Network Working Group Jim Petty Internet Draft Hewlett-Packard expires in six months October 1993 PPP Hewlett-Packard Packet-by-Packet Compression (HP PPC) Protocol draft-ietf-pppext-hpppc-00.txt Status of this Memo This document is the product of the Point-to-Point Protocol Working Group of the Internet Engineering Task Force (IETF). Comments 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 for transporting multi-protocol datagrams over point-to-point links. The PPP Compression Control Protocol [2] provides a method to negotiate and utilize compression protocols over PPP encapsulated links. This document describes the use of the HP PPC compression algorithm for compressing PPP encapsulated packets. Petty expires in six months [Page i]
DRAFT Hewlett-Packard PPC October 1993 1. Introduction The HP PPC compression algorithm is an improvement on the existing implementations of the LZ variant known as LZ2. In particular the scheme uses an intermediate dictionary initialization. This method allows for a dictionary with fewer entries than the alphabet size. Thus, compression is possible with very small dictionaries, requiring very little memory. This is particularly attractive for networks where each packet is compressed independently. Other enhancements include run length encoding and parameter initialization based on input packet size. Since this is a packet by packet scheme, only one compression dictionary is needed per link and no reliable link is required or necessary. If the compressed packet is larger than the input packet, the input packet is sent uncompressed. 1.1. Licensing This paragraph will contain some lawyer and management approved words. The contact person for evaluation under NDA and licensing is: Mary Ryan Hewlett-Packard MS R3NF3 8000 Foothills Blvd Roseville, CA 95747 (916)785-5744 Fax: (916)786-9185 EMail: Mary_Ryan@hp5200.desk.hp.com Petty expires in six months [Page 1]
DRAFT Hewlett-Packard PPC October 1993 2. HP PPC Packets Before any HP PPC packets may be communicated, PPP must reach the Network-Layer Protocol phase, and the CCP Control Protocol must reach the Opened state. Exactly one HP PPC datagram is encapsulated in the PPP Information field, where the PPP Protocol field indicates type hex 00FD (compressed datagram). The maximum length of the HP PPC datagram transmitted over a PPP link is the same as the maximum length of the Information field of a PPP encapsulated packet. Reliability and Sequencing Each HP PPC packet is considered a separate entity. Therefore, the compression tables are reset for each packet. Reliable links are not necessary. Packets need not be delivered in sequence. Data Expansion Although the compression algorithm might occasionally expand a data packet, there is no expansion in HP PPC since such packets are sent uncompressed. Petty expires in six months [Page 2]
DRAFT Hewlett-Packard PPC October 1993 2.1. Packet Format The encapsulation is the same for every packet. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PPP Protocol |C| Uncompressed Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Compressed Data ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ PPP Protocol The PPP Protocol field is described in the Point-to-Point Protocol Encapsulation [1]. When the HP PPC compression protocol is successfully negotiated by the PPP Compression Control Protocol [2], the value is 00FD hex. This value MAY be compressed when Protocol-Field-Compression is negotiated. C In the off chance that a packet expanded during compression, this bit is set. 0 = compressed 1 = uncompressed Uncompressed Length This is the length of the uncompressed data. It is used as a limit during the decompression process. 3. Configuration Option No configuration option is required. Petty expires in six months [Page 3]
DRAFT Hewlett-Packard PPC October 1993 Security Considerations Security considerations are not discussed in this memo. References [1] Simpson, W.A., "The Point-to-Point Protocol (PPP)", work in progress. [2] Rand, D., "The PPP Compression Control Protocol (CCP)", work in progress. [3] Lempel, Abraham and Seroussi, Gadiel., "Compression Using Small Dictionaries with Applications to Network Packets", HP Technical Report HPL-92-112, Patent application, HP docket No. 1092545, 1993. Acknowledgments Original algorithm and mathematical advice provided by Gadiel Seroussi (HP). Initial testing of algorithm by Gadiel Seroussi and Dave Langley (HP). Bill Simpson provided the table of contents macros. Petty expires in six months [Page 4]
DRAFT Hewlett-Packard PPC October 1993 Chair's Address The working group can be contacted via the current chair: Fred Baker Advanced Computer Communications 315 Bollay Drive Santa Barbara, California 93117 EMail: fbaker@acc.com Author's Address Questions about this memo can also be directed to: Jim Petty Hewlett-Packard Company 8000 Foothills Boulevard, MS R3NF3 Roseville, CA 95747 (916)785-5744 Fax: (916)786-9185 EMail: jpetty@hprnd.rose.hp.com Petty expires in six months [Page 5]
DRAFT Hewlett-Packard PPC October 1993 1. Introduction .......................................... 1 1.1 Licensing ....................................... 1 2. HP PPC Packets ........................................ 2 2.1 Packet Format ................................... 3 3. Configuration Option .................................. 3 SECURITY CONSIDERATIONS ...................................... 4 REFERENCES ................................................... 4 ACKNOWLEDGEMENTS ............................................. 4 CHAIR'S ADDRESS .............................................. 5 AUTHOR'S ADDRESS ............................................. 5
