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

Scott Berkman scott at sberkman.net
Tue Jul 24 16:27:08 EDT 2012

Some systems (such as BroadSoft Broadworks) only use diversion headers to
describe historical information about a call was routed.  I don't think in
these cases the Diversion header is meant to have any impact on delivered
caller ID or charge number.  I've only even recently come across someone
wanting to use the diversion header for this, and they didn't have a good
reason to say why except that another carrier had supported it and they have
a checkbox in their system to enable it.


-----Original Message-----
From: voiceops-bounces at voiceops.org [mailto:voiceops-bounces at voiceops.org]
On Behalf Of Jay Hennigan
Sent: Tuesday, July 24, 2012 12:50 AM
To: voiceops at voiceops.org
Subject: Re: [VoiceOps] Caller-ID: SIP From vs. P-Asserted-Identity

On 7/23/12 5:32 PM, Jeff MacDonald wrote:
> Greetings,
> On Monday, July 23, 2012 07:58:29 PM Colin Brown wrote:
>> The best way is to define and agree with each termination carrier how 
>> they will handle it. I'm speaking about mostly sending international 
>> traffic and believe  me they all want it different ways.
> Does the PBX software easily accomodate something like that?

The situation comes up most often when migrating a customer from a TDM-based
PRI to a PRI delivered over SIP to an IAD.  Also in the call center/agent
scenario described earlier.

In the PRI/TDM world, the PBX is quite capable of sending the inbound CLID
on a hairpinned call, and the RBOC is happy to deliver whatever is sent.

We want to use PAI to keep our CDRs straight, ensure that 9-1-1 routes
correctly, handle subpoenas easily, etc.

We have two primary domestic termination carriers.  One takes the
information in the From: for display on CLID, the other uses PAI.

RFC3325 section 7 refers to inserting an "id" token to the privacy header
field to preclude forwarding PAI to an untrusted party (which I would think
includes an end user's CLID display).  Whether this would result in the
From: being used or just a "Private" display, I don't know and I haven't
found the appropriate knob on any of our gear yet to test it.

Section 8 of the same RFC seems to indicate that how or if PAI is passed on
is somewhat of a crapshoot.  My inquiry to the list was to see if any form
of consensus has been reached in the decade since this RFC was published.

Summary so far of on-list and off-list replies:

1. Use a diversion header.
   *  Not recommended if call was not actually diverted.
   *  Legacy PBX via PRI doesn't tell if diverted or not.

2. Carriers generally prioritize PAI then RPID then From for CLID.

3. Contact the carrier and ask them to use From.  Reasonable carriers should
be able to do this on a per-trunk-group basis.

4. Sending both PAI and RPID is bad, especially if they are different.

We are pursuing option 3.

Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net Impulse
Internet Service  -  http://www.impulse.net/ Your local telephone and
internet company - 805 884-6323 - WB6RDV
VoiceOps mailing list
VoiceOps at voiceops.org

More information about the VoiceOps mailing list