Re: IP Phone shows empty string rather than "Unknown Number" for inbound SIP Calls

j.a.m.e.s · ‎12-06-2018

Dear All,

I'm migrating from ISDN/MGCP to SIP and I've noticed with SIP when my ITSP sends calls where the caller id (ANI) is withheld the phone displays the empty string rather than "Unknown Number". This is disturbing for our end users.

My Call Flow is:

ITSP -> CUBE v12 -> CUCM v10.5

The SIP Invite on the CUBE is as follows:

! ITSP Invite:
INVITE sip:+44123123123@199.0.0.1:5060 SIP/2.0
Via: SIP/2.0/TCP 199.0.0.2:5060;branch=z9hG4bK548491459
From: <sip:anonymous@anonymous.invalid>;tag=5257BBDE-17E1
To: <sip:+44123123123@199.0.0.1>
Date: Thu, 06 Dec 2018 10:59:56 GMT
Call-ID: 84E55FCC-F87411E8-80F198FC-B323C3A5@199.0.0.2
Supported: 100rel,timer,resource-priority,replaces,sdp-anat
Min-SE:  360
User-Agent: Cisco-SIPGateway/IOS
Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER
CSeq: 101 INVITE
Timestamp: 1544090396
Contact: <sip:anonymous@199.0.0.2:5060;transport=tcp>
Expires: 180
Allow-Events: telephone-event
Max-Forwards: 26
Resource-Priority: dsn-000000.routine
Session-Expires:  1800;refresher=uac
Content-Type: application/sdp
Content-Disposition: session;handling=required
Content-Length: 271

[...]

! CUBE Relays this to the CM:
INVITE sip:+44123123123@10.0.0.2:5060 SIP/2.0
Via: SIP/2.0/TCP 10.0.0.226:5060;branch=z9hG4bKED51DF1
From: <sip:anonymous@10.0.0.226>;tag=221C185-2312
To: <sip:+44123123123@10.0.0.2>
Date: Thu, 06 Dec 2018 09:59:56 GMT
Call-ID: 84E58722-F87411E8-AA5DAFDC-B1823B0D@10.0.0.226
Supported: 100rel,timer,resource-priority,replaces,sdp-anat
Min-SE:  360
User-Agent: Cisco-SIPGateway/IOS
Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER
CSeq: 101 INVITE
Timestamp: 1544090396
Contact: <sip:anonymous@10.0.0.226:5060;transport=tcp>
Expires: 180
Allow-Events: telephone-event
Max-Forwards: 25
Resource-Priority: dsn-000000.routine
Session-ID: fcd5850e8020511b9cdc442e72084001;remote=00000000000000000000000000000000
Session-Expires:  1800;refresher=uac
Content-Type: application/sdp
Content-Disposition: session;handling=required
Content-Length: 250

Is anyone aware of a smart way on CUBE or CM to indicate the ringing phone should display "Unknown Number"?

The only solution that comes to mind is to insert a PAI field, then modify it, but this seems unusual that a modification like this would be needed to keep the original behaviour under MGCP.

voice service voip
 sip  
  asserted-id pai
!
voice class sip-profiles 1
 rule X request ANY sip-header P-Asserted-Identity modify "<sip:anonymous@" "\"Unknown Number\" <sip:anonymous@"

Regards

James.

Jonathan Schulenberg · ‎12-22-2018

Your provider is complying with RFC3261 which specifically calls for this format when calling party information is being withheld. See section 8.1.1.3.

I would not suggest manipulating this on CUBE since you would be purposely deviating from the standard. The phone doesn’t show ANI data because there is none. It does show the Anonymous/Unknown state in CNAM directly above the number though.

j.a.m.e.s · ‎12-26-2018

Hi Jonathan,

Thank you for pointing me to the RFC. I'm not sure that the ITSP is adhering to the standard though because section 8.1.1.3 states:

 A UAC SHOULD use the display name "Anonymous", along with a syntactically correct, but otherwise meaningless URI

I would say the ITSP failed to send the display name "Anonymous" so I have added it via the PAI as "Unknown Number". This appears to be working so far with my testing.