##### Relationship between Propogation time and Transmission time

If efficiency (η)≥0.5 then relation ship between Tp and Tt are:

T/Tt +2*Tp ≥ 1/2

⇒        2Tt ≥ T +2*Tp

⇒        Tt  ≥  2*Tp

⇒         L/B ≥2*Tp

⇒           L ≥2*Tp*B

Example:

bandwidth=4mbps

Tp  =1msec

L =?

η≥0.5

Sol:

L ≥2*Tp*B

≥2*1*10-3*4*106

≥8*103bits

Factor Affecting the efficiency:

η =1/1+2a

=1/1+2*(Tp/Tt)

η=1/1+2*(d/v)*(B/L)

bandwidth and velocity are fixed ,now on increasing distance, efficiency  decrease i.e better for LAN not for WAN.

If Length of packet increase ,efficiency increase.i.e stop and wait is better for big packet(busty)

##### Delay in computer network

1) Transmission delay(Tt): If there is a host and if it is  having a data packet,the time taken by the host to put the data packet on to the outgoing link is called transmission delay.

Tt=L/B sec example:

L=1000bits  Bandwidth=1Kbps  what is Tt?

Sol:

Tt=L/B

1000/1000=1sec

2) Propogation delay (Tp): Time taken by the single or one bit to reach from one end of the link to other link is called propogation delay.

factor on which propogation delay depands:

a)distance(d)

b)velocity(v)

Tp=d/v sec

example:

Distance=2.1 km

velocity=2.1*10^8 m/s

Tp ?

Sol:

Tp =2.1*103/2.1*108

=10-5 sec

= 10µsec

3) Queuing delay(Tq): Time taken to stay in queue before processing the last packet on receiver.

4) Processing delay(Tproc): Time taken to process next packet from queue to the processor on receiver end.