path Module

Andreas Granig

   Inode GmbH

Edited by

Andreas Granig

   Copyright © 2006 Inode GmbH
   Revision History
   Revision $Revision$ $Date: 2009-07-21 10:45:05 +0300
                              (Tue, 21 Jul 2009) $
     __________________________________________________________

   Table of Contents

   1. Admin Guide

        1.1. Overview

              1.1.1. Path insertion for registrations
              1.1.2. Outbound routing to NAT'ed UACs

        1.2. Dependencies

              1.2.1. OpenSIPS Modules
              1.2.2. External Libraries or Applications

        1.3. Exported Parameters

              1.3.1. use_received (int)
              1.3.2. enable_double_path (integer)

        1.4. Exported Functions

              1.4.1. add_path()
              1.4.2. add_path(user)
              1.4.3. add_path_received()
              1.4.4. add_path_received(user)

   List of Examples

   1.1. Set use_received parameter
   1.2. Set enable_double_path parameter
   1.3. add_path usage
   1.4. add_path(user) usage
   1.5. add_path_received() usage
   1.6. add_path_received(user) usage

Chapter 1. Admin Guide

1.1. Overview

   This module is designed to be used at intermediate sip proxies
   like loadbalancers in front of registrars and proxies. It
   provides functions for inserting a Path header including a
   parameter for passing forward the received-URI of a
   registration to the next hop. It also provides a mechanism for
   evaluating this parameter in subsequent requests and to set the
   destination URI according to it.

1.1.1. Path insertion for registrations

   For registrations in a scenario like “[UAC] -> [P1] -> [REG]”,
   the "path" module can be used at the intermediate proxy P1 to
   insert a Path header into the message before forwarding it to
   the registrar REG. Two functions can be used to achieve this:
     * add_path(...) adds a Path header in the form of “Path:
       <sip:1.2.3.4;lr>” to the message using the address of the
       outgoing interface. A port is only added if it's not the
       default port 5060.
       If a username is passed to the function, it is also
       included in the Path URI, like “Path:
       <sip:username@1.2.3.4;lr>”.
     * add_path_received(...) also add a Path header in the same
       form as above, but also adds a parameter indicating the
       received-URI of the message, like “Path:
       <sip:1.2.3.4;received=sip:2.3.4.5:1234;lr>”. This is
       especially useful if the proxy does NAT detection and wants
       to pass the NAT'ed address to the registrar.
       If the function is called with a username, it's included in
       the Path URI too.

1.1.2. Outbound routing to NAT'ed UACs

   If the NAT'ed address of an UAC is passed to the registrar, the
   registrar routes back subsequent requests using the Path header
   of the registration as Route header of the current request. If
   the intermediate proxy had inserted a Path header including the
   “received” parameter during the registration, this parameter
   will show up in the Route header of the new request as well,
   allowing the intermediate proxy to route to this address
   instead of the one propagated in the Route URI for tunneling
   through NAT. This behaviour can be activated by setting the
   module parameter “use_received”.

1.2. Dependencies

1.2.1. OpenSIPS Modules

   The following modules must be loaded before this module:
     * The "rr" module is needed for outbound routing according to
       the “received” parameter.

1.2.2. External Libraries or Applications

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

1.3. Exported Parameters

1.3.1. use_received (int)

   If set to 1, the “received” parameter of the first Route URI is
   evaluated and used as destination-URI if present.

   Default value is 0.

   Example 1.1. Set use_received parameter
...
modparam("path", "use_received", 1)
...

1.3.2. enable_double_path (integer)

   There are some situations when the server needs to insert two
   Path header fields instead of one. For example when using two
   disconnected networks or doing cross-protocol forwarding from
   UDP->TCP. This parameter enables inserting of 2 Paths.

   Default value is 1 (yes).

   Example 1.2. Set enable_double_path parameter
...
modparam("path", "enable_double_path", 0)
...

1.4. Exported Functions

1.4.1.  add_path()

   This function is used to insert a Path header in the form
   “Path: <sip:1.2.3.4;lr>”, where “1.2.3.4” is the address of the
   outgoing interface.

   This function can be used from REQUEST_ROUTE.

   Example 1.3. add_path usage
...
if (!add_path()) {
        sl_send_reply("503", "Internal Path Error");
        ...
};
...

1.4.2.  add_path(user)

   This function adds a Path header in the form “Path:
   <sip:user@1.2.3.4;lr>”.

   Meaning of the parameters is as follows:
     * user - The username to be inserted as user part.

   This function can be used from REQUEST_ROUTE.

   Example 1.4. add_path(user) usage
...
if (!add_path("loadbalancer")) {
        sl_send_reply("503", "Internal Path Error");
        ...
};
...

1.4.3.  add_path_received()

   This function adds a Path header in the form “Path:
   <sip:1.2.3.4;received=sip:2.3.4.5:1234;lr>”, setting it's own
   outgoing address as domain-part, and the address the request
   has been received from as received-parameter.

   This function can be used from REQUEST_ROUTE.

   Example 1.5. add_path_received() usage
...
if (!add_path_received()) {
        sl_send_reply("503", "Internal Path Error");
        ...
};
...

1.4.4.  add_path_received(user)

   This function adds a Path header in the form “Path:
   <sip:user@1.2.3.4;received=sip:2.3.4.5:1234;lr>”, setting
   'user' as username part of address, it's own outgoing address
   as domain-part, and the address the request has been received
   from as received-parameter.

   This function can be used from REQUEST_ROUTE.

   Example 1.6. add_path_received(user) usage
...
if (!add_path_received("inbound")) {
        sl_send_reply("503", "Internal Path Error");
        ...
};
...
