Unit - II 2 Marrks

8/17/2019 Unit - II 2 Marrks

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UNIT-II

DATA LINK LAYER

Error Control Methods questions

1.What are the resonsi!ilities o" data lin# la$er% &e'i(' resonsi!ilities o" data

lin# la$er in'lude the "ollo)in*.

a+ ,rain*

!+ h$si'al addressin*

'+ ,lo) 'ontrol

d+ Error 'ontrol

e+ A''ess 'ontrol

/. Mention the t$es o" errors. There are / t$es o" errors

a+ &in*le-!it error.

!+ 0urst-!it error.

. De(ne the "ollo)in* ters.

a+ &in*le !it error2 The ter sin*le !it error eans that onl$ one !it

o" a *i3en data unit 4su'h as !$te 'hara'ter5data unit or a'#et+ is

'han*ed "ro 1 to 6 or "ro 6 to 1.

!+ 0urst error2 Means that / or ore !its in the data unit ha3e

'han*ed "ro 1 to 6 "ro 6 to 1.

7. What is redundan'$%

It is the error dete'tin* e'hanis8 )hi'h eans a shorter *rou o" !its or e9tra

!its a$ !e aended at the destination o" ea'h unit.

:. List out the a3aila!le dete'tion ethods.

There are 7 t$es o" redundan'$ 'he'#s are used in data 'ouni'ation.

a+ ;erti'al redundan'$ 'he'#s 4;RC+.

!+ Lon*itudinal redundan'$ 'he'#s 4LRC+.

'+ C$'li' redundan'$ 'he'#s 4CRC+.

d+ Che'#su.


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sequen'e o" redundant !its8 'alled the CRC reainder is aended to the end o"

data unit.

. Write short notes on CRC *enerator.

A CRC *enerator uses a odulo-/ di3ision.

a+ In the (rst ste8 the 7 !it di3isor is su!tra'ted "ro the (rst7 !it o" the di3idend.

!+ Ea'h !it o" the di3isor is su!tra'ted "ro the 'orresondin*

!it o" the di3idend )ithout distur!in* the ne9t hi*her !it.

16. Write short notes on CRC 'he'#er.

A CRC 'he'#er "un'tions e9a'tl$ li#e a *enerator. A"ter re'ei3in*

the data aended )ith the CRC it does the sae odulo-/ di3ision. I" the

reainder is all 6=s the CRC is droed and the data a''eted. Bther)ise8 the

re'ei3ed strea o" !its is dis'arded and the dates are resent.

11. i3e the essential roerties "or ol$noial.A ol$noial should !e sele'ted to ha3e at least the "ollo)in* roerties.

a+ It should not !e

!+ It should !e di3isi!le !$491+.

1/. De(ne 'he'#su.

The error dete'tion ethod used !$ the hi*her la$er roto'ol is 'alled 'he'#su.

Che'#su is !ased on the 'on'et o" redundan'$.

1. Mention the t$es o" error 'orre'tin* ethods. There are / error-'orre'tin*

ethods.

a+ &in*le !it error 'orre'tion

!+ 0urst error 'orre'tion.

17. What is the urose o" hain* 'ode%

A hain* 'ode 'an !e desi*ned to 'orre't !urst errors o" 'ertain len*ths.

&o the sile strate*$ used !$ the hain* 'ode to 'orre't sin*le !it errors

ust

!e redesi*ned to !e ali'a!le "or ultile !it 'orre'tion.

1:.

1. What are the "un'tions o" LLC%

The IEEE roe't ?6/ odel ta#es the stru'ture o" an @DLC "rae and di3ides it

into / sets o" "un'tions. Bne set 'ontains the end user ortion o" the @DLC "rae

- the

lo*i'al address8 'ontrol in"oration8 and data. These "un'tions are handled !$

the IEEE

?6/.


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/. What are the "un'tions o" MAC%

MAC su! la$er resol3es the 'ontention "or the shared edia. It 'ontains

s$n'hroniFation8 Ga*8 Go) and error 'ontrol se'i('ations ne'essar$ to o3e

in"oration "ro one la'e to another8 as )ell as the h$si'al address o" the

ne9t station

to re'ei3e and route a a'#et.

.. De(ne Go) 'ontrol.

,lo) 'ontrol re"ers to a set o" ro'edures used to restri't the aount o"

data. The sender 'an send !e"ore )aitin* "or a'#no)led*ent.

7. What is a !uHer%

Ea'h re'ei3in* de3i'e has a !lo'# o" eor$ 'alled a !uHer8 reser3ed "or

storin* in'oin* data until the$ are ro'essed.

:. Mention the 'ate*ories o" Go) 'ontrol. There are / ethods ha3e !een de3eloed to 'ontrol Go) o" data a'ross

'ouni'ation lin#s.

a+ &to and )ait- send one "ro at a tie.

!+ &lidin* )indo)- send se3eral "raes at a tie.


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Advantages of stop-and-wait ARQ are: a. Sip!e to ip!eent ". #rae nu"ering is odu!o-$% i.e.

on!y 1 "it is required.

&he ain disadvantage of stop-and-wait ARQ is that when the propagation de!ay is !ong% it is

e'tree!y inefficient.

1/. What is i**$ !a'#in*%

i**$ !a'#in* eans 'o!inin* data to sent and a'#no)led*eent o" the

"rae re'ei3ed in one sin*le "rae.

i**$ !a'#in* 'an sa3e !and)idth !e'ause the o3erhead "ro a data

"rae and an ACK "rae 'an !e 'o!ined into ust one "rae

1(. )onsider the use of 1* +-"it si,e fraes on a 1* M"ps sate!!ite channe! with

$* s de!ay. hat is the !ink uti!i,ation for stop-and-wait ARQ technique

assuing / 0 1*-(?

Ans: Lin# utiliFation 41-+ 5 41/a+ Where a 4roa*ation Tie+ 5

4Transission Tie+ roa*ation tie />6 se' Transission tie 4"rae

len*th+ 5 4data rate+ 416 K-!it+ 5 416 M!s+ 1 se' @en'e8 a />651 />6

Lin# utiliFation 6.541//>6+ 6.661? 6.1?

17. What is the 'hannel utiliFation "or the *o-!a'#-N roto'ol )ith )indo) siFe

o" > "or the ro!le %

Ans2 Channel utiliFation "or *o-!a'#-N N41 O + 5 41 /a+41-N+

ro!a!ilit$ o" sin*le "rae error 16- Channel utiliFation 6.61/?: 1./?:

17. List the t$es o" stations is @DLC. @DLC diHerentiates !et)een t$es o"

stations.

a+ riar$

!+ &e'ondar$

:+ Co!ined

1


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19. hat is the difference "etween a passive and an active hu"?

An active hu" contains a repeater that regenerates the received "it patterns "efore

sending the out. A passive hu" provides a sip!e physica! connection "etween the

attached devices.

/6. Mention the 3arious ar'hite'ture in a LAN.

LAN is doinated !$ 7 ar'hite'tures.

a+ Ethernet

!+ To#en !us

'+ To#en rin*

d+ ,i!er distri!uted data inter"a'e 4,DDI+

/1. De(ne a standard ?6/.

IEEE ?6/. suorts a LAN standard ori*inall$ de3eloed !$ Pero9 and later

e9tended !$ a oint 3enture !et)een di*ital equient 'ororations. Intel

Cororation

and Pero9. This )as 'alled QEthernet=.

//. List the ost 'oand #inds o" 0ase !and ?6/. LAN.

a+ 16 0ase :

!+ 16 0ase /

'+ 16 0ase T

d+ 1 0ase :

e+ 166 0ase T

/. Mention the diHerent #inds o" Ethernet net)or#s.a+ &)it'hed Ethernet

!+ ,ast Ethernet

'+ i*a!it Ethernet

/. Write short notes on ,DDI.

,i!er distri!uted data inter"a'e is a lo'al areas. Net)or# roto'ol standardiFed !$

AN&I and ITU->. It suorts data rates o" 166 M!s and ro3ides a hi*h-seed

alternati3e to Ethernet and to#en rin* a''ess ethod used here is to#en assin*.

$.;ive the re!ationship "etween propagation speed and propagation tie?

/ropagation tie 0 distance 7 propagation speed

&he tie required for a signa! or a "it to trave! fro one point to another is ca!!ed /ropagation tie.

/ropagation speed is the distance% a signa! or a "it trave! through a ediu in one second.

E9ale 1 1. eterine the iniu transission rate required "etween nodes = and ) so


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that the "uffers at node = are not f!ooded% "ased on the fo!!owing2&he data rate "etween A and = is 1** k"ps.

&he propagation de!ay is 8 sec7k for "oth !ines .&here are fu!!dup!e'% errorfree !ines

"etween the nodes. A!! data fraes are 1*** "its !ong@ A)+ fraes are separate fraes of

neg!igi"!e !ength. =etween A and =% a s!idingwindow protoco! is used% with a window si,e of ( 5three6.

=etween = and )% stop and wait is used.

*** k 1*** k . protoco!. #ind the iniu frae !ength for a 1M"ps "it rate and

a'iu network span of 1* ki!oeters with no repeaters. Assue a ediu propagation

de!ay of .8 nanoseconds per eter. a reasona"!e protoco! for a network of thisspan and "itrate .


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So!ution

Miniu frae si,e for )SMA7)> is $ B &pr.

/ropogation >e!ay :

&pr 0 5.8 B 1*-96B51* B 1*(6 0 .8 B 1*-8 sec.

&hus% 51.* B 1*26 B 59.* B 1*-86 0 11.$8 "ytes.

)SMA7)> wou!d "e a very reasona"!e protoco! for a network of this span and speed sincethe iniu frae si,e is not G e'cessiveG 5e.g.% !arger than 2 "ytes6

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Unit - II 2 Marrks