Question

a) Assume that we are using datagram switching (i.e. we are not using virtual circuits). Is it possible to guarantee bandwidth to each source-destination pair? Are there disadvantages of doing this using datagram switching?
b) What is the big-O complexity of processing the header of a packet if we are using virtual circuits? Briefly explain why.

Answer 1

a) Is it possible to guarantee bandwidth to each source-destination pair? - Yes, it is possible to guarantee b/w to each source-destination pair as it is connectionless service. There is no need of reservation of resources as there is no dedicated path for a connection session. But because it is connectionless, we will need bandwidth of the network to transfer data packets from source to destination, so bandwidth needs to be guaranteed.

Are there disadvantages of doing this using datagram switching? - Yes, Since the datagrams consist of the full destination address, they generate more overhead and thus lead to wastage of the bandwidth. This in turn makes using datagram approach quite costly.

b) What is the big-O complexity of processing the header of a packet if we are using virtual circuits? Briefly explain why.

ANS - O(1) = it makes sense to consider adding fields to packet headers to speed up the packet processing, so Source Hashing, which is a technique for adding an index field to protocol identifiers at all layers to reduce lookup costs and protocol processing. Source hash indices are similar to Virtual Circuit Identifiers (VCIs) in that they reduce lookup times from O(log(n)) to O(1), where n is the number of flows. So by applying Source Hashing in Virtual Circuits the packet headers can now be processed in O(1) only, which is comparatively fast wrt O(log N).

Please let me know in case of any clarifications required. Thanks!