[SIPForum-discussion] P-Asserted Identity handling by UAS

[Andrew Yu]

Dear Members,

I'm experiencing strange behavior from an UAS on the way P-Asserted 
Identity is being handled in call forwarding & transfer scenario.

*Call forward Scenario*

UAS receives INVITE from B2BUA proxy of the following format:

Request-line: INVITE sip:12345678 at UAS.com
To: sip:12345678 at UAS.com
From: sip:87654321 at B2BUA.com
P-Asserted-Identity: sip:12345678 at B2BUA.com

UAS call forwards and sent the following invite to the gateway:

Request-line: INVITE sip:91234567 at gateway.com
To: sip:6512345678 at UAS.com
From: sip:87654321 at UAS.com
P-Asserted-Identity: sip:87654321 at UAS.com

Why does the UAS replacing  the P-Asserted identity? I was expecting the 
following UAS behavior to use the P-Asserted Identity when performing 
Call forward:

Request-line: INVITE sip:91234567 at gateway.com
To: sip:6512345678 at UAS.com
From: sip:12345678 at UAS.com
P-Asserted-Identity: sip:12345678 at UAS.com

Or,

Request-line: INVITE sip:91234567 at gateway.com
To: sip:6512345678 at UAS.com
From: sip:87654321 at UAS.com
P-Asserted-Identity: sip:12345678 at UAS.com

*Call transfer Scenario*

UAS receives INVITE from B2BUA proxy of the following format, follow by 
resolving of UAC location and sent the call to UAC:

Request-line: INVITE sip:12345678 at UAS.com
To: sip:12345678 at UAS.com
From: sip:87654321 at B2BUA.com
P-Asserted-Identity: sip:12345678 at B2BUA.com

UAS receives REFER from UAC of the following format:

Request-line: REFER sip:UAS.com
To: sip:12345678 at UAS.com
From: sip:6587654321 at UAS.com
Refer-to: sip:91234567 at UAS.com
Refer-By: sip:6587654321 at UAS.com

UAS process REFER request and sent INVITE for call transfer:

Request-line: INVITE sip:91234567 at gateway.com
To: sip:91234567 at gateway.com
From: sip:87654321 at UAS.com
P-Asserted-Identity: sip:87654321 at UAS.com

Why does the UAS replacing the P-Asserted identity again? I was 
expecting the following UAS behavior to use the P-Asserted Identity when 
performing Call transfer as well...

Request-line: INVITE sip:91234567 at gateway.com
To: sip:91234567 at gateway.com
From: sip:12345678 at UAS.com
P-Asserted-Identity: sip:12345678 at UAS.com

Or,

Request-line: INVITE sip:91234567 at gateway.com
To: sip:91234567 at gateway.com
From: sip:87654321 at UAS.com
P-Asserted-Identity: sip:12345678 at UAS.com

Please advice how should UAS behave when P-Asserted Identity is 
received, whether the received P-Asserted Identity should be used for 
Call forward and transfer. Thank you.

-- 
Cheers,

Asiatel Singapore Pte Ltd
Andrew Yu

19 Jalan Kilang Barat
#06-01, Acetech Centre
Singapore 159361

Tel: +65 6271 8233
Fax: +65 6274 4266