The un-stuffed message is then sent to the upper layers. When the receiver receives the message, it removes the stuffed 0s after each sequence of five 1s. Whenever a 0 bit is followed by five consecutive 1bits in the message, an extra 0 bit is stuffed at the end of the five 1s. In order to differentiate the message from the flag in case of same sequence, a single bit is stuffed in the message. Most protocols use the 8-bit pattern 01111110 as flag. Here, the delimiting flag sequence generally contains six or more consecutive 1s. If the ESC sequence is found in the message byte, then another ESC byte is stuffed before it. Here, a special byte called the escape character (ESC) is stuffed before every byte in the message with the same pattern as the flag byte. If the pattern of the flag byte is present in the message byte sequence, there should be a strategy so that the receiver does not consider the pattern as the end of the frame. This is also called bit - oriented framing. This is also called character-oriented framing.īit - Stuffing − A pattern of bits of arbitrary length is stuffed in the message to differentiate from the delimiter. However, if the pattern occurs in the message, then mechanisms needs to be incorporated so that this situation is avoided.īyte - Stuffing − A byte is stuffed in the message to differentiate from the delimiter. So, a pattern of bits is used as a delimiter to mark the end of one frame and the beginning of the next frame. In variable - length framing, the size of each frame to be transmitted may be different. The data frames can be of fixed length or variable length. In Data Link layer, the stream of bits from physical layer are divided into data frames.
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