Computer Networks Question Answer the following short answer questions regarding

Question

Computer Networks Question

Answer the following short answer questions regarding Layer 3 (Networks).
a) What are the two key functions of Layer 3?
b) Can packets get out of order in a virtual circuit network? In a datagram service network? Explain why and how.
c) What is the primary function of a network?
d) We say that we seek a “least cost” path between a sender and a receiver. Give at least three examples of metrics that
can be used as “cost”.
e) What are the criteria for a good routing algorithm?

Explanation / Answer

a)

The two key functions of Layer 3 are:

1. Translating logical address to physical address.

2. Routing packets through the network

b)

In virtual circuit network, a path is established between a destination and a source and all the packets are routed through this path. Hence packets wont get out of order in a virtual circuit network. Whereas, in a datagram service network, no path is established between a destination and a source. In this service, each packet is treated as a separate entity called as a datagram and they travel independently across the network. Hence the packets received are out of order in a datagram service network.

c)

The primary function of a network is to share resources and data among computer systems.

d)

The metrics that can be used as cost are:

1. Level of congestion in the link

2. Physical distance traversed by that link

3. Reliability of the link.

e)

Criteria for good routing algorithm:

1. Correctness: That the packet is delivered at the destination

2. Complexity: Less time and space complexity

3. Robustness: WIth any changes in the link, the routing table is to be updated efficiently

4. Fairness in delivering packets

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