ppt ch5 DCN.pp

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Chapter 5Chapter 5

Network topologies, Network topologies, Switching and routing Switching and routing

algorithmsalgorithms

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Figure 1.4 Categories of topology

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Figure 1.5 A fully connected mesh topology (five devices)

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Figure 1.6 A star topology connecting four stations

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TREE TopologyTREE Topology It is a special case of Star Topology.It is a special case of Star Topology.

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Figure 1.7 A bus topology connecting three stations

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Figure 1.8 A ring topology connecting six stations

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Figure 1.9 A hybrid topology: a star backbone with three bus networks

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Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

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Switching

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Figure 8.1 Switched network

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Figure 8.2 Taxonomy of switched networks

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8-1 CIRCUIT-SWITCHED NETWORKS8-1 CIRCUIT-SWITCHED NETWORKS

A circuit-switched network consists of a set of switches A circuit-switched network consists of a set of switches connected by physical links. A connection between two connected by physical links. A connection between two stations is a dedicated path made of one or more links. stations is a dedicated path made of one or more links. However, each connection uses only one dedicated However, each connection uses only one dedicated channel on each link. Each link is normally divided channel on each link. Each link is normally divided into n channels by using FDM or TDM.into n channels by using FDM or TDM.

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A circuit-switched network is made of a set of switches connected by physical

links, in which each link is divided into n channels.

Note

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Figure 8.3 A trivial circuit-switched network

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In circuit switching, the resources need to be reserved during the setup phase;the resources remain dedicated for the entire duration of data transfer until the

teardown phase.

Note

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Figure 8.4 Circuit-switched network used in Example 8.1

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Figure 8.6 Delay in a circuit-switched network

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Switching at the physical layer in the traditional telephone network uses

the circuit-switching approach.

Note

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Packet Switching:Packet Switching:Types:-Types:-Datagram Packet SwitchingDatagram Packet SwitchingVirtual Circuit Packet SwitchingVirtual Circuit Packet Switching

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8-2 DATAGRAM NETWORKS8-2 DATAGRAM NETWORKS

In data communications, we need to send messages In data communications, we need to send messages from one end system to another. If the message is from one end system to another. If the message is going to pass through a packet-switched network, it going to pass through a packet-switched network, it needs to be divided into packets of fixed or variable needs to be divided into packets of fixed or variable size. The size of the packet is determined by the size. The size of the packet is determined by the network and the governing protocol.network and the governing protocol.

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In a packet-switched network, there is no resource reservation;

resources are allocated on demand.

Note

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Figure 8.7 A datagram network with four switches (routers)

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The destination address in the header of a packet in a datagram network

remains the same during the entire journey of the packet.

Note

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Figure 8.9 Delay in a datagram network

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Switching in the Internet is done by using the datagram approach

to packet switching at the network layer.

Note

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VIRTUAL-CIRCUIT NETWORKSVIRTUAL-CIRCUIT NETWORKS

A virtual-circuit network is a cross between a circuit-A virtual-circuit network is a cross between a circuit-switched network and a datagram network. It has switched network and a datagram network. It has some characteristics of both.some characteristics of both.

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Figure 8.10 Virtual-circuit network

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In virtual-circuit switching, all packets belonging to the same source and destination travel the same path;but the packets may arrive at the destination with different delays

if resource allocation is on demand.

Note

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Figure 8.16 Delay in a virtual-circuit network

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Switching at the data link layer in a switched WAN is normally

implemented by using virtual-circuit techniques.

Note

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Message Switching: Message Switching:

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RoutersRoutersRouters are devices that Routers are devices that

connect two or more connect two or more networks. networks.

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Routing AlgorithmRouting AlgorithmThe important functions of network The important functions of network

layer is to route the packets from the layer is to route the packets from the source to destination.source to destination.

Routing algorithm is a part of network Routing algorithm is a part of network layer software.layer software.

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Features of Routing Features of Routing AlgorithmAlgorithm

CorrectnessCorrectnessRobustnessRobustnessStabilityStabilityFairnessFairnessOptimalityOptimality

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Types of Routing Types of Routing AlgorithmAlgorithm

Non-adaptive /Fixed / Static Non-adaptive /Fixed / Static AlgorithmAlgorithm

Adaptive /Dynamic AlgorithmAdaptive /Dynamic Algorithm

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Non-adaptive /Fixed / Non-adaptive /Fixed / Static AlgorithmStatic Algorithm

The choice of route is done The choice of route is done in advance, off line and it is in advance, off line and it is downloaded to the routersdownloaded to the routers

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Adaptive /Dynamic Adaptive /Dynamic AlgorithmAlgorithmThe routing decision can be The routing decision can be

changed if there are any changes changed if there are any changes in the topology or traffic.in the topology or traffic.

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Static AlgorithmStatic Algorithm Shortest path routingShortest path routing Flooding Flooding Flow based routingFlow based routing

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