Diversion Module

Jan Janak

   FhG FOKUS

Edited by

Jan Janak

   Copyright © 2004 FhG FOKUS
   Revision History
   Revision $Revision: 4630 $ $Date: 2008-08-06 12:08:33 +0200
                              (Mi, 06 Aug 2008) $
     __________________________________________________________

   Table of Contents

   1. Admin Guide

        1.1. Overview
        1.2. Dependencies

              1.2.1. Kamailio Modules
              1.2.2. External Libraries or Applications

        1.3. Exported Parameters

              1.3.1. suffix (string)

        1.4. Exported Functions

              1.4.1. add_diversion(reason)

        1.5. Diversion Example

   2. Developer Guide

   List of Examples

   1.1. suffix usage
   1.2. add_diversion usage

Chapter 1. Admin Guide

1.1. Overview

   The module implements the Diversion extensions as per
   draft-levy-sip-diversion-08. The diversion extensions are
   useful in various scenarios involving call forwarding.
   Typically one needs to communicate the original recipient of
   the call to the PSTN gateway and this is what the diversion
   extensions can be used for.

Warning

   The draft-levy-sip-diversion-08 is expired!! See IETF I-D
   tracker.

1.2. Dependencies

1.2.1. Kamailio Modules

   None.

1.2.2. External Libraries or Applications

   The following libraries or applications must be installed
   before running Kamailio with this module loaded:
     * None.

1.3. Exported Parameters

1.3.1. suffix (string)

   The suffix to be appended to the end of the header field. You
   can use the parameter to specify additional parameters to be
   added to the header field, see the example.

   Default value is "" (empty string).

   Example 1.1. suffix usage
modparam("diversion", "suffix", ";privacy=full")

1.4. Exported Functions

1.4.1. add_diversion(reason)

   The function adds a new diversion header field before any other
   existing Diversion header field in the message (the newly added
   Diversion header field will become the topmost Diversion header
   field). The inbound (without any modifications done by the
   proxy server) Request-URI will be used as the Diversion URI.

   Meaning of the parameters is as follows:
     * reason - The reason string to be added as the reason
       parameter

   This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

   Example 1.2. add_diversion usage
...
add_diversion("user-busy");
...

1.5. Diversion Example

   The following example shows a Diversion header field added to
   INVITE message. The original INVITE received by the user agent
   of sip:bob@sip.org is:
INVITE sip:bob@sip.org SIP/2.0
Via: SIP/2.0/UDP 1.2.3.4:5060
From: "mark" <sip:mark@sip.org>;tag=ldgheoihege
To: "Bob" <sip:bob@sip.org>
Call-ID: adgasdkgjhkjha@1.2.3.4
CSeq: 3 INVITE
Contact: <sip:mark@1.2.3.4>
Content-Length: 0

   The INVITE message is diverted by the user agent of
   sip:bob@sip.org because the user was talking to someone else
   and the new destination is sip:alice@sip.org :
INVITE sip:alice@sip.org SIP/2.0
Via: SIP/2.0/UDP 5.6.7.8:5060
Via: SIP/2.0/UDP 1.2.3.4:5060
From: "mark" <sip:mark@sip.org>;tag=ldgheoihege
To: "Bob" <sip:bob@sip.org>
Call-ID: adgasdkgjhkjha@1.2.3.4
CSeq: 3 INVITE
Diversion: <sip:bob@sip.org>;reason=user-busy
Contact: <sip:mark@1.2.3.4>
Content-Length: 0

Chapter 2. Developer Guide

   According to the specification new Diversion header field
   should be inserted as the topmost Diversion header field in the
   message, that means before any other existing Diversion header
   field in the message. In addition to that, add_diversion
   function can be called several times and each time it should
   insert the new Diversion header field as the topmost one.

   In order to implement this, add_diversion function creates the
   anchor in data_lump lists as a static variable to ensure that
   the next call of the function will use the same anchor and
   would insert new Diversion headers before the one created in
   the previous execution. To my knowledge this is the only way of
   inserting the diversion header field before any other created
   in previous runs of the function.

   The anchor kept this way is only valid for a single message and
   we have to invalidate it when another message is being
   processed. For this reason, the function also stores the id of
   the message in another static variable and compares the value
   of that variable with the id of the SIP message being
   processed. If they differ then the anchor will be invalidated
   and the function creates a new one.

   The following code snippet shows the code that invalidates the
   anchor, new anchor will be created when the anchor variable is
   set to 0.
static inline int add_diversion_helper(struct sip_msg* msg, str* s)
{
    static struct lump* anchor = 0;
    static int msg_id = 0;

    if (msg_id != msg->id) {
        msg_id = msg->id;
        anchor = 0;
    }
...
}
