1. Iptrtpproxy module

Tomas Mandys

Revision History
Revision $Revision$ $Date$

1.1. Overview
1.2. Dependencies
1.3. Parameters
1.3.1. config (string)
1.3.2. switchboard (string)
1.4. Functions
1.4.1. iptrtpproxy_alloc(gate_a_to_b, switchboard_id)
1.4.2. iptrtpproxy_update(gate_a_to_b, session_ids)
1.4.3. iptrtpproxy_adjust_timeout(gate_a_to_b, session_ids)
1.4.4. iptrtpproxy_delete(session_ids)
1.4.5. iptrtpproxy_find(gate_a, gate_b)
1.4.6. @iptrtpproxy.session_ids
1.4.7. @iptrtpproxy.sdp_ip
1.4.8. @iptrtpproxy.switchboard
1.4.9. @iptrtpproxy.direction

1.1. Overview

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

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.


  • only IPv4 addresses are supported.

  • more media streams per session supported

1.2. Dependencies

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


The module Makefile must be edited and iptdir setup to the directory with the iptable sources (if different from ~/iptables). Alternatively compile the module using:

		make -C modules/iptrtpproxy iptdir=path_to_iptables_src

1.3. Parameters

1.3.1. config (string)

References iptrtpproxy.cfg, see iptrtpproxy_helper. Default value is /etc/iptrtpproxy.cfg.

1.3.2. switchboard (string)

References xt_RTPPROXY switchboard for usage by ser module.

The format is:

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

  name =  "name" | "*" | ( "ringing-timeout " ) | ( ( "learning-timeout-" | "always-learn-") ("a" | "b") )

The meaning of parameters is described in libipt_RTPROXY and iptrtpproxy documentation. ringing timeout is explicit timeout in sec regarding ringing. Ringing requires manual callee action, i.e. it may takes long time. Default value is 60 sec.

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

Example 1. Declare switchboard

	modparam("iptrtpproxy", "config", "/etc/iptrtpproxy.cfg");
	modparam("iptrtpproxy", "switchboard", "name=*;learning-timeout-a=10;learning-timeout-b=10;ringing-timeout=90");
	modparam("iptrtpproxy", "switchboard", "name=my;ringing-timeout=60");

1.4. Functions

1.4.1.  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 bit 0 is set then SDP regards to gate-a to gate-b direction. If bit 1 is set then ringing timeout is used instead of learning timeout for particular gate timeout.

  • switchboard_id is reference to a switchboard with name declared as switchboard modparam. If empty then use switchboard found by iptrtpproxy_find (equal using @iptrtpproxy.switchboard).

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

Example 2. iptrtpproxy_alloc usage

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

1.4.2.  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 bit 0 is set then SDP regards to gate-a to gate-b direction. If bit 1 is set then ringing timeout is used instead of learning timeout for particular gate timeout.

Example 3. iptrtpproxy_update usage

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

1.4.3.  iptrtpproxy_adjust_timeout(gate_a_to_b, session_ids)

Adjust timeout for particular gate. It's useful in "200 OK" decrease timeout to learning timeout if INVITE has set (long) ringing timeout.

  • if gate_a_to_b bit 0 is set then it regards to gate-a to gate-b direction. If bit 1 is set then ringing timeout is used instead of learning timeout for particular gate timeout.

Example 4. iptrtpproxy_adjust_timeout usage

	# load $sess_ids from dialog
	if (iptrtpproxy_adjust_timeout("0", $sess_ids)) {

1.4.4.  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.

Example 5. iptrtpproxy_delete usage

	# load $sess_ids from dialog

1.4.5.  iptrtpproxy_find(gate_a, gate_b)

Find corresponding switchboard and set @iptrtpproxy.switchboard and @iptrtpproxy.direction.

  • if gate_a/b switchboard identification

  • function returns true if switch was found

Example 6. iptrtpproxy_find usage

	if (iptrtpproxy_find("@received.ip", "@next_hop.src_ip")) {
		if (iptrtpproxy_alloc("1", "")) {
			  $sess_ids = @iptrtpproxy.session_ids;


1.4.6.  @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

1.4.7.  @iptrtpproxy.sdp_ip

Return first rewritten IP provided in SDP c= line.

1.4.8.  @iptrtpproxy.switchboard

Switchboard found by iptrtpproxy_find.

1.4.9.  @iptrtpproxy.direction

Direction determined by iptrtpproxy_find. 1..gate A->B, 0..gate B->A