BCS041 Solved Question Paper December, 2017

BACHELOR OF COMPUTER APPLICATIONS (BCA) (Revised)

Term-End Examination December, 2017

BCS-041 : FUNDAMENTALS OF COMPUTER NETWORKS

1. (a) Find CRC for the data polynomial x5+ x4+ x2+ 1 with generator polynomial x3+ 1.

(b) Match the following to one or more layers of the OSI model. (Write the name(s) of layer(s))

1. Running FTP applications

2. Managing congestion control

3. Fragmentation and reassembly of packets

4. Encryption/Decryption

Sol: 1. Running FTP Applications --> Application Layer File Transfer Protocol used for exchanging files over the internet. It is most commonly used to download a file from a server using the internet or to upload a file to a server.

2. Managing congestion control -->Transport Layer some times Network Layer

3. Fragmentation and reassembly of packets --> Network Layer If the network layer determines that a next router's maximum transmission unit (MTU) size is less than the current frame size, a router can fragment a frame for transmission and re-assembly at the destination station.

4. Encryption/Decryption --> Presentation Layer This ensures the security of the data as it travels down the protocol stack.

(c)How is sampling done from analog signals ? Explain through an illustration.

Sol: Sampling is the reduction of a continuous signal to a discrete signal. A sample refers to a value or set of values at a point in time and/or space. The process is illustrated in the Figure

Steps in Sampling:

1. Original Analog Signal: Smooth continuous waveform (e.g., voice, sound).

2. Sampler: Takes samples of the analog signal at regular time intervals.

3. Sampled Signal: Sequence of pulses showing amplitude at each sampled point.

4. Quantization and Encoding (Next Step in ADC): Each sample is converted into binary.

(d) How many networks can each IP address class A, B and C have ? Also find the number of hosts per network in each given address class

Sol: The classes of IP Addresses are explained below.

Class A: If the first bit of an IP address is 0, it is the address of a class A network. The next 7 bits identify the network, and the last 24 bits identify the host.

Class B: If the first 2 bits of the address are 1 0, it is a class B network address. The first 2 bits identify class; the next 14 bits identify the network, and the last 16 bits identify the host.

Class C: If the first 3 bits of the address are 1 1 0, it is a class C network address. In a class C address, the first 3 bits are class identifiers; the next 21 bits are the network address, and the last 8 bits identify the host.

Below table shows the details:

(e) The following Figure 1(a) is a subnet having six routers A, B, C, D, E and F.

The first three columns in Figure 1(b) show the delay vectors received from neighbours of E (i.e., from B, D and F). Suppose that E has also measured its delay to neighbours B, D and F.

Show how the router E calculates its delay to A and C.