What is delay, the performance metric of the network layer?

Computer NetworkInternetMCA

The performance of a network can be measured in terms of Delay, Throughput and Packet loss.

Let us try to understand the concept of Delay.


A packet from its source to its destination, encounters delays. The delays in a network can be divided into four types as follows −

Transmission delay

Transmission delay is the amount of time taken by the router to transfer the packet to the outgoing link is called transmission delay.

For example, assume that you have 100 kb of data. For this data, you have to keep on this outgoing link and this is known as Transmission delay.

Suppose you are vacating the house so while vacating the house you made parcel all the goods, all this goods transfer one location to another location (source to destination), that time all this goods load into the vehicle one by one so this process take some amount of time, so how much time it is taken that is called Transmission delay.

The formula to calculate transmission delay is as follows −

Transmission delay=Length/Bandwidth=L/Bw


  • Length is always bits. For example, 100 bits, 1000bits etc.

  • Bandwidth always take bits/time=bits/sec


Transmission delay=l(bits)/bw(bits/sec)=l/bw sec^-1

Propagation delay

The amount of time taken by the packet to make a physical journey from one router to another router is known as Propagation delay.

Here how much time taken to transfer packets source to destination is known as Propagation delay.

It has the formula to calculate time taken by source to destination while transferring packets.

Propagation delay=D/V


  • D is a Distance
  • V is a velocity

Processing delay

The amount of time taken by the router to process a packet (looking at destination IP, extracting network IP, and searching in routing table x deciding outgoing route) is called Processing delay.

Assume R1 is a router; you have the buffer that contains packets. Taking 1 packet from the buffer that is the first packet and it will pick the destination IP address. From this destination IP address you have to be extracting a Network IP address.


Suppose you are posting a letter, so while posting a letter you will write the following details about yourself −

  • Name
  • Street address
  • City
  • State

This is the hierarchy you will write in your address so if you see here whenever by the postman in a particular post office.

Now, suppose you are posting a letter from Delhi to Andhra Pradesh. Here, it is not required for the postman to consider the entire address. He only checks the state and then sends it accordingly

Here, he is extracting the state address. So in the same way you have the Network part, local part and host part.

So it is extracted in the host part, then after extracting the host part he has to look in his routing table like after extracting the Andhra Pradesh which direction to forward.

So he will look in his table for edges or data whatever he is mentioning in the post office. He will look like he came to know how to be forward.

Same as searching in the routing table so that he came to know which direction he has to forward, then it will send means it will decide the route by seeing this routing table to decide the route this all together we are taking as a Processing delay.

Formula of processing delay is as follows −

Processing delay = Time required to process a packet in a router or a destination host

Queuing delay

Amount of time the packet is waiting in the queue before being taken up for processing is known as Queuing delay.

Here as a name implies here that queuing so queues how much time it is going to wait means before going to be processed.


Assume here R1 is a router, That router have buffer ,this buffer have packets so whatever packet will come, so if router is processing some other packet , so whatever packet is coming those are all should be stayed, in this one, so here how much time you are going to be stay. In case of your packet how much time is going to be spent in this buffer that we are calling a queuing delay.

This delay varies from 0 to infinite.

Queuing delay is dependent on the following −

  • Buffer size.
  • Router speed processing.

0 cases is whenever the packet comes the router becomes idle, it need not stay in buffer in that case queuing delay becomes 0.

Updated on 16-Sep-2021 06:29:29