Tomas
Mandys
Iptel.org

    		    tomas dot mandys at iptel dot org

2007
Tomas Mandys
$Revision: 1.1 $
$Date: 2007/07/30 21:27:59 $

# Iptrtpproxy module

## Overview

It provides similar functionality as nathelper but communicates with netfilter kernel xt_RTPPROXY module using libipt_RTPPROXY userspace library. See http://www.2p.cz/en/netfilter_rtp_proxy All RTP streams are manipulated directly in kernel space, no data are copied from kernel to userspace and back, it reduces load and delay.

The ser module is written as light-weighted, there is not implemented any dialog managment as in nathelper, the reason is that such API should be provided by core or specialized dialog manager module. Because such module is not in CVS, session information may be stored in extra attributes of avp_db module and session id itself in record route as cookie, see rr module.

It should be able to support all cases as re-invites when SIP client offers media change in SDP and when number of medias in offer/answer are different.

Nathelper may be still used for testing if client is behind the NAT.

Limitations:

- only IPv4 addresses are supported.

- more media streams per session supported

## Dependencies

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

- netfilter xt_RTPROXY & libipt_RTPPROXY, see http://www.2p.cz/en/netfilter_rtp_proxy

## Parameters

### `switchboard` (string)

References xt_RTPPROXY switchboard for usage by ser module.

The format is:

      name "=" value * ( ";" name "=" value )

      name =  "name" | ( ( "addr-" | "port-" | "learning-timeout-" | "always-learn-") ("a" | "b") )

The meaning of parameters is described in libipt_RTPROXY and iptrtpproxy documentation.

The name" is identifier that will be used by script functions and references switchboard. It's mandatory parameter. More switchboards may be declared.

#### Declare `switchboard`

    	...
    	modparam("iptrtpproxy", "switchboard", "name=my;addr-a=1.2.3.4;port-a=50000");
    	...

## Functions

### `iptrtpproxy_alloc(gate_a_to_b, switchboard_id)`

Parses SDP content and allocates for each RTP media stream one RTP proxy session. SDP is updates to reflect allocated sessions.

- if gate_a_to_b non equal to zero then SDP regards to gate-a to gate-b direction.

- switchboard_id is reference to a switchboard with name declared as `switchboard` modparam.

- function returns true is a session was created, identifier is available via select `@iptrtpproxy.session_ids`.

#### `iptrtpproxy_alloc` usage

    	...
    	if (iptrtpproxy_alloc("1", "my")) {
    	  $sess_ids = @iptrtpproxy.session_ids;
    	  # save sess_ids in dialog
    	}
    	...

### `iptrtpproxy_update(gate_a_to_b, session_ids)`

Parses SDP content and updates sessions provided by session_ids and updates SDP. If succesfull then session_ids may be changed (in case e.g. media stream has port zero particular session is released), the result of `@iptrtpproxy.session_ids` should be stored for future in-dialog usage.

- if gate_a_to_b non equal to zero then SDP regards to gate-a to gate-b direction.

#### `iptrtpproxy_update` usage

    	...
    	# load $sess_ids from dialog
    	if (iptrtpproxy_update("0", $sess_ids)) {
    	  $sess_ids = @iptrtpproxy.session_ids;
    	  # save sess_ids in dialog
    	}
    	...

### `iptrtpproxy_delete(session_ids)`

Delete sessions identified by session_ids. May be used when dialog is being destroyed (BYE) or when INVITE failed in failure route.

#### `iptrtpproxy_delete` usage

    	...
    	# load $sess_ids from dialog
    	iptrtpproxy_delete($sess_ids);
    	...

### `@iptrtpproxy.session_ids`

Returns sessions allocated/updated in `iptrtpproxy_alloc/update`.

The format is:

    	switchboard_name [ ":" [ session_id *( "," session_id) ] ]
    	session_id = *( [0-9] )   ; empty when no session allocated

### `@iptrtpproxy.sdp_ip`

Return first rewritten IP provided in SDP c= line.