Define the following parameters for a switching network: N = number of hops betw

Question

Define the following parameters for a switching network:

N = number of hops between two given end systems

L = message length in bits

B = data rate, in bits per second (bps), on all links

P = fixed packet size, in bits

H = overhead bits per packet

S = call setup time in seconds

D = propagation delay per hop in seconds

a) For N=4, L=3200,B= 9600,P=1024,H=16,S=0.2,D=0.001, compute the end-to-end delay for circuit switching,virtual circuit packet switching, and datagram packet switching. Assume that there are no acknowledgments. Ignore processing delay at the nodes.

b) Derive general expressions for the three techniques of part (a), taken two at a time( three expressions in all), showing the conditions under which the delays are equal.

Explanation / Answer

A.circuit:
Latency=SetupTime(+)TransmitTime(+)PropagationTime(+) QueuingDelay
=(S) + (Size/Bandwidth) + (N*D) + 0
=(S) + L/B + N*D= 0.2 + 3200/9600 + 4*0.001 =537ms

packet:
Latency =TransmitTime(+)PropagationTime(+)QueuingDelay
=(Size/Bandwidth)+(N*D)+0,where Size=(number-of-packets)*(overhead+size-of-packet)
= (L/P)*(H+P)/B+N*D=(3200/1024)*(16+1024)/9600+4*0.001=343 ms

virtual circuit:
Latency=SetupTime(+)TransmitTime(+)PropagationTime(+) QueuingDelay
= (S) + (Size/Bandwidth) + (N*D) + 0, where Size=(number-of-packets)*(overhead+size-of-packet)
= S + (L/P)*(H+P)/B + N*D =0.2 + (3200/1024)*(16+1024)/9600 + 4*0.001=543 ms

B.Circuit Switching
T = Call setup time + Message delivery time
= Call setup time + (Propagation delay + Transmission time)
= S+N*D+L/B
Message switching
T = N × Message delivery time for 1 hop
N*(D+L/B)

B.Circuit Switching
T = Call setup time + Message delivery time
= Call setup time + (Propagation delay + Transmission time)
= S+N*D+L/B
Message switching
T = N × Message delivery time for 1 hop
N*(D+L/B)
Circuit switching vs Message switching
The condition can be derived by equating the delay expressions determined above:
Circuit switching delay = Message switching delay
S+N*D+L/B=N*(D+L/B)
= S*B=(N – 1) × L
Circuit switching vs datagram packet switching
Circuit switching delay = Datagram packet switching delay
S+N*D+L/B=L(P-H)*P/B+D+(N-1)(P/B+D)
S+N*D+L/B=L(P-H)P/B+D+(N-1)*P/B+(N-1)D
S+ND+L/B=(L/P-H+N-1)P/B+ND
S+L/B=(L/P-H+N-1)P/B

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