Using segmentation for packets to reduce end-to-end delay In classroom, we discu

Question

Using segmentation for packets to reduce end-to-end delay

In classroom, we discussed the possible reduction in end-to-end delay if we segment a large message into a number of segments, and transmit each segment independently This problem pursues this aspect analytically. The parameters and assumptions of the model are given below. ·M bits: the length of a large message to be transmitted from host A to host B ·n: the number of links on a path from A to B (the path has n-1 routers) ·R bits/sec: the data rate of each of the n links S bits: the large message is split into segments of S bits each

Explanation / Answer

Answer (a)-
dend-end= N[ dtrans + dprop + dproc + dqueue]
where

dend-end= end-to-end delay
dtrans= transmission delay
dprop= propagation delay
dproc= processing delay
dqueue= Queuing delay

N= number of links (Number of routers - 1)

Each router will have its own dtrans, dprop, dproc hence this formula gives a rough estimate.

These four components are further subdivided:

1. Nodal processing:
Check bit errors
Determine output link
2. Queuing:
Time waiting at output link for transmission
Depends on congestion level of router
3. Transmission delay:
R=Link bandwidth (bit/s)
L=Packet length (bits)
Time to send bits into link = L/R

4. Propagation delay:
d = Length of physical link
s = Propagation speed in medium
Propagation delay = d/s

(b)(i) - M - 8Mbits = 8*10^6 bits. n=5 links R =200Kbps = 2*10^5 bits per second ,N =5
Transmission delay = 8*10^6/2*10^5 = 40 seconds neglecting 100 bits of header field as its 10^-3 second more to add on.
No propagation delay, processing delay and Queuing delay without segmentation.
Total delay = 40 *5 =200 seconds

(b)(ii) -

When the file is divided into 5 segments .
The total transmission delay is L*N/R + L*(P-1)/R where P and N are the numbers of packet in the file and number of Links respectively.

Thus answer = 40*(1.6 + 4)/5 = 8*5.6 = 44.8seconds

All other delays are still ignored according to problem.

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