PPP in HDLC-like Framing
RFC 1662
Document | Type |
RFC - Internet Standard
(July 1994; Errata)
Obsoletes RFC 1549
Also known as STD 51
|
|
---|---|---|---|
Last updated | 2013-03-02 | ||
Stream | IETF | ||
Formats | plain text pdf htmlized with errata bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 1662 (Internet Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group W. Simpson, Editor Request for Comments: 1662 Daydreamer STD: 51 July 1994 Obsoletes: 1549 Category: Standards Track PPP in HDLC-like Framing Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Abstract The Point-to-Point Protocol (PPP) [1] provides a standard method for transporting multi-protocol datagrams over point-to-point links. This document describes the use of HDLC-like framing for PPP encapsulated packets. Table of Contents 1. Introduction .......................................... 1 1.1 Specification of Requirements ................... 2 1.2 Terminology ..................................... 2 2. Physical Layer Requirements ........................... 3 3. The Data Link Layer ................................... 4 3.1 Frame Format .................................... 5 3.2 Modification of the Basic Frame ................. 7 4. Octet-stuffed framing ................................. 8 4.1 Flag Sequence ................................... 8 4.2 Transparency .................................... 8 4.3 Invalid Frames .................................. 9 4.4 Time Fill ....................................... 9 4.4.1 Octet-synchronous ............................... 9 4.4.2 Asynchronous .................................... 9 4.5 Transmission Considerations ..................... 10 4.5.1 Octet-synchronous ............................... 10 4.5.2 Asynchronous .................................... 10 Simpson [Page i] RFC 1662 HDLC-like Framing July 1994 5. Bit-stuffed framing ................................... 11 5.1 Flag Sequence ................................... 11 5.2 Transparency .................................... 11 5.3 Invalid Frames .................................. 11 5.4 Time Fill ....................................... 11 5.5 Transmission Considerations ..................... 12 6. Asynchronous to Synchronous Conversion ................ 13 7. Additional LCP Configuration Options .................. 14 7.1 Async-Control-Character-Map (ACCM) .............. 14 APPENDICES ................................................... 17 A. Recommended LCP Options ............................... 17 B. Automatic Recognition of PPP Frames ................... 17 C. Fast Frame Check Sequence (FCS) Implementation ........ 18 C.1 FCS table generator ............................. 18 C.2 16-bit FCS Computation Method ................... 19 C.3 32-bit FCS Computation Method ................... 21 SECURITY CONSIDERATIONS ...................................... 24 REFERENCES ................................................... 24 ACKNOWLEDGEMENTS ............................................. 25 CHAIR'S ADDRESS .............................................. 25 EDITOR'S ADDRESS ............................................. 25 1. Introduction This specification provides for framing over both bit-oriented and octet-oriented synchronous links, and asynchronous links with 8 bits of data and no parity. These links MUST be full-duplex, but MAY be either dedicated or circuit-switched. An escape mechanism is specified to allow control data such as XON/XOFF to be transmitted transparently over the link, and to remove spurious control data which may be injected into the link by intervening hardware and software. Some protocols expect error free transmission, and either provide error detection only on a conditional basis, or do not provide it at all. PPP uses the HDLC Frame Check Sequence for error detection. This is commonly available in hardware implementations, and a software implementation is provided. Simpson [Page 1] RFC 1662 HDLC-like Framing July 1994 1.1. Specification of Requirements In this document, several words are used to signify the requirements of the specification. These words are often capitalized.Show full document text