Code: AC12 / AT10                               Subject: DATA COMMUNICATION & NETWORKS

Time: 3 Hours                                                                                                     Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1       Choose the correct or best alternative in the following:                                         (2x10)

a. In Go-Back-N ARQ, if frames 3, 4, 5 are received successfully, the receiver sends an ACK _________ to the sender.

(A)  4                                                  (B)  5

(C)   8                                                 (D)  16

b. As the data packet moves from the upper to the lower layers, headers are __________.

(A) added                                          (B)  removed

(C)  rearranged                                    (D)  modified

             c.   Before data can be transmitted, they must be transformed to ___________.

(A) periodic signals                             (B)  aperiodic signals

(C)  electromagnetic waves                  (D)  low frequency sinewaves

             d.   In CRC, there is no error if the remainder at the receiver is ___________.

(A)  equal to the remainder at the sender  

(B)  zero

(C)  non zero                                     

(D)  is equal to the quotient at the sender  

             e.   Wifi refers to

(A)  Wireless fidelity                            (B)  Wireless Internet Fidelity

(C)  Wired Fiber                                 (D)  Wired Internet Fidelity

             f.    Identify the class of IP address 227.12.14.87;________.

(A) Class A                                        (B)  Class B

(C)  Class C                                        (D)  Class D

             g.   UDP needs the _____________ address to deliver the user datagram to the correct application program.

(A) port                                             (B)  application

(C)  internet                                         (D)  physical

             h.   RSVP uses __________ messages.

(A) path                                             (B)  Resv

(C)  resource                                       (D) (A) & (B)

             i.    A one-to many communication between a source and a specific group of hosts is classified as ____________ communication.

(A) unicast                                          (B) multicast

(C) broadcast                                      (D) (A) and (B)

             j.    The VPI of a UNI is __________ bits. 

(A)  8                                                  (B)  12

(C)  16                                                (D)  24

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   Differentiate between services and protocols.  Explain the process of exchanging data units (DU) within a layer and between layers with a suitable diagram.                                                               (2+6)

             b.   Discuss the standard arrangement in the handling of analog information by digital transmission system with a block schematic.                                  (8)

Q.3     a.   A channel of 3MHz bandwidth has an intended capacity of 20 Mbps.  What signal to noise ratio is required to achieve this capacity?                       (6)

             b.   Bring out the principle of CRC method of error detection with an example.          (6)

c.   Draw the signal constellation diagram for

                   (i)  4 points                                         

                   (ii) 16 points.                                                                                                     (4)

Q.4     a.   What do you mean by space division switching?  Discuss the functioning of a multistage switch with a suitable figure.                                                  (6)

b.   Explain Selective Repeat ARQ protocol with diagrams.                                      (6)

             c.   Two computers are connected by an intercontinental link with a one-way propagation delay of 100 ms. The computers exchange 1-Megabyte files that they need delivered in 250 ms or less.  The transmission lines have a speed of R Mbps, and the bit error rate is .  Design a transmission system by selecting the bit rate R, the ARQ protocol, and the frame size.                                                     (4)

Q.5     a.   Discuss CSMA/CD protocol as applied to LAN networks with relevant diagrams.             (6)

b.   A slotted ALOHA system generates 50 requests/sec which includes both originals and retransmissions.  A time slot is 40msec.  Find                    

(i) chance of success in the first attempt.

(ii) Probability of success after five collisions.

(iii) Average number of retransmissions per packet.                                           (6)

c.   What are the functions of LLC sublayer.                                                             (4)

  Q.6     a. Compare IEEE standards 802.3 and 802.4 with special reference to frame format. Explain FDDI.                                                             (6)

             b.   What is the fundamental difference between datagram and virtual circuit packet switching?  Compare with diagrams showing various delays.         (6)

             c.   A token ring has 100 stations and token rotation time of 40 msec.  The token holding time is 10 msec.  Find the maximum achievable efficiency of the ring.                                                                    (4)

Q.7     a.   What are the goals needed in achieving a good routing algorithm?  Explain the principle of flooding with suitable diagrams.                                (8)

b.   Consider the following six-node network, Assume all links have the same bit rate R.

(i) Suppose the network uses datagram routing.  Find the routing table for each node, using minimum-hop routing.

(ii) Explain why the routing tables in Part (i) lead to inefficient use of network bandwidth. 

(iii) Can VC routing improve efficiency in the use of network bandwidth?  Explain why or why not.

(iv) Suggest an approach in which the routing tables in datagram routing are modified to improve efficiency.  Give the modified routing tables.                                                           (8)

Q.8     a.   Differentiate between                          

(i) IPv4 and IPv6

(ii) Reverse path broadcasting and reverse path multicasting.                      (12)

             b.   A class B network on the internet has a subnet mask of 255.255.240.0; what is the maximum number of hosts per subnet?                                 (4)

Q.9     a.   Discuss AAL1 process with a diagram and PDU structure.                                 (6)

b.   Give format of RTP (Real-time Transport Protocol) and explain the meaning of each field in it.                                                                   (6)

c.   Suppose that an ATM connection carries voice over AAL1.  Suppose that the packetization delay is to be kept below 10 ms.

(i) Calculate the percentage of overhead if the voice is encoded using PCM.

(ii) Calculate the percentage of overhead if the voice is encoded using a 12 kbps speech-encoding scheme from cellular telephony.                                                              (4)