Delays in Computer Networks-
- 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-
- Transmission delay
- Propagation delay
- Queuing delay
- Processing delay
1. Transmission Delay-
|Time taken to put the data packet on the transmission link is called as transmission delay.|
- Transmission delay ∝ Length / Size of data packet
- Transmission delay ∝ 1 / Bandwidth
2. Propagation Delay-
|Time taken for one bit to travel from sender to receiver end of the link is called as propagation delay.|
- Propagation delay ∝ Distance between sender and receiver
- Propagation delay ∝ 1 / transmission speed
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.
|Total delay in sending one data packet or End to End time|
= Transmission delay + Propagation delay + Queuing delay + Processing delay
|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.
|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.
- For any particular transmission link, bandwidth and transmission speed are always constant.
- This is because they are properties of the transmission medium.
|Bandwidth is always expressed in powers of 10 and data is always expressed in powers of 2.|
(Remember while solving numerical problems)
- 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,
Next Article- Types Of Channels in Computer Networks
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