cs.lectures: Packet Switching & Circuit Switching

Circuit Switching

Circuit switching is defined as the method of switching which is used for establishing a dedicated communication path between the sender and the receiver.
The link which is established between the sender and the receiver is in the physical form.
Analog telephone network is a well-known example of circuit switching.
Bandwidth is fixed in this type of switching.

Advantages

The bandwidth used is fixed.
The quality of communication is increased as a dedicated communication channel is used.
The rate at which the data is transmitted is fixed.
While switching, no time is wasted in waiting.
It is preferred when the communication is long and continuous.

Since dedicated channels are used, the bandwidth required is more.
The utilization of resources is not full.
Since a dedicated channel has been used, the transmission of other data becomes impossible.
The time taken by the two stations for the establishment of the physical link is too long.
Circuit switching is expensive because every connection uses a dedicated path establishment.
The link between the sender and the receiver will be maintained until and unless the user terminates the link. This will also continue if there is no transfer of data taking place.

Packet Switching

Packet switching is defined as the connectionless network where the messages are divided and grouped together and this is known as a packet.
Each packet is routed from the source to the destination as individual packets.
The actual data in these packets are carried by the payload.
When the packet arrives at the destination, it is the responsibility of the destination to put these packets in the right order.

Advantages

There is no delay in the delivery of the packets as they are sent to the destination as soon as they are available.
There is no requirement for massive storage space as the information is passed on to the destination as soon as they are received.
Failure in the links does not stop the delivery of the data as these packets can be routed from other paths too.
Multiple users can use the same channel while transferring their packets.
The usage of bandwidth is better in case of packet switching as multiple sources can transfer packets from the same source link.

Installation costs of packet switching are expensive.
The delivery of these packets becomes easy when complicated protocols are used.
High-quality voice calls cannot use packet switching as there is a lot of delay in this type of communication.
Connectivity issues may lead to loss of information and delay in the delivery of the information.
Types of Packet Switching

Virtual Circuits

Virtual circuits are connection-oriented, which means that there is a reservation of resources like buffers, bandwidth, etc. for the time during which the newly setup VC is going to be used by a data transfer session.
A virtual circuit network uses a fixed path for a particular session, after which it breaks the connection and another path has to be set up for the next the next session.
All the packets follow the same path and hence a global header is required only for the first packet of connection and other packets will not require it.
Packets reach in order to the destination as data follows the same path.
Virtual Circuits are highly reliable.
Implementation of virtual circuits is costly as each time a new connection has to be set up with reservation of resources and extra information handling at routers.

Datagram Networks

It is connectionless service. There is no need for reservation of resources as there is no dedicated path for a connection session.
A Datagram based network is a true packet switched network. There is no fixed path for transmitting data.
Every packet is free to choose any path, and hence all the packets must be associated with a header containing information about the source and the upper layer data.
Data packets reach the destination in random order, which means they need not reach in the order in which they were sent out.
Datagram networks are not as reliable as Virtual Circuits.
But it is always easy and cost-efficient to implement datagram networks as there is no need of reserving resources and making a dedicated path each time an application has to communicate.