data link control.ppt

8/9/2019 Data link control.ppt

1/49

Data Link Control

(DLC)


2/49

Outline

11

DLC SERVICES DLC SERVICES

2 2 DATA-LINK LAYER PROTOCOLS DATA-LINK LAYER PROTOCOLS

3 3 HDLC HDLC

4 4 Point –to-point Protocol Point –to-point Protocol


3/49

DLC SERVICES DLC SERVICES

The data link control (DLC) deals with procedures for communication between two

adacent nodes no matter whether the link is

dedicated or broadcast! Data link control functions include framin" and

flow and error control!

In this section# we first discuss framin"# or how

to or"ani$e the bits that are carried b% the ph%sical

la%er!


4/49

& 'ramin" & 'ramin"

The datalink la%er needs to pack bits into frames#

so that each frame is distin"uishable from another!

ur postal s%stem practices a t%pe of framin"!

'ramin" in the datalink la%er separates amessa"e from one source to a destination b% addin"

a sender address and a destination address!

The destination address defines where the packetis to "o* the sender address helps the recipient

acknowled"e the receipt!


5/49

Figure : A frame in a character-oriented protocol


6/49

Figure : Byte stung and unstung


7/49

Figure : A frame in a bit-oriented protocol


8/49

Figure: Bit stung and unstung


9/49

+! 'low and Error Control +! 'low and Error Control

ne of the responsibilities of the datalink controlsubla%er is flow and error control at the datalink

la%er!


10/49

Figure : Flow control at the data link layer


11/49

,! Connection,! Connection

- DLC protocol can be either connectionless orconnectionoriented!


12/49

+ D-T-LI./ L-0ER 1RTCLS + D-T-LI./ L-0ER 1RTCLS

Traditionall% four protocols ha2e been defined

for the datalink la%er to deal with flow and error

control3 Simple# Stopand4ait# 5o6ack.# and

Selecti2eRepeat!

-lthou"h the first two protocols still are used at

the datalink la%er# the last two ha2e disappeared!


13/49

Figure : FSMs


14/49

& Simple 1rotocol & Simple 1rotocol

ur first protocol is a simple protocol with neither flow nor error control!

4e assume that the recei2er can immediatel%

handle an% frame it recei2es!

In other words# the recei2er can ne2er be

o2erwhelmed with incomin" frames!


15/49

Figure : Simple protocol


16/49

Figure : FSM for the simple protocol


17/49

Figure : Flow diagram


18/49


19/49

Figure : Stop-and-wait Protocol


20/49

Figure : FSM for the stop-and-wait protocol


21/49

Figure : Flow diagram for !ample


22/49

,! 1i""%backin" ,! 1i""%backin"

The two protocols we discussed in this section are

desi"ned for unidirectional communication# in whichdata is flowin" onl% in one direction althou"h the

acknowled"ment ma% tra2el in the other direction!

1rotocols ha2e been desi"ned in the past to allow data

to flow in both directions!

8owe2er# to make the communication more efficient#the data in one direction is pi""%backed with the

acknowled"ment in the other direction!


23/49

HDLCHDLC

8i"hle2el Data Link Control (8DLC) is a bit

oriented protocol for communication o2er point

topoint and multipoint links!

It implements the Stopand4ait protocol we

discussed earlier!

-lthou"h this protocol is more a theoretical

issue than practical# most of the concept defined in

this protocol is the basis for other practical

protocols such as 111# Ethernet# or wireless L-.s!


24/49

Transfer 9odesTransfer 9odes

8DLC pro2ides two common transfer modes thatcan be used in different confi"urations3 normal

response mode (.R9) and as%nchronous balanced

mode (-69)!


25/49

Figure : "ormal response mode


26/49

Figure : Asynchronous balanced mode

+ ' i


27/49

+ 'ramin" + 'ramin"

To pro2ide the fle7ibilit% necessar% to support allthe options possible in the modes and confi"urations

ust described# 8DLC defines three t%pes of frames3

information frames (Iframes)#

super2isor% frames (Sframes)# andunnumbered frames (:frames)!


28/49

Figure : #$%& frames


29/49

Figure : &ontrol 'eld format for the di(erent frametypes


30/49

Figure : !ample of connection and disconnection

Figure : !ample of piggybacking with and without


31/49

Figure : !ample of piggybacking with and withouterror


32/49

4. Point-To-Point Protocol4. Point-To-Point Protocol

ne of the most common protocols for pointto point access is the 1ointto1oint 1rotocol (111)!

Toda%# millions of Internet users who need toconnect their home computers to the ser2er of an

Internet ser2ice pro2ider use 111!

To control and mana"e the transfer of data# there

is a need for a pointtopoint protocol at the data

link la%er!

111 is b% far the most common!

S iS i


33/49

Ser2ices Ser2ices

The desi"ners of 111 ha2e included se2eral ser2icesto make it suitable for a pointtopoint protocol# but

ha2e i"nored some traditional ser2ices to make it

simple!

' i' i


34/49

'ramin" 'ramin"

111 uses a characteroriented (or b%teoriented)

frame!


35/49

Figure : PPP frame format

T iti 1hT iti 1h


36/49

Transition 1hasesTransition 1hases

- 111 connection "oes throu"h phases which canbe shown in a transition phase dia"ram (see

'i"ure)!


37/49

Figure : )ransition phases

9 lti l i9ultiple7in"


38/49

9ultiple7in" 9ultiple7in"

-lthou"h 111 is a linkla%er protocol# it uses

another set of protocols to establish the link#

authenticate the parties in2ol2ed# and carr% the

networkla%er data!

Three sets of protocols are defined to make 111

powerful3 the Link Control 1rotocol (LC1)# two

-uthentication 1rotocols (-1s)# and se2eral

.etwork Control 1rotocols (.C1s)!

Figure : Multiple!ing in PPP


39/49

Figure : Multiple!ing in PPP


40/49

Figure : %&P packet encapsulated in a frame


41/49

LCP Packets


42/49

Common options


43/49

Figure: PAP packets encapsulated in a PPP frame

Figure : AP packets encapsulated in a PPP frame


44/49

Figure : AP packets encapsulated in a PPP frame


45/49

Figure : *P&P packet encapsulated in PPP frame


46/49

Code values for IPCP Packets


47/49

Figure : *P datagram encapsulated in a PPP frame

Figure +++,.: Multilink PPP


48/49

11.48

Figure +++,.: Multilink PPP

Figure : An e!ample


49/49

Figure : An e!ample

data link control.ppt

Documents