Sunday, 28 May 2017

Delays in computer networks


There are following delays encountered in computer networks:
  • Transmission delay
  • Propagation delay
  • Queuing delay
  • Processing delay

Transmission delay:

It is the amount of time taken to transmit a packet onto the outgoing link.
How to find the transmission time?
⟶It's defined as (size of the data) ∕(bandwidth).

Example: If bandwidth is 1 bits per second, it means we can transmit 1-bit onto the network in 1 second. If the data size is 10 bits then the time taken to transmit 10 bits onto the network is 10 seconds.
If data is given as 1Kb then it's interpreted as 1024 bits. But if bandwidth is given as 1Kbps then it's interpreted as 1000 bits per second.

Propagation delay:

It is the amount of time taken for a packet to reach from source to destination.
How to find the propagation time?
⟶ It's defined as (distance travelled)/(velocity of the medium).
Example: If a packet size is 1kb. Bandwidth is 1kbps, distance is 2 km and the packet travels through an optical fibre. Find out the propagation delay?
⟶ As we know propagation time is (distance travelled)/(velocity of the medium), here distance is given but velocity is not given directly. But it's given that packet travels through an optical fibre. In an optical fibre, the speed of light is 2 * 10⁸ m/s.
So we propagation time = (2 * 10³/2 * 10⁸) = 10┬Ás.

Queuing delay:

It is the amount of time a packet spends in the waiting queue.
Whenever a packet reaches a router or any node, it is not processed immediately as there are many packets arriving at the router and it's not possible to process all of them simultaneously. So some packets are stored in a queue for processing.

Processing delay:

It is the amount of time taken by the routers or any node to process a packet. Processing delay depends on the specification of the machine which is processing the packet.

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