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Modem Basics - Init Strings

Links:  How to Add Init Strings | V34 Init Strings | V90 Init Strings | Additional Init String Resources |

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Init Strings:

Before your modem dials a phone number, your computer software initializes your modem by sending it a series of commands (strings or AT commands) known as initialization strings (commonly referred to as init strings).  Strings configure the modem's parameters for error correction, data compression, flow control, etc. 

You can add init strings to change the operation of your modem. These are typically not required, but can be useful in correcting connection problems. 

Init strings can be used to force a V.90 56k modem to act like a V.34 33.6k modem, which often improves throughput.  V34 is much more stable and handles older static-prone phone lines better.  If you are already connecting at under 34k, you should experience higher throughput and more stable connections by forcing the modem to use V34.

Note:  Before trying init strings, try altering Maximum Speed & Flow Control, as described here.

 

How To Add Init Strings:

Windows 95/98

Windows ME

Windows 2000

Windows XP

 

V.34 init strings

If you have an internal 56k modem and you just can't get a stable connection due to your phone lines or your modem software, you may be able to fix the problem by putting in a V34 init string. This will cause your modem to connect at only 33.6 kbps, but at least you'll have a reliable connection.  In fact, you will often experience faster throughput when using V34 instead of V90, since the V34 protocol handles the static of older phone lines better than the V90 protocol.

Generic V.34 Init Strings:
    AT+MS=V34
        -or-
    ATS37=19
        -or-
    ATS37=13

    Note: Not all modems can handle AT or MS commands. 
             PCTel modems can't handle MS commands.

Specific V.34 Init Strings for Common Modems:

    HSP & PCTel (9x, ME & XP): n0s37=12 -or- AT&F&C1&D2&K3W1
    PCTel Platinum V.90: atn0s37=0
   
  LT Win (9x & ME): x3
   
  LT Win (XP): AT&FS0=0V1&C1&D2 (zeros not capital letter "O"s)
    Conexant (9x & ME): +ms=v34 
                  (AT part isn't needed and might not work with many modems inc. this one)
    USR WinModems (9x, ME & XP): s32=66

See "Additional Init String Resources" below for links to other sites with init strings.

 

V.90 init strings

The latest 56k standard to come out is the V.92 protocol.  It adds a few improvements to the V.90 standard for 56k modems.  The problem is that most ISPs have not yet upgraded all of their modems to support the new V.92 protocol.Note that our Level3 POPs are usually v92 even though POP checker lists them as v90.  Since the POP Checker does not yet make this distinction, a little trial and error may be involved here.

So, if you have a V.92 modem, but your Internet service provider does not support the V.92 protocol, we recommend you add one of the following init strings to your dialing program's modem command string or "Extra Settings".

Generic V.90 Init Strings:
    AT+MS=V90
        -or-
    S7=150+MS=V90    (Note that "1" is a one and "0" is a zero.)
        S7=150 extends the negotiation time to 150 seconds (if needed). 
        +MS=V90 forces V.90 operation. 

Specific V.90 Init Strings for Common Modems:

    Conexant V.92 HSF    AT&F&C1&D2+MS=v90,0

    U.S. Robotics: There are three v.92 modem features that may be disabled

AT+PIG=1+PMH=1+PQC=3      Disabling all three features at once

1) Modem on Hold [this lets you suspend your internet connection in order to
receive incoming calls]
    AT+PMH=1

2) Quick Connect [this will try to connect with the same settings as was
used on the previous connecion if possible]
    AT+PQC=3

3) V.PCM Upstream [this increases uploads from the 31.2k max of v.90 to 48k]
    AT+PIG=1

 

See "Additional Init String Resources" below for links to other sites with init strings.

 

Additional Init String Resources:

http://www.otenet.gr/hd/HTML/extra_settings_modemen.htm (Highly Recommended)

http://www.modemhelp.net/quickref.shtml   (Highly Recommended)
http://www.modemhelp.net/stringlist.shtml

http://www.modemhelp.org/inits/

http://www.modemsite.com (pay to see init strings, but good info before that)

http://www.56k.com/inits/a2z.shtml (init strings & drivers link -> sort by manufacturer)

http://www.jenera.com/modems/ 

http://www.netins.net/dialup/modems/init/ 

http://modems.rosenet.net/init/  

Command Sets: http://www.modemhelp.org/sets.html

 

   

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