For some time, SLIP was a de facto standard in the Unix community as a means for establishing a point-to-point connection between two computers. It was finally documented in RFC 1055, "A Nonstandard for Transmission of IP Datagrams over Serial Lines: SLIP," in 1988. Yes, you read that righta nonstandard. Although there are standards for IP, there is no standard for SLIP that concisely defines the protocol. SLIP is a simplified protocol that encapsulates and sends data across a connection. SLIP has been implemented in many ways, using different packet sizes, but the basic protocol consists of using two special characters:
Note ASCII ( American Standard Code for Information Interchange) was the standard method for representing alphanumeric characters in non-IBM systems, from early VT-style terminals to more modern enhanced terminal emulators. IBM used its own character coding scheme, EBCDIC (Extended Binary-Coded Decimal Interchange Code), for its mainframes and some other systems. More recently, UNICODE has been adopted by systems such as Windows NT/2000/XP/2003, and many other operating systems, including Unix and Linux. UNICODE can be used to represent not just the basic alphanumeric character set used for English, but also more than 34,168 characters, covering about 24 different languages. The coding scheme used by UNICODE is extensible, so in addition to historical and many modern language scripts, UNICODE can be adapted to include lesser-used languages as time goes by. SLIP is a simple protocol. Just start sending the characters of a packet and send the END character at the end of each packet. Use the ESC character inside the packet if one of the data bytes is the same as the END character so that the receiving end can interpret the byte correctly. Although it was a good start, several problems can occur when using SLIP:
Because SLIP was widely deployed when the Internet became commercially available, it was a common protocol that many people used for an Internet connection early on. Initially, when first released, Microsoft's desktop offerings (Windows 9x) supported SLIP and that continues today. (Windows Server 2003 supports the SLIP and PPP remote access protocols.) All that said, you can probably understand why the Point-to-Point Protocol was developed. PPP replaces SLIP and provides a more robust method for sending and receiving data across serial connections, such as when dialing into a corporate modem bank or accessing the Internet. For more information about SLIP, see RFC 1055, "A Nonstandard for Transmission of IP Datagram's over Serial Lines: SLIP" and RFC 1144, "Compressing TCP/IP Headers for Low-Speed Serial Links." Note Although Windows XP and Server 2003 do include support for SLIP, keep in mind that newer systems only support outgoing connections. Windows Server 2003 and Microsoft Windows XP do not support SLIP for incoming connections. |