Applies To: Polycom SoundStation 2W and other Analog Poly conference phones
Issue: After switching from a copper PSTN line to a fibre or VoIP-based line, the SoundStation 2W can make and receive calls but is unable to join teleconferences or send additional DTMF tones (e.g., meeting codes or PINs) once the call is connected.
Root Cause: This issue is not caused by the phone itself, as the SoundStation 2W uses DTMF (Dual-Tone Multi-Frequency) signalling for all number inputs — both for dialling and in-call tones.
If the phone can successfully dial out to connect the initial call, it confirms that DTMF is functioning correctly on the device.
The most likely cause is related to how the new Fiber/VoIP connection or ATA (Analog Telephone Adapter) handles DTMF signalling after the call is established.
Technical Explanation:
The SoundStation 2W and all Poly Analog phones send DTMF tones the same way, regardless of whether the tones are for dialling a number or entering a conference code.
If the phone can dial a number, it has already transmitted valid DTMF tones.
In many VoIP or PABX environments, the ATA or VoIP trunk may convert or suppress DTMF signals once the call is in progress.
Some codecs (e.g., G.729) used in compressed VoIP calls can distort or block DTMF tones, preventing them from being recognized by the conference system.
Recommended Actions:
Verify DTMF Configuration: Check that the ATA or VoIP gateway is configured to pass DTMF correctly (using RFC2833, SIP INFO, or in-band signalling as required).
Test Using a Traditional Analog Line: Connect the SoundStation 2W directly to a standard Analog line to confirm that DTMF tones are working properly.
Check Codec Settings: Ensure that the call path does not use a compressed codec (e.g., G.729), which can interfere with DTMF transmission.
Contact the Line Provider: If the phone works on a standard Analog line, the issue lies with the service provider, ATA, or PABX configuration. Contact the provider to enable proper DTMF passthrough.
Conclusion:
The SoundStation 2W relies on Analog DTMF signalling and functions correctly when connected to a compatible Analog line. If DTMF fails during a VoIP or Fiber-based call, it is typically caused by the line adapter or codec settings, not the phone itself.
For resolution, please engage the telecom provider or system integrator who manages the Analog-to-VoIP conversion.
