Telecommunications Industry Association
(TIA)
TR-30.1/99-12-071
Clearwater, Fla Nov 30, 1999
COMMITTEE CONTRIBUTION
Technical Committee TR-30 Meetings
SOURCE:
Hughes Network Systems
CONTACT:
Jeff Heath
Hughes Network Systems
10450 Pacific Center Court
San Diego, CA 92121
Phone:
(619) 452-4826
Fax:
(619) 597-8979
E-mail:
jheath@hns.com
TITLE:
Data Compression Issues
PROJECT:
PN-xxxx
DISTRIBUTION:
Members of TR-30 and TR-30.1 and meeting attendees
ABSTRACT
This paper presents some clarification to the Data Compression discussions held November 29,
1999 in the TR30.1 meeting. Also includes some test results and plans for the TR30.1 January
meeting.
Copyright Statement
The contributor grants a free, irrevocable license to the Telecommunications Industry Association
(TIA) to incorporate text contained in this contribution and any modifications thereof in the creation
of a TIA standards publication; to copyright in TIA's name any TIA standards publication even
though it may include portions of this contribution; and at TIA's sole discretion to permit others to
reproduce in whole or in part the resulting TIA standards publication.
Intellectual Property Statement
The individual preparing this contribution knows of patents, the use of which may be essential to
a standard resulting in whole or in part from this contribution.
1.
ADI Contribution Notes (TR301-99-12-060)
1.1.
256 Dictionary Tests
The ADI testing of LZJH with a 256 dictionary (1024 history buffer) was flawed because LZJH
does not support a 256 dictionary (neither does V.42bis). The LZJH initialization procedure
returned an error code back to the ADI test driver which was ignored. Consequently, none of
LZJH variables was initialized prior to compressing the data causing unpredictable results.
1.2.
Transparent Mode
The code sent to ADI on Nov. 23rd, 1999, had a bug in the transparent mode where every
character was counted twice in the output length returned to the test driver. The LZJH test driver
masked that bug since it used a different output calculation (i.e. the actual length of the output
buffer). Thus the testing of any file where transparent mode is entered was flawed.
2.
Comparison Testing
Comparison testing between the ADI and LZJH algorithms. In all cases LZJH used a 2048 entry
dictionary with a 10,000 byte history buffer. The ADI algorithm was compared using 2048, 4096,
and 8182 history buffer.
Testing was done in this manner because 2048 is a typical dictionary size for V.42bis. The ADI
algorithm was compared with the history buffer range of 2048 to 8192 since it is not clear how big
the supporting hash and/or lookup tables would have to be to reduce the complexity (i.e. CPU
time) of the encoder to within the same order of magnitude as the LZJH encoder.
2.1.
Mail File
The electronic mail file consists of the following:
1. Jokes received from a friend. All subjects, typically about 2,000 to 4,000 bytes each.
2. TR30.1 meeting notices and some mail.
3. Mail with attachments (C code, word documents, etc):
File
File Size
Mail File
1,444,029
Mail File
1,444,029
Mail File
1,444,029
Mail File
Frame Mode
2.2.
1,444,029
ADI
compressed
-2048637,221
-4096496,711
-8192450,202
-1500753,477
LZJH
Compressed
-2048525,256
-2048525,256
-2048525,256
-1500690,926
Difference
Percent
101,965
20
-28,545
-5
-75,054
-14
62,551
9
Amazon Web Browse
Created from an Amazon.com web browsing HTML’s. with about 20,000 bytes of random data
(random image, gif, files etc.) merged in between (i.e. after) each of the HTML files. In all cases
at least 2 and up to 7 image, jpeg, or gif files are required to total 20,000 bytes of random data. In
addition, the resulting file was run though a program that inserted a 60 byte simulated
PPP/TCP/IP header every 1440 bytes. This simulates a web browse session where the web
pages have several images which are loaded after the HTML.
File
File Size
Amazon
571,212
Amazon
571,212
Amazon
Test Mode
3.




571,212
ADI
compressed
-2048247,000
-8192222,000
-1500338,314
LZJH
compressed
-2048249,550
-2048249,550
-1500326,557
Difference
Percent
-2,550
-1
-27,550
-11
11,757
4
Plans for January TR30.1 Meeting
Have the HNS counsel review any pertinent patents (Stac, UNISYS, IBM, etc.).
Document counsel opinion as to any possible IPR infringement by LZJH.
Submit a contribution with the details of counsels document to the TR30.1 committee.
Submit other contributions as necessary.