BLA and SBCs

[pmkr...@gmail.com]

I'm testing remote phones with SBCs using Sangoma's upper registration feature - have everything working except for MoH when line on remote phone goes on hold (being worked) and shared line support.

A standards question on shared line support first - in the wiki documentation around BLA support, it was stated that Sipxecs BLA was built to this standard - http://tools.ietf.org/id/draft-anil-sipping-bla-02.txt. Is that still the case?

What we're seeing without the SBC (Polycom local phones with BLA-enabled extensions) is that after the shared extension registers to Sipxcom:

1. Sipxcom issues a subscribe with the SLA event to the Polycom phone (UA) with Contact IP address being the voice server IP and port of 5170.
   
2. The Notify back to Sipxcom from the phone uses port 5170.
3. The Phone subsequently always uses port 5170 when issuing Subscribe requests to Sipxcom with the SLA event specified for all new call-ids.
   

With the SBC inserted between Sipxcom and the remote phone, we're seeing the following:

1. Sipxcom issues a Subscribe to the SBC with the SLA event to the Polycom phone (UA) with the Contact IP address being the voice server IP and port of 5170. The SBC replaces the Contact IP address with the SBC IP address and port number of 5060 and sends the subscribe to the remote phone.
   
2. The Notify back to Sipxcom from the Polycom phone to the SBC uses port 5060 - however, the SBC translates the 5060 to port 5170 when the Notify is sent to Sipxcom as the call-ids are the same. So far, so good.
3. The remote Polycom phone issues Subscribe requests with new call-ids to the SBC with SLA events using port 5060. As it is a new call-id, the SBC passes the Subscribe request to Sipxcom using port 5060 instead of 5170 that Sipxcom is expecting.

Questions:

• In the Polycom world of shared lines, does the port number of the first subscribe with event SLA from the 'state agent' after a shared line registers is what the phone uses when it issues subsequent Subscribes with SLA events. This appears to be the case, but confirmation from others would be helpful
  
• Sipxcom responds with 408 timeout requests when it receives Subscribes with SLA events using port 5060. Is that because Sipxcom is expecting these subscribes using port 5170?
• More generally has anyone done any testing of shared lines on remote phones with SBCs and have gotten success.
  

Know I'm pushing the envelope here - any insights or feedback is appreciated.

All the best

Peter