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".

1.2.1. OpenSER 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 OpenSER with this module loaded:

• None.

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.

...
modparam("path", "use_received", 1)
...

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.

...
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.

...
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.

...
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.

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