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Why Is It All?
 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
devices(mesh topology)
a point-to-point
connection b/w each pair of
OR
B/w a central device & every other device(star topology)
 When applied to very large N/W, these methods are impractical & wasteful.
 Other topologies employing multipoint connections, such as a bus ,all ruled out
because distance b/w devices & the total no. of devices increases beyond the
capacities of the media & equipment.
 To overcome this, networking introduced Switching
Contents:
 Introduction to Switching.
 Concepts Of Switching.
1.Circuit Switching.
 Advantages & Disadvantages of Circuit Switching.
2.Packet Switching.
 Advantages & Disadvantages of Packet Switching.
 Categorized into
1. Datagram Packet Switching.
2. Virtual Circuit Packet Switching.
3. Message Switching
 Advantages & Disadvantages of Message Switching.
 Differences B/W Circuit Switching And Packet Switching.
Introduction
Switches:
A switch is a device that channels incoming data from any of multiple input ports to the
specific output port that will take the data toward its intended destination.
Switching:
Switching are the base packet or data delivering methods in network and each device like
router , switch , hub , firewall , proxy , cash server, modem are using one of these methods.
Concepts Of Switching:
SWITCHING
CIRCUIT
SWITCHING
PACKET
SWITCHING
Datagram Packet
Switching
MESSAGE
SWITCHING
Virtual Circuit
Packet Switching
CIRCUIT SWITCHING:

Circuit switching is a mechanism of assigning a predefined path from source node to destination node during the
entire period of connection.

A circuit-switched network is excellent for data that needs a constant link from end-to-end. For example real-time
video.

old telephone system (POTS) is a well known example of analogue circuit switching.
Packet Switching:

In this network type, no specific path is used for data transfer. Instead, the data is broken down into small pieces called
packets and sent over the network.

The packets can be routed, combined or fragmented, as required to get them to their eventual destination.

On the receiving end, the process is reversed—the data is read from the packets and re-assembled into the form
of the original data.
Advantages And Disadvantages
Advantages of Circuit Switching:
 Once the circuit has been set up, communication is fast and without error.
 It is highly reliable
Disadvantages of Circuit Switching:
 Inefficient – the equipment may be unused for a lot of the call, if no data is being sent,
the dedicated line still remains open.
 Waists a lot of bandwidth, especial in speech where by a user is sometimes listening,
and not talking.
 Channel set up may take longer.
Each packet is sent with a ‘header address’. This tells it where its final destination is,
so it knows where to go.
 The header address also describes the sequence for reassembly at the destination
computer so that the packets are put back into the correct order.
One packet also contains details of how many packets should be arriving so that the
recipient computer knows if one packet has failed to turn up.
If a packet fails to arrive, the recipient computer sends a message back to the
computer which originally sent the data, asking for the missing packet to be resent.
Two major packet switching
 Connectionless/Datagram packet switching:
In this case each packet includes complete addressing or routing information. The
packets are routed individually, sometimes resulting in different paths and out-of-order
delivery. Ex:-Ethernet , IP,UDP
 connection-oriented/ virtual circuit packet switching:
In this case a connection is defined and reallocated in each involved node during a
connection phase before any packet is transferred. The packets include a connection identifier
rather than address information, and are delivered in order.
Advantages & Disadvantages
Of Packet Switching
Advantages of Packet Switching

It makes very efficient use of the network - no tied-up lines.

It can easily get around broken bits of the network.

As customers increase, the network only has to expand slowly compared
to circuit switching.
Disadvantages of Packet Switching

The time it takes to put back the data package changes each time, which can be a problem for
time-critical information such as an emergency signal. The fancy name is for this is 'latency'.

Not very good for small data packages - for example if the data package itself is only 600 bytes
long, then two packets of 512 bytes need to be used, plus the address information.
Message switching:
 Message switching systems are nowadays mostly implemented
over packet-switched or circuit-switched data networks.
 Each message is treated as a separate entity. Each message
contains addressing information, and at each switch this
information is read and the transfer path to the next switch is
decided.
 Depending on network conditions, a conversation of several
messages may not be transferred over the same path. Each
message is stored (usually on hard drive due to RAM limitations)
before being transmitted to the next switch.
 Because of this it is also known as a 'store-and-forward' network.
 Email is a common application for Message Switching.
Advantages & Disadvantages Of Message Switching
Advantages
 Data channels are shared among communication devices improving the use of
bandwidth.
 Messages can be stored temporarily at message switches, when network
congestion becomes a problem.
 Priorities may be used to manage network traffic.
Disadvantages
• The only real disadvantage to Message Switching is it's not suitable for real
time applications such as data communication, video or audio.
Packet Vs Circuit Switching
Circuit Switching
Packet Switching
 In circuit switching, there are various nodes


used in the network through which the signals
are passed from one system to another.
In packet switching, the data is sent over the
network in the form of packets i.e. a large unit
of data items wrapped into a single bigger
unit.
In this a number of nodes are available
between two devices and hence multiple
paths are available to pass a signal.
 In these, the packets follows the same path
 This concept is mainly used in telephony
systems.
 This is best used for transmission of audio
signals and not suitable for data transmission.
 This type of switching is connection oriented
and may be connectionless also.

Due to its old version, this technique is less
popular and more expensive.
that is defined for them before passing into
the network.

It can be used for telephony, DSL services and
other data transmission services.

It is best used for sending data over the
network and audio and video signals can also
be sent over the network in the form of
packets.
 It is usually a connection less service.
 It is a new technology and economic than the
circuit switching approach.
Bibliography:• http://en.wikipedia.org/wiki/Network_switch/
•http:// www.tcpipguide.com/free/t_CircuitSwitchingand/
•http:// www.ustudy.in/node/3759
•http://www.indiastudychannel.com/
•www.voipnsms.com/ tag/circuit-switching
•Data Communications & Networking - Forouzan (4th Edition)