Switching: Circuit Switching and Packet Switching, Lecture notes of Computer science

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SWITCHING

CIRCUIT SWITCHING & PACKET SWITCHING

UNIT II: CHAPTER III

Switched Network

 A network is a set of connected devices. Whenever we have multiple devices, we have the

problem of how to connect them to make one-to-one communication possible. One solution

is to make a point-to-point connection between each pair of devices. But these methods,

however, are impractical and wasteful when applied to very large networks. The number

and length of the links require too much infrastructure to be cost-efficient, and the majority

of those links would be idle most of the time.

 A better solution is switching. A switched network consists of a series of interlinked nodes,

called switches. Switches are devices capable of creating temporary connections between

two or more devices linked to the switch. In a switched network, some of these nodes are

connected to the end systems (computers or telephones, for example). Others are used

only for routing.

 Every time in computer network you access the internet or another computer

network outside your immediate location, your messages are sent through a

maze of transmission media and connection devices.

The mechanism for moving information between different computer

network and network segment is called switching in computer

SWITCHING METHODS

Circuit-Switched Network



Circuit-switched is a type of

network in which a physical

path is obtained for and

dedicated to a single

connection between two end-

points in the network for the

duration of the connection.



Ordinary voice phone service

is circuit-switched.



The telephone company

reserves a specific physical

path to the number you are

calling for the duration of your

call.

Circuit-Switched Network: Three

Phases



A circuit S witched

communication system involves three

phases :



Circuit establishment

(setting up dedicated links

between the source and

destination);



Data transfer (transmitting

the data between the source

and destination); and



Circuit disconnect (removing

the dedicated links).

Switch

CIRCUIT SWITCHING

 A crossbar switch connects n inputs to m outputs in a grid, using electronic

micro-switches (transistors) at each crosspoint.

 The major limitation of this design is the number of crosspoints required.

 To connect n inputs to m outputs using a crossbar switch requires n x m

crosspoints.

Crossbar Switch ( Space-Division Switch)



The solution to the limitations of the crossbar switch is the multistage switch,

which combines crossbar switches in several (normally three) stages, as shown

in Figure.



In a single crossbar switch, only one row or column (one path) is active for any

connection.



So we need N x N crosspoints.



If we can allow multiple paths inside the switch, we can decrease the number of

crosspoints. Each crosspoint in the middle stage can be accessed by multiple

crosspoints in the first or third stage.

Multistage Switch

Switching Path

Switching Path

Time-division switching uses time-division

multiplexing (TDM) inside a switch.

TDM without TSI ( Time-Division Switch )

TDM with TSI



The most popular technology is called the time-slot interchange (TSI).



Time-Slot Interchange shows a system connecting four input lines to four

output lines. Imagine that each input line wants to send data to an output

line according to the pattern.

Time-Slot Interchange



If the message is going to pass through a packet-switched network, it needs to

be divided into packets of fixed or variable size.



The size of the packet is determined by the network and the governing protocol.



In packet switching, there is no resource allocation for a packet.



This means that there is no reserved bandwidth on the links, and there is no

scheduled processing time for each packet. Resources are allocated on demand.

The allocation is done on a firstcome, first-served basis.



When a switch receives a packet, no matter what is the source or destination, the

packet must wait if there are other packets being processed.



As with other systems in our daily life, this lack of reservation may create delay.



For example, if we do not have a reservation at a restaurant, we might have to

wait.

Packet-Switched Network (DATAGRAM

NETWORKS)

Datagram Approach

Datagram Approach, Multiple Channels

Switched Virtual Circuit

A virtual-circuit network is a cross between a circuit-

switched network and a datagram network. It has some

characteristics of both.

Switched Virtual Circuit

Thank you