Frames in Coumper Networking

• 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.

                  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.

            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.

           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)

        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.

                 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.