US 4,748,638 AGranted

Data telecommunications system and method for transmitting compressed data

AssigneeMicrocom, Inc.

InventorsPaul Friedman, Nathan Melhorn

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Abstract

Disclosed is a data compressing modem for connection to a decompressing modem over communication lines. The compressing modem receives an input data stream, and each character in the data stream is recodified with a compressed character code, the length of which is dependent on the frequency of the character in the data stream. A frequency table is maintained so that changes in the relative frequency of characters in the data stream will be recognized by the compressing modem and the compressed character codes representing such characters will be exchanged accordingly. A decompressing modem, which is connected over communication lines to the compressing modem, processes the compressed character code in a reverse order from the manner in which the compressing modem processing the codes. The decompressing modem also maintains a relative frequency table and as the relative frequencies of the various characters change, the actual characters represented by the compression codes must also change.

Claims6

Dependent claims

A method of transmitting data in a compressed form between an initiating unit of data terminal equipment and a receiving unit of data terminal equipment connected over communication lines, one of said units having a compressing modem connected between said unit and telephone lines, and the other of said units having a decompressing modem connected between said other unit and telephone lines, said method comprising the steps of:

(a) fetching a next data character from a data stream to be sent over communication lines;
(b) transmitting a compressed character code assigned to said next data character to the decompressing modem, said compression code having a length indicating header part and a data part;
(c) incrementing a relative frequency counter for said next data character;
(d) comparing said relative frequency counter for said next data character to a relative frequency counter of a next more frequently occurring character;
(e) if the relative frequency of said next data character is greater than the relative frequency of said next more frequently occurring character, exchanging the compressed character codes assigned to said next data character and to said next more frequently occurring character;
(f) repeating steps (d) through (e) until the relative frequency of said next data character is less than the relative frequency of said next more frequently occurring character or it is the most frequent character;
(g) repeating steps (a) through (f) until said data stream is transmitted.

4 more elements

Dependencies are inferred from the claim text.