BCS-041 2016

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Page | 1PIXELES CLASSES BCA &MCA (IGNOU)

Course Code : BCS-041Course Title: Fundamentals of Computer Networks

Assignment Number: BCA !"#$041$Assignment$%01&'a(imum 'arks : 100 )ast *ates for Submission: 1&

+,tober %01& For .ul/ %01& Session# April %01 For .anuar/ %01 Session )1.

a# ow 2ualit/ of ser3i,e 2oS# and ,ongestion ,ontrol are related 5(plain6 &'arks#Ans:

A stream of packet, from a source to a destination is called a flow. In connection orientednetwork, all the packets belonging to a flow the same route. But in connection less networkthey may follow different routes.Congestion in a network may occur if the load on the network—the number of packets sentto the network—is greater than the capacity of the network—the number of packets anetwork can handle. Congestion control refers to the mechanisms and techni ues to controlthe congestion and keep the load below the capacity.!he main focus of congestion control and uality of ser"ice is data traffic. In congestioncontrol we try to a"oid traffic congestion. In uality of ser"ice, we try to create an appropriateen"ironment for the traffic. #o, before talking about congestion control and uality of ser"ice,we discuss the data traffic itself. Congestion control refers to techni ues and mechanisms that can either pre"ent congestion,before it happens, or remo"e congestion, after it has happened. In general, we can di"idecongestion control mechanisms into two broad categories$ open%loop congestion control&pre"ention) and closed%loop congestion control &remo"al).

b# *ifferentiate between ,lassful and ,lassless addressing in !7346 & 'arks#Ans:ClassfulIn classful addressing, An I' addresss is di"ided into four parts separated by dot &.) . It isgrouped into the netid and hostid. . If the number in the first byte is between (%1 *, then theI' address is in the Class A. If it is between 1 +%1 1 it is in Class B. If it is between 1 % -it is in the Class C range. If it is between % - it is in the Class / range, and if it isbetween (% 00, then it belongs to Class .

5(ample:1%0610646&

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• Classful routing$ 2outing 'rotocol that do not send subnet mask information when aroute update is sent out. All de"ices in the network must use the same subnet mask

g $ 2I' 31ClasslessClassless Inter%/omain 2outing allocates address space to Internet ser"ice pro"iders andend users on any address bit boundary, instead of on +%bit segments. CI/2 notation issynta4 of specifying I' addresses and their associated routing prefi4. It appends to theaddress a slash character and the decimal number of leading bits of the routing prefi4, e.g.,1 .(. .(5 for I'"

• Classless routing$ 2outing that sends subnet mask information in the routingupdates. Classless routing allows 36#7 &3ariable 6ength #ubnet 7asking) g $ 2I'3 , I82' , 9 :#';.

.a# *ifferentiate between single bit error and burst error6 Also dis,uss t8e

me,8anisms used for error dete,tion for single bit error and burst error6 'arks#

Ans:

!he term single %bit error means that only one bit of gi"en data unit is changed from 1 to (or from ( to 1.

Burst 5rror !he term burst error means that two or more bits in the data unit ha"echanged from ( to 1 or "ice%"ersa.

7arit/ bits 'et8od'arity bit method is "ery simple error detection method in the digital communication. A binarydigit called

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Page | 3PIXELES CLASSES BCA &MCA (IGNOU)&b) Assume we ha"e de"ices in a network. Calculate and write the number of cable linksre uired for a mesh, ring, bus and star topology.& 7arks)-.

a# 8at is fragmentation at network la/er *ifferentiate between t8e fragmentationspro,esses in !734 and !73 6 'arks#Ans:;ragmentation is when a datagram has to be broken up in to smaller datagram to the framesi@e of a certain network. /ifferent networks ha"e different 7! s &ma4imum transfer unit),when a datagram enters a network with a smaller 7! the gateway5router needs tofragment this packet in to smaller packets that the new 7! .

In I'" , routers perform fragmentation, whereas in I'" , routers do not fragment, but dropthe packets that are larger than their 7! . !hough the header formats are different for I'"and I'" , analogous fields are used for fragmentation, so the same algorithm can be reused

for I'" and I'" fragmentation and reassembly.

In I'" , hosts must make a best%effort attempt to reassemble fragmented I' datagrams witha total reassembled si@e of up to 0* bytes &the minimum 7! for I'" ). !hey may alsoattempt to reassemble fragmented I' datagram larger than 0* bytes, but they are alsopermitted to silently discard such larger datagram.In I'" , hosts must make a best%effort attempt to reassemble fragmented datagrams with atotal reassembled si@e of up to 10(( bytes, larger than I'" Ds minimum 7! of 1 +( bytes;ragmented datagram with a total reassembled si@e larger than 10(( bytes may optionallybe silently discarded.

b# *is,uss t8e importan,e of modulation6 8at are t8e limitations of amplitudemodulation 4 'arks#Ans:-7odulation is the 'rocess by which a property or a parameter of a signal is "aried inproportion to another signal.Benefits$

• 7odulation can shift the fre uency spectrum of a message signal into a band whichis better suited to the channel.

• 7odulation permits the use of multiple4ing. 7ultiple4ing means allowingsimultaneous communication by multiple users on the same channel.

•

7odulation can pro"ide some control o"er noise and interference.Amplitude 'odulation A'#:-It was the earliest modulation techni ue used to transmit "oice by radio. !his type ofmodulation techni ue is used in electronic communication. In this modulation, the amplitudeof the carrier signal "aries in accordance with the message signal, and other factors likephase and fre uency remain constant.)imitations of Amplitude 'odulation

• Amplitude modulation easily gets the noise and hence the performance is "ery weak.• #ignal of A7 is not stronger than ;7.• :nly one sideband of A7 transmits Information #ignal.• oise mi4es A7 #ignal in amplitude when it propagates in free space that it makes it

difficult to reco"er the original signal at recei"er end


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46a# Compare and ,ontrast between ;o-ba,k-N A92 proto,ol wit8 sele,ti3e repeat

A926 'arks#Ans:;o-Ba,k-N A92 is a specific instance of the Automatic 2epeat%re uest &A2E) 'rotocol, inwhich the sending process continues to send a number of frames specified by a window sizee"en without recei"ing an ACF packet from the recei"er. 8o back uses a windowmechanism where the sender can send packets that are within a

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Page | 5PIXELES CLASSES BCA &MCA (IGNOU);rame is unacknowledged in a window so only ;rame is retransmitted with ne4t window.b# ow t8ree wa/ 8ands8aking is used in ,onne,tion establis8ment and termination

in TC7 5(plain using t8e suitable diagrams64 'arks#

Ans$%

!C' uses a three%way handshake. Before a client attempts to connect with a ser"er, theser"er must first bind to and listen at a port to open it up for connections$ this is called apassi"e open. :nce the passi"e open is established, a client may initiate an acti"e open. !oestablish a connection, the three%way &or -%step) handshake occurs$

1. S

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• Congestion control protocol$% As we know, congestion control is global issue so thereis a protocol implemented to control the congestion which control the forwardingprocess between the router sometime caring capacity is decreased then congestionis occurred.

Congestion Control

Congestion control concerns controlling traffic entry into a telecommunications network , soas to a"oid congesti"e collapse by attempting to a"oid o"ersubscription of any of theprocessing or link capabilities of the intermediate nodes and networks and taking resourcereducing steps, such as reducing the rate of sending packets . It should not be confused withflow control , which pre"ents the sender from o"erwhelming the recei"er.

Congestion Control 7oli,/!C'Js general policy for handling congestion is based on - phases$

• #low start,• Congestion a"oidance, and• Congestion detection• !he sender starts with a "ery slow rate of transmission but increases the rate rapidly

to reach a threshold. >hen threshold is reached, the data rate is reduced to a"oidcongestion.

Congestion A3oidan,e: Additi3e !n,rease• In the congestion a"oidance algorithm, the si@e of the congestion window increases

additi"ely until congestion is detected.Congestion *ete,tion: 'ultipli,ati3e *e,rease

• An implementation reacts to congestion detection in one of the following ways$• If detection is by time%out, a new slow%start phase starts.• If detection is by three &acknowledgements) Acks, a new congestion A"oidance

phase starts.

b# 5(plain about Bit oriented data link ,ontrol proto,ol using a suitable diagram64 'arks#

Ans: A bit-oriented proto,ol is a communications protocol that sees the transmitted data as anopaque stream of bits with no semantics, or meaning. Control codes are defined in terms of

bit se uences instead of characters . Bit oriented protocol can transfer data framesregardless of frame contents. It can also be stated as K bit stuffing K this techni ue allows thedata frames to contain an arbitrary number of bits and allows character codes with arbitrarynumber of bits per character.#ynchronous framing Ligh%6e"el /ata 6ink Control is a popular bit%oriented protocol.#ynchronous framing Ligh%6e"el /ata 6ink Control may work like this$

• ach frame begins and ends with a special bit pattern (111111(, called a flag byte.

• A bit stuffing techni ue is used to pre"ent the recei"er from detecting the special flag

byte in user data e.g. whene"er the senderDs data link layer encounters 0 consecuti"eones in the data, it automatically stuffs ( into the outgoing stream.


http://en.wikipedia.org/wiki/Telecommunications_networkhttp://en.wikipedia.org/wiki/Congestive_collapsehttp://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Packet_(information_technology)http://en.wikipedia.org/wiki/Packet_(information_technology)http://en.wikipedia.org/wiki/Flow_controlhttps://en.wikipedia.org/wiki/Data_(computing)https://en.wikipedia.org/wiki/Bithttps://en.wikipedia.org/wiki/Bithttps://en.wikipedia.org/wiki/Control_codehttps://en.wikipedia.org/wiki/Control_codehttps://en.wikipedia.org/wiki/Character_(computing)https://en.wikipedia.org/wiki/Character_(computing)https://en.wikipedia.org/wiki/Data_framehttps://en.wikipedia.org/wiki/Bit_stuffinghttps://en.wikipedia.org/wiki/High-Level_Data_Link_Controlhttp://en.wikipedia.org/wiki/Congestive_collapsehttp://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Packet_(information_technology)http://en.wikipedia.org/wiki/Flow_controlhttps://en.wikipedia.org/wiki/Data_(computing)https://en.wikipedia.org/wiki/Bithttps://en.wikipedia.org/wiki/Control_codehttps://en.wikipedia.org/wiki/Character_(computing)https://en.wikipedia.org/wiki/Data_framehttps://en.wikipedia.org/wiki/Bit_stuffinghttps://en.wikipedia.org/wiki/High-Level_Data_Link_Controlhttp://en.wikipedia.org/wiki/Telecommunications_network

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6a# Compare between ?6%& and Frame 9ela/6 5(plain t8e use of F5CN and B5CN in

Frame 9ela/6 'arks#

Ans:. 0 is an old standard protocol suite for packet based wide area network. !he old networks

mainly telecommunications companies were following . 0 protocols for packet switchingbased network.!he . 0 protocol allows computers on different public networks tocommunicate through an intermediary computer at the network layer le"el. . 0Ds protocolscorrespond closely to the data%link, physical%layer and etwork 6ayer protocols defined :#Icommunication model.

• . 0 has a low kbps data rate.• It is designed for pri"ate use• It creates large o"erhead


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Page | PIXELES CLASSES BCA &MCA (IGNOU)

• It describes connection between /! and /C but not describes internal #tructure.Frame rela/Frame rela/ is a standardi@ed wide area network technology that specifies the physical andlogical link layers of digital telecommunications channels using a packet switchingmethodology.

• It is less e4pensi"e than . 0.• It operates a higher speed& 1.0mbps to .-* mbps)• It operates in only physical and data link layer.• It allows frame si@e of ((( bytes.• It has detection at data link layer only.

F5CN Forward 5rror Congestion Notifi,ation#

B5CN Ba,kward 5rror Congestion Notifi,ation#

A ; C tells the recei"ing de"ice that the path is congested so that the upper layer protocols should e4pect some delay. !he B C tells the transmitting de"ice that the;rame 2elay network is congested and that it should Kback offK to allow better throughput.

b# Compare between S"C and 7"C of ?6%& 4 'arks#Ans:

!he . 0 specification allows for two types of connections, or circuits$

• '3Cs are 'ermanent 3irtual Circuits. !hese connections are always open, ready for data to be sent and5or recei"ed. '3C connections are less fle4ible, in that only oneendpoint at a time can be connected with another on a gi"en 6C . #3C connectionsare "ery fle4ible in that it is possible for multiple callers to call the same number.


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Page | !PIXELES CLASSES BCA &MCA (IGNOU)

• #3Cs are #witched 3irtual Circuits. !hese connections must be re%established e"erytime a new session of data e4change is to take place, and the connections arebroken at the end of the session.

• An . 0 network, the phones are replaced by synchronous adapters and modems,and the people talking are replaced by computer applications that know how to placeand recei"e calls. :therwise, the situation is "ery similar.

@6a# rite '*& algorit8m and e(plain it using an e(ample6 'arks#

Ans:!he 7/0 message-digest algorit8m is a widely used ,r/ptograp8i, 8as8 fun,tion producing a 1 +%bit &1 %byte) 8as8 3alue , typically e4pressed in te4t format as a - digithe4adecimal number. 7/0 has been utili@ed in a wide "ariety of cryptographic applications,and is also commonly used to "erify data integrity.

7/0 algorithm operates on a 1 +%bit state, di"ided into four - %bit words, denoted A , B, C ,and D. !hese are initiali@ed to certain fi4ed constants. !he main algorithm then uses each01 %bit message block in turn to modify the state. !he processing of a message blockconsists of four similar stages, termed rounds M each round is composed of 1 similar operations based on a non%linear function F , modular addition, and left rotation. ;igure 1illustrates one operation within a round. !here are four possible functions F M a different oneis used in each round$

b# )ist and e(plain an/ two fun,tions of ea,8 +S! la/er6 4 'arks#Ans:Appli,ation )a/er !he application layer pro"ides format and configuration for the user to access information onthe network through an application. !his layer is the main interface for users to interact withthe application and therefore the network.Ser3i,es:-

• 2esource sharing and de"ice redirection• 2emote file access• 2emote printer access

7resentation )a/er !he presentation layer transforms data to pro"ide a standard interface for the applicationlayer. ncoding, data compression, data encryption and similar manipulation of thepresentation is done at this layer to present the data as a ser"ice or protocol de"eloper seesfit.Ser3i,es:-


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Page | 1"PIXELES CLASSES BCA &MCA (IGNOU)

*ata representation: *ata se,urit/:• *ata ,ompression:

Session )a/er !he session layer controls the connections &sessions) between computers. It establishes,manages and terminates the connections between the local and remote application.Ser3i,es:-

Simple(: alf *uple( Full *uple(

Transport )a/er !he transport layer pro"ides transparent transfer of data between end users, thus relie"ingthe upper layers from transfer concerns while pro"iding reliable data transfer. !he transportlayer controls the reliability of a gi"en link through flow control, segmentation5 de%segmentation, and error control.Ser3i,es:-

9esour,e tili ation multiple(ing#: Conne,tion 'anagement establis8ing terminating• Flow Control Buffering $ indowing#:

Network )a/er !he network layer pro"ides the means of transferring data se uences from a source to adestination by using one or more networks while maintaining the uality of ser"ice re uestedby the !ransport layer. !he etwork layer performs network routing functions, and might alsoperform segmentation5de%segmentation, and report deli"ery errors.Ser3i,es:-

• Connection setup• Addressing• ;ragmentation

*ata )ink )a/er !he data link layer pro"ides the means to transfer data between network entities and todetect and possibly correct errors that may occur in the 'hysical layer. It arranges bits fromthe physical layer into logical chunks of data, known as frames.Ser3i,es:-

Frame Traffi, Control: Frame Se>uen,ing: Frame A,knowledgment:

78/si,al )a/er !he physical layer defines all the electrical and physical specifications for de"ices. !hisincludes the 6ayout of pins, "oltages, and cable specifications.Ser3i,es:-

*ata en,oding: Transmission te,8ni>ue:• 78/si,al medium transmission:

D6


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a# 8at are t8e different digital modulation te,8ni>ues 8/ digital modulation isbetter t8an t8e Analog 'odulation 'arks#

Ans:*!;!TA) '+* )AT!+N T5C N!2 5S:-

• Amplitude S8ift =e/ing: - Any digital modulation scheme uses a finite number of distinct signals to represent digital data. A#F uses a finite number of amplitudes,each assigned a uni ue pattern of binary. sually, each amplitude encodes an e ualnumber of bits. ach pattern of bits forms the symbol that is represented by theparticular amplitude.

• Fre>uen,/ S8ift =e/ing FS=#:- ;re uency%shift keying &;#F) is a fre uencymodulation scheme in which digital information is transmitted through discretefre uency changes of a carrier wa"e. !he simplest ;#F is a binary ;#F &B;#F).B;#F uses a pair of discrete fre uencies to transmit binary &(s and 1s) information.>ith this scheme, the K1K is called the mark fre uency and the K(K is called the spacefre uency.

• 78ase-s8ift ke/ing 7S=#:- 'hase%shift keying &'#F) is a digital modulation schemethat communicates the data by changing, or modulating, the phase of the carrier wa"e. Any digital modulation scheme uses a finite number of distinct signals torepresent digital data. '#F uses a finite number of phasesM each assigned a uni uepattern in the form of a binary code. ach pattern of bits forms the symbol that isrepresented by the particular phase.

*igital modulation is better t8an t8e Analog 'odulation

/igital technology has been most efficient in cellular phone industry. Analog phones ha"ebecome redundant e"en though sound clarity and uality was good.

Analog technology comprises of natural signals like human speech. >ith digitaltechnology this human speech can be sa"ed and stored in a computer. !hus digitaltechnology opens up the hori@on for endless possible uses.

b# rite differen,es between F*' and T*'6 4 'ark#Ans:;re uency di"ision multiple4ing &;/7)$% ;re uency di"ision multiple4ing &;/7) is thetechni ue used to di"ide the a"ailable bandwidth into a number of smaller independentlogical channels with each channel ha"ing a small bandwidth.

Ad3antages of F*':• !he users can be added to the system by simply adding another pair of transmitter

modulator and recei"er demodulators. ;/7 system support full duple4 information

*isad3antages of F*':• In ;/7 system, the initial cost is high.


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• A problem with one user can sometimes affect the others.• ach user re uires a precise carrier fre uency for transmission of the signals.

Time *i3ision 'ultiple(ing T*'#ach user of the channel is allotted a small time inter"al during which it may transmit a

message. !hus the total time a"ailable in the channel is di"ided and each user is allocated atime slot. /ata from each user is multiple4ed into a frame which is transmitted o"er thechannel. It is e4tended as time di"ision multiple Channel &!/7A)

Ad3antages of T*'• It uses a single link• It does not re uire precise carrier matching at both end of the links.• se of the channel capacity is high.• ach to e4pand the number of users on a system at a low cost.• !here is no need to include identification of the traffic stream on each packet.

*isad3antages of T*'• !he sensiti"ity to other user is "ery high and causes problems• Initial cost is high• !echnical comple4ity is more


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