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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.
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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
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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.
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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.
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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.
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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
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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