Switched communication networks are those in which data transferred from source to destination is routed between various intermediate nodes. Switching is the technique by which nodes control or switch data to transmit it between specific points on a network.
In
large networks, there can be multiple paths from sender to receiver. The
switching technique will decide the best route for data transmission. Switching
technique is used to connect the systems for making one-to-one communication.
Various
switching techniques are-
1. Circuit Switching
The
Circuit Switching technique establishes
a dedicated path or channel between the sender and receiver for
data transmission, and once a dedicated path is established then it does not
terminate it until and unless the connection between the two data transmission
point terminates.
Circuit
switching in a network operates in a similar way as the telephone works. A
complete end-to-end path must exist before the communication takes place.
In
case of circuit switching technique, when any user wants to send the data, a
request signal is sent to the receiver then the receiver sends back the
acknowledgment to ensure the availability of the dedicated path. After
receiving the acknowledgment, dedicated path transfers the data.
Circuit
switching is used in public telephone network. It is used for voice
transmission. Fixed data can be transferred at a time in circuit switching
technology.
Communication through circuit switching has 3 phases:
- Circuit establishment
- Data transfer
- Circuit Disconnect
Advantages of Circuit Switching:
- Establishment of a dedicated channel
- Improves data transmission rate
- Improves data loss
- Improves delay in the data flow
Disadvantages of Circuit Switching:
- Establishing a dedicated channel sometimes takes
a very long duration of time.
- The amount of bandwidth required is more for
establishing a dedicated channel.
- Even if a channel is free, it cannot be used to
transmit any other data from any other source.
2. Packet Switching
The
packet switching technique transmits data through the network by breaking it down into several data
packets for more
efficient transfer and it also utilizes multiple vacant resources,
these network devices direct or route the data packets to the destination where
the receiving device then collects all of them and reassembles to get the
proper orientation of the message.
The
packet switching is a switching technique in which the message is sent in one
go, but it is divided into smaller pieces, and they are sent individually.
The
message splits into smaller pieces known as packets and packets are given a
unique number to identify their order at the receiving end. Every packet
contains some information in its headers such as source address, destination
address and sequence number.
Packets
will travel across the network, taking the shortest path as possible. All the
packets are reassembled at the receiving end in correct order.
If
any packet is missing or corrupted, then the message will be sent by receiver
to resend the message.
If
the correct order of the packets is reached, then the acknowledgement message
will be sent by the receiver.
There
are two approaches to Packet Switching:
Datagram Packet switching:
- It is a packet switching technology in which packet is
known as a datagram, is considered as an independent entity. Each packet
contains the information about the destination and switch uses this
information to forward the packet to the correct destination.
- The packets are reassembled at the receiving end in
correct order.
- In Datagram Packet Switching technique, the path is not
fixed.
- Intermediate nodes take the routing decisions to
forward the packets.
- Datagram Packet Switching is also known as
connectionless switching.
Virtual Circuit Switching
- Virtual Circuit Switching is also known as connection-oriented
switching.
- In the case of Virtual circuit switching, a preplanned
route is established before the messages are sent.
- Call request and call accept packets are used to
establish the connection between sender and receiver.
- In this method the path is fixed for the duration of a
logical connection.
Advantages of Packet Switching:
- Cost-effective: In
packet switching technique, switching devices do not require massive
secondary storage to store the packets, so cost is minimized to some
extent. Therefore, we can say that the packet switching technique is a
cost-effective technique.
- Reliable: If
any node is busy, then the packets can be rerouted. This ensures that the
Packet Switching technique provides reliable communication.
- Efficient: Packet
Switching is an efficient technique. It does not require any established
path prior to the transmission, and many users can use the same
communication channel simultaneously, hence makes use of available
bandwidth very efficiently.
Disadvantages of Packet Switching:
- Packet Switching technique cannot be implemented in
those applications that require low delay and high-quality services.
- The protocols used in a packet switching technique are
very complex and requires high implementation cost.
- If the network is overloaded or corrupted, then it
requires retransmission of lost packets. It also lead to the loss of
critical information if errors are nor recovered.
3. Message Switching
The
Message Switching Technique was developed to act as an alternative to circuit switching, this
was before packet switching was
introduced.
Message
Switching is a switching technique in which a message is transferred as a
complete unit and routed through intermediate nodes at which it is stored and
forwarded.
In
Message Switching technique, there is no establishment of a dedicated path
between the sender and receiver.
The
destination address is appended to the message. Message Switching provides a
dynamic routing as the message is routed through the intermediate nodes based
on the information available in the message.
Message
switches are programmed in such a way so that they can provide the most
efficient routes. Each and every node stores the entire message and then forwards
it to the next node. This type of network is known as store and forward
network.
Message
switching treats each message as an independent entity. These message switched
data networks are also known as a hop-by-hop system.
Advantages of Message Switching
- Data channels are shared among the communicating
devices that improve the efficiency of using available bandwidth.
- Traffic congestion can be reduced because the message
is temporarily stored in the nodes.
- Message priority can be used to manage the network.
- The size of the message which is sent over the network
can be varied. Therefore, it supports the data of unlimited size.
Disadvantages of Message Switching
- The message switches must be equipped with sufficient
storage to enable them to store the messages until the message is
forwarded.
- The Long delay can occur due to the storing and
forwarding facility provided by the message switching technique.