Important: Mandatory Caller ID

We’ve blogged before about the importance of sending valid caller ID on all calls, and warned that we will begin rejecting call attempts with invalid CLI.

Simwood is committed to reducing misuse of telecommunications networks, and it has long been a requirement at an interconnect level to provide CLI for all calls. Despite this, we still see a number of calls without CLI.

There is no reason not to send valid CLI on all calls, and indeed it is a legal requirement, therefore effective from February 1st we will not accept any calls that do not have a valid CLI provided. Initially this will apply only to Developer and Start-Up account types, as well as those who have not upgraded to our new packages.

For customers with a legitimate need to withhold caller ID, mainly those providing services to individual end users, you can continue to do so ensuring that a valid originating number is provided using the P-Asserted-Identity header, which is supported by all modern SIP platforms.

We have, for some time, sent an X-Warning header indicating “Invalid CLI” in the response to any INVITE which doesn’t contain CLI.  You can check your SIP traces and logs for the presence of this header, indicating these calls would have been rejected;

The vast majority of our customers will not be affected by this, and are fully compliant with CLI requirements, but we would ask that you take your time to check that you’re sending valid caller ID with all your calls, even those that are withheld.

An example of a valid INVITE is as follows

INVITE sip:447700900123@london.out.simwood.com SIP/2.0
Max-Forwards: 70
From: "Anonymous" <sip:anonymous@anonymous.invalid>;tag=as7fb2d045
To: <sip:447700900123@london.out.simwood.com>
Contact: <sip:anonymous@10.0.0.1:5060>
Call-ID: 119ae923074211d301ab53e4290577ca@10.0.0.1:5060
CSeq: 102 INVITE
User-Agent: Asterisk PBX 13.3.2
Date: Tue, 19 Jan 2016 18:20:57 GMT
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, SUBSCRIBE, INFO, PUBLISH, MESSAGE
Supported: replaces, timer
Privacy: id
P-Asserted-Identity: <sip:441632960123@10.0.0.1>

Note that the From header does not contain any identifying information, replaced instead with anonymous@anonymous.invalid and a corresponding ‘name’ of “Anonymous”, and the caller’s number is present only in the P-Asserted-Identity header.

The presence of the Privacy header, with the value “id”, ensures that the P-Asserted-Identity value is not passed to the called party.