[SR-Users] Converting Cisco SIP NOTIFY DTMF to SIP INFO (Binary operations)

Marrold kamailio at marrold.co.uk
Wed Aug 4 17:17:05 CEST 2021


I am using an old Cisco 2811 with an FXS card and trying to get it to
convert between POTS and SIP. Mostly for "fun". For the most part it works,
however there are some problems with DTMF in the call.

Because the end device uses pulse dialling it seems that only the Cisco
Proprietary SIP NOTIFY method of sending DTMF is supported. It sends 4
bytes in the message body that indicate the DTMF digit sent. I'd like to
convert it to the more standard SIP INFO method. The docs about the
encoding are here -

I looked at the transformations but couldn't find anything relevant. Is it
possible to extract the binary from the body and decode it?

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