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By the end of this subtopic, you should be able to:
Circuit switching is a method of communication where a dedicated path is set up between the sender and the receiver before any data is sent.
A dedicated path means the route is reserved for that communication only. No other user can use that same path while the connection is active.
This means that when two devices communicate using circuit switching, the network first finds one complete route between them. That route stays in place for the whole communication. All the data uses that same path from start to finish.
Circuit switching normally happens in three main stages.
1. A connection is set up First, the system checks whether the receiver is available. If the receiver is ready, a path is created through the network from sender to receiver.
2. Data is transferred Once the path has been created, the data is sent. Because the route is fixed, all the data travels along the same path.
3. The connection is ended When the communication is finished, the dedicated path is removed and the network resources are released.
So, in simple words, circuit switching is like reserving a private road before starting your journey. Once the road is reserved, only your traffic uses it until the journey ends.
Circuit switching has some important features:
These features make circuit switching very suitable for communication that must happen smoothly and in the correct order.
One benefit is that the whole bandwidth of the connection is available to that communication. Bandwidth means the amount of data that can be sent per second. Because the path is not being shared, the communication can be steady and predictable.
Another benefit is that data arrives in the correct order. Since everything follows the same route, there is no need to rearrange data at the destination.
Circuit switching is also good for real-time communication. Real-time means the data must be received immediately, or almost immediately, while the communication is happening. For example, in a live conversation, delays are a problem. A dedicated path helps reduce this problem.
It is also less likely that data will be lost during transfer because the same route is being used throughout the communication.
A major drawback is that the dedicated path is not shared. Even if no data is being sent for a moment, the path still belongs to that communication. This means network resources can be wasted.
Another drawback is that it can take time to set up the connection before any data can be sent.
Circuit switching is also less flexible. If a fault happens on the chosen route, there may be no easy alternative path during that session. The communication may fail and need to be started again.
It also needs a dedicated channel for the whole session, which can require more bandwidth and cost more.
Circuit switching is mainly used where a smooth, continuous connection is needed.
Examples include:
A good example is a live voice call. During a call, people expect the sound to arrive in order and without long pauses. Circuit switching is suitable here because it provides a steady, dedicated connection.
Packet switching is a method of communication where a message is broken into smaller parts called packets before it is sent.
A packet is a small piece of the original message. Each packet is sent through the network separately.
Unlike circuit switching, packet switching does not require one dedicated path to be set up first. Different packets from the same message can travel by different routes across the network.
At the destination, the packets are put back together in the correct order to rebuild the original message.
You can think of packet switching like sending a large book by tearing it into numbered pages, sending the pages through different delivery routes, and then putting the pages back into order when they arrive.
Networks often carry a lot of traffic at the same time. If one large message stayed together as one single block, it would be harder to manage. Breaking the message into packets makes the network more flexible and efficient.
Each packet can be sent on the route that is best at that moment. This helps the network deal with congestion or faults.
Congestion means there is too much traffic on part of the network, so packets may be delayed.
Each packet contains a header.
A header is the part of the packet that stores important control information. This information helps the network move the packet correctly and helps the destination rebuild the message.
A packet header may contain things such as:
You do not need to memorise every possible field, but you must understand the important ones.
These show where the packet came from and where it is going.
This tells the destination where the packet belongs in the original message. It is needed because packets may arrive out of order.
A checksum is a value used to check whether the packet has been damaged during transmission. If an error is found, that packet can be sent again.
A hop is one step from one router to another router.
The hop number is used to stop packets from moving around the network forever if they cannot reach the destination. Each time a packet goes through a router, the hop number is reduced by 1. If it reaches 0 before the destination is reached, the packet is deleted.
This prevents the network from getting clogged with packets that are going nowhere.
Here is the packet switching process in simple steps.
1. The message is split into packets A large message, such as a web page or email, is divided into smaller packets.
2. A header is added to each packet Each packet receives control information such as destination IP address and sequence number.
3. Packets are sent independently The packets travel across the network. They do not all have to use the same route.
4. Routers forward the packets As each packet reaches a router, the router decides where to send it next.
5. Packets may arrive in a different order Because different routes can be used, packet 3 might arrive before packet 1, for example.
6. Error checking takes place If a packet is missing or damaged, it can be sent again.
7. The destination reassembles the message Using the sequence numbers, the receiving device puts all the packets back into the correct order.
This is how packet switching is used to pass messages across a network, including the internet.
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