path Module

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:

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”.

The following modules must be loaded before this module:

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

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)
...

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).

...
modparam("path", "enable_double_path", 0)
...

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

Meaning of the parameters is as follows:

This function can be used from REQUEST_ROUTE.

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

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.

Meaning of the parameters is as follows:

This function can be used from REQUEST_ROUTE.

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