Hook flashing an FXO SIP Gateway

Asterisk Asterisk Support
1

Hello everyone,

I apologize in advance if this question has been answered elsewhere on this forum. I have been searching the web for several weeks and have yet to find a solution.

I have three regular POTS lines connected to a Grandstream GXW 4104 FXO gateway, each FXO port is setup with its own SIP trunk into Asterisk. I have an IVR built with a custom extension that when a caller presses 1 it goes to the custom extension that plays a recording saying your call will be transferred, it issues a hook flash to the FXO gateway, dials a telephone number of a third party and hangs up to have the telephone company transfer the call. The problem is I haven’t found a way to send a command to the gateway to hook flash. I read on the web I need to send a DTMF 16, or an “r” character. I tried using SendDTMF with the commands mentioned but Asterisk rejects it. I have the latest firmware loaded into the Gateway which does support hook flash, but the problem I am having is sending the message to the gateway to make it do a hook flash. I am using Asterisk 11.

Any help or direction on how to proceed would be greatly appreciated.

Thank you,

Brad

2

Asterisk code RFC 2833 code 16 as “f”, not “r”. There are some limitation on where it is supported.

Does the SDP from the gateway actually specify support for 0-16?

3

Thank you for the reply. I went through the documentation on the gateway and the best I can find is that it should support DTMF 0-16 as it says “Flexible DTMF transmission method,
User interface of In-audio, RFC2833, and SIP Info”. I do have the trunk configured for RFC2833, and I tried SendDTMF with an f and I get a message in the asterisk log stating I can’t use the “f” character. What is the proper way to send ‘f’?
I can post config and logs tonight.

4

I’d need to read the source code to be sure of where Asterisk supports sending flash via RFC 2833.