Diversion Module

Jan Janak


Edited by

Jan Janak

Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Parameters
3.1. suffix (string)
4. Functions
4.1. add_diversion(reason [, uri])
5. Diversion Example
2. Developer Guide

List of Examples

1.1. suffix usage
1.2. add_diversion usage

Chapter 1. Admin Guide

1. Overview

The module implements the Diversion extensions as per RFC 5806. 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.


Note that RFC 5806 has historic status.

2. Dependencies

2.1. Kamailio Modules


2.2. External Libraries or Applications

The following libraries or applications must be installed before running Kamailio with this module loaded:

  • None.

3. Parameters

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")

4. Functions

4.1. add_diversion(reason [, uri])

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). If 'uri' parameter is missing, 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

  • uri - The URI to be set in Diversion header

The parameters can contain pseudo-variables.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE, BRANCH_ROUTE.

Example 1.2. add_diversion usage

add_diversion("user-busy", "$ru");

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
From: "mark" <sip:mark@sip.org>;tag=ldgheoihege
To: "Bob" <sip:bob@sip.org>
Call-ID: adgasdkgjhkjha@
Contact: <sip:mark@>
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
Via: SIP/2.0/UDP
From: "mark" <sip:mark@sip.org>;tag=ldgheoihege
To: "Bob" <sip:bob@sip.org>
Call-ID: adgasdkgjhkjha@
Diversion: <sip:bob@sip.org>;reason=user-busy
Contact: <sip:mark@>
Content-Length: 0

Chapter 2. Developer Guide

According to the specification a 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, the 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;