Computer Networks 2marks

8/12/2019 Computer Networks 2marks

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SNS COLLEGE OF ENGINEERING, COIMBATORE 641107

DEPARTMENT OF MCA

2010-2011 III SEM – COMPUTER NETWORKS

TWO MARKS QUESTIONS AND ANSWERS

I-UNIT

1. W!" #$ %!"! &'(()*#&!"#'*+

Data communication is the exchange of data between two devices via some form

of transmission medium (wire cable). It is considered as local if the communicating

devices are in the same building and is considered remote if the devices are farther apart.

2. L#$" ')" " &!!&"#$"#&$ "' #('/ " &"#/*$$ ' %!"! &'(()*#&!"#'*

$$"(.

•

Deliver

• !ccurac

• Timeliness

. W!" #$ %3#/ !*% !&&)!&+

D3#/ The sstem must deliver data to the correct destination. Data must be received

b the intended device or user and onl b that device or user.

A&&)!& The sstem must deliver data accuratel. Data that have been altered in

transmission and left uncorrected are unusable.

4. W!" #$ "#(3#*$$+

The sstem must deliver data in a timel manner. Data delivered late are useless.

In the case of video" audio and voice data" timel deliver means delivering data as the

are produced" in the same order that the are produced" and without significant dela.

This #ind of deliver is called real-time transmission.

5. W!" ! " &'('**"$ ' %!"! &'(()*#&!"#'* $$"(+

1



• $essage

• %ender

• &eceiver

• $edium

• 'rotocol

6. W!" %' ') (!* ($$!, $*% !*% &#/+

M$$! The message is the information to be communicated. It consists of text"

number" pictures" sound or video or an combination of these.

S*% The sender is the device that sends the data message. It can be a computer"

wor#station" telephone handset" video camera and so on.

R&#/ The receiver is the device that receives the message. It can be a computer"

wor#station" telephone handset" television and so on.

7. W!" #$ (!*" "!*$(#$$#'* (%#)(+

The transmission medium is the phsical path b which a message travels from

sender to receiver. It consists of twisted pair wire" coaxial cable" fiber-optic cable" laser or

radio waves.

8. W!" #$ '"'&'3+

! protocol is a set of rules that govern data communication. It represents an

agreement between the communicating devices. ithout a protocol" two devices ma be

connected but cannot be communicated.

9. W!" #$ ! *":';+

! networ# is a set of devices connected b media lin#s. ! node can be a computer"

printer" or an other device capable of sending andor receiving data generated b other

nodes on the networ#. The lin#s connecting the devices are often called communication

channels.

2



10. W!" #$ %#$"#)"% '&$$#* !*% 3#$" #"$ !%/!*"!$+

In distributed processing" a tas# is divided among multiple computers.

!dvantages*

• %ecurit+ncapsulation

• Distributed databases

• ,aster problem solving

• %ecurit through redundanc

• ollaborative processing.

11. W!" ! " &#"#!$ ' *":';+

• 'erformance

• &eliabilit

• %ecurit

12. <': " '(!*& &!* (!$)%+

'erformance can be measured b

Transmit time* Transmit time is the amount of time reuired for a message to travel from

one device to another.

&esponse time* &esponse time is the elapsed time between an inuir and a response.

1. W!" ! " !&"'$ "!" #('/ " '(!*& ' *":';+

The performance of a networ# depends on a number of factors including

• Number of users

• Tpe of transmission medium

3



• /ardware

• %oftware

14. <': " 3#!#3#" ' ! *":'; &!* (!$)%+

• ,reuenc of failure

• &ecover time of a networ# after failure

• atastrophe

15. W!" #$ *":'; $&)#"+

Networ# securit issues including protecting data from unauthori0ed accessand viruses.

16. L#$" $'( ' " !3#&!"#'*$ ' *":';+

• $ar#eting and sales

• ,inancial services

• $anufacturing

• +lectronic messaging

• Director services

• Information services

• +lectronic data interchange(+DI)

• Teleconferencing

• ellular telephone

• able television

17. D#* 3#*; !*% 3#* &'*#)!"#'*.

4



L#*; ! lin# is the phsical communication pathwa that transfers data from one device

to another.

L#* &'*#)!"#'* 1ine configuration refers to the wa two or more communication

devices attach to a lin#.

18. W!" ! " '$$#3 3#* &'*#)!"#'*$+

'oint-to-point* It provides a dedicated lin# between two devices.

$ultipoint* ! multipoint line configuration is one on which more than two specific

devices share a single lin#. The capacit of the channel is shared either spatiall or

temporall.

19. W!" #$ (!*" "''3'+

The term topolog refers to the wa a networ# is laid out" either phsicall or

logicall. The topolog of a networ# is the geometric representation of the relationship of

all the lin#s and lin#ing devices.

20. W!" ! " "''3'#$ !/!#3!3+

• $esh topolog

• %tar topolog

• Tree topolog

• 2us topolog

• &ing topolog

21. W!" ! " ":' "$ ' 3!"#'*$#$ '$$#3 #* "''3'+

P-"'- In this" the devices share the lin# euall. +xamples* &ing and mesh

topolog.

P#(!-$&'*%! In this" one device controls traffic and the others must transmit

through it. +xamples* %tar and tree topolog.

5



22. W!" #$ ($ "''3'+ S"!" #"$ !%/!*"!$ !*% %#$!%/!*"!$.

In mesh topolog" ever device has a dedicated point-to-point lin# to ever other

device.

A%/!*"!$

• +liminates traffic problems

• &obust

• 'rivac or securit

• +as fault identification and fault isolation.

D#$!%/!*"!$

• Installation and reconfiguration are difficult

• %heer bul# of the wiring can be greater than the available space can

accommodate.

• The hardware reuired to connect each lin# can be prohibitivel

expensive.

2. W!" #$ $"! "''3'+ S"!" #"$ !%/!*"!$.

In a star topolog" each device has a dedicated point-to-point lin# onl to acentral controller" usuall called a hub. The devices are not directl lin#ed to each other.

!dvantages*

• 1ess expensive

• +as to install and reconfigure

• !dditions" moves and deletions involve onl one connection between that

device and the hub.

• &obustness

• +as fault identification and fault isolation.

24. W!" #$ " "''3'+

6



The tree topolog is a variation of a star. !s in a star" nodes in a tree are lin#ed to

a central hub that controls the traffic to the networ#. The central hub in the tree is an

active hub.

25. W!" #$ !&"#/ ) !*% !$$#/ )+

!ctive hub* !n active hub contains a repeater" which is a hardware device that

regenerates the received bit patterns before sending them out.

'assive hub* ! passive hub provides a simple phsical connection between the attached

devices.

26. W!" ! " !%/!*"!$ ' " "''3'+

The advantage is same as of star. In addition" it has two advantages*

• It allows more devices to be attached to a single central hub and can therefore

increase the distance a signal can travel between devices.

• It allows the networ# to isolate and prioriti0e communications from different

computers.

27. W!" #$ " )$ "''3'+

In bus topolog" one long cable acts as a bac#bone to lin# all the devices in

the networ#.

28. W!" ! " !%/!*"!$ !*% %#$!%/!*"!$ ' )$ "''3'+

A%/!*"!$

• +as installation

• Uses less cabling

D#$!%/!*"!$

• Difficult reconfiguration and fault isolation.

• !ddition of new device reuire modification or replacement of the

bac#bone.

7



• ! fault or brea# in the bus cable stops all transmission.

• The damaged area reflects signals bac# in the direction of origin" creating

noise in both directions.

29. W!" #$ #* "''3'+

In a ring topolog" each device has a dedicated point-to-point line configuration

onl with the two devices on either side of it. ! signal is passed along the ring in one

direction from device to device until it reaches its destination.

0. W!" ! " !%/!*"!$ ' #* "''3'+

• +as to install and reconfigure.

• !dding or deleting a device reuires moving onl two connections.

• +as fault isolation

• %ignal will be circulating at all times.

1. S"!" %#$!%/!*"!$ ' #* "''3'.

•

Unidirectional traffic

• ! brea# in the ring can disable the entire networ#.

2. W!" #$ "!*$(#$$#'* ('% !*% #"$ "$+

The transmission mode is used to define the direction of signal flow between

two lin#ed devices.

T$*

• %implex

• /alf-duplex

• ,ull-duplex.

8



. W!" ! " &!"'#$ ' *":';$+

• 1ocal area networ#

• $etropolitan area networ#

• ide area networ#.

4. D#* '"'&'3.

! protocol is a set of rules that govern data communication. ! protocol defines

what is communicated" how it is communicated" and when it is communicated. The #e

elements of a protocol are

• %ntax

• %emantics

• Timing

5. W!" #$ $*"!=, $(!*"#&$ !*% "#(#*+

S*"!= %ntax refers to the structure or format of the data" meaning the order in which

the are presented.

S(!*"#&$ %emantics refers to the meaning of each section of bits.

T#(#* Timing refers to two characteristics*

• hen data should be sent

• /ow fast the can be sent.

6. W!" #$ $"!*%!% !*% 3#$" #"$ &!"'#$.

! standard provides model for development that ma#es it possible to wor#regardless of the individual manufacturer.

ategories*

• De facto (b fact)

• De 3ure (b law)

9



7. W!" #$ D !&"' $"!*%!%$+

It is developed into two classes*

• 'roprietar standards

• Nonproprietar standards

8. W!" ! '#"! !*% *'*'#"! $"!*%!%$+

P'#"! $"!*%!%$ These standards are those originall invented b a commercial

organi0ation as a basis for the operation of its procedure. The are called closed standards

because the close off communications between sstems produced b different vendors.

N'*'#"! $"!*%!%$ These standards are those originall developed b groups or

committees that have passed them into the public domain. The are called open standards because the open communications between different sstems.

9. W' %/3'% $"!*%!%$+

%tandards are developed b cooperation among

• %tandards creation committees

•

,orums

• &egulator agencies

40. W!" ! " $"!*%!%$ #*/'3/% #* $"!*%!%$ &!"#'* &'((#""$+

• I%4 (International %tandards 4rgani0ation)

• ITU-T (International Telecommunications Union-Telecommunication

standards sector)

• !N%I (!merican National %tandards Institute)

• I+++ (Institute of +lectrical and +lectronics +ngineers)

• +I! (+lectronic Industries !ssociation)

10



• Telcordia

41. W!" #$ ISO+

The I%4 is an organi0ation dedicated to worldwide agreement on international

standards in a variet of fields.

42. D#* ITU-T.

ITU-T is an international standards organi0ation related to the United Nations that

develops standards for telecommunications. Two popular standards developed b ITU-T

are

• 5 series

• 6 series

4. D#* ANSI.

!N%I" a nonprofit organi0ation" is the U.%. voting representative to both the I%4

and the ITU-T.

44. D#* IEEE.

The I+++ is the largest national professional group involved in developing

standards for computing" communication" electrical engineering and electronics.

45. D#* EIA.

+I! is an association of electronics manufacturers in the United %tates. It is

responsible for developing the +I!-787-D and +I!-98: standards.

46. W!" #$ "3&'%#!+

Telcordia provides research and development resources for the advancement of

telecommunications technolog.

11



;<. L#$" $'( #('"!*" ')($.

• ,rame rela forum

• !T$ ,orum and !T$ consortium

• I+T,(Internet +ngineering Tas# ,orce) and

I%4(Internet %ociet

;=.W!" #$ R)3!"' A*&+

,(,ederal communication ommission) is one of the regulator agenc.

R$'*$##3#"$

• To review rate and service-charge applications made b telegraph and

telephone providers

• To review the technical specifications of communications hardware

• To establish reasonable common carrier rates of return

• To doivide and allocate radio frenuencies

• To assign carrier freuencies for radio and television broadcasts

;>.W!" #$ (*!" '* $$"(+

! open sstem is a model that allows an two different sstems to communicate regardless

of their underling architecture

9:. W!" #$ OSI ('%3+

The open sstem Interconnection model is a laered framewor# for the design of

networ# sstems that allows for communication across all tpes of computer sstems.

The purpose of 4%I model is to open communication between different sstems withoutreuiring changes to the underling hardware and software.

9?.I$ OSI ('%3 #$ ! '"'&'3+ E=3!#*.

The 4%I models not a protocol" It is a model for understanding and designing a networ#

architecture that is flexible" robust and interoperable.

12



97. L#$" ')" " 3!$ ' OSI ('%3+

The model is built of seven ordered laers

• 'hsical laer (laer ?)

• Datalin# laer (laer 7)

• Networ# laer (laer 8)

• Transport laer (laer ;)

• %ession laer (laer 9)

• 'resentation laer (laer @)

• !pplication laer (laer <)

98. W!" #$ (!*" #*"!&+

+ach interface defines what information and services a laer must provide for the

laer above it. ell-defined interfaces and laer functions provide modularit to a networ#.

9;. <': " 3!$ ' OSI ('%3 #$ '/#%%+

The phsical" data lin# and networ# laer are the networ# support laers.The deal

with the phsical aspects of moving data from one device to another.

The %ession" presentation application laer are user support laers. The allow

interoperabilit among unrelated software sstems.

99. W!" #$ $#&!3 3!+

The phsical laer coordinates the functions reuired to transmit a bit stream over a

phsical medium.

It deals with the mechanical and electrical specifications of the interface and

transmission medium.

It also defines the procedures and functions that phsical devices and interfaces have to

perform for transmission to occur.

9@. S"!" " &!!&"#$"#&$ ' $#&!3 3!+

• 'hsical characteristics of interfaces and media.

• &epresentation of bits(:s and ?s)

13





The networ# laer is responsible for the source-to-destination deliver of a pac#et

possibl across multiple networ#s. hereas the data lin# laer oversees the deliver of the

pac#et between two sstems on the same networ#" the networ# laer ensures that each pac#et

gets from its point of origin to its final destination.

@:. W!" ! " $'*$##3#"#$ ' *":'; 3!+

• 1ogical addressing

• &outing

@?. W!" #$ (!*" "!*$'" 3!+

The transport laer is responsible for source-to-destination deliver of the entire

message. hereas the networ# laer oversees end-to-end deliver of individual pac#ets" it does

not recogni0e an relationship between those pac#ets.

@7. S"!" $'( ' " $'*$##3#"#$ ' "!*$'" 3!.

• %ervice-point addressing

• %egmentation and reassembl

• onnection control

• ,low control

• +rror control

@8. W!" #$ (!*" $$$#'* 3!+

The session laer is the networ# dialog controller. It establishes" maintains" and

snchroni0es the interaction between communicating sstems.

@;. S"!" " $'*$##3#"#$ ' $$$#'* 3!.

• Dialog control

• %nchroni0ation

@9. W!" #$ $*"!"#'* 3! !*% 3#$" #"$ $'*$##3#"#$.

The presentation laer is concerned with sntax and semantics of the information

exchanged between two sstems.

R$'*$##3#"#$

• Translation

15



• +ncrption

• ompression

@@. W!" #$ !3#&!"#'* 3!+

The application laer enables the user" whether human or software to access the

networ#. It provides user interfaces and support for services such as electronic mail" remote fileaccess and transfer" shared database management and other tpes of distributed information

services.

@<. W!" ! " $/#&$ '/#%% !3#&!"#'* 3!+

• Networ# virtual terminal

• ,ile transfer" access and management (,T!$)

• $ail services

• Director services

@=. L#$" ')" "$ ' "!*$(#$$#'* (%#!.

• Auided media

• Unguided media

@>. W!" #$ (!*" )#%% (%#!+

Auided media" which are those that provide a conduit from one device to another. It

includes

• Twisted-pair cable

• oaxial cable

• ,iber-optic cable

<:. W!" #$ (!*" ":#$"%-!# &!3+

Twisted-pair cable use metallic conductors that accept and transport signals in the form

of electrical current. It includes

• Unshielded twisted-pair (UT') cable

• %hielded twisted-pair (%T') cable.

16



The twisted pair consists of two conductors each surrounded b an insulating material.

<?. W!" #$ )*$#3%% ":#$"%-!# &!3+

! twisted pair consists of two conductors" each with its own colored plastic

insulation. The plastic insulation is color-banded for identification.

olors are used both to identif the specific conductors in a cable and to indicatewhich wires belong in pairs and how the relate to other pairs in a larger bundle.

<7. W!" #$ (!*" $#3%% ":#$"%-!# >STP? &!3+

%hielded twisted pair cable has a metal foil or braided-mesh covering that encases

each pair of insulated conductors. The metal casing prevents the penetration of electromagnetic

noise. It also can eliminate a phenomenon called crosstal#" which is the undesired effect of one

circuit on another circuit.

<8. W!" #$ &'!=#!3 &!3+

oaxial cable carries signals of higher freuenc ranges than twisted-pair cable" in

part because the two media are constructed uite differentl.

Instead of having two wires" coax has a central core conductor of solid or stranded

wire enclosing in an insulating sheath" which is in turn" encased in an outer conductor of metal

foil" braid" or a combination of the two.

<;. W!" ! " /!#')$ &'!=#!3 &!3 $"!*%!%$+

Different coaxial cable design are categori0ed b their radio government (&A)

ratings. +ach &A number denotes a uniue set of phsical specifications" including the wiregauge of the inner conductor" the thic#ness and tpe of the inner insulator" the construction of the

shield" and the si0e and tpe of the outer casing.

S"!*%!%$

• &A-=(used in thic# +thernet)

• &A->(used in thic# +thernet)

• &A-??(used in thic# +thernet)

• &A-9=(used in thin +thernet)

• &A-9>(used for T5)

<9. W!" ! %#*" &'!=#!3 &!3 &'**&"'$+

The commonl used connectors are

17



T-C'**&"'$ It allows a secondar cable to branch off from a main line.

T(#*!"'$ Terminators are reuired for bus topologies where one main cable acts as a

bac#bone with branches to several devices but does not itself terminate in a device.

<@. W!" #$ (!*" '"#&!3 #+

4ptical fiber is made of glass or plastic and transmits signals in the form of light. It

includes

• Nature of light

&efraction

ritical angle

&eflection

• 'ropagation

$ulti mode

%ingle mode

• ,iber si0es

• able connection

1ight sources for optical cable

<<. D#* !&"#'*.

1ight travels in a straight line as long as it is moving through a single uniform

substance. If a ra of light traveling through one substance suddenl enters another substance" its

speed changes abruptl" causing the ra to change direction. This change is called refraction.

78. W!" #$ (!*" !*3 ' #*&#%*& !*% !*3 ' !&"#'*+

The angles made b the beam of light in relation to the vertical axis are called I" for

incident and &" for refracted.

If the beam travels from a denser medium into a less dense medium" the value of I is

smaller than the value of &.

18



hen light travels into more dense medium" the angle of incidence is greater than angle

of refraction and when light travels into a less dense medium" the angle of incidence is less than

the angle of refraction.

<>. D#* &#"#&!3 !*3.

!t some point in the process" the change in the incident angle results in a refracted angle

of >: degrees" with the refracted beam ling along the hori0ontal. The incident angle at this point

is #nown as critical angle.

=:. D#* R3&"#'*.

hen the angle of incidence becomes greater than the critical angle" reflection occurs.

/ere" the angle of incidence is alwas eual to the angle of reflection.

=?. W!" ! " /!#')$ '!!"#'* ('%$ !/!#3!3+

•$ultimode

%tep-index fiber

Araded-index fiber

• %ingle mode

=7. W!" #$ $#*3-('% !*% ()3"#-('%+

%ingle mode* %ingle mode uses step-index fiber and a highl focused source of light that

limits became to a small range of angles" all close to the hori0ontal.

$ultimode* It is named as multi-mode because multiple beams from a light source move

through the core in different paths.

=8. D#*"#!" $"-#*%= # !*% !%%-#*%= #.

%tep-Index fiber Araded-Index fiber

?. The densit of the core remains

constant from the center to the edges.

Densit is highest at the center of the core and

decreases graduall to its lowest at the edge.

7. %ome beams stri#e the interface of the

core and cladding at an angle smallerthan the critical angle.

2eams at angles move through a series of

constantl changing densities.

=;. S"!" " !%/!*"!$ !*% %#$!%/!*"!$ ' '"#&!3 #.

A%/!*"!$

• Noise resistance

19



• 1ess signal attenuation

• /igher bandwidth

D#$!%/!*"!$

• ost

• Installationmaintenance

• ,ragilit.

=9. S"!" !')" )*)#%% (%#!.

Unguided media also #nown as wireless communication. It includes"

(?) &adio freuenc allocation

'ropagation of &adio waves.

• %urface propagation

• Tropospheric propagation

• Ionospheric propagation

• 1ine-of-sight propagation

'ropagation of specific signals

• 5er low freuenc(51,)

• 1ow freuenc(1,)

• $iddle freuenc($,)

• 5er high freuenc(5/,)

• Ultrahigh freuenc(U/,)

•

%uperhigh freuenc(%/,)

• +xtremel high freuenc(+/,)

(7). Terrestrial microwave.

&epeaters

20



!ntennas

• 'arabolic dish antenna

• /orn antenna

(8) %atellite communication

Aeosnchronous satellites

,reuenc 2ands for satellite communication

(;) ellular telephon

ellular bands

Transmission

&eceiving

/andoff

Digital

=@. W!" #$ ('%(+

$odem stands for modulatordemodulator. ! modulator converts a digital signal intoan analog signal. ! demodulator converts an analog signal into digital signal.

87. <': " "!*$(#$$#'* !" &!* (*"#'*%+

2andwidth* +ver line has an upper limit and lower limit on the freuencies of the signals

it can carr. This limited range is called the bandwidth.

M'%( $%

!%B(!mplitude shift #eing) manipulates freuenc.

,%B(,reuenc %hift Being) manipulates freuenc.

'%B('hase %hift Being) manipulates phase.

C!$(Cuadrature !mplitude $odulation) manipulates both phase and

amplitude.

21



88. W!" ! " %#*" ('%( $"!*%!%$+

2ell modems

ITU-T $odem standards

Intelligent modems.

89. W!" %'$ )3'!%#* (!*+

Transmission of data from the subscriber to the Internet provider (uploading) follows

these steps*

• Digital data are modulated b the modem at site !.

• !nalog data are sent from the modem to the switching station at site ! on the local

loop.

• !t the switching station" data are converted to digital using '$('ulse codemodulation).

• Digital data travel through the digital networ# of the telephone compan and are

received b the Internet provider computer.

90. W!" %'$ %':*3'!%#* (!*+

Transmission of data from the Internet provider to the modem at site !(downloading

follows these steps*

• Digital data are sent b the computer of the Internet provider through thedigital telephone networ#.

• !t the switching station" digital data are converted to analog using '$.

• !nalog data are sent from the switching station at site ! to the modem on the

local loop.

• !nalog data are demodulated b the modem at site !.

22



UNIT-2

?. hat are the tpes of errors

• %ingle-bit error

• 2urst error

7. hat is meant b single-bit error and burst error

S#*3-#" ' The term single bit error means that onl one bit of a given data unit such as a

bte" character" data unit or pac#et is changed from : to ?.

B)$" ' The term burst error means that two or more bits in the data unit have changed from

? to : or from : to ?. (ie) multiple bits are changed.

8. hat is redundanc

+rror detection uses the concept of redundanc" which means adding extra bits for detecting

errors at the destination. Instead of repeating the entire data stream" a shorter group of bits ma beappended to the end of each unit. This techniue is called redundanc because the extra bits are redundant

to information" the are discarded as soon as the accurac of the transmission has been determined.

;. hat are tpes of redundanc chec#s available

• 5erticals redundanc chec#(5&) #nown as parit chec#

• 1ongitudinal redundanc chec#(1&)

• clical redundanc chec#(&)

• hec#sum

9. +xplain parit chec#

In verticals redundanc chec#" a parit bit is added to ever data unit so that the total number of

?s becomes even. %ome sstem ma also use odd-parit chec# where the number of ?s should be odd.

5& can detect all single bit errors. It can detect burst errors onl if the total number of errors in

each data unit odd.

@. hat is 1&

In longitudinal redundanc chec#" a bloc# of bits is organi0ed in a table and divided into rows

and a redundant row of bits is added to the whole bloc#.

<. hat is &

& is based on binar division. In &" instead of adding bits together to achieve a desired

parit" a seuence of redundant bits called & or the & remainder is appended to end of data unit son

23



that the resulting data unit becomes exactl divisible b a second" predetermined binar number. !t its

destination" the incoming data unit is divided b the same number.

& includes (?) & generator (7) & chec#er (8) 'olnomials.

=. hat is the role of remainder in &

If there is no remainder" the data unit assumed to be intact and is therefore accepted. If there is a

remainder" it indicates that the data unit has been damaged in transit and therefore must be re3ected.

>. hat are the ualities of the valid &

• It much have exactl one less bit than the divisor.

• !ppending it to the end of the data string must ma#e the resulting bit seuence exactl divisible

b the divisor.

?:. hat are the properties of a polnomial

•

It should not be divisible b x.

• It should be divisible b (xE?).

??. %tate the performance of &.

& is a ver effective error detection method.

• & can detect all burst errors that affect an odd number of bits.

• & can detect all burst errors of length less than or eual to the degree of the

polnomial.

• & can detect with a ver high probabilit burst errors of length greater than the degree

of the polnomial.

?7. hat is meant b chec#sum

hec#sum if the field used for error detection. It is formed b adding bit streams using ?s

complement arithmetic and then complementing the result.

?8. hat does the sender do in chec#sum

• The unit is divided into # sections" each of n bits.

• !ll sections are added together using ?s complement to get the sum.

• The sum is complemented and becomes the chec#sum.

• The chec#sum is sent with the data.

?;. hat does the receiver do in chec#sum

24



• The unit is divided into # sections" each of n bits.

• !ll sections are added together using ?s complement to get the sum.

• The sum is complemented.

• If the result is 0ero" the data are accepted" otherwise the are re3ected.

?9. /ow the error correction can be handled

+rror correction can be handled in two was.

• In one" when an error is discovered" the receiver can have the sender retransmit the entire

data unit.

•

In the other" a receiver can use an error correcting code" which automaticall correctscertain errors.

?@. hat is hamming code

/amming code is a method that adds redundant bits to a data unit to detect and correct bit errors.

The hamming code can be applied to data units of an length and uses the relationship between data and

redundanc bits. In the hamming code" for a data unit of m bits" use the formula 7rFGmErE? to determine

r" the number of redundant bits needed.

?<. Define flow control.

,low control refers to a set of procedures used to restrict the amount of data the sender can send before waiting for ac#nowledgement. Incoming data must be chec#ed and processed before the can be

used. The rate of such process is slower than the rate of transmission. ,or this reason" each receiving

device has a bloc# of memor called the buffer" reserved for storing incoming data until the are

processed. If the buffer begins to fill up" the receiver must be able to tell the sender to halt transmission

until it is once again able to receive.

?=. hat are the categories of flow control

• %top-and-wait method

•

%liding window

?>. Define stop-and-wait method.

In the stop-and-wait method of flow control" the sender sends one frame and waits for an

ac#nowledgement before sending the next frames. The process of sending and waiting repeats until the

sender transmits an end of transmission frame.

7:. hat are the advantages and disadvantages of stop-and-wait method

25



A%/!*"! simplicit (+ach frame is chec#ing and ac#nowledged before the next frame is sent.)

D#$!%/!*"! Inefficienc (%top-and-wait is slow).

7?. hat is sliding window method

In the sliding window method of flow control" several frames can be in transit at a time. The

sliding window refers to imaginar boxes at both the sender and the receiver.

77. hat does the sender window do

The sliding window of the sender shrin#s from the left when frames of data are sent. The sliding

window of the sender expands to the right when ac#nowledgements are received.

78. hat does the receiver window do

The sliding window of the receiver shrin#s from the left when frames of data are received. The

sliding window of the receiver expands to the right when ac#nowledgments are sent.

7;. hat is meant b the term error control

+rror control refers primaril to methods of error detection and retransmission. +rror control in

the data lin# laer is based on automatic repeat reuest (!&C)" which means retransmission of data in

three cases* damaged frame" lost frame" and lost ac#nowledgment.

79. hat are the categories of error control

(?) %top-and-wait !&C

(7) %liding window !&C

Ao-bac#-n

%elective re3ect

7@. hat are the features of basic flow control mechanism in stop-and-wait

• The sending device #eeps a cop of the last frames transmitted until it receives an

ac#nowledgment for that frames.

• ,or identification purposes" both data frames and !B frames are numbered alternatel : and ?.

• If an error is discovered in a data frame" indicating that it has been corrupted in transit" a N!B

frame is returned.

• The sending device is euipped with a timer.

7<. hat are the features of basic flow control mechanism in sliding window

• The sending device #eeps copies of all transmitted frames until the have been ac#nowledged.

26



• In addition to !B frames" the receiver has the option of returning a N!B frame if the data have

been received damaged.

• 1i#e stop-and-wait !&C" the sending device in sliding window !&C is euipped with a timer to

enable it to handle lost ac#nowledgments. N-? frames ma be sent before an ac#nowledgment

much be received.

7=. Difference between go-bac#-in !&C and selective re3ect !&C.

G'-!&;-* ARQ S3&"#/ @&" ARQ

If one frame is lost or damaged" all frames

sent since the last frame ac#nowledged are

transmitted.

In selective re3ect !&C" onl the specific

damaged or lost frame is retransmitted.

Duplicate frames are discarded Duplicate frames are not discarded.

&etransmission begins with the last

ac#nowledged frame even if subseuent

frames have arrived correctl.

4nl the unac#nowledged frame is

retransmitted.

1ess performance 2etter performance

+as to implement /ard to implement

7>. hat are all the bit oriented protocols available

• %nchronous data lin# control (%D1)

• /igh-level data lin# control (/D1)

• 1in# access procedures (1!')

• 1ocal area networ#s (1!N)

8:. hat is /D1

/D1 is a bit-oriented data lin# protocol designed to support both half-duplex and full-duplex

communication over point-to-point and multipoint lin#s. %stems using /D1 can be characteri0ed b

their" tpes" their configuration" and their response modes.

8?. hat are the station tpes available in /D1

/D1 differentiates between three tpes of stations*

• 'rimar station

• %econdar station

• ombined station

87. %tate the function of primar and secondar station.

The primar station sends commands to the secondar station. In other words" the primar station

sends commands and secondar station sends responses.

27



88. Describe about combined station.

! combined station sends both commands and responses. ! combined station is one of a set of

connected peer devices programmed to behave either as a primar or as a secondar depending on the

nature and direction of the transmission.

8;. %tate configuration and its tpes in /D1.

The word configuration refers to the relationship of hardware devices on a lin#. The

configurations are of three tpes*

• Unbalanced configuration

• %mmetrical configuration

• 2alanced configuration

89. Define unbalanced configuration.

!n unbalanced configuration (also #nown as masterslave configuration) is one in which onedevice is primar and the others are secondar. Unbalanced configuration can be point-to-point if onl

two devices are involved. The can be multipoint with one primar controlling several secondaries.

8@. Define smmetrical configuration.

! smmetrical configuration is one in which each phsical station on a lin# consists of two

logical stations" one a primar and the other a secondar. %mmetrical configuration behaves li#e an

unbalanced configuration except that control of the lin# can shift between the two stations.

8<. hat is balanced configuration

! balanced configuration is one in which each phsical station in a point-to-point topolog are ofthe combined tpe. The stations are lin#ed b a single line that can be controlled b either station.

8=. hat are the modes of communication in /D1

/D1 supports three modes of communication between stations.

• Normal response mode (N&$)

• !snchronous response mode (!&$)

• !snchronous balanced mode (!2$)

8>. hat is N&$

Normal response mode refers to the standard primar-secondar relationship. In this mode" a

secondar device must have permission from the primar device transmission of one or more frames

containing data.

;:. hat is !&$

28



In asnchronous response mode" a secondar ma initiate a transmission without permission from

the primar whenever the channel is idle. !ll transmission from a secondar must still be made to

primar for rela to final destination.

;?. hat is !2$

In asnchronous balanced mode" all stations are eual and therefore onl combined stations

connected in point-to-point are used. +ither combined station ma initiate transmission with the othercombined station without permission.

;7. hat are the tpes of frames available in /D1

/D1 defines three tpes of frames.

• Information frames (I-frames)

• %upervisor frames (%-frames)

• Unnumbered frames (U-frames)

;8. hat are the functions of various frames

• I-frames are to transport user data and control information relating to user data.

• %-frames are used onl to transport control information" primaril data lin# laer flow and error

controls.

• U-frames are reserved for sstem management. Information carried b u-frames intended for

managing the lin# itself.

;;. hat are the fields does the frame in /D1 holds

+ach frame in /D1 ma contain up to@ fields.

• ! beginning flag field

• !ddress field

• ontrol field

• Information field

• ,rame chec# seuence (,%) fields

• +nding flag field.

;9. hat is meant b bit stuffing

2it stuffing is the process of adding one extra : whenever there are five consecutive ?s in the data

so that the receiver does not mista#e the data for a flag.

29



;@. hat is ', bit

The control fields of all three tpes of frames contain a bit called pollfinal (',) bit. !n I-frame

contains two 8-bit flow and error control seuences" called N(%) and N(&). N(%) specifies the number of

the frame being sent and N(&) is the ac#nowledgement field and it indicates the number of the frame

expected in return in a two-wa exchange.

;<. Define piggbac#ing

'iggbac#ing means combining data to be sent and ac#nowledgement of the frames received in

one single frame.

;=. hat are the tpes of %-frame

• &eceive read frame (&&)

• &eceive not read (&N&)

• &e3ect (&+H)

• %elective-re3ect (%&+H)

;>. hat are the categories of U-frame

The U-frame commands and response can be divided into five basic functional categories.

• $ode setting

• Unnumbered-exchange

• Disconnection

• Initiali0ation

• $iscellaneous

9:. hat are the tpes of lin# access procedures (1!')

• 1in# access procedure" balanced (1!'2)

• 1in# access procedure for D channel (1!'D)

• 1ind access procedure for modems (1!'$)

9?. Define 1!N.

! local area networ# is usuall privatel owned and lin#s the devices in a single office" building"

or campus. 1!Ns are designed to allow resources to be shared between personal computers or

wor#stations.

30



1!Ns are distinguished from other tpes of networ#s b their transmission media and topolog.

The will use onl one tpe of transmission medium. The most common 1!N topologies are bus" ring

and star.

97. Define +thernet.

I+++ =:7.8 supports a 1!N standard called +thernet. It defines two categories* 2aseband and

2roadband.

98. Difference between baseband and broadband.

BASEBAND BROADBAND

2aseband specifies digital signal 2roadband specifies analog signal

The standards of baseband are ?:2ase9(thic#

+thernet)"?:2ase7(thin +thernet)" ?:2ase-

T(Twisted-pair +thernet)" ?2ase9(%tar1!N)

and ?::2ase-T

?:2road8@ is the standard

9;. hat does the number and letter in standard means

The first number (?:" ? or ?::) indicates the data rate in $bps. The last number or letter (9" 7" ?

or T) indicated cable length or the tpe of cable. +xample* ?:2ase;" ?2ase9

99. hat is a collision

henever multiple users have unregulated access to a single line" there is a danger of signals into

unusable noise" are called collisions. !s traffic increases on a multiple-access lin#" collision also

increases.

9@. hat is %$!!

The access mechanism used in an +thernet is called carrier sense multiple access with collision

detection (%$!D). %$!D is the result of an evolution from multiple access ($!) to carrier

sense multiple access (%$!) and finall to carrier sense multiple access with collision detection.

9<. /ow the frame in I+++ =:7.8 will be

I+++ =:7.8 specifies one tpe of frame containing seven fields*

• 'reamble

• %tart frame delimiter (%,D)

• Destination address (D!)

• %ource address (%!)

• 1engthtpe of 'DU

31



• =:7.7 frame

• &

9=. hat is I+++ =:7.9

I+++ =:7.9 is also #nown as to#en ring. To#en ring allows each station to send one frame per

turn. The mechanism that coordinates this rotation is called to#en passing. ! to#en is a simple placeholder frame that is passed form station to station around the ring.

9>. hat are the tpes of frames in to#en ring protocol

(?) Datacommand frame

• %tart delimiter (%D)

• !ccess control (!)

• ,rame control (,)

• Destination address (D!)

• %ource address (%!)

• =:7.7 'DU frame

• &

• +nd delimiter (+D)

• ,rame status (,%)

(7) To#en frame

(8) !bort frame

@:. hat is ,DDI

,iber distributed data interface (,DDI) is a local area networ# protocol. It supports data rates of

?:: $bps and provides a high speed alternative to +thernet and to#en ring.

@?. hat are the two tpes of data frames in ,DDI

• S*&'*')$ It refers to information that is real time. It is #nown as %-frames.

• A$*&'*')$ It refers to information that is not real. It is #nown as !-frames.

@7. hat are the tpes of time registers in ,DDI

32



• %nchronous !llocation (%!)

• Target To#en &otation Time (TT&T)

• !bsolute $aximum Time (!$T)

@8. hat is %!" TT&T J !$T

• S*&'*')$ A33'&!"#'* >SA? The %! register indicates that the length of time allowed each

station for sending snchronous data.

• T!" T';* R'"!"#'* T#( >TTRT? The TT&T register indicates the average time reuired

for a to#en to circulate around the ring exactl once.

• A$'3)" M!=#()( T#( >AMT? The !$T register holds a value eual to twice the TT&T.

@;. hat are the timers available in ,DDI

• T';* R'"!"#'* T#( >TRT? The T&T runs continuousl and measures the actual time ta#en

b the to#en to complete a ccle.

• T';* <'3%#* T#( >T<T? It shows how much time remains for sending asnchronous

frames once the snchronous frames have been sent.

@9. hat are the tpes of frames available in ,DDI

The ,DDI standard divides transmission functions into four protocols

• 'hsical $edium Dependent ('$D)

• 'hsical ('/K)

• $edia !ccess ontrol ($!)

• 1ogical 1in# ontrol (11)

@@. hat are the frame fields in ,DDI

• %tart Delimiter (%D)

• ,rame ontrol (,)

•

!ddresses

• Data

• &

• +nd Delimiter (+D)

33



• ,rame %tatus (,%)

@<. hat are the three tpes of notes in ,DDI

• Dual !ttachment %tation (D!%)

• %ingle !ttachment %tation (%!%)

• Dual !ttachment oncentration (D!)

@=. hat is meant b bridges

2ridges operate in both the phsical and data lin# laers of 4%I model. 2ridges can divide a large

networ# into smaller segments. It can also rela frames between two originall separate 1!N. 2ridges

contain logic that allows them to #eep the traffic for each segment separate. It also provides securit

through the partitioning of traffic.

@>. hat are the tpes of 2ridges

• %imple 2ridge

• $ultiport 2ridge

• Transparent 2ridge

<:. hat are the issues to be considered in connecting a bridge to different 1!N

• ,rame format

• 'aload si0e

• Date rate

• !ddress bit order

• !c#nowledgment

• ollision

• 'riorit

34



UNIT L III

T4 $!&B%

?. hat is an internetwor#

hen two or more are connected" the become an internetwor#" or internet. Individual

networ#s devices such as routers and gatewas.

7. hat is switching and list its tpes

! switched networ# consists of a series of inter lin#ed nodes. called switches.

%witches are hardware or software devices capable of creating temporar connections between

two or more devices lin#ed to the switch but not to each other.

Tpes*

• ircuit switching

• 'ac#et switching

• $essage switching

8. hat is circuit switching

ircuit switching creates a direct phsical connection between two devices such as phones or

computers. It transmits onl analog signals. 5oice communication is onl possible.

It includes an one of the two technologies*

• %pace-division switches

• Time-division switches

;. hat are disadvantages of circuit switching

• 1ess suited for data and non voice transmission.

• Data rate

• Inflexible

• onsiders all transmissions as eual.

9. hat is pac#et switching

35



In a pac#et switched networ#" data are transmitted in discrete units of potentiall variable

length bloc#s called pac#ets. 1onger transmissions are bro#en into multiplepac#ets.+ach pac#et

contains not onl but also a header with control information(such as and source and destination

addresses).

@. hat are the pac#et switching approaches

• Datagram approach

• 5irtual circuit approach

i.switched virtual circuit

ii. 'ermanent virtual circuit

<. +xplain datagram approach.

In datagram approach" each pac#et is treated independentl from all others. 'ac#ets are

#nown as datagrams.ommunication is achieved through multiplexing (Time divisionmultiplexing and freuenc division multiplexing) and demultiplexing.

=. +xplain virtual circuit approach.

In virtual circuit approach" the relationship between all pac#ets belonging to a message or

session is preserved. ! single route is chosen between sender and receiver at the beginning of the

session. hen the data are sent" all pac#ets of the transmission travel one after another along that

route.

>. hat is %5 and '5

S:#"&% /#")!3 &#&)#"

It is comparable to dial-up lines in circuit switching. In this method" 5irtual circuit is

created whenever it is needed and exists onl for the duration of the specific exchange.

P(!**" /#")!3 &#&)#"

These are comparable to leased lines in circuit switching. In this method" the same virtual

circuit is provided between two users on a continuous basis. The circuit is dedicated to the

specific users. No one else can use it.

?:. Difference between circuit switching and virtual switching.

C#&)#" $:#"&#* #")!3 $:#"&#*

It creates a path between two points.

The phsical path is created b

setting the switches for the durationof the dial or leased line

It creates a route between two points.

This means each switch creates an entr in its routing

table for the duration of the session or duration of theleased line

36



The lin#s that made here arededicated. The cannot be used b

other connection

The lin#s that ma#e a route can be shared b otherconnections

11.W!" #$ ($$! $:#"&#*+

$essage switching is #nown as store and forward switching.In this mechanism" a nodereceives a message" stores it until the appropriate route is free" then sends it along. There is no

direct lin# between the sender and receiver of a transmission. In message switching" the

messages are stored and relaed from secondar storage (dis#)" while in pac#et switching the

pac#ets are stored and forwarded from primar storage(&!$).

?7. hat are the protocols available in networ# laer

!t the networ# laer" T'I' supports the internetwor# protocol (I').I' in turn contains four

supporting protocols* !'&" &!&'" I$' and IA$'.

?8. Describe about I'.

I' is the transmission mechanism used b the T'I' protocols. It is an unreliable and

connectionless datagram protocol a best-effort deliver service. The term best-effort means that

I' provides no error chec#ing or trac#ing. I' transports data in pac#ets called datagramMs" each

of which is transported separatel.

?;. /ow will be the addressing in I'

+ach internet address consists of four btes (87 bits) defining three fields*

class tpe" net id" host id.

?9. hat is net id and host id

N" #%

This is assigned b internetwor# information center. It identifies the devices to-which a

device is attached.

<'$" #%

This is assigned b networ# administrator. It identifies the specific device on that

networ#.

?@. hat are tpes of classes available

C3!$$ A The use onl one bte to identif class tpe and net id" The remaining three btes

available for host id. The possible networ# addresses are ?.:.:.: to ?7<.:.:.:.

37



C3!$$ B The use two btes to identif net id and two btes for host id. The possible

networ# addresses are ?7=.:.:.: to ?>?.799.:.:.

C3!$$ C The use two btes to identif net id and one bte for host id.The possible networ#

address is ?>7.:.:.: to 778.779.799.:.

C3!$$ D

lass D is reserved for multicasting. $ulticasting allows copies of a datagram to be passed

to select group of hosts rather to an individual host.It is similar to broadcasting" but where

broadcasting reuires that a pac#et be passed to all possible destinations" multicasting allows

transmission to a selected subset. The address are 77;.:.:.: to 7;:.:.:.:.

C3!$$ E

lass + addresses are reserved for future use. The possible address areFG7;:.:.:.

?<. hat is sub netting

In I' addressing one portion of the address indicates a networ# (net id)and the other portion

indicates the host on the networ#(host id).

In man cases" these two levels of hierarch are not enough.

4ne solution to this problem is subnetting" the further division of a networ#s called

subnetwor#s.

?= .what are the levels of hierarch in sub netting

• Net-id* This is the first level which defines the site.

• %ubnet id* this is the second level. It defines the phsical subnetwor#.

• /osted* This is the third level.It defines the connection of the host to the subnetwor#

?>./ow will be the routing of I' datagram

The routing of an I' datagram involves three steps*

• Deliver to the site

• Deliver to the subnetwor#

• Deliver to the host

7:. Define mas#ing.

38



$as#ing is the process that extracts the address of the phsical networ# from an I' address.

$as#ing can be done whether we have sub netting or not. If there is no sub netting" mas#ing

+xtracts the networ# address from an I' address. If there is sub netting" mas#ing extracts the

subnetwor# address from an I' address.

7?. hat are tpes of mas#ing

• 2oundar level mas#ing

• Nonboundar level mas#ing

77 .hat are the rules to be followed in boundar level mas#ing

• The btes in the I' address that correspond to 799 in the mas# will be repeated in

the subetwor# address.

• The btes in the I' address that correspond to : in the mas# will change to : in

the subnetwor# address.

78. hat are the rules to be followed in nonboundar level mas#ing

• The btes in the I' address that correspond to 799 in the mas# will be repeated in

the subnetwor# address.

• The btes in the I' address that correspond to : in the mas# will change to : in the

subnetwor# address.

• ,or other btes" use the bit-wise !ND operator.

7;. hat is !&'

The address resolution protocol associates an I' address with the phsical address. I, the

NI on particular machine fails" the phsical address changes. The I' address" on the hand" have

universal 3urisdiction cannot be changed. !&' is used to find the phsical address of the node

when its internet address is #nown.

79. hat is &!&'

The reverse address resolution (&!&') allows a host to discover its internet address when it

#nown onl to its phsical address. The host wishing to retrieve its internet address broadcasts an

&!&' uer pac#et that contains its phsical address to ever host on its phsical networ#.

! server on the networ# recogni0es the &!&' pac#et the hostMs internet address.

7@ .hat is I$'

39



The internet group message protocol (I$') has been designed to help a multicast touter the

hosts in a 1!N that are members of a multicast group.

It also handles both control and error messages" but its sole function is to respect problems" not

correct them. &esponsibities for correction lies with the sender.

7<. hat is IA$'

The internet group message protocol (IA$') has been designed to help a multicast router

identif the hosts in a 1!N that are members of a multicast group. It is a companion to the I'

protocol

7= hat is router

&outer is an internetwor#ing device operating at the first three 4%I laers router is attached

to two or more networ#s and forwards pac#ets from one networ# to another.The process

performed b the router is #nown as routing.

7>. hat are the routing concepts available

• 1east-cost routing

• Non adaptive and adaptive routing

8:. hat is 1east-cost routing

1east-cost routing*

The least-cost routing is based on efficienc* which of the available

pathwas is the cheapest or shorest.hen shortest means the pathwa reuiring the smallestnumber of relas" it is called hop-count routing"in which ever lin# is considered to be of eual

length and given the value one.

8?. hat is nonadaptive and adaptive routing

N'*!%!"#/ ')"#*

In nonadaptive routing" the routing decisions are not made based on the

condition or topolog of the networ#s.

A%!!"#/ ')"#*

In adaptive routing" the router ma select a new route for each pac#et in

response to changes in condition and topolog of the networ#s.

87. hat is routing algorithm

40



The algorithm used b a router to determine the optimum path for a pac#et is #nown as

routing algorithm. The following are the routing algorithms

• Distance vector routing

• 1in# state routing

88. hat is distance vector routing

In distance vector routing" each router periodicall shares its #nowledge about the entire networ#

with its neighbors. The three #es to understand how this algorithm wor#s are as follows*

• Bnowledge about the whole networ#

• &outing onl to neighbors

• Information sharing at regular intervals

8;./ow the information will be shared in distance vector routing

! router sends its #nowledge to its neighbors. The neighbors add this #nowledge to their

own #nowledge and send the whole table to their own neighbors. In this wa" the first router gets

its own information bac# plus new information about its neighborMs other neighbors. In distance

vector routing" the cost is based on hop count

89. hat is routing table

! table containing information a router needs to route pac#ets. The information mainclude the networ# address the cost" the address of the next hop" and so on.

Networ# ID ost Next hop

---------------------- ----------------------------- ---------------------------------

The networ# ID is the final destination of the pac#et. The cost is the number of hops a pac#et

must ma#e to get there. The next router is the router to which a pac#et must be delivered on its

wa to a particular destination.

8@. hat is lin# state routing

In lin# state routing" each router shares its #nowledge of its neighborhood with everother router in the internetwor#. It has

• Bnowledge about the neighborhood

• To all routers

• Information sharing when there is a change

41



8<. hat are factors to be considered when cost is applied to pac#et

• ost is applied onl b routers and not b an other stations on a networ#

• ost is applied as a pac#et leaves the router rather than as its enters.

8=. hat is mean b flooding

,looding means that a router sends its information to all of its neighbors. +ach neighbor

sends the pac#et to all of its neighbors" and so on. +ver router that receives the pac#et sends

copies to all of its neighbors. ,inall" ever router receives a cop of the same information.

8>. hat is 1in# %tate 'ac#et (1%')

hen a router floods the networ# with information about its neighborhood" it is said to

be advertising. The basis of this advertising is a %hort pac#et called a lin# state pac#et. !n 1%'

contains four fieldsO

!dvertiser Networ# ost Neighbor ----------------- ------------------- ----------------- --------------

42



UNIT ITRANS PORT LAER

?. W!" #$ )*&"#'* ' "!*$'" 3!+

The protocol in the transport laer ta#es care in the deliver of data from

one application program on one device to an application program on another

device. The act as a lin# between the upper laer protocols and the services

provided b the lower laer.

2. W!" ! " %)"#$ ' " "!*$'" 3!+

The services provided b the transport laer

+nd-to- end deliver

!ddressing &eliable

deliver ,lowcontrol $ultiplexing

. W!" #$ " %#*& ":* *":'; 3! %3#/ !*% " "!*$'"

3! %3#/+

N":'; 3! %3#/ T!*$'" 3! %3#/

The networ# laer is responsible for

the the source-to-destination

deliver of pac#et

The transport laer is responsible for

source-to-destination deliver of the

entire message.

4. W!" ! " ') !$&"$ 3!"% "' " 3#!3 %3#/ ' %!"!+

The four aspects are"

+rror control %euence

control 1oss control

Duplication control

5. W!" #$ (!*" $(*"+

!t the sending and receiving end of the transmission" T' divides long

transmissions into smaller data units and pac#ages each into a frame called a segment.

6. W!" #$ (!*" $(*"!"#'*+

hen the si0e of the data unit received from the upper laer is too long for the

networ# laer datagram or data lin# laer frame to handle" the transport protocol

43



divides it into smaller usable bloc#s. The dividing process is called segmentation.

<. W!" #$ (!*" C'*&!"*!"#'*+

The si0e of the data unit belonging to single sessions are so small that several

can fit together into a single datagram or frame" the transport protocol combines them into a

single data unit. The combining process is called concatenation.

8. W!" ! " "$ ' ()3"#3=#*+

The tpes of multiplexing are"

Upward multiplexing

Downward multiplexing

9. W!" ! " ":' '$$#3 "!*$'" $/#&$+

Two basic tpes of transport services are"

onnection service

onnectionless services

10. T "!*$'" 3! &!"$ " &'**&"#'* ":* $')& !*% %$"#*!"#'*. W!"

! " " /*"$ #*/'3/% #* " &'**&"#'*+

,or securit" the transport laer ma create a connection between the two

end ports. ! connection is a single logical path between the source and destination that

is associated with all pac#ets in a message. reating a connection involves three

steps*

•

onnection establishment• Data transfer J onnection release.

11. W!" #$ (!*" &'*$"#'*+

ongestion in a networ# occurs if user sends data into the networ# at a rate

greater than that allowed b networ# resources.

12. W " &'*$"#'* '&&)$ #* *":';+

ongestion occurs because the switches in a networ# have a limited buffer

si0e to store arrived pac#ets.

?8. W!" #$ (!*" )!3#" ' $/#&+

The ualit of service defines a set of attributes related to the performance of

the connection. ,or each connection" the user can reuest a particular attribute each service

class is associated with a set of attributes.

14. W!" ! " ":' &!"'#$ ' Q'S !""#)"$+

44



The two main categories are

User 4riented

Networ# 4riented

15. L#$" ')" " )$ 3!"% !""#)"$+

User related attributes are

%& L %ustainable ell &ate

'& L 'ea# ell &ate

$&- $inimum ell &ate

5DT L ell 5ariation Dela Tolerance

16. W!" ! " *":';$ 3!"% !""#)"$+

The networ# related attributes are"

ell loss ratio (1&)

ell transfer dela (TD)

ell dela variation

(D5) ell error ratio

(+&)

17. W!" #$ " %#*& ":* $/#& '#*" !%%$$, 3'#&!3 !%%$$ !*%

$#&!3 !%%$$+

S/#& '#*" !%%$$#* L'#&!3 !%%$$#* P$#&!3 !%%$$#*

The transport laer header

includes a tpe of address

called a service point

address or port address"

which ma#es a data deliver

from a specific process on

one computer to a specific

process on another

computer.

If a pac#et passes the

networ# boundar we need

another addressing to

differentiate the source and

destination sstems. The

networ# laer adds a

header" which indicate the

logical address of the sender

and receiver.

If the frames are to be

distributed to different

sstems on the networ#" the

data lin# laer adds the

header" which defines the

source machineMs address

and the destination

machineMs address.

45



UNIT-5

?. What is domain name system?

Domain name sstem (DN%) is a client server application that identifies each host

on the Internet with a uniue user-friendl name.

DN% is a T'PI' application service that converts user-friendl names to I' address.

7. 1ist out the various sections of domain name space

In the internet" domain name space is divided into different sections*

-FAeneric domains

-Fountr domains

-FInverse domains

8. Describe about generic domains

The generic domains define registered hosts according to their generic behavior.

+ach node in the tree defines a domain. hich is an index to the domain name space database It

allows three-character labels.

;. 1ist some of the generic domain labels with description

1abel Description

om ommercial organi0ation

+ddo +ducational Institutions

Aov Aovernment Institutions

Int International organi0ations.

$il $ilitar groups

Net Networ# support centers

4rg Nonprofit organi0ations

!rts ultural organi0ations

,irm 2usinesses or firms

Info Information service providers

No personal nomenclatures

46



9. Describe about countr domains

The countr domain section follows the same format as the generic domain but

uses two-character countr abbreviations in pave of the three character organi0ational

abbreviation at the first level.

%econd-level labels can be organi0ational or the can be more specific national designations.

@. rite about inverse domain

The inverse domain is used to map an address to a name.

<. at is %$T'

The T'I' protocol that supports electronic mail on the Internet is called simple

mail Transfer protocol (%$T').

It is a sstem for sending messages to other computer users based on e-mail address.

%$T' provides for mail exchange between users on the same or different computers and

supports.

-Fsending a single message to one or move recipients.

-Fsending messages that include text" voice" video or graphics.

-Fsending messages to users on networ#s outside the Internet.

=.hat are the components of %$T'

The %$T' client and server is divided into two components.

-FU$ !*" >UA)* the U! prepares the message creates the envelope" and puts the

message in the envelope.

-F The $T! transfers the mail across the Internet.

>. rite about addressing sstem in %$T'

The addressing sstem used b %$T' consists of two parts*

-FL'&!3 !"* The local parts define the name of a special file" called the user mailbox" where

all of the mail received for a user is stored for retrieval b the user agent.

-FD'(!#* *!(* The second part of the address is the domain name. !n organi0ation usuall

selects one or more hosts to receive and send e-mailO the are sometimes called mail exchangers.

47



?:. Define $I$+

$ultipurpose Internet mail +xtension ($I$+) is a supplementar protocol that

allows the transfer of multimedia messages.

??. hat is post office protocol

'ost office 'rotocol is a protocol used b mail server in con3unction with %$T' to

receive and hold mail for hosts.

It is a client-server protocol that is used between a user wor# station and a mail server.

?7. hat is file transfer protecting

,ile transfer protocol (,T') is the standard mechanism provided batchPI' for

coping a file from one host to another.

,T'differs from other clientMs server applications in that it establishes two connections between

the hosts.ont connections is used for data transfer. The other for control information.

?8. hat are the components available in ,T'

In ,T'" the client has three components*

-Fthe user interface.

-Fclient control process.

-Fclient data transfer process.

The server has two components*

-Fserver control process.

-Fserver data transfer process.

?;. hat is /TT'

The /pertext transfer protocol is a protocol uses mainl to access data on the orld ide eb.

The protocol transfers data in the form of plain text" hpertext" audio" and video and so on.

It is called as hpertext transfer protocol because its efficienc allows its use in a hpertextenvironment where there are rapid 3umps from one document to another.

?9. rite about the functions of /TT'

/TT' functions li#e a combination of ,T' and %$T'.

It is similar to ,T' because it transfers files and uses the services of T'.

48



/TT' is li#e %$T' because the data transferred between the client and server loo#

li#e %$T' $essages.

?@. %tate the Difference 2etween /TT' and %$T'*

/TT' %$T'

The messages are sent from the clientto the %erver and from the %erver

from the lient.

The /TT' messages are read and

interpreted b onl /TT' server and

/TT' client.

/TT' messages are delivered

immediatel.

The messages are sent from the client tothe server.

The %$T' messages can be read b

humans.

%$T' messages are stored and

forwarded.

?<. hat is U&1

The Uniform &esource 1ocator (U&1) is a standard for specifing an #ind of

information on the Internet. The U&1 defines four things*

- M"'%* The method is the protocol used to retrieve the document.

-F'$" &'()"* /ost is the computer where he information is located.

-FP'" 'ort is potional.if port is included" it should be inserted between the host and the pathand it should be separated from the host b a colon.

-FP!" 'ath is the pathname of the file where the information is located.

$ethod * /ost * 'ort 'ath

?=. at is orld ide eb

The orld ide eb is the repositor of information spread all over the

world and lin#ed together. The www has a uniue combination of flexibilit portabilit and user-

friendl features that dist anguish it from other services provided b the Internet.

?>. hat is meant b /pertext and hpermedia

/pertext and hpermedia are documents lin#ed to one another through the

49



concept of pointers./pertext documents contain onl text" whereas hpermedia documents

cand contain pictures" graphics and sound.

7:. Describe about 2rowser !rchitecture

+ach browser usuall consists of three parts*

-FC'*"'33* The controller receives input from the #eboard or the mouse.

-FC3#*" P'!($* The controller uses the client programs to access the document. The client

program can be one of the methods such as /TT'" ,T' or T+1N+T.

-FI*""$* The controller uses interpreter to displa the document on the screen. The

interpreter can be /T$1 or 3ava" depending on the tpe of document.

7?. 1ist out the categories of web pages

-F%tatic documents.

-FDnamic documents.

-F!ctive documents.

77. rite about static document

%tatic document are fixed content documents that are created are stored in a server.

(+gg)/T$1. /T$1 is a language used to create static web pages.

The webpage contains" head" which contains title of the page" bod" which includes text and tags"

which provide structure to a document" format text" insert" figures" lin# different documentstogether etc.

78. hat is dnamic document

The dnamic document is created b a server onl at a browser reuest. hen reuest arrives"

the web server runs an application program that creates the dnamic document. (+gg) AI.AI

is a standard for creation Jhandling dnamic web documents.

7;. hat are the steps to be followed b a server when it handles dnamic document

! server that handles dnamic documents follows these steps*

-F The server examines the U&1 to find if it defines a dnamic document.

-FIf the U&1 defines a dnamic document" the server executes the program.

-FThe server sends the output of the program to the client.

79. hat is active document

50



!n active document is a cop of the program retrieved b the client and run at the

client site.

(+gg) 3ava.

Hava is a combination of high-level programming language. ! run time environment

and a class librar that allows programmer to write an active document and a browser to run it.

Computer Networks 2marks

Documents