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8/6/2019 ASSIGNMNET CCN
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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.
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08TL16 CCN SALMAN AHMED
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
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08TL16 CCN SALMAN AHMED
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.
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08TL16 CCN SALMAN AHMED
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.
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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.