ku bscit 63 - advance computer networks

8/13/2019 KU BSCIT 63 - Advance computer networks

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BSIT 63 (Advanced Computer Networks)

CHAPTER! (App"#cat#on $a%er)

!& $#st t'e unct#ons o app"#cat#on "a%er&

Answer-

The functions of the application layer are:

It is responsible for facilitating interaction between many applications like WWW, EMAIL, T!,

an" #$%, an" ser&ers like mail ser&er an" T! ser&er'

It interfaces "irectly to an" performs common application ser&ices for the application processes( it

also issues re)uests to the presentation layer'

*& +'at #s ,NS

Answer-

#$% is a name resolution ser&ice that resol&es host names to the I! a""resses' #$% has a hierarchical an"

"istribute" "atabase that contains mappings of host names with the correspon"ing I! a""resses'

3& E-p"a#n t'e work#n. o ,NS w#t' an e-amp"e&

Answer-

#$% is a name resolution ser&ice that resol&es host names to I! a""resses' A #$% ser&er resol&es host

names to I! a""resses for #$% )ueries sent by the #$% clients' These )ueries can be in the form of a name

resolution )uery or a resource recor"' The resol&er sen"s a *ser #atagram !rotocol +*#! packet to the

local #$% ser&er' The #$% ser&er searches its table an" returns the I! a""ress, which matches the "omainname' #$% has a hierarchical an" "istribute" "atabase that contains mappings of host names with the

correspon"ing I! a""resses'

esource recor"s are store" in a specific portion of the #$% "atabase calle" the #$% .one' A #$% .one

contains resource recor"s along with the owner names'

or e/ample, an application program calls a proce"ure with its "omain name as parameter' The proce"ure

sen"s an *#! packet to the local #$% ser&er' The #$% ser&er searches its table an" returns the I! a""ress

which matches the #omain name' The program can now establish a T0! connection or sen" *#! packets'

/& +'at #s #terat#ve reso"ut#on 0#ve e-amp"e&

Answer-

Iterati&e resolution refers to the name resolution techni)ue in which a ser&er sen"s back the information to a

client or sen"s the name of the ser&er that has the information' The client then iterates by sen"ing a re)uest

to this referre" ser&er' This ser&er may return the information itself or sen" the name of another ser&er' This

process continues till the time the client recei&es the re)uire" information'

1& +'at are t'e unct#ons o t'e user a.ent #n t'e Ema#" arc'#tecture

Answer-

In the e-mail architecture, the user agent helps users to interact with the e-mail systems' The functions of the

user agent in e-mail architecture are:

Compos#t#on: It refers to writing the mail' 1ere users type the message that they want to con&ey'The users ha&e to mention the recipient2s e-mail a""ress'

Rece#v#n.: It refers to retrie&ing the e-mails from the !3!4 ser&er'

Rep"%#n. to messa.es: It refers to replying to a recei&e" e-mail' To reply to the e-mail, the user has

to click reply, type the message, an" sen" it back'
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Support man#pu"at#on o ma#" 2o-: It refers to customi.ation of the mail bo/' 1ere users can create

fol"ers an" manage the mail accor"ing to the sen"er'

6& ,#scuss t'e send#n. and rece#v#n. process #n Ema#"

Answer-

The prere)uisites for sen"ing an" recei&ing an e-mail are:

5oth the sen"er an" recipient shoul" ha&e an e-mail account'

The sen"er must pro&i"e the "estination a""ress an" write a message'

The following is the se)uence of the e-mail sen"ing process:

6' When the sen"er clicks send, the machine establishes a connection with the %MT! ser&er by using

port 78'

7' An %MT! configure" e-mail "aemon9process uses this port' This "aemon9process accepts incoming

connections an" sen"s the mails to its appropriate "omain' or e/ample if you sen" the mail from

yahoo'com to hotmail'com, the mail goes to the yahoo %MT! ser&er, an" then the %MT! ser&er

sen"s it to the !3!4 ser&er of hotmail'com'

4' If a message cannot be "eli&ere", an error report containing the first part of the un"eli&erablemessage is returne" to the sen"er'

In the implementations of !3!4, the ser&er maintains a collection of te/t files, one for each e-mail

account' When a message arri&es, the !3!4 ser&er simply appen"s it to the bottom of the recipients file'

The following is the se)uence of the e-mail recei&ing process:-

6' The e-mail client connects to the !3!4 ser&er by using port 66;' The !3!4 ser&er re)uires an

account name an" a passwor"'

7' After pro&i"ing a &ali" username an" passwor", the user gets &erifie" by the !3!4 ser&er'4' If the username an" passwor" are &ali", the !3!4 ser&er opens your te/t file an" allows you to

access it'

& +r#te a 2r#e note on S4TP

Answer-

%MT! is a protocol that transfers mail reliably an" efficiently' %MT! is in"epen"ent of a particular

transmission subsystem an" nee"s only a reliable or"ere" "ata stream channel' An important feature of

%MT! is its capability to relay mail across transport ser&ice en&ironments'

5& ,#scuss t'e work#n. o PP3 #n an Ema#" s%stem +'at are #ts "#m#tat#onsAnswer-

When users check their e-mail, the e-mail client connects to the !3!4 ser&er by using port 66;' The !3!4

ser&er re)uires an account name an" a passwor"'

The !3!4 ser&er issues a series of comman"s to bring copies of user e-mail messages to user2s local

machine'


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be "elete"' #uring the authori.ation state, at times, when the ser&er is set for three passwor"s trials, if you

gi&e the wrong passwor" thrice, your mail bo/ will get locke"'

!3!4 ser&ers ha&e certain limitations such as :-

There is no fol"er structure for sorting e-mail messages that are sa&e" on the !3!4 ser&er' The

ser&er has only one fol"er for incoming mails, which is the inbo/'

$o rules can be set at the !3!4 ser&er' All rules are set at the client en" only' If a user2s machine

crashes, e-mail messages can only be reco&ere" if a copy of them is left on the ser&er' To check e-mail, users ha&e to "ownloa" them first an" only then they can &iew their mails on the

e-mail client software' *ser cannot see mails first an" then "ownloa" the re)uire" mails' If there are

spam e-mail messages in the inbo/ that can be "angerous for the computer, these will also get

"ownloa"e" an" the user has to "elete them'

7& +'at #s www

Answer-

WWW is a hyperte/t-base" system that pro&i"es a uniform an" a user-frien"ly interface for accessing the

resources on the Internet' It is an information space in which the items of interest, referre" to as resources,are i"entifie" by global i"entifiers calle" *niform esource I"entifiers +*I'

!8& ,#scuss t'e arc'#tecture o +++

Answer-

The architecture of WWW is two tiere"' It consists of the client an" the ser&er' The client +web browser

re)uests for a web page' This page is retrie&e" from the ser&er' The architecture "epen"s on three key

stan"ar"s: 1TML for enco"ing "ocument content, *niform esource Locator +*L for naming remote

information ob=ects in a global namespace, an" 1TT! for staging the transfer' The following figure shows

the two-tiere" architecture of WWW

e)uest0LIE$T ------------------ >%E?E @--------------

esponse

Two-Tier Architecture of WWW

If the web pages are interacting with the "atabase, then the architecture becomes three-tiere", as shown in

the following figure'

e)uest

C$IENT ---------------> SER9ER -----------------> ,ATA BASE

@--------------- @----------------

esponse

three-Tier Architecture of WWW

!!& E-p"a#n t'e c"#ent s#de and server s#de events w'en a user c"#ck on a :R$

Answer-

The client si"e e&ents when a user clicks on a *L are as follows:

6' The browser locates the *L'

7' The browser asks #$% for the I! a""ress'

4' #$% replies with the I! a""ress'

' The browser makes the Transmission 0ontrol !rotocol +T0! connection to !ort B; on the machine


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with the abo&e I! a""ress'

8' The browser sen"s a re)uest for the specific file'

C' The ser&er sen"s the re)uire" file'

D' The T0! connection is close"'

B' The browser "isplays all te/t information'

' The browser "isplays all images'

When a user clicks on a *L, the ser&er si"e e&ents are as follows:

6' %er&er accepts a T0! connection from a client'

7' %er&er searches the file associate" with the web page'

4' ile from the "isk is retrie&e"'

' The web page is returne" to the client'

8' T0! connection is release"'

!*& E-p"a#n w'at #s a server arm 0#ve an e-amp"e&

Answer-

A ser&er farm is a group of networke" ser&ers that are house" in one location' A ser&er farm streamlinesinternal processes by "istributing the workloa" between the in"i&i"ual components of the farm an"

e/pe"ites computing processes by harnessing the power of multiple ser&ers' The farms rely on loa"

balancing software that accomplishes the following tasks:

Tracking "eman" for processing power from "ifferent machines'

!rioriti.ing the tasks'

%che"uling an" resche"uling tasks "epen"ing upon priority an" "eman" that users put on the

network'

When one ser&er in the farm fails, another can step in as a backup'

0ombining ser&ers an" processing power into a single entity has been relati&ely common for many

years in research an" aca"emic institutions' To"ay, more an" more companies are utili.ing ser&er

farms as a way of han"ling the enormous amount of computeri.ation of tasks an" ser&ices that they

re)uire'

%er&er farm, or web farm, refers to either a web site that runs on more than one ser&er or an Internet

%er&ice !ro&i"er +I%! that pro&i"es web hosting ser&ices by using multiple ser&ers'

%er&er compute farms are making their way into large manufacturing en&ironments for electronic

"esign automation, an" to accelerate processes an" complete tasks' A ser&er farm accomplishes this by harnessing computing power from multiple machines an"

combining that power' E/ample of a ser&er farm inclu"es


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the same physical network or if the packet "eli&ery is between the last router an" the "estination

host A$# In in"irect routing, the packet goes from router to router until it reaches the router

connecte" to the same physical network as its final "estination'

7' In "irect routing, the a""ress mapping is between the I! a""ress of the final "estination an" the

physical a""ress of the final "estination A$# In an in"irect routing, the a""ress mapping is between

the I! a""ress of the ne/t router an" the physical a""ress of the ne/t router'

4' A packet "eli&ery always in&ol&es one "irect routing A$# A packet "eli&ery may or may not

in&ol&e in"irect routing'

*& ,#scuss d#erent approac'es used to make t'e rout#n. ta2"e more e#c#ent

Answer-

There are many approaches to make a routing table efficient such as:

Ne-t 'op rout#n.: In this techni)ue, the routing table hol"s only the a""ress of the ne/t hop instea"

of hol"ing information about the complete route' outing tables are thereby consistent with each

other'

Network spec##c rout#n.: In this techni)ue, routing tables are ma"e smaller so that the search

process becomes simpler' Instea" of ha&ing an entry for e&ery host connecte" to the same physical

network, we ha&e only one entry to "efine the a""ress of the network itself'

3& Name RIP;s var#ous sta2#"#t% eatures&

Answer-

The stability features of I! are:

Hopcount "#m#t: This feature limits the number of hops allowe" in a path from source to

"estination' The ma/imum number of hops in a path is 68' If for some reasons the router recei&es a

routing up"ate that contains a new or change" entry, an" if increasing the metric &alue by 6 causes

the metric to be infinity +that is, 6C, the network "estination is consi"ere" unreachable' Ho"ddown t#mers: This feature is useful in pre&enting routing information from floo"ing the

network when network links are unstable'

Sp"#t 'or#


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*& +'at #s an aud#o +'at #s a v#deo

Answer-

Aud#o: It "eals with only &oice' or e/ample, a song or a lecture on any uni&ersity site'

9#deo: It has got both &oice an" li&e image, such as a mo&ie, a song, or a clipping of a lecture'

3& +'at #s stream#n.

Answer-

%treaming is the process of recei&ing store" au"io9&i"eo application from a ser&er where they are place"' Aclient begins to play either an au"io or a &i"eo once the me"ia player of the client2s !0 begins recei&ing the

au"io or &i"eo file from the ser&er' #uring the process, the client will be playing au"io9&i"eo from one

location in the file while it is recei&ing the remaining parts of the file from the ser&er' In other wor"s,

streaming a&oi"s long "ownloa" times an" the nee" to store the entire file on the users computer'

/& $#st t'e draw2acks o t'e current #nternet to dr#ve t'e mu"t#med#a data

Answer-

The Internet has some "rawbacks with regar" to multime"ia "ata' or e/ample, the me"ia player "oes not

communicate with the streaming ser&er "irectly' This "elay, before play-out begins, is typically

unacceptable for au"io9&i"eo clips of mo"erate length' or this reason, au"io9&i"eo streaming

implementations typically ha&e the ser&er sen" the au"io9&i"eo file "irectly to the me"ia player process' Inother wor"s, a "irect socket connection is ma"e betwen the ser&er process an" the me"ia player process'

1& How t'e e-#st#n. #nternet can 2e made to port mu"t#med#a data

Answer-

or making the e/isting Internet portable to multime"ia "ata, the following mo"ifications nee" to be "one:

6' A protocol is re)uire" that reser&es ban"wi"th on behalf of the streaming ser&er applications'

7' The sche"uling policies in the router )ueues shoul" be mo"ifie" so that the ban"wi"th reser&ations

can be "one' With the new sche"uling policies, not all packets get e)ual treatment, instea" the

packets from the multime"ia pro&i"er sites that reser&e an" pay more, get more ban"wi"th'

4' The applications must gi&e the network a "escription of the traffic that they inten" to sen" to the

network'

' The ban"wi"th an" switching capacity shoul" be enhance" to pro&i"e satisfactory "elay an" packet

loss performance within the network'

8' 0aches must be installe" in the networks' 0aches bring store" content +web pages as well as store"

au"io an" &i"eo closer to users, thereby re"ucing the traffic in the higher-tier I%!s'

C' 0ontent pro&i"ers that pay for a 0ontent #istribution $etworks +0#$ ser&ice shoul" "eli&er

content faster an" more effecti&ely'

D' Multicast o&erlay networks can be "eploye"' A multicast o&erlay network consists of ser&ers

scattere" throughout the I%! network an" potentially throughout the entire Internet' %er&ers an" the

logical links between ser&ers collecti&ely form an o&erlay network, which multicasts traffic from asource to millions of users'

6& E-p"a#n t'e +'% Aud#o and 9#deo need to 2e compressed

Answer-

0ompression is re)uire" to re"uce the si.e of au"io an" &i"eo so that they can be easily transmitte" o&er the

Internet' or e/ample, a single image consisting of 6;7 pi/el 6;7 pi/els, with each pi/el enco"e" into

7 bits re)uires 4 M5 of storage without compression' There are eight bits, three each for the colors re",

green, an" blue' It woul" take appro/imately se&en minutes to sen" the image o&er a C kbps link' If the

image is compresse" at a mo"est 6;:6 compression ratio, the storage re)uirement is re"uce" to 4;; Jbytes

an" the transmission time also "rops by a factor of 6;'

& E-p"a#n aud#o stream#n. process

Answer-

Au"io streaming is the transfer of au"io-enco"e" packets that are "eco"e" an" sent to the client2s soun"car"


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upon reception' The host si"e is responsible for enco"ing an" packeti.ing the au"io stream' The client si"e

is responsible for "eco"ing the packets an" sen"ing the "eco"e" au"io to the soun" car"' There are "elays

inherent in the o&erall system' These "elays are contribute" by the enco"e9"eco"e "elay, transfer "elay,

buffer "elay, mo"em "elay, soun" car" "elay, an" other "elays' As long as the "elays are kept constant, then

the au"io will be "eli&ere" uninterrupte"'

5& +'at #s a stream#n. server

Answer-

%treaming ser&ers are meant for the au"io9&i"eo streaming applications' *pon client re)uest, a ser&er "irectsan au"io or a &i"eo file to the client by sen"ing the file into a socket' 5oth the T0! an" *#! socket

connections are use"' 5efore sen"ing the au"io9&i"eo file to a network, the file is segmente", an" the

segments are typically encapsulate" with special hea"ers appropriate for au"io an" &i"eo traffic' %treaming

ser&ers sen" "igital &i"eo for news, entertainment, or e"ucational content o&er the Internet by using

T!9T%!' A multime"ia file gets uploa"e" on the ser&er an" streaming ser&ers enco"es content in the

latest me"ia formats inclu"ing M!E


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6& Compare 58*&!!a> 58*&!!2> 58*&!!. and 2"ue toot'&

Answer-

=eature 58*&!!a 58*&!!2 58*&!!. B"uetoot'

,ata rate-- 1/*42ps- !!42ps 1/42ps-- *!2ps--16 2ps

=reDuenc%--10'


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transmission A$# In this case, shiel"ing is not so simple' Therefore, ra"io transmission can interfere

with other sen"ers an" electrical "e&ices can "estroy "ata transmission &ia ra"io'

8' $o licenses are re)uire" for infrare" technology 5*T a"io transmission is only permitte" in certain

fre)uency ban"s' ?ery limite" ranges of license-free ban"s are a&ailable worl"wi"e, an" those

a&ailable are typically not the same in all countries'

C' Infrare" technology is normally use" for "e&ices like !#As, laptops, notebooks, mobile phones, an"

so on A$# a"io transmission is use" for wi"e area networks +WA$ such as microwa&e links an"

mobile cellular phones'

D' In Infrare" 3nly IEEE B;7'66 makes use of this type of transmission A$# In a"io transmissionWLA$ technologies such as IEEE B;7'66, 1I!ELA$, an" 5luetooth make use of this type of

transmission'

7& ,#scuss t'e arc'#tecture o +$AN

Answer-

WLA$ architecture consists of three components:

6' Wireless en" stations

7' Access points

4' 5asic ser&ice sets +5%%

The wireless en" station can be any "e&ice that can communicate using the B;7'66 stan"ar"' These "e&ices

inclu"e laptops, workstations, an" !#As, as well as printers an" scanners'

The access point +A! is a "e&ice' It acts as a network platform for connections between WLA$s or to a

wire" LA$ an" as a relay between stations attache" to the same A!'

5%% is the logical component of wireless architecture' In general, it is a set of wireless stations controlle" by

a single management function an" has two configuration options that is, Infrastructure 5%% +I5%% an"

E/ten"e" %er&ice %et +E%%'

In an I5%%, the stations communicate "irectly to one another without the nee" for an access point' An E%%

is a set of infrastructure 5%%s that appear as a single 5%%' This is important for connection re"un"ancy but

has some security issues that nee" to be a""resse"'

!8& Br#e"% e-p"a#n t'e +$AN protoco" arc'#tecture

Answer-

In a typical WLA$ setup, the IEEE B;7'66 stan"ar" WLA$ +Access !oint gets connecte" to an IEEE

B;7'4 stan"ar" Ethernet +%witch91*5 &ia a bri"ge' The higher layers +application, T0!, I! look the same

for the wireless no"e as for the wire" no"e' The IEEE B;7'66 stan"ar" only co&ers the physical layer +!1G

an" me"ium access layer +MA0 like the other B;7'/ LA$s "o' The physical layer is sub "i&i"e" into the!hysical Layer 0on&ergence !rotocol +!L0! an" the !hysical Me"ium #epen"ent %ub Layer' The basic

tasks of the MA0 layer comprise me"ium access, fragmentation of user "ata, an" encryption' The !L0!

sublayer pro&i"es a carrier sense signal calle" 0lear 0hannel Assessment +00A, an" pro&i"es a common

!1G interface for the MA0, which is in"epen"ent of the transmission technology'

!!& +r#te a note on ,SSS

Answer-

#irect %e)uence %prea" %pectrum +#%%% is the alternati&e sprea" spectrum metho", in which the signal is

sprea" o&er a wi"e range of fre)uencies using a chipping co"e' In the case of IEEE B;7'66 #%%%, sprea"ing

is achie&e" by using the 66-chip se)uence +6,-6,6,6,-6,6,6,6,-6,-6,-6, which is also calle" the

5arker co"e'

!*& ,#scuss 4AC "a%er o +$AN&

Answer-

MA0 layer controls me"ium access, an" also offers support for roaming, authentication, an" power


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conser&ation' The ser&ices offere" by MA0 are man"atory asynchronous "ata ser&ice an" an optional time-

boun"e" ser&ice'

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

CHAPTER1 (Cr%to.rap'% and Network Secur#t%)

!& +'at #s cr%pto.rap'%

Answer-0ryptography is the science of using mathematics to encrypt an" "ecrypt "ata' 0ryptography enables us to

store or transmit sensiti&e information across insecure networks +like the Internet so that unauthori.e" users

e/cept the inten"e" recipient cannot rea" it'

*& E-p"a#n cr%pto.rap'#c a".or#t'ms&

Answer- A cryptographic algorithm, also referre" to as cipher, is a mathematical function use" in the

encryption an" "ecryption process' A cryptographic algorithm works in combination with a key' The key

may be a wor", number, or phrase use" to encrypt the plain te/t, also calle" a message' The plain te/t

encrypts to cipher te/t with "ifferent keys' The security of encrypte" "ata is entirely "epen"ent on the

strength of the cryptographic algorithm an" the secrecy of the key'

3& E-p"a#n d#erent t%pes o attacks&

Answer-

Attacks are of two types' The types are:

!&Pass#ve attack: In this attack, the goal of the unauthori.e" user is to obtain information that is being

transmitte"' !assi&e attacks ha&e two subtypes, release of message contents an" traffic analysis'

The release of message contents inclu"es con&ersation o&er the phone or through email or

transferring a file from one place to another, which might contain sensiti&e information'

The traffic analysis is more "elicate' %uppose that we ha" a way of masking the contents of

messages or other information traffic so that unauthori.e" users coul" not e/tract the informationfrom the message' The common techni)ue for masking contents is encryption' If we ha" encryption

protection in place, an opponent might still be able to obser&e the pattern of these messages' The

opponent coul" "etermine the location an" i"entity of communication hosts, an" coul" obser&e the

fre)uency an" length of messages being e/change"' This information might be useful in guessing the

nature of the communication that was taking place'

!assi&e attacks are &ery "ifficult to "etect because they "o not in&ol&e any alteration of the "ata' The

emphasis in "ealing with passi&e attacks is to pre&ent the attack rather than to "etect it'

*&Act#ve attacks: These attacks in&ol&e some mo"ification of the "ata stream or the creation of a false

stream' These attacks are "i&i"e" into four categories such as mas)uera"e, replay, mo"ification ofmessages, an" "enial of ser&ice +#o%'

4asDuerade: It takes place when an entity preten"s to be "ifferent than the other entity' This

inclu"es one of the other forms of an acti&e attack, which is mo"ification of messages or "enial of

ser&ice'

Rep"a%: It in&ol&es the passi&e capture of a "ata unit an" its subse)uent retransmission to pro"uce an

unauthori.e" effect'

4od##cat#on o messa.es: It implies that some portion of the message is altere" or messages are

"elaye" or reor"ere" to pro"uce an unauthori.e" effect'

,oS: It pre&ents or inhibits the normal use or the management of communications facilities' Thistype of attack has a specific target' or e/ample, an entity may suppress all messages "irecte" to a

particular "estination' Another form of #o% is the "isruption of an entire network, either by "isabling

the network or by o&erloa"ing it with messages to "egra"e the performance of the network'


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ku bscit 63 - advance computer networks

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