[VoiceOps] Caller-ID: SIP From vs. P-Asserted-Identity

Alex Balashov abalashov at evaristesys.com
Mon Jul 23 17:21:58 EDT 2012

Almost all commercial softswitch and SBC equipment we've run into
prioritises CLID presentation thusly:

1. P-Asserted-Identity
2. Remote-Party-ID
3. From

However, this is not so ubiquitous that it can be counted on one hundred
percent.  Some folks don't do it.  Some only use RPID (even though it's
a long-expired draft supplanted by PAI).  Some expect RPID or PAI to
play only a supplementary role, with their various screening and
presentation options, and thus deny calls where the CLID in the PAI or
RPID is inconsistent with the CLID in the From.

Most, however, look at PAI, then RPID, then From.  I can't speak to
whether this is "correct" or is grounded in some sort of best-practical
recommendation somewhere.  It's just what they do.

On 07/23/2012 05:08 PM, Jay Hennigan wrote:

> Question for the experts:
> We have a scenario where a SIP user originates a call to the PSTN (not
> 9-1-1) with a SIP From: header containing one DID and
> P-Asserted-Identity showing a different DID.
> We expect the carrier to use the P-Asserted-Identity for billing and
> recordkeeping but send the SIP From: out as the CLID to be displayed to
> the called party.
> Typically this is done in a call center type scenario where an agent
> wants the CLID to display the main number of the agent  pool and not the
> specific DID of the agent.  Another scenario is a customer PRI-based PBX
> that hairpins inbound calls back out to a traveling user and wants to
> preserve the original caller's information.
> One of our terminating carriers uses the P-Asserted-Identity as the
> displayed CLID and not the SIP From:.  I feel that this is not correct.
>   Opinions?
> Numbers have been changed to protect the guilty...
> TO: <sip:8055550123 at www.xxx.yyy.zzz;user=phone>
> FROM: "Fred
> Flintstone"<sip:+18055550199 at www.xxx.yyy.zzz;user=phone>;tag=1689985881-1343063740200-
> P-Asserted-Identity: "Fred
> Flintstone"<sip:+18055550177 at www.xxx.yyy.zzz;user=phone>
> TIME/DATE: Mon Jul 23 17:15:39 2012  (GMT)
> RESULT: Called party (8055550123) is seeing 8055550177 as calling
> party's caller ID instead of 8055550199

Alex Balashov - Principal
Evariste Systems LLC
235 E Ponce de Leon Ave
Suite 106
Decatur, GA 30030
Tel: +1-678-954-0670
Fax: +1-404-961-1892
Web: http://www.evaristesys.com/, http://www.alexbalashov.com/

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