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Understanding initialization strings

Contributed by: Steven Dao
This tip is valid for: Both BeOS and Haiku

In R4.5, Be includes detailed documentation on building custom initialization strings. You can access this documentation by clicking the “AT Commands…” button in the Modem panel in the DialUp-Networking Preferences. Below are the pre-R4.5 instructions.

When you set up a modem under MS Windows, settings such as modem speaker volume and enable/disable call waiting are taken care of for you. Under BeOS, you need to understand the modem initialization string to control these features. The best place to look for a complete table of init string options is always in your modem’s manual or on the vendor’s web site. Here are some common ones that apply to US Robostics modems.

A new entry in /boot/beos/etc/modems.ppp might look like:

3COM_V90_mystring AT&F1S0=2L0S32=34


AT&F1 means: load default modem hardware configuration.
S0=2 means: modem answer incoming call after 2 rings.
L0 means: modem speaker set at low volume. To turn off speaker, use M0.
S32=34 means: diable X2 protocol, enable V.90 protocol.

Note: For every USR modem, the string AT&F1 should work fine, and you can append some or all of these options as you seee fit.

For more information, please go to, select his/her product, and select “manual” button. Download the .PDF technical reference file for full information about the initilization string.

Posted in Networking

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