Network Working Group W A Simpson Internet Draft Daydreamer expires in six months March 1993 PPP over ISDN Status of this Memo This memo is the product of the Point-to-Point Protocol Working Group of the Internet Engineering Task Force (IETF). Comments on this memo should be submitted to the ietf-ppp@ucdavis.edu mailing list. Distribution of this memo is unlimited. This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress.'' Please check the 1id-abstracts.txt listing contained in the internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net, nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the current status of any Internet Draft. Abstract The Point-to-Point Protocol (PPP) [1] provides a standard method of encapsulating Network Layer protocol information over point-to-point links. This document defines a method for using PPP to transport multi- protocol datagrams over Integrated Services Digital Network (ISDN) B and D channel circuits. Simpson expires in six months [Page i] DRAFT PPP over ISDN March 1993 1. Introduction PPP has three main components: 1. A method for encapsulating datagrams over serial links. 2. A Link Control Protocol (LCP) for establishing, configuring, and testing the data link connection. 3. A family of Network Control Protocols (NCPs) for establishing and configuring different network layer protocols. PPP was designed as a standard method of communicating over point- to-point links. Initial deployment has been over short local lines, leased lines, and plain-old-telephone-service (POTS) using modems. As new packet services and higher speed lines are introduced, PPP is easily deployed in these environments as well. One protocol to carry them all. One protocol to mind them. One protocol to link them all, and in the network bind them. This specification is primarily concerned with the use of standard PPP frames over ISDN links. Since ISDN is a point-to-point circuit, PPP is well suited to use over ISDN. The ISDN Primary Rate Interface (PRI) may support hundreds of concurrent links. The PPP LCP and NCP mechanisms are particularly useful in this situation in reducing or eliminating hand configuration, and facilitating ease of communication between diverse implementations. 2. Encapsulation PPP provides an encapsulation protocol over both bit-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. This fits the ISDN model. PPP uses HDLC [2] as a basis for the encapsulation. It is completely suitable for use with the ISDN B channel. It is distinguishable from other uses of the ISDN D channel. By default, it is recommended that the PPP HDLC framing be used directly over the B or D channel via the native ISDN interface, with a synchronous NRZ encoding. By prior configuration, PPP may also be Simpson expires in six months [Page 1] DRAFT PPP over ISDN March 1993 used with NRZI encoding, and with asynchronous terminal adapters conforming to V.120 [3]. 3. In-Band Protocol Detection The PPP HDLC framing may be easily distinguished from other framing methods such as Frame Relay or X.25 [4]. Initial PPP packets will contain the sequence ff-03-c0-21. Initial X.25 packets will likely have a first octet of 1 or 3. Initial Frame Relay packets will have a first octet which is even. 4. Out-of-Band signaling Experience has shown that the LLC Information Element is not reliably transmitted end to end. No values which pertain to PPP have been assigned, as yet. Therefore, the LLC-IE SHOULD NOT be sent, and SHOULD be ignored on receipt. 5. Configuration Details The standard LCP configuration defaults apply to ISDN links. The LCP recommended options apply to ISDN links. A maximum PDU size of 1600 is commonly available. This translates to a PPP MRU size of 1598. The basic HDLC header is significantly shorter than the full-sized X.25 or Frame Relay headers, which may give additional leeway. Since the typical network feeding the link is unlikely to have a MRU of greater than 1500, it is not expected to be worth the trouble to negotiate a higher MRU. Simpson expires in six months [Page 2] DRAFT PPP over ISDN March 1993 Security Considerations Security issues are not discussed in this memo. References [1] Simpson, W. A., "The Point-to-Point Protocol", RFC 1331, May 1992. [2] International Organization For Standardization, ISO Standard 3309-1979, "Data communication - High-level data link control procedures - Frame structure", 1979. [3] CCITT, "Recommendation V.120: Data Communications over the Telephone Network", Blue Book, ITU 1988 [4] Malis, A., Robinson, D., Ullman R., "Multiprotocol Interconnect on X.25 and ISDN in the Packet Mode", RFC 1356, August 1992. Acknowledgments Chair's Address The working group can be contacted via the current chair: Brian Lloyd B.P. Lloyd & Associates 3420 Sudbury Road Cameron Park, California 95682 Phone: (916) 676-1147 EMail: brian@lloyd.com Author's Address Questions about this memo can also be directed to: William Allen Simpson Daydreamer Computer Systems Consulting Services P O Box 6205 East Lansing, MI 48826-6205 EMail: Bill.Simpson@um.cc.umich.edu Simpson expires in six months [Page 3] DRAFT PPP over ISDN March 1993 Table of Contents 1. Introduction .......................................... 1 2. Encapsulation ......................................... 1 3. In-Band Protocol Detection ............................ 2 4. Out-of-Band signaling ................................. 2 5. Configuration Details ................................. 2 SECURITY CONSIDERATIONS ...................................... 3 REFERENCES ................................................... 3 ACKNOWLEDGEMENTS ............................................. 3 CHAIR'S ADDRESS .............................................. 3 AUTHOR'S ADDRESS ............................................. 3 Bill.Simpson@um.cc.umich.edu