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V.92 Commands

    V.92 is essentially the evolution of 56k flex.. (ok the X2 guys will disagree but essentially it is). Many of the modulation commands (+ms= ) commands are similar.

    +ms=V92 is the standard your modem should be set for for full v92 support.

    US Robotics v92 modems should use s32=130 to disable V.92..

    PCM Upstream - The command +PIG=# will control PCM upstream. The values are 0 to enable PCM upstream, and 1 to disable it. (+PCM=0)

    Quick Connect - The command +PQC=# controls Quick Connect. The values are - 0 to enable Quick Connect (short phase 1 and phase 2 enabled); 1 - enable short phase 1 only; 2 - enable short phase 2 only; 3 - disable short phase 1 and phase 2.

    Call Waiting - +PCW=# will determine the behavior of the modem if a call-waiting signal is detected: the options are 0 - enable for modem-on-hold and collect caller-id info if available; 1 - Hang up; 2 - Ignore.

    Modem on Hold - The ISP V.92 client and server can be set to allow or deny modem on hold. The command +PMH=# enables or disables modem on hold. Both client and server modems need #=0 to allow allow modem on hold during a V.92 connection. (#=1 disables modem on hold.) If it is enabled,

    The command +PMHT=# sets the modem as follows:
    # Description
    0 Deny V.92 Modem-on-hold Request
    1 Grant MOH with 10 second timeout
    2 Grant MOH with 20 second timeout
    3 Grant MOH with 30 second timeout
    4 Grant MOH with 40 second timeout
    5 Grant MOH with 1 minute timeout
    6 Grant MOH with 2 minute timeout
    7 Grant MOH with 3 minute timeout
    8 Grant MOH with 4 minute timeout
    9 Grant MOH with 6 minute timeout
    10 Grant MOH with 8 minute timeout
    11 Grant MOH with 12 minute timeout
    12 Grant MOH with 16 minute timeout
    13 Grant MOH with indefinite timeout

    To initiate a modem on hold (the client could place an outgoing call while keeping the ISP connect on hold), compatible software would issue escape code to modem and give it the Initiate Modem on Hold - +PMHR command. The response to the command will be one of the values in the chart above which will allow the client software to keep track of, and alert the user to, the status of the modem hold. Modem on hold is also invoked in conjunction with call waiting if +PMH=0 and +PCW=0.

    +PMHF initiates a hook flash.

    To make an outgoing call while holding your Internet connection:
    AT+PMHR - response will be value from above chart - server starts timer
    AT+PMHF - your modem does a hook flash; gives you dial-tone on extension phone plugged into modem; You can place yourcall. When finished and you hang up, the line will RING.

    V.44 Compression - V.44 and V.42 are enabled/disabled with the +DS44= command. The V.250 spec includes up to 9 numeric values. The first two values control direction and compression negotiation:
     +DS44=direction,compression-negotiation where
      direction = 0, 1, 2 or 3:
        0 = No V.44
        1 = V.44 on Transmit Only
        2 = V.44 on Receive Only
        3 = V.44 in both or any direction

    compression negotiation = 0 or 1:
    0 = Do not disconnect if V.44 is not negotiated in specified direction
    1 = Disconnect if V.44 is not negotiated in specified direction

    The additional 7 values, which may not be supported in all client modems, specify capability, maximum codewords, stringsize, and history:

    Capability: 0,1, or 2 where 0=Stream method; 1=Packet Method; 2=Multi-packet method
    Maximum codewords (tx and rx) = 256 - 65536
    Maximum stringsize (tx and rx) = 32 - 255
    Maximum history (tx and rx) = 512 - 65536
    To examine your modem's setting: AT+DS44?
    To list valid values for your modem: AT+DS44=?

    Some Lucent/Agere modems use +DCS (not a V.250 command) to control compression:
    +DCS= command:
    +DCS=#,# where # = 0 or 1. The first # is for V.42, the second for V.44; a value of 0 disables, 1 enables.
    To disable V.44 but keep V.42: +DCS=1,0

  • Description/Dissection of AT Commands used in Init Strings

  • HAYES 56K AT Command Summary

  • Motorola SM56 AT Command Summary

    Download Acrobat and Link

    Last Updated December 1, 2011.