SIP Trunk Config: adding ;otg= tag after IP address of sip provider in the Sip INVITE From: header


I am trying to configure a sip trunk for a Windstream sip product called SIP OTT (over the top) as my customer doesn’t want to migrate from this provider.

The trunk is being used as primary for incoming and outgoing calls and also for blind transfers, forwarding and follow-me settings and therefore the trunk needs to be able to pass caller ID’s that are not associated with any DID on the sip account. Without the proper authentication in the sip INVITE From: header the carrier does not allow you to pass any caller IDs that’s not a number on the sip account and the forwards or blind transfers fail. They consider these “unscreened calls”. In order to pass these unscreened calls with the original caller id of the incoming call, they require an OTG tag (originating trunk group, which is like an account number) in the From: header of the sip INVITE in order to properly authenticate and complete an outgoing call. The failure happens only when blind transferring an incoming call to a cell phone or anytime an extension forwards or uses follow me to a cell phone so that the original caller ID is passed to the phone that is receiving the call.

The OTG tag needs to be added to the FROM: sip header in this format after the providers IP address “;otg=G70008163-1” so that the header looks like this:
From: “3057057875” sip:3057057875@;otg=G70008163-1;tag=as0e8d5056

However currently my From: header looks like this without the otg info:
From: “3057057875” sip:3057057875@;tag=as0e8d5056

The 305 number in the call example above is a cell phone that an extension has forwarded to. Since it’s not a DID on the sip account the call fails because the OTG tag is missing in the From: header.

In my current configuration the trunk works perfectly to receive incoming and outgoing calls. The only way I can blind transfer a call or set up a forward/follow me to a cell phone is to force the trunk to use the CID of the DID which is on the sip account however then the person receiving the call cannot see the original caller ID.

Can anyone think of a way to set this up or tell me if it’s even possible with Vitalpbx? or if not is there any custom programming that would allow this behavior on a specific trunk? Any help would be appreciated.

@russgreco ,

As far as I know, this is not possible on Asterisk per se. I think that you have to use a SBC like Kamalio or OpenSIPs to manipulate the Headers.

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