General Basic Network questions
Posted on 1997-03-16
Some General Basic network questions
Please help. Thanks in advance.
1. To transmit packets with virtual-circuit transport, we first set up a
virtual-circuit and then transmit the packets.
The network is lightly loaded, and our packets do not face any
queueing delay. The virtual-circuit set up time is 400 ms.
The packets travel over a path that goes through ten nodes, and the
links transmit at 56 kbps.
Each packet has 400 bits of data, a header of 5 bytes (to indicate the
virtual-circuit number and the packet's sequence number), and a trailer
of 2 bytes (for error detection).
When we use datagram transport, no virtual-circuit is set up, but each
packet needs a header of 10 bytes instead of 5 (to indicate the full
destination address and source address, in addition to the packet's
sequence number). These packets also have the 2-byte trailer. Assume
that datagrams also happen to follow the same path through the ten nodes.
(a) How long does it take to transmit N packets under each of the two
(b) For what values of N is it faster to use virtual-circuit transport?
2. A series of packets of length 1000 bits are to be transmitted across a
data link 4,000 km long at a data rate of 2 Mbps.
If the link has a velocity of propagation of 200,000 km/s and a bit error
rate (NOT packet error rate)
of 0.0001, determine the link efficiency using the following protocols.
Also, indicate the effect of bit errors on each of the results obtained.
(b) selective repeat with a window size of 7
(c) go-back-N with a window size of 127
3. Consider the transfer of a file containing one million chars. from one station to another. What is the total elapsed time and effective throughput for the following cases:
a. A circuit-switched, star topology local network. Call setup time is negligible, and the data rate on the medium is
b. A bus topology local network with 2 stations a distance D apart, a data rate of B bps, and a packet size P with 800 bits of overhead. Each packet is acknowledged with an 88 bit packet before the next is sent. The propagation speed on the
bus is 200m/us Solve for
1. D=1 km, B =1MBps, P =256 bits
2. D=1 km, B =10Mbps, P =256 bits
3. D=10 km, B = 1 Mbps, P = 256 bits
4. D=1km, B = 50 Mbps, p = 10000 bits
c. A ring topology with a total circular length of 2D, with the 2 stations a distance D apart. Acknowledgment is achieved by allowing a packet to circulate past the destination station, back to the source station. There are N repeaters on the ring, each of which introduces a delay of one bit time. Repeat the calculation for each of b(1) through b(4) for N=10; 100; 1000.