如何通过调制解调器发起CSD（电路交换数据）呼叫？

I’ve tackled plenty of CSD (Circuit Switched Data) modem connection issues before, so let’s walk through troubleshooting your Error 6xx problem step by step:

1. Verify Your Dial-Up Connection Configuration #

Since your colleague’s setup works, start by cross-checking your dial-up settings against theirs—small mismatches here are often the culprit:

• Dial-up number: CSD requires a dedicated data access number (not a regular voice number). Common examples are *99#, *99***1#, or carrier-specific codes. Make sure you’re not using a standard voice number by accident.
• Modem initialization commands: Windows lets you add custom AT commands to prime the modem for CSD. Check your colleague’s setup for commands like:
  • AT+FCLASS=0: Forces the modem into data mode (instead of voice/fax)
  • AT+CRLP=6,6: Configures CSD link parameters (adjust based on your carrier’s specs)
    To access this: Go to your dial-up connection properties → Modem tab → Configure → Extra initialization commands.

2. Test CSD Calls Manually with AT Commands #

Eliminate the Windows dial-up layer by testing directly via a serial tool (PuTTY, TeraTerm):

1. Connect to your modem via its serial port.
2. Send AT+CMEE=2 to enable detailed error messages (this makes troubleshooting way easier).
3. Initiate a CSD call with ATD<CSD-access-number>;—don’t forget the trailing semicolon! Without it, the modem defaults to a voice call.
   • If you get CONNECT, the CSD link works, and the issue is with your dial-up configuration.
   • If you get an error (e.g., ERROR 3 for no dial tone, ERROR 67 for line busy), you’ll know the problem is with the modem, SIM card, or carrier network.

3. Diagnose the Exact Error 6xx Code #

Error 6xx covers several specific issues—here’s how to address the most common ones:

• Error 619: Connection terminated by remote computer. Check if the target modem is set to auto-answer data calls (send ATS0=1 to the remote modem) and configured for CSD mode, not voice.
• Error 678: No response from remote computer. This could be a carrier-side issue (verify your SIM has CSD service enabled via your provider’s support), weak signal (move to a better location), or mismatched CSD parameters (ensure both modems use the same baud rate, e.g., AT+IPR=9600).
• Error 629: Connection closed by remote computer. Double-check the remote modem’s CSD settings and confirm the target device is powered on and listening for data calls.

4. Check Driver & System Services #

• Update modem drivers: Outdated drivers often break CSD compatibility. Uninstall your current driver, download the latest version from the modem manufacturer’s site, and reinstall it.
• Enable critical Windows services: Ensure these services are running (search for "Services" in Windows):
  • Remote Access Connection Manager
  • Telephony
    Set both to Automatic startup and start them if they’re stopped.

5. Clone Your Colleague’s Working Configuration #

If all else fails, export your colleague’s dial-up profile (right-click their dial-up connection → Export) and import it into your system. This bypasses any manual configuration mistakes and confirms if the issue is specific to your setup.

内容的提问来源于stack exchange，提问作者ezpzlmnsqz1337