Tag: Queuing Delay Example

Delays in Computer Networks | Formulas

Computer Networks

Delays in Computer Networks-

 

Consider-

  • Two hosts A and B are connected over a transmission link / transmission media.
  • A data packet is sent by the Host A to Host B.

 

Following different types of delay occur during transmission-

 

 

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

 

1. Transmission Delay-

 

Time taken to put the data packet on the transmission link is called as transmission delay.

 

Mathematically,

  • Transmission delay ∝ Length / Size of data packet
  • Transmission delay ∝ 1 / Bandwidth

 

Thus,

 

2. Propagation Delay-

 

Time taken for one bit to travel from sender to receiver end of the link is called as propagation delay.

 

Mathematically,

  • Propagation delay ∝ Distance between sender and receiver
  • Propagation delay ∝ 1 / transmission speed

 

Thus,

 

3. Queuing Delay-

 

Time spent by the data packet waiting in the queue before it is taken for execution is called as queuing delay.

 

  • It depends on the congestion in the network.

 

4. Processing Delay-

 

Time taken by the processor to process the data packet is called as processing delay.

 

  • It depends on the speed of the processor.
  • Processing of the data packet helps in detecting bit level errors that occurs during transmission.

 

Important Points-

 

Note-01:

 

Total delay in sending one data packet or End to End time

= Transmission delay + Propagation delay + Queuing delay + Processing delay

 

Note-02:

 

In optical fibre, transmission speed of data packet = 2.1 x 108 m/sec

 

  • In optical fibre, signals travel with 70% speed of light.

70% speed of light

= 0.7 x 3 x 108 m/sec

= 2.1 x 108 m/sec

  • So, consider transmission speed = 2.1 x 108 m/sec for calculations when using optical fibre.

 

Note-03:

 

Both queuing delay and processing delay are dependent on the state of the system.

 

This is because-

  • If destination host is busy doing some heavy processing, then these delays will increase.
  • If destination host is free, then data packets will be processed immediately and these delays will decrease.

 

Note-04:

 

  • For any particular transmission link, bandwidth and transmission speed are always constant.
  • This is because they are properties of the transmission medium.

 

Note-05:

 

Bandwidth is always expressed in powers of 10 and data is always expressed in powers of 2.

(Remember while solving numerical problems)

 

Examples-

 

  • 1 kilo bytes = 210 bytes
  • 1 kilo bits = 210 bits
  • 1 Mega bytes = 220 bytes
  • 1 kilo bytes per second = 103 bytes per second
  • 1 kilo bits per second = 103 bits per second
  • 1 Mega bytes per second = 106 bytes per second

 

To gain better understanding about delays in computer networks,

Watch this Video Lecture

 

Next Article- Types Of Channels in Computer Networks

 

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