# Computer Networks May-2011

UNIT – I

1. (a)  Consider an M/M/1 queue with two types of customers. The mean service of all customers is 5 minutes. The arrival tare of typel customer is 4 customers per hour and for type2 customers it is 5 customers per hour. Typel customers are treated with priority over type2 customers.

(i)  Determine the mean sojourn time of typel and 2 customers under the preemptive-resume priority rule.

(ii) Determine the mean sojourn time of typel and customers under the non-preemptive priority rule.

(b)   Consider an M/G/l queue where the server successfully completes a service time with probability P. If a service time is not completed successfully, it has to repeated until it is successful. Determine the mean sojourn time of a customer in the following two cases :

(i)  The repeated service times are identical.

(ii) The repeated service times are independent, thus (possibly) different.

OR

1. (a) What is the queueing model ? How you characterize queueing model ?

(b) Explain Kendall notation of queueing models.

(c) Explain Little’s law with an example.

(d) A repair man fixes broken televisions. The repair time is exponentially distributed with a mean of 30 minutes. Broken televisions arrive at his repair shop according to a Poisson stream, on average 10 broken televisions per day

(i)  What is the fraction of time that the repair man has no work to do ?

(ii) How many televisions are on average, at his repair shop?

(iii)    What is the mean throughput time of a television ?

UNIT – II

2. (a)  Explain stop and wait protocol with the help of a suitable diagram.

(b) Explain in detail, the OSI reference model. How is it different from TCP/IP model ? Also list functionality of data link layer.

OR

2. (a)  What are disadvantages of circuit switching ? Compare it with packet and message switching in detail. Also, write, which of these switching you prefer for telephone networks and why?

(b) Explain the operation of a selective repeat protocol with the help of a diagram.

(c)  Draw the diagram for header format of the user-network interface of ATM network.

UNIT – III

3. (a) Explain the token passing technologies used in FDDI. How are new tokens generated on an FDDI network ? What advantages does this method have when adding and deleting stations to/from the network of when error occurs ?

(b) How does CSMA/CD work ? Explain in detail the frame format of CSMA/CD.

OR

3. (a) What happens in a token bus if a station accepts the token and then crashes immediately.

(b) A network using CSMA/CD has a bandwidth of 10 Mbps. If the maximum propagation time is 25.6 n-v, what is the minimum size of the frame ?

(c) Explain Bridges, Hubs, Routers and Gateways briefly.

UNIT – IV

4. (a) Differentiate between the following :

(i) Distance vector routing and Link state routing.

(ii) Congestion control and Flow control.

(iii) TCP and UDP.

(a)  How OSPF is implemented in if network ? Illustrate.

OR

4. (a)  Draw the TCP/IP network architecture ? What are the functionalities of network layer in internet.

(b) Write any three situations where congestion can occu in network. What are the different techniques, which network designer can use for congestion avoidance ? If congestion occures, how is it dealt ?

UNIT – V

5. (a)  Explain the ATM layered architecture.

(b) Write short notes on :

(i) Frame relay

(ii) ISDN system architecture.

OR

5. (a)  Explain the various congestion control algorithms used in ATM networks.

(b) Write short notes on any two :

(i)  X.25