What is framing in computer network?
- A Framing is techniques which is used by data link layer of osi model.
- data link layer takes a packets from network layer then add source address and destination address on packets which is received from network layer.
- now data link layer convert theme into frames.
- frames size may be a large or small BUT NOTE that small frame is very effective because if any kind of error occurred then small data affect.
Frame size
frame can be fixed and it can be different in size.
Fixed Size Frameing:
in fixed size frameing there are no any boundation of defining the size of frames the size itself can be used as a delimiter. ETC. ATM WAN.
variable-size framing:
we need a way to define the end of one frame and the beginning of the next.
there is TWO METHOD for variable size framing.
Character-Oriented Framing :
- this is also called byte-oriented framing.
- in this data to be carried are 8 bit characters.
- in this header carries the source and destination addresses.
- trailer, carries error detection redundant bits, which is also multiples of 8 bits.
- for separate one frame from the another frames added FLAG at the beginning and the end of a frame.
- this type of framing was popular when only text was exchange by the data link layers.
- if want to send graphs, audio, and video and other types of information this problem is fix by a byte stuffing strategy.
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| A frame in a character-oriented protocol Flag Flag Data from upper lay |
Bit oriented apporach
- in this framing, the data section of a frame is a sequence of bits to be interpreted by the upper layer as text, graphic, audio, video, and soon.
- for separate one frame from the other, most protocols use a special 8 bit pattern flag. which is define the begining and the end of frame.
- but this flag can create same type of problem which kind we saw in the character-oriented protocols.
- if that flag pattern appears in data, so we need to at any cost inform the receiver that this not the end of the frame.
- this is done by stuffing 1 single bit rather than 1 byte to prevent the pattern from looking like a flag. this is bit stuffing.
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| A frame in a bit-oriented protocol |
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