Distinctive Ringing for Internal Extensions with 3CX and Yealink

A customer using 3CX v.15 with Yealink T42S phones would like calls from internal extensions to have a distinctive ring.

As explained in this thread, it turns out that internal calls already have a distinctive ring, but it sounds so similar to external calls that it is hard to distinguish. Here is how and where the ring tones are defined.

External Calls

3CX tags external calls with this line in the SIP INVITE:

Alert-Info: <http://www.notused.invalidtld>;info=external

The 3CX Yealink configuration template maps

distinctive_ring_tones.alert_info.2.text = external distinctive_ring_tones.alert_info.2.ringer = 2

This means “external” calls will use Ring2.wav. See also the phone UI’s Settings > Ring screen.

Internal Calls

3CX does not tag internal calls with an Alert-Info field in the SIP INVITE, so they are handled by the phone’s default ring, set in the phone UI as Settings > Preference > Ring Type or in the configuration file as phone_setting.ring_type. The default is Ring1.wav, which is very similar to Ring2.wav. Setting that to Ring3.wav has a lower pitch and is more distinctive. In the configuration file, that is this setting:

phone_setting.ring_type = Resource:Ring3.wav

SIP Trace

As additional background, here are two SIP INVITEs showing first an external and then an internal call. Note the Alert-Info line on the external call:

INVITE sip:[email protected]:5060 SIP/2.0
Via: SIP/2.0/UDP 192.168.99.7:5060;branch=z9hG4bK-524287-1---92001632c76e1867;rport
Max-Forwards: 70
Contact: &lt;sip:[email protected]:5060&gt;
To: &lt;sip:[email protected]&gt;
From: &quot;OUTSIDE CALLER:Daytime Ring Group&quot;&lt;sip:[email protected]:5060;nf=e&gt;;tag=a771915a
Call-ID: oeaRTEe7GVBSkwftwAeKuQ..
CSeq: 1 INVITE
Alert-Info: &lt;http://www.notused.invalidtld&gt;;info=external
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REGISTER, SUBSCRIBE, NOTIFY, REFER, INFO, MESSAGE
Content-Type: application/sdp
Supported: replaces
User-Agent: 3CXPhoneSystem 15.0.62928.5 (62293)
Content-Length: 295

Via: SIP/2.0/UDP 192.168.99.7:5060;branch=z9hG4bK-524287-1---45667a6a56746b5a;rport
Max-Forwards: 70
Contact: &lt;sip:[email protected]:5060&gt;
To: &lt;sip:[email protected]&gt;
From: &quot;Mark Test2&quot;&lt;sip:[email protected]:5060&gt;;tag=762f0d33
Call-ID: 6iA1Bfx-lZ_UX0DoL-MD9g..
CSeq: 1 INVITE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REGISTER, SUBSCRIBE, NOTIFY, REFER, INFO, MESSAGE
Content-Type: application/sdp
Supported: replaces
User-Agent: 3CXPhoneSystem 15.0.62928.5 (62293)
Content-Length: 447

External Calls

Internal Calls

SIP Trace

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