CS601 Data Communication Assignment 1 Solution Fall 2013

Question 1:   (10 Marks)

Which of the layer(s) of the OSI model performs the following functions?

Sr. No.

Functions

OSI Layer(s)

1

Route determination  Network Layer

2

Reliable process to process delivery  Transport Layer

3

Provides user services such as email and file transfer  Application Layer

4

Error correction and retransmission  Data Link Layer

5

Establishes, manages and terminates session  Session Layer

6

Defines frames  Data Link Layer

7

Transmission of bits across medium  Physical Layer

8

Format and code conversion services  Presentation Layer

9

Ensures reliable transmission of data  Transport Layer

10

Communicates directly with user’s application program  Session Layer
Question 2:   (10 Marks)

Discuss the consequences if a connection fails in each of the following five network topologies having four devices.

  1. Devices arranged in a mesh topology
  2. Devices arranged in a star topology (not including the hub)
  3. Devices arranged in a bus topology
  4. Devices arranged in a ring topology
  5. Devices arranged in a dual ring topology

Solution:

a) Mesh Topology

If five devices arranged in a mesh topology so we will have 10 links and 4 I/O ports in each hardware device. If any link goes down from them so it will be easy to find out which one is down and it won’t effect on other links. But a bulk of wires and can create problem in re-installation and re-configuration

b) Star Topology

In Star topology each device has a dedicated point-to-point link to a Hub. If any link goes down and connections fail so the other won’t be effected. It is easier to reconfigure and sort out the problem area.

c) Bus Topology

In Bus topology, a backbone wire is connected with device and further taps and drop lines link the clients. If any link goes down so signals won’t pass on and get back to origin which will create noise on both sides. And if backbone wire is broken so the whole communication will be disabled. Its reconfiguration and modification is difficult than others.

d) Ring Topology

If we have devices arranged in a ring topology so we have to follow either dual ring technique or switch to prevent whole network down time. Else due to its unidirectional traffic flow will require all links up because signal travels in one direction and completes the ring through point to point until reach its destination. Every point receive the signal and regenerate it by the repeater incorporated in it. If any point is down so the network will be alarmed for network operator.

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