sca Module

Andrew Mortensen

   University of Pennsylvania

   Copyright © 2012 Andrew Mortensen, admorten@isc.upenn.edu
     _________________________________________________________________

   Table of Contents

   1. Admin Guide

        1. Overview
        2. Dependencies

              2.1. Modules

        3. Parameters

              3.1. hash_table_size (integer)
              3.2. call_info_max_expires (integer)
              3.3. line_seize_max_expires (integer)
              3.4. purge_expired_interval (integer)
              3.5. db_url (str)
              3.6. subs_table (str)
              3.7. db_update_interval (integer)

        4. Functions

              4.1. sca_handle_subscribe() 
              4.2. sca_call_info_update() 

        5. Exported RPC Commands

              5.1. sca.all_subscriptions
              5.2. sca.all_appearances
              5.3. sca.seize_appearance
              5.4. sca.update_appearance
              5.5. sca.release_appearance

   List of Examples

   1.1. Set hash_table_size:
   1.2. Set call_info_max_expires:
   1.3. Set line_seize_max_expires:
   1.4. Set purge_expired_interval:
   1.5. Set db_url parameter:
   1.6. Set subs_table parameter:
   1.7. Set db_update_interval:
   1.8. sca_handle_subscribe usage:
   1.9. sca_call_info_update usage:

Chapter 1. Admin Guide

   Table of Contents

   1. Overview
   2. Dependencies

        2.1. Modules

   3. Parameters

        3.1. hash_table_size (integer)
        3.2. call_info_max_expires (integer)
        3.3. line_seize_max_expires (integer)
        3.4. purge_expired_interval (integer)
        3.5. db_url (str)
        3.6. subs_table (str)
        3.7. db_update_interval (integer)

   4. Functions

        4.1. sca_handle_subscribe() 
        4.2. sca_call_info_update() 

   5. Exported RPC Commands

        5.1. sca.all_subscriptions
        5.2. sca.all_appearances
        5.3. sca.seize_appearance
        5.4. sca.update_appearance
        5.5. sca.release_appearance

1. Overview

   The sca module implements Shared Call Appearances. It handles SUBSCRIBE
   messages for call-info and line-seize events, and sends call-info NOTIFYs to
   line subscribers to implement line bridging. The module implements SCA as
   defined in Broadworks SIP Access Side Extensions Interface Specifications,
   Release 13.0, version 1, sections 2, 3 and 4.

   SCA group members receive call state notifications when other group members
   participate in calls. An SCA caller can place a call on hold, and the call
   may be retrieved from hold by another member of the group.

   Subscribers to SCA call-info events SUBSCRIBE to their address-of-record
   (AoR), asking the application server to send call-info NOTIFYs with line
   state information as lines in the subscriber group are used.

   For example, when an SCA subscriber takes the phone off hook, it sends a
   line-seize SUBSCRIBE to the application server. The application server
   acknowledges the request, and sends to the subscriber a line-seize NOTIFY
   with  the appearance index of the line claimed for the subscriber. The
   application also sends call-info NOTIFYs to the other SCA subscribers to the
   AoR, letting them know that an appearance within the group has gone off
   hook. Subscribers update their display appropriately.

   Subscribers to an SCA address-of-record will receive call-info NOTIFYs when
   a  member  of the group seizes a line (seized); receives a 180 ringing
   response  from  the remote party (ringing); receives a 183 progressing
   response from the remote party (progressing); when the remote party answers
   the call (active); when either party in the call places the call on hold
   (held); and when an SCA line goes back on hook (idle).

   The call-info subscriber information is stored in memory and is periodically
   written to the database. Call state information is stored in memory. A
   future release may periodically write call state to the database, as well.
   The database is purely for restoring subscriptions after a restart of the
   application server. Subscriber information is also flushed to the database
   when the service is stopped.

   At  the  time of this writing, Polycom and Cisco handsets are known to
   implement  the  call-info and line-seize event packages defined in the
   document, which may be found freely on the web.

   To date, this module has only been tested with Polycom Soundpoint 550s and
   650s running Polycom SIP 3.3.4.

2. Dependencies

   2.1. Modules

2.1. Modules

   The following modules must be loaded before this module:
     * a database module
     * sl
     * tm

3. Parameters

   3.1. hash_table_size (integer)
   3.2. call_info_max_expires (integer)
   3.3. line_seize_max_expires (integer)
   3.4. purge_expired_interval (integer)
   3.5. db_url (str)
   3.6. subs_table (str)
   3.7. db_update_interval (integer)

3.1. hash_table_size (integer)

   Size, as a power of two, of the shared memory hash table containing the
   call-info subscriptions and the appearance state. A larger power of two
   means better performance (fewer collisions, making for fewer subscriber URI
   comparisons) at the expense of increased shared memory use.

   Default value is 9 (2 ^ 9 == 512). 

   Example 1.1. Set hash_table_size:
...
# create shared memory hash table with 2^8 (256) slots
modparam( "sca", "hash_table_size", 8 )
...

3.2. call_info_max_expires (integer)

   The maximum allowed call-info subscription time in seconds.

   Default value is 3600 (1 hour). 

   Example 1.2. Set call_info_max_expires:
...
modparam( "sca", "call_info_max_expires", 1800 )
...

3.3. line_seize_max_expires (integer)

   The maximum allowed line-seize subscription time in seconds.

   Default value is 15 (15 seconds). 

   A maximum line-seize subscription time of 15 seconds is recommended in the
   SIP Access Side Extensions document. This interval is purposely short to
   prevent  a client from seizing an appearance without making a call for
   extended periods of time.

   Example 1.3. Set line_seize_max_expires:
...
modparam( "sca", "line_seize_max_expires", 30 )
...

3.4. purge_expired_interval (integer)

   The  period of time in seconds between purges of expired call-info and
   line-seize subscriptions.

   Default value is 120 (2 minutes). 

   On finding an expired subscription, the module removes the subscription from
   the shared memory hash table, and sends a NOTIFY with Subscription-State
   "terminated;expired" header value to the subscriber. It also NOTIFYs other
   members of the group, in the event that the expired subscription was a
   line-seize.

   Example 1.4. Set purge_expired_interval:
...
modparam( "sca", "purge_expired_interval", 60 )
...

3.5. db_url (str)

   URL of database to which subscribers will be written.

   Default value is mysql://kamailio:kamailiorw@localhost/kamailio

   Example 1.5. Set db_url parameter:
...
modparam( "sca", "db_url", "mysql://kamailio:kamailiorw@localhost/kamailio" )
...

3.6. subs_table (str)

   Name of the database table where call-info subscriptions are written.

   Default value is “sca_subscriptions”. 

   Example 1.6. Set subs_table parameter:
...
modparam( "sca", "subs_table", "call_info_subscriptions" )
...

3.7. db_update_interval (integer)

   Period in seconds between writes of call-info subscriber information to the
   database.

   Default value is 300 (5 minutes). 

   Example 1.7. Set db_update_interval:
...
modparam( "sca", "db_update_interval", 120 )
...

4. Functions

   4.1. sca_handle_subscribe() 
   4.2. sca_call_info_update() 

4.1.  sca_handle_subscribe()

   The function handling call-info and line-seize SUBSCRIBE requests. It stores
   or updates the subscriptions in shared memory, and sends NOTIFYs to the
   subscriber and other members of the group as needed.

   For example, a line-seize SUBSCRIBE will cause the module to reserve an
   appearance  index  for the subscriber; send a line-seize NOTIFY to the
   subscriber indicating which appearance index it must use; and send call-info
   NOTIFYs to other subscribers to the address-of-record letting them know the
   appearance is off hook.

   This function can be used from the REQUEST_ROUTE.

   Return code:
     * 1 - successful
     * -1 - failed, error logged

   Example 1.8. sca_handle_subscribe usage:
...
if ( method == "SUBSCRIBE" &&
        ( @hf_value.event == "call-info" || @hf_value.event == "line-seize" ))
{
    sca_handle_subscribe();
}
...

4.2.  sca_call_info_update()

   The sca_call_info_update function updates call state for SCA appearances. If
   a request or response packet contains a Call-Info header, the function
   extracts call state from the header and sends NOTIFYs to subscribers if
   needed. If no Call-Info header is included in the packet, the module looks
   up the To and From URIs to see if either are SCA addresses-of-record. If
   either the To or From URI are SCA AoRs, the function looks up the appearance
   by dialog and updates call state as needed, sending NOTIFYs to members of
   the group if the call state has changed.

   The sca_call_info_update function updates call state for INVITE, CANCEL,
   BYE, PRACK and REFER requests and responses.

   This  function  can  be  used from the REQUEST_ROUTE, REPLY_ROUTE, and
   FAILURE_ROUTE.

   Return code:
     * 1 - successful
     * -1 - failed, error logged

   Example 1.9. sca_call_info_update usage:
...
route
{
    ...
    if ( $fu.sca == "y" || $tu.sca == "y" ) {
        sca_call_info_update();
    }
    ...
}

onreply_route[REPLY_ROUTE]
{
...
    if ( status =~ "[456][0-9][0-9]" ) {
        # don't update SCA state here, since there may be
        # failure route processing (e.g., call forwarding).
        # update state in failure route instead.
        break;
    }

    sca_call_info_update();
...
}

failure_route[FAILURE_ROUTE]
{
...
    sca_call_info_update();
...
}
...

5. Exported RPC Commands

   5.1. sca.all_subscriptions
   5.2. sca.all_appearances
   5.3. sca.seize_appearance
   5.4. sca.update_appearance
   5.5. sca.release_appearance

5.1. sca.all_subscriptions

   List all current call-info and line-seize subscriptions.

   Name: sca.all_subscriptions

   Parameters: none

   Example:
            sercmd sca.all_subscriptions

5.2. sca.all_appearances

   List all SCA appearances with non-idle state.

   Name: sca.all_appearances

   Parameters: none

   Example:
            sercmd sca.all_appearances

5.3. sca.seize_appearance

   Seize an appearance index for a specific contact within an SCA group, and
   notify other members of the group that the appearance is off hook. Useful
   for testing SCA signaling.

   Name: sca.seize_appearance

   Parameters: 2
     * SCA Address-of-Record
     * SCA Contact URI

   Example:
            # seize next available appearance of sip:215@voice.example.com
            # for contact sip:215@10.0.1.2
            sercmd sca.seize_appearance sip:215@voice.example.com sip:215@10.0.
1.2

5.4. sca.update_appearance

   Update the state of an in-use appearance index, and notify other members of
   the group. Useful for testing SCA signaling.

   Name: sca.update_appearance

   Parameters: 3 or 4
     * SCA Address-of-Record
     * Index of In-Use Appearance
     * Appearance  State  (seized,  ringing,  progressing,  active, held,
       held-private)
     * Appearance Display Info (Optional)

   Example:
            # update in-use appearance index 3 of sip:215@voice.example.com
            # state held.
            sercmd sca.update_appearance sip:215@voice.example.com 3 held

5.5. sca.release_appearance

   Set a non-idle appearance index to idle and NOTIFY members of the group.

   Name: sca.release_appearance

   Parameters: 2
     * SCA Address-of-Record
     * Appearance Index

   Example:
            # release appearance of sip:215@voice.example.com with
            # appearance index 3
            sercmd sca.release_appearance sip:215@voice.example.com 3