assignmnet ccn

8/6/2019 ASSIGNMNET CCN

http://slidepdf.com/reader/full/assignmnet-ccn 1/5

08TL16 CCN SALMAN AHMED

CCN ASSIGNMENT

Q 1. One of the most impotent design issues is the packet size to be used in the network.Discus briefly the significant relationship between packet size and transmission time giving

suitable examples?

Answer. This example shows up the relation between packet size and transmission time. In this

example it is assumed that there is a virtual circuit from station X through nodes a and b to

station Y. The message to be sent comprises 40 octets and each packet contains 3 octets of

control information placed in beginning of the cell. Now if entire message sent as a packet then

the packet will first transmit from station X to node a and when the entire packet received at

node b it is then transferred to station Y.

Now if we break the message into 3 packets each having 20 octets and the same 3

control information octets node begin to start first packet arrived from X without waiting for

second packet due to which transmission time drops. Hence by using more and more smaller

packets we can decrease transmission time.




Q.2 By drawing a suitable diagram give the comparison between circuit and packet switching?

Answer.

COMPARISON BETWEEN CIRCUIT AND PACKET SWITCHING

S.NO CIRCUIT SWITICHING PACKET SWITCHING

1 Band width guaranteed. Bandwidth dynamically allocated or on needs

2 Circuit capacity not reduced by other

circuit capacity.

May have transmissions over physical

channels.

3 Circuit costs independent of amount of

data transmitted, resulting in wasted

bandwidth

May have delay and congestions.

4 Expensive circuitry. More cost effective offer betterperformance.

5 Provides transmission at constant rates Each station connects to the local node at its

own speed.

6 It is designed for voice mainly. It is designed for voice and data both.

Circuit

Switching

Packet

Switching




Q3. A telephone line normally has the bandwidth of 3000Hz and SNR is 3162. for this channel

capacity how will you send the data at faster rate.

Answer. We know that channel capacity can be found by Shannon capacity formula ,

putting the given values in the formula we get ,

C=3000*(1+3162)= 34881bps .

If we want to send the data at much faster rate in this channel we should either increase the

bandwidth of the line or we have to improve the SNR.

Q.4. Explain briefly the comparison between two approaches of synchronization?

Answer. Synchronization is important because, if the source and destination are out of step, data on all

channels are lost. One of the pictures given below showing the scenario that if synchronization is not

done properly it may happen,

The two most used approaches of synchronization are

a. Framing

b. Pulse Stuffing

COMPARISON BETWEEN TWO APPROACHES OF SYNCHRONIZATION

Framing is perhaps the most commonly known method also known as added-digit framing. In this

method one control bit is added to each frame and identifiable bits from frame to frame are used as

control channel. In this method the receiver compares the incoming bits and waits for expected bits. If

the bit patterns not matched then certain bit position are searched until the pattern matches. Once the

synchronization is done the receiver continues the monitoring of framing bit channels. If the pattern

breaks down, the receiver must again have to enter framing search mode.




An example picture of framing is shown below taken from the book of forouzan (data communication

and networking).

Synchronizing the various data sources is a bit difficult task. If each source have separate clock timings

and any variations among those clocks may cause loss of data. For that purpose we use pulse stuffing

method. It is an effective technique. With pulse stuffing the outgoing data rate of the multiplexer,

excluding framing bits is higher than the sum of the maximum instantaneous incoming rates. Extra we

use extra capacity in stuffing dummy bits into each incoming signals until its rate raised so that of

generated clock signal. The stuffed pulses are inserted at fixed locations that they can be identified and

remove at the de multiplexer.

An example picture is shown below taken from the book of forouzan (data communication and

networking)

Q.5. what are network protocols and why are they necessary?

Answer. A protocol is a set of rules that governs the communications between computers on a

network. These rules include guidelines that regulate the following characteristics of a network:

access method, allowed physical topologies, types of cabling, and speed of data transfer. A

network protocol defines rules and conventions for communication between network devices.

These protocols are necessary because without a set of rules, computers would not

have the capability of "talking" to each other across the Internet. Certain protocols help

computers identify themselves on the Internet. The same scenario is with the other devices

apart from computers.




NNEETTWWOORRKK PPRROOTTOOCCOOLLSS

The most common network protocols are:

y Ethernet

y Local Talk

y Token Ring

y FDDI

y ATM

Q.6. What services are provided by ATM AAL layer types?

Answer. The AAL stands for Application Adaption Layer. ATM defines the AAL layers and breaks

them into further sub layers according to their services.

1.

AAL1:

This layer supports applications that transfer information at constant bit rate such as video and

voice. It provides services to connect ATM to digital telephone networks such as voice channels.

2. AAL 2:

In the beginning this layer supports the variable data rate bit stream but then it has been

redesigned and now being used for the services like low bit rate traffic and short frame traffic

such as audio (compressed & uncompressed), video, fax.

3. AAL 3/4:

AAL 3 initially support the services of connection oriented data services and AAL4 supports the

connectionless services. After some time it has been evolved that the fundamental issues of

both layers are same hence combined into one layer and names as ALL3/4.

4. AAL 5:

AAL3/4 provides comprehensive sequencing and error control mechanism that are not

necessary for every application. Hence ATM the designers of ATM provided this layer for such

types of applications into fifth sub layer and called it simple and efficient adaption layer (SEAL).This layer assumes all cells are belonging to single message travel sequentially and then control

functions included in the upper layers.

assignmnet ccn

Documents