Delays in Computer Networks and Communication – Formula with examples ( Transmission delay, Propagation delay, Processing delay, Queuing delay)

In this article, we will talk about Delays in Computer Networks and Communication with formulas and examples. First, explain what is a computer network delay. A delay in computer networking is the time taken for a packet to go from its sender to its receiver. You might know that the packet starts from a source, passes through some routers, and then reaches its destination. When it passes from one node (Host or Router) to another node (Host or Router), it experiences different delays on its path at each node. Some of the important delays experienced are transmission, propagation, queuing, and processing delay. Let’s explain in detail each of these delay types.

Transmission Delay

It is the time taken to transmit every bit of the packet onto the outbound link (transmission medium). If the transmission rate (Bandwidth) is R and the size of the packet is L, the transmission delay formula is given as:

Ttrans = L/ R

Example of Transmission Delay

Find the transmission delay if the bandwidth is 10 Mbps and the number of bytes in the packet is 3000.

Ttrans =L / R = (3 × 8× 10-3)/10 = 0.0024 seconds or 2.4 milliseconds.

Propagation Delay

When a bit gets transmitted onto the link, it has to travel through that transmission medium to reach its destination. The Propagation Delay is the time for a single bit to propagate from the link to its destination. It depends on the distance between the sender and the receiver and the link’s propagation speed. It is directly proportional to the distance and inversely proportional to the speed. If D is the distance between sender and receiver and S is the link’s propagation speed, then the propagation delay formula is given as:

Tprop = D/ S

The propagation speed depends upon what the physical medium of the link is. For example, for optical fiber, the propagation speed is 2.1×108 m/s.

Example of Propagation Delay

Find the propagation delay if a packet is sent through an optical fiber and the distance between source and destination is 5000 km.

Tprop = D/S = 5×106/ 2.1×108 = 0.0238 seconds or 23.8 milliseconds.

Queuing Delay

When a packet reaches its destination, it may not get processed by the processor directly. It will have to wait in a queue (buffer) if other packets are present at the destination and waiting to get transmitted. The amount of time a packet stays in a buffer to get processed is known as the Queuing Delay. Moreover, it varies from packet to packet. Therefore, there is not a specific formula to find it. It depends upon various factors. For example, if packets’ average arrival rate at the queue increases, then queuing delay will also be large. It also depends upon the packet’s length and the transmission rate.

Processing Delay

It is the time required by the processor to process a packet. It includes the time spent to inspect the packet’s header, where to send it, and check the bit-level errors, etc. Processing Delay also does not have a formula since it depends upon the processor’s speed, which differs from system to system.

The sum of all delays (Transmission, Propagation, Queuing, and Processing) is known as the Nodal Delay and is given as:

Tnodal = Ttrans + Tprop + Tqueue + Tproc

The effects of these delays can range from negligible to significant. Ttrans and Tprop can sometimes be negligible and sometimes be considerable. Tproc, on the other hand, is often insignificant.

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