantages of the various LAN topologies highlighted.

2. Discuss the importance of the IEEE 802 standards committee towards the networks used today and which do you think is important for the near future.



Slide 28 of 27

Follow Up Assignment

Carry out a research on which LAN topology is most commonly used in LANs today and subsequently, discuss the relationship between the topology you have identified with the efforts of the IEEE 802 standards committee if applicable. Should the chosen topology be of a proprietary standard, you have to discuss the origins of it and the functionality/operations.



Slide 29 of 27

Summary of Main Teaching Points



Slide 30 of 27

Q & A

Question and Answer Session



Slide 31 of 27

Topic and Structure of next session

• Network Protocol Models and Architecture

Network Protocols The ISO-OSI Model Comparing TCP/IP Architecture and the OSI Model

Next Session

lan topologies and standards networks and protocols prepared by: tgk first prepared on: last...

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