Topic:-Framing

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Presentation On Computers Network

• Topic-Framing its methods

Group members- Anuj Panday Chander kishore
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Framing

• Frames Are The Small data Units Created By Data
  Link Layer And The Process Of Creating Frames By
  The Data Link Layer Is Known As Framing.

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Framing Method Implemented By Data Link Layer
Are-

• Character Count.
• Starting Ending Characters With Character
  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 In particular Frame.
• This Information Is specified By using a Special
  Field In the Header Frame.

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Character count
3
0
4
1
1
5
7
7
0
2
4
1
2
6
1
2
Frame 4
Frame 1
Frame 2
Frame 3
Character Count Method
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Starting Ending Characters With Character
Stuffing.

• In this Method Frame Starts End With a special
  Character That Mark The Beginning End Of Frame.
• Each character Begins With the ASCII Character
  Sequence DLE STX (data link Escape Start Of Text
  ) And End With ASCII Character Sequence DLE ETX
  (data link escape End Of text)

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Starting Ending Characters With Character
Stuffing.
A
B
D
C
Data From Network Layer
DLE
A
STX
B
D
C
ETX
DLE
Start Of Frame
Data
End Of Frame
Starting Ending Characters Added By Link Layer
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Character Stuffing.
data on Sender side
A
B
D
C
DLE
DLE
A
STX
B
D
C
ETX
DLE
DLE
DLE
Start Of Frame
Data
End Of Frame
data on Reciever side
A
B
D
C
DLE
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Starting ending Flags With Bit Stuffing.

• In this Method , Each Begins Ends With a
  Special Bit pattern 01111110 Called Flags.
• There for Each frame starts With 01111110 also
  Ends with 01111110.
• The Main Problem arises in this Method When The
  Flag byte 01111110 Appear as data.
• This Problem Is Handled By technique called Bit
  stuffing That Is similar To character stuffing.

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Starting ending Flags With Bit Stuffing.
Stuffing Performed By Data Link layer
0
1
1
0
0
1
0
1
1
1
1
0
1
1
0
01111110
01111110
Ending Flag BIT
Shifted Bit
Starting flag Bit
Data received by Network layer On reciever side
After Performing Destuffing By data link Layer
0
1
1
0
0
1
0
1
1
1
1
0
1
1
0
1
BIT stuffing
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Physical Layer Coding Violation.

• This Framing Method Is Used only In those network
  In which Encoding On The Physical Medium Contain
  some Redundancy.
• Some LANs Encode Each 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 Encoded Into low-high(01)pair
  shown in figure.

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Physical Layer Coding Violation.
0
1
1
0
0
1
Menchester Encoding
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