Solution of Problem 23 of Data Link Layer Kurose

298 views

Skip to first unread message

Dwiti Gajab

unread,

Dec 11, 2011, 5:24:02 PM12/11/11

to SJSUee281

Hello All,

I have a doubt in Part (b) of problem 23 of Chapter 5-Data link layer
Kurose.. Part b of P-23 asks about efficiency of ethernet when L=1500
bits.

Q)Suppose four nodes, A, B, C, and D, are all connected to a hub via
10Mbps Ethernet cables. The distances between the hub and the 'e four
nodes are 300m, 400m, 500m, and 700m, respectively. Recall that the
CSMA/CD protocol is used for this Ethernet. Assume that the signal
propagation speed is 2*10^8 m/sec.
b. If all frames are 1500 bits long, find the efficiency of this
Ethernet.

Ans) We know that formula used is:
efficiency = 1/(1+5(dprop/dtrans)).

According to my understanding, to calculate efficiency, minimum
propagation delay is to be found because efficiency will be decreased
after collisions start. Node A offers min dprop i.e. 1.5micro second.
Rest nodes gives dprop as 2, 2.5, 3.5 micro seconds. Hence Node A's
dprop is considered. So, using above formula efficiency determined is
66% .

So, is my understanding correct? Let me know if some different
technique is used.