Data communication and network-frame formation at the data link layer

Document directory

• 1. Fixed Length into frame
• 2. Variable Length into frame

The data link layer needs to combine bitwise into frames so that the frames are identifiable.

In the data link layer, a message from the source end to the destination end is separated by adding the Sending address and receiver address. The destination address defines where the group is going, and the sender address helps the recipient confirm the receipt.

Frames can be divided into fixed-length and variable-length frames.

1. fixed-length frames do not need to define the boundary of frames. The length itself can be used as a separator. An example of this frame type is the atm wan, which uses a fixed-length frame called a cell. 2. Variable Length to frame variable length to frame separated from the next frame by adding a tag at the beginning and end of the frame, mainly including character-oriented and bit-oriented. 2.1 character-oriented protocol the character-oriented Protocol adds an 8-bit (1 byte) mark at the beginning and end of a frame to edit a special character combination related to the Protocol, indicates the start and end of a frame. The following describes the frame format in the character-oriented protocol. What if the data content contains the same bytes as the mark? You need to use the Escape Character (ESC character), which can be defined by yourself. It is a frame processing process that contains the ESC characters. What if the data content must contain the ESC character? Please note: it should be clear that you do not need to explain it.

The 2.2 bit-oriented protocol is similar to the character-oriented protocol, but the mark may not be 8 characters (1 character ). The ESC character is no longer used in the data. If the data contains the same bit as the tag, modify the data content to make it different from the tag. Please refer, in the figure, assume that the start and end of the frame are marked as 01111110.