Delays in Computer Networking

In order to transfer the file fast and efficient manner over the network and minimise the transmission latency, the data is broken into small pieces of variable length, called Packet. At the destination, all these small-parts (packets) has to be reassembled, belonging to the same file. A packet composes of payload and various control information.

Packet Switching uses Store and Forward technique while switching the packets; while forwarding the packet each hop first store that packet then forward. This technique is very beneficial because packets may get discarded at any hop due to some reason. More than one path is possible between a pair of source and destination. Each packet contains Source and destination address using which they independently travel through the network. In other words, packets belonging to the same file may or may not travel through the same path. If there is congestion at some path, packets are allowed to choose different path possible over existing network.

To send a packet from A to B there are delays since this is a Store and Forward network.

Delays in Packet switching :

1. Transmission Delay
2. Propagation Delay
3. Queuing Delay
4. Processing Delay

Transmission delay
Transmission delay refers to the time it takes to transmit a data packet onto the outgoing link. The delay is determined by the size of the packet and the capacity of the outgoing link. If a packet consists of L bits and the link has a capacity of B bits per second, then the transmission delay is equal to: L/B

Propagation delay
Propagation delay is the time that it takes for a bit to reach from one end of a link to the other. The delay depends on the distance (D) between the sender and the receiver, and the propagation speed (S) of the wave signal. It is calculated as:D/S

Queuing delay
Queuing delay refers to the time that a packet waits to be processed in the buffer of a switch. The delay is dependent on the arrival rate of the incoming packets, the transmission capacity of the outgoing link, and the nature of the network’s​ traffic.

Processing Delay
Processing delay is the time it takes routers to process the packet header. Processing of packets helps in detecting bit-level errors that occur during transmission of a packet to the destination. Processing delays in high-speed routers are typically on the order of microseconds or less.

Let us consider that One user in USA and other user is in India(Pune) and both of them want to access to the server which is in India (Mumbai ) then the significance of the propagation delay would be more

The distance between the user in USA server is approximately 15000 km, on the other hand, the distance between the user in Pune and server is approximately 300 km. Proportion delay is the ratio of distance to the velocity of the signal (data) transmitted. The velocity of the signal depends on the medium used for proportion

Let us consider the medium as an optical fibre medium so the velocity is approx 210000 km /sec. So it will take 1.4 milliseconds to travel to user in India and approx 71 milliseconds to travel to user in the USA. The proportion delay becomes significant with increase in distance and it is directly proportional to the distance