COMPUTER NETWORKS -TWO MARKS(6th Semester-ECE)

TWO MARK QS:

1.Define protocol with respect to computer networks.

Protocol is a Set of rules to govern data communications.

2. For n devices in a network, what is the number of cable links required for a
mesh, ring, bus and star topology?
N devices . no. of links
Mesh - n(n-1)/2
Ring - N
Bus - 1+n
Star – N

3.Draw a Hybrid topology with star backbone and four ring networks.

4. What is the significance of twisting in twisted pair cable?
By twisting balance is maintained. Suppose in one twist, one wire is closer to noise source and
the other is farther. In the next twist the reverse is true.Twisting makes both wires are equally
affected by external influences.

5. What is the main function of a modem in data communications?
Modulation & demodulation
6. State the major functions performed by the presentation layer of the ISO
OSI model.
It is concerned with the syntax and semantics of the information exchanged
between two systems.
Major functions are 1)Translation 2)Encryption 3)Compression

7. What is the function of a router in the Internet?
Determines where to send information from one computer to another. It ensures that information
doesn.t go where its not needed. It ensures that information does make it to the intended
destination.

8. Stop and Wait Method:
After transmitting one frame, the sender waits for an acknowledgment before transmitting the
next frame. If the acknowledgement does not arrive after a certain period of time, the sender
times out and retransmit the original frame.

9. What is the necessity of flow control?
They are needed to overcome a fast transmitter overwhelming a slow receiver with data. Flow
control is a mechanism by which the receiver of data throttles the transmission rate of the sender,
so that data will not arrive too quickly to be processed.

10. List out the four basic network topologies.
11. What is the main function carried out by a bridge in computer networks?
Divides the LAN segments. Operate at Data link layer of OSI model.Decides whether to forward
or discard the frame by checking the MAC (physical)address.

12. Assume a Go-Back .N protocol is used with a window size of 4 and assume that frame 2 get
lost. Show the events until packet 2 is acknowledged at the sender side.

13.Define flow control and error control.
Refer P.No. 311
14. What is meant by data communication?
Refer P.No. 4
15.Compare piconet and scatter net?
Refer P.No 435
16. Define an internetwork.
Connecting two or more distinct computer networks or network segments.
17. Where is a routing table maintained? Also state the purpose of maintaining a routing table.
A routing table is maintained in a router. It aids the router in making routing decisions on how to
forward packets from one hop to another.

18. What are the two types of implementation formats in virtual circuits?
Virtual circuit transmission is implemented in 2 formats.
• Switched virtual circuit
• Permanent virtual circuit.
Switched virtual circuit format is comparable conceptually to dial-up line in circuit switching. In
this method, a virtual circuit is created whenever it is needed and exits only for the duration of
specific exchange.
Permanent virtual circuits are comparable to leased lines in circuit switching.In this method, the
same virtual circuit is provided between two users on a continuous basis. (i.e)both the parties
have to pay for the connection even when it is not in use.The circuit is dedicated to the specific
users.
19.Distinguish between ADSL and SDSL.
Refer P.No 252 and 255.
20. What is the main function of a modem in data communications?
Modulation & demodulations
21.How is a repeater different from an amplifier?
Refer P.No.447
22. How does a single-bit error differ from a burst error?
Single bit - 1 bit error
Burst bit - 2 or more bits are changed.
23.List out the five components of data communication system.
Refer P.No 4
24.Which ARQ mechanism utilizes pipelining?
• Go back N ARQ
• Selective repeat ARQ
25.State the responsibilities of network layer.
Refer P No.36