Whenever we are dealing with a large network or say a very long-distance data transmission has to take place, this can't be done directly without any external hardware support. Hence, we must have a dedicated path for our data packets to traverse. Since there are so many choices for which path to take, so we have to select a particular path. This selecting of the path on which our data packets will be transmitted is known as Switching.
We can now categorize and sub-categorize the switching techniques as shown below:
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. We can say that it operates in a similar manner in which a telephonic network operates when you call someone, then a dedicated communication channel or path is established between you two, which remains open till you disconnect the phone call.
Let's explore the process in detail.
Imagine you try to call someone through the phone or you try to send a video or audio message. Now before the transmission takes place, a request signal is sent to the receiver who approves or notifies its availability by sending back the acknowledgment, this ensures that a dedicated path can be established here. After receiving the acknowledgment from the receiver end, the sender then transmits the data through the dedicated path.
Fixed data can be transferred at a time in this technique. For example, this technique is used in the public telephonic network for audio transmission.
While communicating through the circuit switching technique a message has to go through three phases which are circuit establishment, the transmission of data, and circuit termination or getting disconnected.
There are two methods through which we can perform multiplexing multiple signals into a single channel or path or carrier.
Frequency Division Multiplexing [FDM] as we can observe from its name, this means dividing into multiple frequency bands. We use FDM when multiple data signals are combined for simultaneous data transmission through a shared communication channel. Operating through this technique divides the total bandwidth into a series of non-overlapping frequency sub-bands, where each sub-band carries a different signal for data transmission. We can find its application in radio transmission and optical fiber transmission to share multiple independent signals.
Time Division Multiplexing [TDM] as its name says this technique divides the data transmission into time frames. This is a technique for transmitting and receiving independent signals over a common communication channel through synchronized switches at each end of the transmission line. This technique is widely used for long-distance communication links and also supports heavy data traffic loads from both the ends. It is also known as a digital circuit-switched method.
Establishment of a dedicated channel
Improves data transmission rate
Improves data loss
Improves delay in the data flow
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.
The Message Switching Technique was developed to act as an alternative to circuit switching, this was before packet switching was introduced. Here, the end-users transmit data in form of messages which consist of the entire data to be shared, a message is the smallest individual unit. Unlike circuit switching there's no dedicated path between the sender and the receiver, hence they are connected through several intermediate nodes which helps and ensures proper data transfer. These messages switched data networks are also known as a hop-by-hop system.
They have 2 important characteristics:
Store & forward: since the users aren't directly connected, the intermediate nodes are then responsible for transferring the entire message to the next node in the path. To do so, each node must have a storage capacity, because a message will only be delivered if the next node and the link between them are available to connect otherwise it will be stored indefinitely. A store-and-forward switch thus forwards a message only if sufficient resources are available and the next node is ready to accept the data. Hence, it's called store-&-forward property. The store-and-forward was earlier used in telegraph message switching centers.
Message delivery: here the entire information is compiled into a single message and then that message is transmitted from source to destination. To successfully reach its destination each message must contain the routing information in its header section.
Stores the message when the next node is not available
Reduces traffic congestion.
Data channels are shared by network devices.
Manages traffic efficiently by assigning priorities.
Storing of messages causes delays.
The whole network requires a large storage capacity.
We've seen that in circuit switching we select a dedicated path for data transmission, but let's assume you have a small amount data. 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.
There are 2 major types of packet switching:
This type of packet switching technique consists of multiple data packets, each data packet is individually routed, means every single data packet contains complete routing information in its header section (source address, a destination address, total number of data packets, sequence number) i.e. which routes to follow to reach the destination. When these data packets traverse from different routes then there is a high chance of packet loss or damage depending on the route and out-of-order delivery is possible which depends on the fluctuating loads on the network's nodes (adapters, switches, and routers)at the moment, so this kind of packet switching technique is also known as Datagram switching.
In this type of packet switching the data-packets are first assembled and then sequentially numbered. Now they are ready to travel across a predefined route, sequentially. The information about the address is not required here, because all the data packets are sent in sequence. This technique is also known as Virtual Circuit switching.
Much improved fault tolerance