Sf signalling support in DAHDI?


Currently, I’m running Asterisk/Zaptel 1.2.1.

The original set of patches I applied enabled proper operation of “sf” in-band signalling in Zaptel. This required compiling and installing the “ztcfg-dude” package, which properly sets up sf in-band signalling. The regular “ztcfg” command, used to start Zaptel, did not support any of the sf signalling variants mentioned in sample zaptel.conf file.

With the move to dahdi from Zaptel, the ztfg-dude functionality appears to have been dropped completely. However, support for sf in-band signalling is still referenced in the sample “/etc/dahdi/system.conf” file (that took the place of zaptel’s zaptel.conf).

In dahdi, “dahdi_cfg” has replaced “ztcfg”. It does not support sf signalling either.

It appears there is no possible workaround in dahdi, due to the removal of “ztcfg-dude” functionality.

Example “/etc/dahdi/system.conf”:

; Channel(s) are signalled using in-band single freq tone.
; Syntax as follows:

channel; => sf
; rxfreq is rx tone freq in Hz, rxbw is rx notch (and decode)
; bandwith in hz (typically 10.0), rxflag is either ‘normal’ or
; ‘inverted’, txfreq is tx tone freq in hz, txlevel is tx tone
; level in dbm, txflag is either ‘normal’ or ‘inverted’. Set
; rxfreq or txfreq to 0.0 if that tone is not desired.


… and in chan_dahdi.conf



; sf: SF (Inband Tone) Signalling
; sf_w: SF Wink
; sf_featd: SF Feature Group D (The fake, Adtran style, DTMF)
; sf_featdmf: SF Feature Group D (The real thing, MF (domestic, US))
; sf_featb: SF Feature Group B (MF (domestic, US))


See lists.digium.com/pipermail/aster … 41277.html for a bug report concerning this.

Using Astlinux, I attempted to get sf signalling working over TDMoE. This worked fine for E&M signalling, but “dahdi_cfg” refused to recognize sf signalling and it’s arguments in “/etc/dahdi/system.conf”.

Has anyone found a workaround in dahdi for this?

I realize in-band sf signalling is seldom used over T1/TDMoE, but I am surprised that support for it seems to have been dropped completely.

Thanks and regards,



Hi, I’m not really sure why the ztcfg-dude file was kept separate from the main ztcfg to begin with, but it does look like all the SF tone generation and detection code is still in the DAHDI code base. I could see what would be required for adding that support in if you’re willing to test it.

My guess is that there wasn’t a huge demand (since you’re the first person I’ve seen to ask about this in the last 4 years) and so the decision was to not even try to port it if there wasn’t any evidence that it wasn’t still used by any users of DAHDI.


I’m certainly willing to test it! It would be great to get support for the (existing) in-band code base back into dahdi_cfg.

I have a system that depends on my hacked sf support. I’m stuck with Asterisk 1.2 unless this gets integrated back in.

Thanks much for the offer.

Best regards,



I opened a bug report for this issue at issues.asterisk.org.

The number is “DAHLIN-265”.