Need to know the DTMF used in TDM to VOIP or Vice versa...

[nawaz.pasha]

I want to know what is the DTMF type that is used in TDM circuits and Is the RTP also goes from Internal network phone A to PSTN mobile directly or there is conversion that happens in between.....please explain

I know RTP in voip network happens end to end and does this concept applicable even with Internal VOIP phone to Cellphone/or any phone in PSTN network and let me know how the DTMF conversion happens from Internal network to PSTN cell phones or vice versa...

[Vivek Batra · Accepted solution]

TDM circuit supports DTMF in inband. There are some exceptional cases like GSM gateways which may dial DTMF outband (using standard AT command).

When you connect your VoIP network to PSTN, that is PSTN gateways DSP job to get the DTMF in negotiated type (inband or outband) on VoIP call leg and converted into inband on TDM side.

You are right that RTP will always be end to end. So when call is made between two IP phones, media flows end to end between the phones however when call is made from IP phone to PSTN, PSTN gateway is considered as one of the end device hence media will flow from IP phone to PSTN gateway.

- Vivek