Some views on the TCP/IP protocol (3): Slip protocol and PPP protocol

Today I'll focus on my view on the SLIP Protocol and PPP protocol on the link layer. Today should be written on the third day, for their own insistence point a praise.

Slip agreement In fact not much, it is called Serial Line Imternet protocol, translated into Chinese is a serial Internet protocol. It is a low-speed serial line that can be used for professional lines or for dial-up lines with transmission rates between 1200bps and 19200bps. For the format of a slip frame (because it is a link layer protocol), it is important to remember that an end bit, located at the header and tail of the frame, is used to determine the start and end of the frame. This may exist if there is an end in the middle of the frame, the data frame is destroyed and the receiver reads only the contents of the previous section. Therefore, a similar to the C language of the escape character, which is used in the ESC bit, the even if receiver continuously received esc,end, it is considered that the end does not mean the ending of the frame; if the second-to-last character is ESC, then the ESC bit is added, otherwise the receiver believes that the data frame is not finished, that is, two consecutive ESC Only one of them is processed.

The SLIP protocol is not applicable because of the following reasons:

1. Serial line can only run one protocol (only slip), but not to run other protocols

2. Large data transfer increases network congestion

3. Cannot pass IP to the other end (no source IP bit in the frame)

4. Cannot be verified (no check digit in frame)

Now commonly used is the CSLIP protocol, it is the main difference with slip is to compress the data frame, that is, to transfer 40 bytes of the frame, now only need to transfer a few bytes of the frame.

In addition, PPP protocol should be more understanding, that is, point-to-Point protocol, it has gradually replaced the slip and CSLIP protocol. It uses SOF and EOT bits to represent the beginning and end of the data frame respectively, compared with the previous two protocols, its advantages are:

1. Multiple protocols can be run on a serial line

2. Also has the function of compressing the data frame

3. The data frame can be verified (there is a check digit)

Some views on the TCP/IP protocol (3): Slip protocol and PPP protocol