Eicon Networks DIVA T/A ISDN Modem manual What is Data Compression?

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What is ISDN?

What is Data Compression?

To establish communications over a PPP link, each end of the connection must first send packets to configure and test the data link. After the link has been established, optional facilities may be negotiated as needed. One such facility is data compression. A wide variety of compression methods may be negotiated, although typically only one method is used for both directions of the link.

Data compression is a process where the effective throughput is increased by encoding data in such a way that fewer bits are required to represent it. For example, a text file might be compressed by representing common words with single characters; thus if the word “the” is represented by the character “@”, it will be transmitted three times faster. Popular compression algorithms typically reduce the size of the data by 50%, effectively doubling the rate at which it is transmitted.

The Compression Control Protocol (CCP) works with MLPPP and is responsible for configuring, enabling, and disabling data compression algorithms on both ends of the point-to-point link. PC Compression negotiation takes precedence over the DIVA T/A negotiation for performance considerations (for example, the PC compression may reduce the number of bytes that go through the serial interface, the PC has the quicker CPU, etc.). The DIVA T/A compression negotiation, however, will assume control should no compression be detected or the initial negotiation fail. No user configuration is required to enable the DIVA T/A's compression functionality. Compression algorithms currently supported by the DIVA T/A include Stacker LZS (Hi/fn), MPPC (Microsoft), and Ascend.

DIVA T/A ISDN Modem Reference Guide ◆ Page 13

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Contents Diva T/A Isdn Modem Reference Guide Eight Edition July 206-193-08 Contents Diva T/A Isdn Modem Reference Guide What is ISDN?What is ISDN? Channel Isdn Communication ChannelsChannel Basic Rate Access Connecting to Isdn BRI and PRIWhat is Multilink PPP? What is BACP/BOD? What is DBA? What is Always On / Dynamic Isdn AO/DI? What is Data Compression? Locating AT Commands Locating AT Commands AT Command Groups Alphabetical List of Supported AT Commands Alphabetical List of Supported AT Commands AT! CommandsAlphabetical List of Supported AT Commands AT% Commands AT& Commands AT* Commands AT Commands AT@ Commands Other AT Commands Registers AT$ Utility Commands Mini-monitor Commands General AT Commands General AT Commands Defaults Isdn Configuration CommandsValues for n Isdn Configuration Commands Default1 None defaultINS-Net64, NI-1, or 5ESS, µ law will be used default AT!D3=nAT!N2=n Default null string this is an optional valueNumber. Numbers are separated by a semicolon AT!N3=nAT!X56=n For more details, refer to the Rvscom documentationOn region 255 do not attempt 56k data call retry COM Port Configuration Commands Ring COM Port Configuration CommandsUpon connection, the Diva T/A reports the DCE speed For example, ConnectCall Control Commands ATA Call Control CommandsATH Configuration Commands Configuration Commands AT!V0=n Use the default settingsProfile Commands Multilink PPP Commands Multilink PPP Commands AT%M3=b3c665ac11 Endpoint Discriminator Class/AddressInternet Protocol IP Always On / Dynamic Isdn AT Commands Always On / Dynamic Isdn AT Commands Will be opened after the delay specified by AT!X10 AT!X13=n when Bacp is disabled, seeDefault 1000 bytes AT!X14=nDefault AT!X22=n Default values for each setting, and is defined as followsAT!X18 Defined as followsAT!X25=n Default CF PPP overConnection numbers affects the range ofAT!X21. SeeAT!X21 AT!X26=nUtility Commands Internal TA access command reserved for VU Utility CommandsStart or display the Result of a Lapd trace Start or Display the Result of a PPP traceSoft reset the unit and enter the monitor Enter the monitor on the next resetStart an AO/DI X.25 Trace AT? Register CommandsRegister Commands Analog Device Commands AT*Fn Analog Device CommandsDisable. Recommended for modem/fax calls To be disabledEnable with default values default Enable using same terminal endpoint identifier as data portMini-monitor Commands AT Command Result Codes Connect AT Command Result CodesCarrier Connect Connect 75T/1200R Protocol Transparent ModeConnect 1200T/75R Protocol NoneBACP/BOD Index