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<!-- Module User's Guide -->

<chapter>

	<title>&adminguide;</title>

	<section>
	<title>Overview</title>
	<para>
		This is a module to help with &nat; traversal and reuse
		of <acronym>TCP</acronym> connections. In particular,
		it helps symmetric &ua;s that don't advertise they are symmetric
		and are not able to determine their public address.
	</para>
	<para>
		The function <function>fix_nated_contact()</function> rewrites the <quote>Contact</quote>
		header field with request's source address:port pair. The function
		<function>fix_nated_sdp()</function> adds the active direction indication
		to &sdp; (flag 0x01) and updates the source &ip; address too (flag 0x02). The function
		<function>fix_nated_register()</function> exports the request's source
		address:port into an AVP to be used during <function>save()</function> and should
		be used for <quote>REGISTER</quote> requests.
	</para>
        <para>
		Note: <function>fix_nated_contact()</function> changes the <quote>Contact</quote>
		header, thus it breaks the RFC. Although this is not always an issue, it may
		cause problems with strict SIP clients. An alternative is to use
		<function>add_contact_alias()</function> (or <function>set_contact_alias()</function>)
		that together with the <function>handle_ruri_alias()</function> is standards
		conforming and also supports reuse of TCP/TLS connections.
	</para>
	</section>

	<section>
	<title>NAT pinging types</title>
	<para>
		Currently, the nathelper module supports two types of NAT pings:
	</para>
	<itemizedlist>
		<listitem>
			<para>
			<emphasis>UDP packet</emphasis> - 4 bytes (zero filled) UDP
			packets are sent to the contact address.
			</para>
			<itemizedlist>
				<listitem>
				<para><emphasis>Advantages:</emphasis> low bandwidth traffic,
				easy to generate by &kamailio;;
				</para>
				</listitem>
				<listitem>
				<para><emphasis>Disadvantages:</emphasis> unidirectional
				traffic through NAT (inbound - from outside to inside); As
				many NATs do update the bind timeout only on outbound traffic,
				the bind may expire and get closed.
				</para>
				</listitem>
			</itemizedlist>
		</listitem>
		<listitem>
			<para>
			<emphasis>SIP request</emphasis> - a stateless SIP request is
			sent to the UDP contact address.
			</para>
			<itemizedlist>
				<listitem>
				<para><emphasis>Advantages:</emphasis> bidirectional traffic
				through NAT, since each PING request from &kamailio; (inbound
				traffic) will force the SIP client to generate a SIP reply
				(outbound traffic) - the NAT bind will be surely kept open.
				</para>
				</listitem>
				<listitem>
				<para><emphasis>Disadvantages:</emphasis> higher bandwidth
				traffic, more expensive (as time) to generate by &kamailio;;
				</para>
				</listitem>
			</itemizedlist>
		</listitem>
	</itemizedlist>
	</section>

	<section>
	<title>Dependencies</title>
	<section>
		<title>&kamailio; Modules</title>
		<para>
		The following modules must be loaded before this module:
			<itemizedlist>
			<listitem>
			<para>
				<emphasis>usrloc</emphasis> module - only if the NATed
				contacts are to be pinged.
			</para>
			</listitem>
			</itemizedlist>
		</para>
	</section>
	<section>
		<title>External Libraries or Applications</title>
		<para>
		The following libraries or applications must be installed before
		running &kamailio; with this module loaded:
			<itemizedlist>
			<listitem>
			<para>
				<emphasis>None</emphasis>.
			</para>
			</listitem>
			</itemizedlist>
		</para>
	</section>
	</section>

	<section>
	<title>Parameters</title>
	<section id="nathelper.p.force_socket">
		<title><varname>force_socket</varname> (string)</title>
		<para>
		Socket to be used when sending NAT pings for UDP communication.
		If no one specified, the OS will choose a socket.
		</para>
		<para>
		<emphasis>
			Default value is <quote>NULL</quote>.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>force_socket</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "force_socket", "127.0.0.1:5060")
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.natping_interval">
		<title><varname>natping_interval</varname> (integer)</title>
		<para>
		Period of time in seconds between sending the NAT pings to all
		currently registered &ua;s to keep their &nat; bindings alive.
		Value of 0 disables this functionality.
		</para>
		<note><para>
		Enabling the NAT pinging functionality will force the module to
		bind itself to USRLOC module.
		</para></note>
		<para>
		<emphasis>
			Default value is 0.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>natping_interval</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "natping_interval", 10)
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.ping_nated_only">
		<title><varname>ping_nated_only</varname> (integer)</title>
		<para>
		If this parameter is set to 1 then only contacts that have
		the behind NAT <quote>nat_bflag</quote> flag set in user location
		records get the NAT ping (the <quote>nat_bflag</quote> is specified via
		modparam of usrloc module). By default the ping is done with 4-bytes UDP
		packet. If sipping_bflag is also set, then the ping is done with
		a stateless SIP request (by default: OPTIONS request).
		</para>
		<para>
		If it is 0, then all contacts get a NAT ping, by default being the 4-bytes
		UDP packet. If it is 0 and sipping_bflag parameter is set, then
		SIP-request-based pinging is sent to all contacts.
		</para>
		<para>
		<emphasis>
			Default value is 0.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>ping_nated_only</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "ping_nated_only", 1)
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.natping_processes">
		<title><varname>natping_processes</varname> (integer)</title>
		<para>
		How many timer processes should be created by the module for the
		exclusive task of sending the NAT pings.
		</para>
		<para>
		<emphasis>
			Default value is 1.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>natping_processes</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "natping_processes", 3)
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.natping_socket">
		<title><varname>natping_socket</varname> (string)</title>
		<para>
		Spoof the natping's source-ip to this address. Works only for IPv4.
		</para>
		<para>
		<emphasis>
			Default value is NULL.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>natping_socket</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "natping_socket", "192.168.1.1:5006")
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.received_avp">
		<title><varname>received_avp</varname> (str)</title>
		<para>
		The name of the Attribute-Value-Pair (AVP) used to store the URI
		containing the received IP, port, and protocol. The URI is created
		by fix_nated_register function of nathelper module and the attribute
		is then used by the registrar to store the received parameters. Do
		not forget to change the value of corresponding parameter in
		registrar module if you change the value of this parameter.
		</para>
		<note>
		<para>
		You must set this parameter if you use <function>fix_nated_register</function>. In such
		case you must set the parameter with same name in the <quote>registrar</quote>
		module to same value.
		</para>
		</note>
		<para>
		<emphasis>
			Default value is "NULL" (disabled).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>received_avp</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "received_avp", "$avp(i:42)")
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.sipping_bflag">
		<title><varname>sipping_bflag</varname> (integer)</title>
		<para>
		Which branch flag should be used by the module to identify NATed
		contacts for which it should perform NAT ping via a SIP request
		instead of dummy UDP packet.
		</para>
		<para>
		<emphasis>
			Default value is -1 (disabled).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>sipping_bflag</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "sipping_bflag", 7)
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.sipping_from">
		<title><varname>sipping_from</varname> (string)</title>
		<para>
		The parameter sets the SIP URI to be used in generating the SIP
		requests for NAT ping purposes. To enable the SIP request pinging
		feature, you have to set this parameter. The SIP request pinging
		will be used only for requests marked so.
		</para>
		<para>
		<emphasis>
			Default value is <quote>NULL</quote>.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>sipping_from</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "sipping_from", "sip:pinger@siphub.net")
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.sipping_method">
		<title><varname>sipping_method</varname> (string)</title>
		<para>
		The parameter sets the SIP method to be used in generating the SIP
		requests for NAT ping purposes.
		</para>
		<para>
		<emphasis>
			Default value is <quote>OPTIONS</quote>.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>sipping_method</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "sipping_method", "INFO")
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.natping_disable_bflag">
		<title><varname>natping_disable_bflag</varname> (integer)</title>
		<para>
		What branch flag should be used by the module to disable NAT pings
		on a per-registration basis. If the given flag is set for a
		particular registration, then no NAT pings will be sent at all,
		regardless of any other conditions.
		</para>
		<para>
		<emphasis>
			Default value is -1 (disabled).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>natping_disable_bflag</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "natping_disable_bflag", 8)
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.nortpproxy_str">
		<title><varname>nortpproxy_str</varname> (string)</title>
		<para>
		The parameter sets the SDP attribute used by nathelper to mark
		the packet SDP that information have already been mangled.
		</para>
		<para>
		If empty string, no marker will be added or checked.
		</para>
		<note><para>
		The string must be a complete SDP line, including the EOH (\r\n).
		</para></note>
		<para>
		<emphasis>
			Default value is <quote>a=nortpproxy:yes\r\n</quote>.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>nortpproxy_str</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "nortpproxy_str", "a=sdpmangled:yes\r\n")
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.keepalive_timeout">
		<title><varname>keepalive_timeout</varname> (int)</title>
		<para>
		The parameter sets the interval in seconds after which a natted
		contact is removed from location table if it does not reply to SIP
		keepalives (usually OPTIONS ping requests).
		</para>
		<para>
		The features is available only for UDP contacts that are stored in memory
		(not working for db only mode for usrloc module).
		</para>
		<para>
		Keepalives are sent stateless, not using TM module. The value of this
		parameter has to be few times higher than natping_interval.
		</para>
		<para>
		<emphasis>
			Default value is <quote>0</quote> (feature disabled).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>keepalive_timeout</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "keepalive_timeout", 120)
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.udpping_from_path">
		<title><varname>udpping_from_path</varname> (int)</title>
		<para>
		Enable sending UDP pings (keepalives) using raw socket from Path
		address.
		</para>
		<para>
		<emphasis>
			Default value is <quote>0</quote> (feature disabled).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>udpping_from_path</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "udpping_from_path", 1)
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.append_sdp_oldmediaip">
		<title><varname>append_sdp_oldmediaip</varname> (int)</title>
		<para>
		The parameter controls if oldmediaip field should be appended to the SDP.
		</para>
		<para>
		<emphasis>
			Default value is <quote>1</quote> (feature enabled).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>append_sdp_oldmediaip</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "append_sdp_oldmediaip", 1)
...
</programlisting>
		</example>
	</section>

	<section id="nathelper.p.filter_server_id">
		<title><varname>filter_server_id</varname> (int)</title>
		<para>
		Filter contacts by <quote>server_id</quote> core parameter.
		Use this parameter to limit pinging. When set to <quote>1</quote>,
		only proxy instances which send packets are those where core server_id
		matches server_id saved in usrloc.
		<emphasis>
			Default value is <quote>0</quote> (disabled).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>filter_server_id</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "filter_server_id", 1)
...
</programlisting>
		</example>
	</section>

	<section id="nathelper.p.nat_addr_mode">
		<title><varname>nat_addr_mode</varname> (int)</title>
		<para>
			If set to 0, only default private net addresses are checked by
			nat_uac_test(). If set to 1, other reserved net addresses are
			checked by nat_uac_test() as well.
		</para>
		<para>Default private net addresses are:</para>
		<itemizedlist>
			<listitem>
				<para>10.0.0.0/8</para>
			</listitem>
			<listitem>
				<para>172.16.0.0/12</para>
			</listitem>
			<listitem>
				<para>192.168.0.0/16</para>
			</listitem>
			<listitem>
				<para>100.64.0.0/10 - RFC6598 - Carrier Grade NAT</para>
			</listitem>
			<listitem>
				<para>192.0.0.0/29 - RFC7335 - IPv4 Service Continuity Prefix</para>
			</listitem>
		</itemizedlist>
		<para>Reserved net addresses are:</para>
		<itemizedlist>
			<listitem>
				<para>192.0.0.0/24 - RFC7335 - IETF Protocol Assignments</para>
			</listitem>
		</itemizedlist>
		<para>
		<emphasis>
			Default value is <quote>1</quote>.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>nat_addr_mode</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "nat_addr_mode", 0)
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.p.alias_name">
		<title><varname>alias_name</varname> (string)</title>
		<para>
			The parameter sets the name of the Contact URI parameter set by
			set_contact_alias() or add_contact_alias() and processed by
			handle_ruri_alias() in R-URI.
		</para>
		<para>
		<emphasis>
			Default value is <quote>alias</quote>.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>alias_name</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("nathelper", "alias_name", "saddr")
...
</programlisting>
		</example>
	</section>

	</section>


	<section>
	<title>Functions</title>
	<section id="nathelper.f.fix_nated_contact">
		<title>
		<function moreinfo="none">fix_nated_contact()</function>
		</title>
		<para>
		Rewrites the <quote>Contact</quote> header to contain the request's source
		address:port.
		</para>
		<para>
		This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE, BRANCH_ROUTE.
		</para>
		<example>
		<title><function>fix_nated_contact</function> usage</title>
		<programlisting format="linespecific">
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_contact();};
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.f.fix_nated_sdp">
		<title>
		<function moreinfo="none">fix_nated_sdp(flags [, ip_address])</function>
		</title>
		<para>
		Alters the SDP information in order to facilitate NAT traversal. What
		changes to be performed may be controlled via the
		<quote>flags</quote> parameter. Return value is -1 if error occurred,
		1 if ip's were replaced, 2 if no ip's were replaced.
		</para>
		<para>Meaning of the parameters is as follows:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>flags</emphasis> - the value may be a bitwise OR of
			the following flags:
			</para>
			<itemizedlist>
				<listitem>
					<para><emphasis>0x01</emphasis> - adds
					<quote>a=direction:active</quote> SDP line;
					</para>
				</listitem>
				<listitem>
					<para><emphasis>0x02</emphasis> - rewrite media
					&ip; address (c=) with source address of the message
					or the provided IP address. (a=rtcp) param will be rewritten if exists. (the provided IP address take
					precedence over the source address).</para>
				</listitem>
				<listitem>
					<para><emphasis>0x04</emphasis> - adds
						<quote>a=nortpproxy:yes</quote> SDP line;</para>
				</listitem>
				<listitem>
					<para><emphasis>0x08</emphasis> - rewrite IP from
					origin description (o=) with source address of the message
					or the provided IP address. (a=rtcp) param will be rewritten if exists. (the provided IP address take
					precedence over the source address).</para>
				</listitem>
			</itemizedlist>
			</listitem>
			<listitem><para>
			<emphasis>ip_address</emphasis> - IP to be used for rewriting SDP.
			If not specified, the received signalling IP will be used. The
			parameter allows pseudo-variables usage. NOTE: For the IP to be
			used, you need to use 0x02 or 0x08 flags, otherwise it will have
			no effect. Must be IPv4 address family.
			</para>
			</listitem>
		</itemizedlist>
		<para>
		This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE,
		FAILURE_ROUTE, BRANCH_ROUTE.
		</para>
		<example>
		<title><function>fix_nated_sdp</function> usage</title>
		<programlisting format="linespecific">
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_sdp("3");};
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.f.add_rcv_param">
		<title>
		<function moreinfo="none">add_rcv_param([flag])</function>,
		</title>
		<para>
		Add a received parameter to the <quote>Contact</quote> header fields
		(available for all transports) or to the Contact URI (available only
		for UDP traffic).
		</para>
		<para>
		The parameter will contain the URI created from the
		source IP, port, and protocol (if different than UDP) of the packet
		containing the SIP message. The parameter can be then processed by
		another registrar. This is useful, for example, when replicating register
		messages using <function>t_replicate</function> function to another registrar.
		</para>
		<para>Meaning of the parameters is as follows:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>flag</emphasis> - flags to indicate if the parameter
			should be added to Contact URI or Contact header. If the flag is
			non-zero, the parameter will be added to the Contact URI. If not
			used or equal to zero, the parameter will go to the Contact
			header.
			</para></listitem>
		</itemizedlist>
		<para>
		This function can be used from REQUEST_ROUTE.
		</para>
		<example>
		<title><function>add_rcv_param</function> usage</title>
		<programlisting format="linespecific">
...
add_rcv_param(); # add the parameter to the Contact header
....
add_rcv_param("1"); # add the parameter to the Contact URI
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.f.fix_nated_register">
		<title>
		<function moreinfo="none">fix_nated_register()</function>
		</title>
		<para>
		The function creates a URI consisting of the source IP, port, and
		protocol and stores the URI in an Attribute-Value-Pair. The URI will
		be appended as "received" parameter to Contact in 200 OK and
		registrar will store it in the received column in the location table.
		</para>
		<para>
		Note: You have to set the <quote>received_avp</quote> parameter of the
		nathelper module and the registrar module (both module parameters must
		have the same value) to use this function.
		</para>
		<para>
		This function can be used from REQUEST_ROUTE.
		</para>
		<example>
		<title><function>fix_nated_register</function> usage</title>
		<programlisting format="linespecific">
...
fix_nated_register();
...
</programlisting>
		</example>
	</section>
	<section id="nathelper.f.nat_uac_test">
		<title>
			<function>nat_uac_test(flags)</function>
		</title>
		<para>
			Tries to guess if client's request originated behind a nat.
			The parameter determines what heuristics is used.
		</para>
		<para>Meaning of the flags is as follows:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>1</emphasis> -  The <quote>Contact</quote> header field is searched
			for occurrence of RFC1918 or RFC6598 addresses.
			</para></listitem>
			<listitem><para>
			<emphasis>2</emphasis> -  the "received" test is used: address
			in the <quote>Via</quote> header is compared against source
			IP address of signaling. If the <quote>Via</quote> header contains
			no port, it uses the default SIP port 5060
			</para></listitem>
			<listitem><para>
			<emphasis>4</emphasis> -  The Top Most <quote>Via</quote> is searched
			for occurrence of RFC1918 or RFC6598 addresses
			</para></listitem>
			<listitem><para>
			<emphasis>8</emphasis> -  The SDP is searched for occurrence of
			RFC1918 or RFC6598 addresses
			</para></listitem>
			<listitem><para>
			<emphasis>16</emphasis> -  Test if the source port is different from the port
			in the <quote>Via</quote> header. If the <quote>Via</quote> header contains
			no port, it uses the default SIP port 5060
			</para></listitem>
			<listitem><para>
			<emphasis>32</emphasis> -  Test if the source IP address of
			signaling is a RFC1918 or RFC6598 address
			</para></listitem>
			<listitem><para>
			<emphasis>64</emphasis> -  Test if the source connection of
			signaling is a WebSocket
			</para></listitem>
			<listitem><para>
			<emphasis>128</emphasis> -  Test if the <quote>Contact</quote> header
			URI port differs from the source port of the request (Warning: this is
			might be legal or even intended combination in non NATted scenarios)
			</para></listitem>
			<listitem><para>
			<emphasis>256</emphasis> -  Test if the SDP connection address is different
			from source IP address. It will work also with multiple connection address
			lines.
			</para></listitem>
			<listitem><para>
			<emphasis>512</emphasis> -  Test if the target addresses are different
			or over websocket. For requests, it compares host and port in R-URI ($rU)
			and D-URI ($du). For replies, it compares host and port in 2nd Via
			with received and rport parameters.
			</para></listitem>
			</itemizedlist>
		<para>
		All flags can be bitwise combined, the test returns true if any of
		the tests identified a NAT.
		</para>
		<para>
		This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE, FAILURE_ROUTE, BRANCH_ROUTE.
		</para>
		<example>
		<title><function>nat_uac_test</function> usage</title>
		<programlisting format="linespecific">
...
if(nat_uac_test("19")) {
    rtpproxy_manage("co");
}
...
</programlisting>
		</example>
	</section>

	<section id="nathelper.f.is_rfc1918">
		<title>
		<function>is_rfc1918(ip_address)</function>
		</title>
		<para>
			Determines if the address in the parameter is an rfc1918 or rfc6598 address.
			The parameter allows pseudo-variables usage.
		</para>
		<para>
		This function can be used from ANY_ROUTE.
		</para>
		<example>
		<title><function>is_rfc1918</function> usage</title>
		<programlisting format="linespecific">
...
if(is_rfc1918("$rd")) {
    # domain in r-uri is private address
}
...
</programlisting>
		</example>
	</section>

	<section id="nathelper.f.add_contact_alias">
		<title>
		<function moreinfo="none">add_contact_alias([ip_addr, port, proto])</function>
		</title>
		<para>
		Adds an <quote>;alias=ip~port~transport</quote> parameter to
		the contact URI containing either received ip, port, and
		transport protocol or those given as parameters.  If called
		without parameters, <quote>;alias</quote> parameter is
		only added if received ip, port, or transport protocol differs
        from that in contact URI.
		</para>
		<para>
		This function can be used from
		REQUEST_ROUTE, ONREPLY_ROUTE, BRANCH_ROUTE, and LOCAL_ROUTE.
		</para>
		<example>
		<title><function>add_contact_alias</function> usage</title>
		<programlisting format="linespecific">
...
    if (!is_present_hf("Record-Route")) {
        if (!add_contact_alias("$var(src_ip)", "$Rp", "tcp")) {
            xlog("L_ERR", "Error in aliasing contact $ct\n");
            send_reply("400", "Bad request");
            exit;
        };
    };
...
		</programlisting>
		</example>
	</section>

	<section id="nathelper.f.handle_ruri_alias">
		<title>
		<function moreinfo="none">handle_ruri_alias([mode])</function>
		</title>
		<para>
		Checks if the Request URI has an <quote>alias</quote>
		parameter and if so, removes it and sets the <quote>$du</quote> based
		on its value. Note that this means that routing of request is based on
		<quote>;alias</quote> parameter value of the Request URI rather than
		the Request URI itself. If you call <function>handle_ruri_alias()</function>
		on a request, make sure that you screen the alias parameter value of
		Request URI the same way as you would screen the Request URI itself.
		</para>
		<para>
		The optional parameter mode can be 0 to consume first alias parameter,
		otherwise it consumes the last alias parameter. If the parameter mode is
		not provided, it consumes the first parameter.
		</para>
		<para>
		Returns <emphasis>1</emphasis> if <quote>;alias</quote> parameter was
		found and <quote>$du</quote> was set and the <quote>$ru</quote> rewritten,
		<emphasis>2</emphasis> if the alias parameter was not found and
		nothing was done, or <emphasis>-1</emphasis> in case of error.
		</para>
		<para>
		This function can be used from
		REQUEST_ROUTE, BRANCH_ROUTE, and LOCAL_ROUTE.
		</para>
		<example>
		<title><function>handle_ruri_alias</function> usage</title>
		<programlisting format="linespecific">
...
    if ($du == "") {
        handle_ruri_alias();
        switch ($rc) {
        case -1:
            xlog("L_ERR", "Failed to handle alias of R-URI $ru\n");
            send_reply("400", "Bad request");
            exit;
        case 1:
            xlog("L_INFO", "Routing in-dialog $rm from $fu to $du\n");
            break;
        case 2:
            xlog("L_INFO", "Routing in-dialog $rm from $fu to $ru\n");
            break;
         };
    };
...
		</programlisting>
		</example>
	</section>

	<section id="nathelper.set_contact_alias">
		<title>
		<function moreinfo="none">set_contact_alias([trim])</function>
		</title>
		<para>
		Adds an <quote>;alias=ip~port~transport</quote> parameter to the
		contact URI containing the received ip, port, and transport protocol.
		The update of contact URI is signaled to a few other modules in the
		way the <function>fix_nated_contact()</function> does it by using the
		internal flags. The new value is not visible to pseudo-variables and it
		does not change the SIP message buffer.
		</para>
		<para>Meaning of parameters:</para>
		<itemizedlist>
			<listitem>
				<para>
					<emphasis>trim</emphasis> - by default, set_contact_alias() will not detect and trim an
					already existing alias parameter. If this optional parameter is set to "1", set_contact_alias()
					will trim the existing alias before adding a new one.
				</para>
			</listitem>
		</itemizedlist>
		<para>
		This function can be used from
		REQUEST_ROUTE, ONREPLY_ROUTE, BRANCH_ROUTE, and FAILURE_ROUTE.
		</para>
		<example>
		<title><function>set_contact_alias</function> usage</title>
		<programlisting format="linespecific">
...
    if (!is_present_hf("Record-Route")) {
        if (!set_contact_alias()) {
            xlog("L_ERR", "Error in aliasing contact $ct\n");
            send_reply("400", "Bad request");
            exit;
        };
    };
...
		</programlisting>
		</example>
	</section>
		<section id="nathelper.set_alias_to_pv">
		<title>
		<function moreinfo="none">set_alias_to_pv(target_avp)</function>
		</title>
		<para>
		Reads <quote>;alias=ip~port~transport</quote> from Contact header then
		writes to target pseudo-variable as a sip uri.
		</para>
		<para>
		This function can be used from
		REQUEST_ROUTE, ONREPLY_ROUTE, BRANCH_ROUTE, and FAILURE_ROUTE.
		</para>
		<example>
		<title><function>set_alias_to_pv</function> usage</title>
		<programlisting format="linespecific">
...
		set_alias_to_pv("$avp(aliasuri)");
...
		</programlisting>
		</example>
	</section>

	</section>

	<section>
		<title>Exported Pseudo Variables</title>
		<section>
			<title><function moreinfo="none">$rr_count</function></title>
			<para>
			Number of Record Routes in received SIP request
			or reply.
			</para>
		<example>
		<title>$rr_count usage</title>
		<programlisting format="linespecific">
...
    $avp(rr_count) = $rr_count;
...
		</programlisting>
		</example>
	        </section>

		<section>
			<title><function moreinfo="none">$rr_top_count</function></title>
			<para>
			If topmost Record Route in received SIP request
			or reply is a double Record Route, value of
			$rr_top_count is 2.  If it a single Record
			Route, value of $rr_top_count
			is 1.  If there is no Record Route(s), value of
			$rr_top_count is 0.
			</para>
		<example>
		<title>$rr_top_count usage</title>
		<programlisting format="linespecific">
...
    if ($rr_count == $avp(rr_count) + $rr_top_count) {
        route(ADD_CONTACT_ALIAS);
    };
...
		</programlisting>
		</example>
	        </section>

	</section>

	<section>
		<title>RPC Commands</title>
		<section id="nathelper.r.enable_ping">
			<title><function moreinfo="none">nathelper.enable_ping</function></title>
			<para>
			Enables natping if parameter value different than 0.
			Disables natping if parameter value is 0.
			</para>
			<para>
			The function takes only one parameter - a number in decimal format.
			</para>
			<example>
			<title><function moreinfo="none">nathelper.enable_ping</function> usage</title>
			<programlisting format="linespecific">
...
$ &kamcmd; nathelper.enable_ping 1
...
			</programlisting>
			</example>
		</section>

	</section>

	<section>
		<title>Selects</title>

		<section id="nathelper.s.rewrite_contact">
		<title>@nathelper.rewrite_contact[n]</title>
		<para>
			Get n-th Contact value with IP:Port rewritten to source ip:port. N is counted from 1.
		    Only IP:port is rewritten, remaining parts are left unchanged. Full nameaddr is supported.
		</para>
		<example>
			<title>@nathelper.rewrite_contact usage</title>
			<programlisting>
...
$c = @nathelper.rewrite_contact[1];
...
$c2 = @nathelper.rewrite_contact[1].nameaddr.uri;
			</programlisting>
		</example>
		</section>

	</section>

</chapter>

