Note : Question number 1 is compulsory. Attempt any three questions from the rest.
Q.1. (i) Why can CSMA / CD not be used in wireless networks ? How does the problem of hidden and exposed station get resolved ? Explain the above with the help of diagrams. can there be any collision further?
(ii)
Draw a spanning tree, a multicast ttee for group 1 and for group 2 of the above network.
(iii) Draw a three stage switch. There are 18 inputs and 20 outputs. Stage 1 has three switches, stage 2 has two switches and stage 3 has four switches. How many cross points are needed ? Compare it with a system using just one crossbar switch.
(iv) Consider the following network with the indicated link cost. Use Dijkstra's shortest-path algorithm to compute the shortest paths from A to C and F.
(v) Suppose pure Aloha protocol is used to share a 56 kbps satellite channel. Assume that packets are 1000 bits long. Find the maximum throughput of the system in packets / second.
(vi) Using the RSA public key cryptosystem, if p = 5, q = 13, list five legal values for d.
Q.2. (i) State the concept of channel, capacity. state the Nyquist and shannon theorems and their uses with appropriate examples.
(ii) What is count to infinity problem ? Explain your answer with the help of an example.
(iii) Witn reference to the transport layer, outline the connection set - up operation of 3 - way handshaking through a diagram. What are its advantages?
Q.3. (i) Explain the operation of OSPF with the help of a diagram showing appropriate routers.
(ii) What is the Silly window syndrome ? What is the Clark's solution to overcome it?
(iii) Obtain an expression for average number of the unsuccessful transmission attempts / frame for slotted ALOHA.
Q.4. (i) What are the problems with the following algorithm ? Explain with the help of examples.
(i) Double DES
(ii) Diffie - Hellman key exchange algorithm
(ii) Sketch the Manchester, Differential Manchester, Binary encoding,
RZ and NRZ - I for the bit stream:
11111000101010
(iii) Differentiate between upward and downward multiplexing with the help of a diagram.