[asterisk-dev] Implementation of Broadsoft Sip Access in Asterisk to enable SLA for Sipura/Linksys

[Eugene Grossi]

I started out this summer implementing Asterisk SLA for the Sipura/Linksys
handsets. My strategy was to make Asterisk compatible with the Broadworks
sip access side extensions; this would allow the Sipura shared extensions to
be compatible Asterisk SLA.

Currently I have full SLA compatability with SPA942's working as well as
integration with other (AASTRA 53i) SLA compatible phones. I have described
my implementation strategy below for developer comments, before I post the
code as a potential feature patch.

****************
Listed below are modifications of Asterisk in chan_sip.c and pbx.h to
accommidate rudimentary implementation of Broadsoft Extensions.  The
specifications in "BROADWORKS SIP ACCESS SIDE EXTENSIONS INTERFACE
SPECIFICATIONS -RELEASE 13.0" were used, with the short term goal of
achieving SLA functionality for Sipura phones (tested on SPA942's). 

To Asterisk:

In pbx.h:
AST_EXTENSION_REQLINESEIZE was added to ast_extension_states. A Broadsoft
shared extension can request a line seize.

In chan_sip.c:

Added subscriptiontype of CALL_INFO.  The Call-Info header is specified in
RFC 3261. 

Added to the sip_user configuration and sip_pvt declarations "notify_exten"
as discussed earlier in the fall on the developers list. Originally this was
going to be used due to lack of a subscription setup on the Sipura phones;
Current firmware does generate a subscription to the peer exten
automatically now for "shared" extensions.  I am using this variable to
specifically direct the incoming call when a SLA is already active,
otherwise the INVITE generated by the broadsoft generates an "incomplete
address" from Asterisk.  Should this field be renamed to "sla_connect" ?

Transmit_state_notify subroutine was added and modified to handle CALL_INFO
.  Also added state "LINE_SEIZE" used by Broadsoft and
AST_EXTENSION_REQLINESEIZE handler was added.  When a Broadsoft Shared
extension requests a line seize, it is automatically granted. When other
Broadsoft Shared extensions are sent a notification, there are told that the
call is on "hold" (not private). This allows them to join into the SLA (by
generating an INVITE) if their line key is hit.

Handle_request_invite subroutine was modified. When a Broadsoft Shared
extension attempts to INVITE into an active shared call, the address was
incomplete. This is checked for and the address is "completed" using the
information from the "notify_exten" variable.

Handle_request_subscribe subroutine was modified. Deal with subscription for
Line-Seize event and for Call-info subscriptions. Uses Call-info as the
subscription type for Linksys user agents.

I would appreciate any feedback.
gene
  

-------------------------------      
Eugene A. Grossi, M.D.
Professor of Cardiothoracic Surgery
New York University School of Medicine
Suite 9-V; 530 First Avenue
New York, NY 10016
ph (212) 263-7452
fax(212) 263-5534
grossi at cv.med.nyu.edu
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