Table of Contents Implementations

5.8 Serial Line IP (SLIP)

The TCP/IP protocol family runs over a variety of network media: IEEE 802.3 and 802.5 LANs, X.25 lines, satellite links, and serial lines. Standards for the encapsulation of IP packets have been defined for many of these networks, but there is no standard for serial lines. SLIP is currently a de facto standard, commonly used for point-to-point serial connections running TCP/IP. It is not an Internet standard.

SLIP is just a very simple protocol designed quite a long time ago and is merely a packet framing protocol. It defines a sequence of characters that frame IP packets on a serial line, and nothing more. It does not provide any:

• Addressing: both computers on a SLIP link need to know each other's IP address for routing purposes.
• Packet type identification: thus, only one protocol can be run over a SLIP connection.
• Error detection/correction: error detection is not absolutely necessary at the SLIP level because any IP application should detect corrupted packets (IP header and UDP/TCP checksums should be sufficient). Because it takes so long to retransmit a packet that was altered, it would be efficient if SLIP could provide some sort of simple error correction mechanism of its own.
• Compression.

The SLIP protocol is expected to be replaced by the Point-to-Point Protocol (PPP). Please see Point-to-Point Protocol (PPP).

5.8.1 Implementations

SLIP is implemented in TCP/IP for OS/2, TCP/IP for DOS, and in AIX/6000.

5.8.2 Example

In Figure - SLIP Example, the OS/2 workstation, connected to the LAN using a SLIP connection, can access all the other workstations, assuming that the necessary routing information has been set up. Conversely, all the workstations and hosts connected to the LAN can access the OS/2.

Table of Contents Point-to-Point Protocol (PPP)