relationship between service and protocol

1, What is a service and what is a protocol in layered computer networks? What is the

relationship between service and protocol?

2, The performance of a client-server system is strongly influenced by two major network

characteristics: the bandwidth of the network (that is, how many bits/sec it can transport)

and the latency (a.k.a delay, that is, how many seconds it takes for the first bit to get from

the client to the server). Does a high bandwidth surely lead to low latency? If yes, why?

If not, give an example of a network that exhibits high bandwidth but also high latency

and an example of one that has both low bandwidth and low latency. Discuss now what

determines the latency and what does the bandwidth.

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3, LAN is a broadcast network in that the information sent by a node can be heard by all

nodes in the same LAN. A disadvantage of a broadcast subnet is the capacity wasted

when multiple hosts attempt to access the channel at the same time. As a simplistic

example, suppose that time is divided into discrete slots, with each of the n hosts

attempting to use the channel with probability p during each slot. What fraction of the

slots will be wasted due to collisions?

4, A system has an n-layer protocol hierarchy. Applications generate messages of length

M bytes. At each of the layers, an h-byte header is added. What fraction of the network

bandwidth is filled with headers?

5, When a file is transferred between two computers, two acknowledgement strategies are

possible. In the first one, the file is chopped up into packets, which are individually

acknowledged by the receiver, but the file transfer as a whole is not acknowledged. In the

second one, the packets are not acknowledged individually, but the entire file is

acknowledged when it arrives. Discuss the good and bad sides of these two approaches.

6, How long is a bit in meters? Use a transmission speed of 10 Mbps and assume the

propagation speed in coax is 2/3 the speed of light in vacuum.

7. An image is 1600 × 1200 pixels with 3 bytes/pixel. Assume the image is

uncompressed. How long does it take to transmit it over a 56-kbps modem channel? Over

a 1-Mbps cable modem? Over a 10-Mbps Ethernet? Over 100-Mbps Ethernet? Over

gigabit Ethernet?

8, Suppose the algorithms used to implement the operations at layer k is changed. How

does this impact operations at layers k – 1 and k + 1? Suppose there is a change in the

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