framing methods

8/3/2019 Framing methods

1/15

Topic:-Framing & its methods

Presentation On Computers

Network


2/15

Data Link Layer Design Issues

Services Provided to theNetwork Layer

Framing

Error Control

Flow Control


3/15

Framing

Frames Are The Small data

Units Created By Data LinkLayer And The Process OfCreating Frames By The Data

Link Layer Is Known AsFraming.


4/15

Framing Method Implemented

By Data Link Layer Are:-

Character Count.

Starting & Ending Characters WithCharacter Stuffing.

Starting & ending Flags With Bit

Stuffing. Physical Layer Coding Violation.


5/15

Character Count.

This Method Specifies The Number

Of Characters That Are Present Inparticular Frame.

This Information Is specified Byusing a Special Field In the Header

Frame.


6/15

3 0 41 1 57 7 02 41 26 12

Character count

Character Count Method

Frame 1 Frame 2 Frame 3 Frame 4


7/15

Problems with CharacterCount

A character stream. (a) Without errors.(b) With one error.


8/15

Starting & Ending CharactersWith Character Stuffing.

In this Method Frame Starts & End With aspecial Character That Mark The Beginning

& End Of Frame. Each character Begins With the ASCII

Character Sequence DLE STX (data linkEscape Start Of Text ) And End With ASCII

Character Sequence DLE ETX (data linkescape End Of text)


9/15

Starting & Ending Characters

With Character Stuffing.

DLE ASTX B DC ETXDLE

Start Of Frame Data End Of Frame

A B DC Data From Network Layer

Starting & Ending Characters Added By Link Layer


10/15

Character Stuffing.

DLE ASTX B DC ETXDLE

Start Of Frame Data End Of Frame

A B DCDLE

DLE DLE

A B DCDLE

data onSender side

data onReciever side


11/15

Starting & ending Flags WithBit Stuffing.

In this Method , Each Begins & Ends With aSpecial Bit pattern 01111110 Called Flags.

There for Each frame starts With01111110& also Ends with 01111110.

The Main Problem arises in this MethodWhen The Flag byte 01111110 Appear asdata.

This Problem Is Handled By technique

called Bit stuffing That Is similar Tocharacter stuffing.


12/15

Starting & ending Flags WithBit Stuffing.

0 1 10 0 10 1 11 1 01 1001111110 01111110

Starting flag Bit

Ending Flag BITShifted Bit

BIT stuffing

StuffingPerformed

By DataLink layer

0 1 10 0 10 1 11 1 01 101 Data received byNetwork layer Onreciever side AfterPerformingDestuffing By datalink Layer


13/15

Physical Layer CodingViolation.

This Framing Method Is Used only Inthose network In which Encoding OnThe Physical Medium Contain some

Redundancy. Some LANs EncodeEach Bit Of Data

By using two Physical Bit

i.e. Menchester coding is Used. In this method Bit 1 Is encoded into

high-low(10) Pair And Bit 0 Is EncodedInto low-high(01)pair shown in figure.


14/15

Physical Layer CodingViolation.

0 1 10 01

Menchester Encoding


15/15

Thank you

framing methods

Documents