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Q170825: RAS Auto-Answer Behavior in Windows NT

Article: Q170825
Product(s): Microsoft Windows NT
Version(s): WinNT:3.50,3.51,4.0
Operating System(s): 
Keyword(s): kbnetwork
Last Modified: 09-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0 
- Microsoft Windows NT Server versions 3.5, 3.51, 4.0 
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SUMMARY
=======

This article explains the new behavior of Windows NT remote access service (RAS)
when answering incoming calls, in Windows NT version 4.0. This behavior has
changed because Unimodem support is included in Windows NT version 4.0, but not
in version 3.5x.

MORE INFORMATION
================

In Windows NT 3.5x, RAS initializes analog modems by sending an ATS0=1 command
to the modem when RAS loads. This instructs the modem to answer incoming calls
on the first ring. See the following article in the Microsoft Knowledge Base for
more information about this parameter and how to modify the number of rings
before answering:

  Q114687 Setting Number of Rings for RAS Server Auto-Answer in NT 3.5x

By default in Windows NT version 4.0, the modem is initialized by Unimodem, which
sends an ATS0=0 to the modem when RAS loads. When an incoming call is received,
Unimodem answers the call and passes control to RAS. In this case, the "AA"
light on an external modem is NOT lit, though RAS answers incoming calls. For
information about modifying the number of rings for Unimodem to answer a call in
Windows NT 4.0, see the following article in the Microsoft Knowledge Base:

  Q145879 How to Set the Number of Rings for RAS Auto-Answer in NT 4.0

NOTE: Unimodem can be disabled in Windows NT 4.0, which causes RAS to behave as
it does in Windows NT 3.5x, as described above. For additional information,
please see the following article in the Microsoft Knowledge Base:

  Q150808 Disabling Support for Unimodem Modems in Remote Access

EXAMPLE
-------

The following is an example of Unimodem initializing or answering the line in
Windows NT 4.0 (from the modem log):

06-25-1997 17:06:20.113 - Hayes Accura 288 V.FC + FAX in use.
06-25-1997 17:06:20.143 - Modem type: Hayes Accura 288 V.FC + FAX
06-25-1997 17:06:20.143 - Modem inf path: mdmhayes.inf
06-25-1997 17:06:20.143 - Modem inf section: M1846
06-25-1997 17:06:20.143 - 115200,N,8,1
06-25-1997 17:06:20.143 - 115200,N,8,1
06-25-1997 17:06:20.173 - Initializing modem.
06-25-1997 17:06:20.173 - Send: AT<cr>
06-25-1997 17:06:20.193 - Recv: AT<cr>
06-25-1997 17:06:20.423 - Recv: <cr><lf>OK<cr><lf>
06-25-1997 17:06:20.423 - Interpreted response: OK
06-25-1997 17:06:20.423 - Send: AT&FE0V0W1&C1&D2S95=47<cr>
06-25-1997 17:06:20.534 - Recv: AT&FE0V0W1&C1&D2S95=47<cr>
06-25-1997 17:06:21.064 - Recv: 0<cr>
06-25-1997 17:06:21.064 - Interpreted response: OK
06-25-1997 17:06:21.064 - Send: ATS7=60S30=0L0M1&Q5S36=7S48=7S46=138&K3<cr>
06-25-1997 17:06:21.485 - Recv: 0<cr>
06-25-1997 17:06:21.485 - Interpreted response: OK
06-25-1997 17:06:21.485 - Send: ATB0N1X4<cr>
06-25-1997 17:06:21.685 - Recv: 0<cr>
06-25-1997 17:06:21.685 - Interpreted response: OK
06-25-1997 17:06:21.685 - Waiting for a call.
06-25-1997 17:06:21.685 - Send: ATS0=0<cr>
***(tells the modem not to answer the line when a call comes in; this lets
Unimodem do it)***

06-25-1997 17:06:21.876 - Recv: 0<cr>
06-25-1997 17:06:21.876 - Interpreted response: OK
06-25-1997 17:07:15.703 - Recv: 2<cr>
***(this is the ring coming in on the modem)***

06-25-1997 17:07:15.713 - Interpreted response: Ring
06-25-1997 17:07:15.743 - Answering the call.
06-25-1997 17:07:15.743 - Send: ATA<cr>
***(this is Unimodem telling the modem to answer the call)***

06-25-1997 17:07:27.009 - Recv: 55<cr>
06-25-1997 17:07:27.009 - Interpreted response: Informative
06-25-1997 17:07:27.610 - Recv: 77<cr>
06-25-1997 17:07:27.610 - Interpreted response: Informative
06-25-1997 17:07:27.610 - Recv: 67<cr>
06-25-1997 17:07:27.610 - Interpreted response: Informative
06-25-1997 17:07:27.610 - Recv: 15<cr>
06-25-1997 17:07:27.610 - Interpreted response: Connect
06-25-1997 17:07:27.620 - Connection established at 28800bps.
06-25-1997 17:07:27.620 - Error-control on.
06-25-1997 17:07:27.620 - Data compression on.
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Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTW350 kbWinNTW350search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search
Version           : WinNT:3.50,3.51,4.0

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