Incoming call rejected (420 Bad Extension)

[kot2003]

The call comes from VoIP provider to 3CX:

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)
Session Initiation Protocol
Request-Line: INVITE sip:774724982@3CX_IP_address:5060;rinstance=500f6aa057177b13 SIP/2.0
Message Header
Via: SIP/2.0/UDP VoIP_provider_IP:5060;branch=z9hG4bK-4e67792e-441612
To: <sip:774724982@3CX_IP_address:5060;rinstance=500f6aa057177b13>
From: <sip:33072502@VoIP_provider_IP>;tag=8624386
Call-ID: 1315404078-436545@SIP
CSeq: 1 INVITE
Sequence Number: 1
Method: INVITE
Max-Forwards: 70
Contact: <sip:33072502@VoIP_provider_IP:5060>
Require: 100rel
Expires: 330
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, INFO, PRACK, REFER, SUBSCRIBE, NOTIFY, UPDATE, REGISTER
Accept: application/sdp
Content-Type: application/sdp
Content-Length: 343
Message Body
Session Description Protocol
Session Description Protocol Version (v): 0
Owner/Creator, Session Id (o): - 268883969 1316944546 IN IP4 VoIP_provider_RTP_IP
Session Name (s): -
Connection Information (c): IN IP4 VoIP_provider_RTP_IP
Time Description, active time (t): 0 0
Session Attribute (a): sendrecv
Media Description, name and address (m): audio 7480 RTP/AVP 8 18 101
Media Attribute (a): rtpmap:8 PCMA/8000
Media Attribute (a): rtpmap:18 G729/8000
Media Attribute (a): fmtp:18 annexb=no
Media Attribute (a): cdsc:1 image udptl T38
Media Attribute (a): rtpmap:101 telephone-event/8000
Media Attribute (a): fmtp:101 0-15
Media Attribute (a): silenceSuppff - - - -
Media Attribute (a): ptime:20
Media Attribute (a): maxptime:30
Media Attribute (a): rtcp-xr:

The call is rejected:

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)
Session Initiation Protocol
Status-Line: SIP/2.0 420 Bad Extension
Message Header
Via: SIP/2.0/UDP VoIP_provider_IP:5060;branch=z9hG4bK-4e67792e-441612
To: <sip:774724982@3CX_IP_address:5060;rinstance=500f6aa057177b13>;tag=2935a94d
From: <sip:33072502@VoIP_provider_IP>;tag=8624386
Call-ID: 1315404078-436545@SIP
CSeq: 1 INVITE
Sequence Number: 1
Method: INVITE
Unsupported: 100rel
Content-Length: 0

Any ideas? Why 3CX answers with "Unsupported: 100rel" ?

Regards,
Pavel

 

[SY]

If a 420 (Bad Extension) response is received (Section 21.4.15), the
request contained a Require or Proxy-Require header field listing an
option-tag for a feature not supported by a proxy or UAS. The UAC
SHOULD retry the request, this time omitting any extensions listed in
the Unsupported header field in the response.

 

[kot2003]

Thank you,

So, the bottom line - this is is not supported. I have to ask my VoIP provider not to send "Require: 100rel".

Best regards,
Pavel