Framing methods
Transcript of Framing methods
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Topic:-Framing & its methods
Presentation On Computers
Network
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Data Link Layer Design Issues
Services Provided to theNetwork Layer
Framing
Error Control
Flow Control
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Framing
Frames Are The Small data
Units Created By Data LinkLayer And The Process OfCreating Frames By The Data
Link Layer Is Known AsFraming.
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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.
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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.
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3 0 41 1 57 7 02 41 26 12
Character count
Character Count Method
Frame 1 Frame 2 Frame 3 Frame 4
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Problems with CharacterCount
A character stream. (a) Without errors.(b) With one error.
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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)
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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
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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
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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.
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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
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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.
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Physical Layer CodingViolation.
0 1 10 01
Menchester Encoding
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Thank you