Delays

DELAYS IN TRANSMISSION

All of us want Internet and its services to be able to move as much data as we want
between two end users or hosts, instantaneously and without any loss of data. Unfortunately, this
is just an imaginary perception that is cannot be done in reality. Infact computer networks necessarily
 introduce delays between hosts and can actually lose packets.

There are various types of delays in networks that occur due to various factors . These factors can be      

•          Overhead in the communication link.
•          The slow transmission rate of the link.
•          Position of the hosts from each other.

 There are various reasons that account to the delays in the transmission of data in the network. So lets start  by looking at the delays and understanding them.

 1. Processing Delay (d_proc):

Processing Delay is the time that is taken by the router to access the header of a packet and redirect it to the next path. This time is known as processing delay. Processing also include to check the next destination address of the packet as well as checking for any bit error in the packets, that can occur during transmission of the packet. Processing delay in high speed router is mostly in the order of microseconds. However it can be large, if the router is processing big encryption and decryption algorithms for processing packet header.

After all this processing , the router sends the packet to the queue that precedes the link to the next router( i.e. router B).


 2. Queuing Delay( d_queue):

Queuing Delay is the time that a packet has to wait in the queue before it can be transmitted over the link. Packets are put in the queue when the speed of incoming link to the router is faster than the outgoing link. Queuing delay depends on the number of earlier arrived packets already waiting for getting transmitted. If the queue is empty, then the queuing delay is zero, and if the traffic or the number of incoming packets is high, then the queuing delay is high. Queuing delay is mostly in order from microseconds to milliseconds.

Queuing Delay can be higher if the size of the queue or the buffer is very small.

 3. Transmission Delay( d_trans):

Transmission delay is usually caused by the data rate of the link. It is the time taken to push all the packet bits on to the link. For example : If the date rate of the link is 10 Mbps and your packet size 100 Kbps. Then the transmission Delay = 100 Kbps/10 Mbps = (100*1000)/ (10*1000000) = (1/100)seconds= .01 seconds.

As 1 Mbps = 1000000 bps       &    1 Kbps = 1000 bps.

To generalise this, if our packet is of M bits and link data rate is R bits/sec, then Transmission Delay = M/R seconds.

 4. Propagation Delay( d_prop):

Propagation Delay is the time taken by the 1st bit of the packet to reach the receiver router. It can be calculated by dividing the distance between the two routers and the speed of propagation of the link.

For example:

d= distance between the routers
s=speed of propagation (almost equal to speed of light)

As the communication medium we use as copper wire or fibre optics, so in that propagation speed is equal to speed of light=3*(10^8) metres/second.

Propagation Delay = d/s


A delay for a packet at a router is said to be Nodal Delay (d_nodal).

So the Nodal Delay is equal to the some of all the Delays for a packet.

                                         d_nodal   =  d_proc +  d_queue + d_trans+ d<sub>prop

Now , you should go through this Diagram, then you will be clear with all the Networking Delays.</sub>