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

<chapter>
	
	<title>&adminguide;</title>
	
	<section>
	<title>Overview</title>
	<para>
		This module implements traffic limiting for SIP requests.
	</para>
	<para>
		The module defines in an abstract mode the notion of 'pipe',
		which can be a link to an IP address, to a network or a trunk.
		The associtiation of traffic to a pipe is done in the config file,
		therefore, a pipe could represent SIP traffic coming from a user or
		the flow of specific SIP requests such as INVITE or REGISTER.
	</para>
	<para>
		Pipelimit started from ratelimit module, adding support for definition
		of pipes limits in database and dynamic names. Complexity of keeping
		everything in a module and make it dual mode functional resulted in a
		new module which is focused on just traffic shaping policies.
	</para>
	<section>
		<title>Algorithms</title>
		<para>
			Algorithms are based from the ratelimit module, which describes the
			algorithms in more detail. The algorithms are used by the pipelimit
			module to determine if a message should be blocked.
		</para>
		<para>
			<emphasis>Tail Drop Algorithm (TAILDROP)</emphasis>
		</para>
		<para>
			This is a trivial algorithm that imposes some risks when used in
			conjunction with long timer intervals. At the start of each interval an
			internal counter is reset and incremented for each incoming message.
			Once the counter hits the configured limit pl_check returns an error.
		</para>
		<para>
			<emphasis>Random Early Detection Algorithm (RED)</emphasis>
		</para>
		<para>
			The Random Early Detection Algorithm tries to circumvent the
			synchronization problem imposed by the tail drop algorithm by measuring
			the average load and adapting the drop rate dynamically. When running
			with the RED algorithm (enabled by default) Kamailio will return errors
			to the Kamailio routing engine every n'th packet trying to evenly
			spread the measured load of the last timer interval onto the current
			interval. As a negative side effect Kamailio might drop messages
			although the limit might not be reached within the interval. Decrease
			the timer interval if you encounter this.
		</para>
		<para>
			<emphasis>Network Algorithm (NETWORK)</emphasis>
		</para>
		<para>
			This algorithm relies on information provided by network interfaces.
			The total amount of bytes waiting to be consumed on all the network
			interfaces is retrieved once every timer_interval seconds. If the
			returned amount exceeds the limit specified in the modparam, pl_check
			returns an error.
		</para>
		<para>
			<emphasis>Feedback Algorithm (FEEDBACK)</emphasis>
		</para>
		<para>
			Using the PID Controller model (see Wikipedia page), the drop rate is
			adjusted dynamically based on the load factor so that the load factor
			always drifts towards the specified limit (or setpoint, in PID terms).
		</para>
		<para>
			As reading the CPU load average is relatively expensive (opening
			/proc/stat, parsing it, etc), this only happens once every
			timer_interval seconds and consequently the FEEDBACK value is only at
			these intervals recomputed. This in turn makes it difficult for the
			drop rate to adjust quickly. Worst case scenarios are request rates
			going up/down instantly by thousands - it takes up to 20 seconds for
			the controller to adapt to the new request rate.
		</para>
	</section>
	</section>
	<section>
	<title>Dependencies</title>
	<section>
		<title>&kamailio; Modules</title>
		<para>
		The following modules must be loaded before this module:
			<itemizedlist>
			<listitem>
			<para>
				<emphasis>database connection module</emphasis>.
			</para>
			</listitem>
			<listitem>
			<para>
				<emphasis>sl: Stateless Request Handling</emphasis>.
			</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="pipelimit.p.hash_size">
	    <title><varname>hash_size</varname> (int)</title>
	    <para>
		Used to compute the number of slots for the internal hash table,
		as power of 2 (number of slots = 2^hash_size, aka 1&lt;&lt;hash_size).
		If you have many pipes, increase this value for proper performances,
		but don't go too high (hash_size=10 means 1024 slots).
	    </para>
	    <para>
		<emphasis>
		    Default value is <quote>6</quote> (64 slots).
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>hash_size</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "hash_size", 10)
...
</programlisting>
	    </example>
	</section>
	<section id="pipelimit.p.db_url">
	    <title><varname>db_url</varname> (string)</title>
	    <para>
		URL of the database server to be used.
	    </para>
	    <para>
		<emphasis>
		    Default value is <quote>&defaultdb;</quote>.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>db_url</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "db_url", "&exampledb;")
...
</programlisting>
	    </example>
	</section>

	<section id="pipelimit.p.plp_table_name">
	    <title><varname>plp_table_name</varname> (string)</title>
	    <para>
			Name of DB table where data definition for pipes is stores.
	    </para>
	    <para>
		<emphasis>
		    Default value is <quote>pl_pipes</quote>.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>plp_table_name</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "plp_table_name", "mypipes")
...
</programlisting>
	    </example>
	</section>

	<section id="pipelimit.p.plp_pipeid_column">
	    <title><varname>plp_pipeid_column</varname> (string)</title>
	    <para>
		Name of 'pipeid' column.
	    </para>
	    <para>
		<emphasis>
		    Default value is <quote>pipeid</quote>.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>plp_pipeid_column</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "plp_pipeid_column", "name")
...
</programlisting>
	    </example>
	</section>

	<section id="pipelimit.p.plp_limit_column">
	    <title><varname>plp_limit_column</varname> (string)</title>
	    <para>
		Name of 'limit' column.
	    </para>
	    <para>
		<emphasis>
		    Default value is <quote>limit</quote>.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>plp_limit_column</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "plp_limit_column", "name")
...
</programlisting>
	    </example>
	</section>

	<section id="pipelimit.p.plp_algorithm_column">
	    <title><varname>plp_algorithm_column</varname> (string)</title>
	    <para>
		Name of 'algorithm' column.
	    </para>
	    <para>
		<emphasis>
		    Default value is <quote>algorithm</quote>.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>plp_algorithm_column</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "plp_algorithm_column", "name")
...
</programlisting>
	    </example>
	</section>

	<section id="pipelimit.p.timer_interval">
		<title><varname>timer_interval</varname> (integer)</title>
		<para>
		The initial length of a timer interval in seconds. All amounts of
		messages have to be divided by this timer to get a messages per second
		value.
		</para>
		<para>
		IMPORTANT: A too small value may lead to performance penalties due to
		timer process overloading.
		</para>
		<para>
		<emphasis>
			Default value is 10.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>timer_interval</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "timer_interval", 5)
...
</programlisting>
		</example>
	</section>
	<section id="pipelimit.p.reply_code">
		<title><varname>reply_code</varname> (integer)</title>
		<para>
		The code of the reply sent by &kamailio; while limiting.
		</para>
		<para>
		<emphasis>
			Default value is 503.
		</emphasis>

		</para>
		<example>
		<title>Set <varname>reply_code</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "reply_code", 505)
...
</programlisting>
		</example>
		<para>
		This value can be modified at runtime using &sercmd;
		</para>
		<example>
		<title> Set <varname>reply_code</varname> parameter at runtime </title>
		<programlisting format="linespecific">

&sercmd; cfg.set_now_int pipelimit reply_code 505

		</programlisting>
		</example>
	</section>
	<section id="pipelimit.p.reply_reason">
		<title><varname>reply_reason</varname> (string)</title>
		<para>
		The reason of the reply sent by &kamailio; while limiting.
		</para>
		<para>
		<emphasis>
			Default value is "Server Unavailable".
		</emphasis>
		</para>
		<example>
		<title>Set <varname>reply_reason</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "reply_reason", "Limiting")
...
</programlisting>
		</example>
		<para>
		This value can be modified at runtime using &sercmd;
		</para>
		<example>
		<title> Set <varname>reply_reason</varname> parameter at runtime </title>
		<programlisting format="linespecific">

&sercmd; cfg.set_now_string pipelimit reply_reason "Limiting"

		</programlisting>
		</example>
	</section>
	</section>
	<section>
	<title>Functions</title>
	<section id="pipelimit.f.pl_check">
		<title>
		<function moreinfo="none">pl_check(name [, algorithm, limit])</function>
		</title>
		<para>
		Check the current request against the 'name' pipe.
		</para>
		<para>	
		If algorithm and limit are provided, the function attempts to create a
		new pipe of one with that name doesn't exit. If it exists, no changes
		to algorithm and limit are done. Algorithm is case sensitive.
		</para>
		<para>	
		The pipe name can be provided via a pseudo variabile.
		</para>
		<para>The method will return:
		<itemizedlist>
			<listitem><para><emphasis>-2</emphasis> if no pipe was found</para></listitem>
			<listitem><para><emphasis>-1</emphasis> if pipe limit was reached</para></listitem>
			<listitem><para><emphasis>1</emphasis> if pipe limit was NOT reached</para></listitem>
			<listitem><para><emphasis>2</emphasis> if pipe has NOP algorithm</para></listitem>
		</itemizedlist>
		</para>
		<para>Meaning of the parameters is as follows:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>name</emphasis> - the string or pseudovariable with the pipe name.
			</para></listitem>
			<listitem><para>
			<emphasis>algorithm</emphasis> - the string or pseudovariable with the
			algorithm. The values can be: TAILDROP, RED, NETWORK, or FEEDBACK - see
			readme of ratelimit module for details on each algorithm.
			</para></listitem>
			<listitem><para>
			<emphasis>limit</emphasis> - the integer or pseudovariable with the limit value.
			</para></listitem>
		</itemizedlist>
		<para>
		This function can be used from ANY_ROUTE.
		</para>
		<example>
		<title><function>pl_check</function> usage</title>
		<programlisting format="linespecific">
...
	# perform pipe match for current method
	if (!pl_check("one")) {
		pl_drop();
		exit;
	}
...
	# use pipe 'one' for the current method via PV
	$var(p) = "one";
	$var(check_result) = pl_check("$var(p)");
	switch($var(check_result)) {
	case -2:
		xlog("L_ALERT","pl_check(\"$var(p)\") drop -pipe NOT found\n");
		pl_drop();
		exit;
		break;
	case -1:
		xlog("L_ALERT","pl_check(\"$var(p)\") drop\n");
		pl_drop();
		exit;
		break;
	case 1:
		xlog("L_INFO", "pl_check(\"$var(p)\") pass\n");
		break;
	case 2:
		xlog("L_ALERT","pl_check(\"$var(p)\") pass -NOP algorithm\n");
		break;
	default:
		xlog("L_ERR","pl_check(\"$var(p)\") dropping \
with unexpected retcode=$var(check_result)\n");
		pl_drop();
		exit;
	}
...
	# perform pipe match for authenticated user
	$var(limit) = 20;
	if (!pl_check("$au", "TAILDROP", "$var(limit)")) {
		pl_drop();
		exit;
	}
...
	# perform pipe match for INVITE
	if (is_method("INVITE")) {
		$var(invlimit) = 10;
		if (!pl_check("$si", "TAILDROP", "$var(invlimit)")) {
			pl_drop();
			exit;
		}
	}
...
</programlisting>
		</example>
	</section>
	<section id="pipelimit.f.pl_drop">
		<title>
		<function moreinfo="none">pl_drop([ [min ], max ])</function>
		</title>
		<para>
		For the current request, a "503 - Server Unavailable" reply is sent back.
		The reply may or may not have a "Retry-After" header.  If no parameter is given,
		there will be no "Retry-After" header.  If only the
		<emphasis>max</emphasis> parameter is given, the
		reply will contain a "Retry-After: <emphasis>max</emphasis>" header.  If both
		<emphasis>min</emphasis> and <emphasis>max</emphasis> params are given, the
		reply will contain a "Retry-After: <emphasis>random</emphasis>" header with
		<emphasis>random</emphasis> being a random value between the given min and max.
		</para>
		<para>Meaning of the parameters is as follows:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>min</emphasis> - the minimum value of "Retry-After" header.
			</para>
			</listitem>
			<listitem>
			<para>
			<emphasis>max</emphasis> - the maximum value of "Retry-After" header.
			</para>
			</listitem>
		</itemizedlist>
		<para>
		This function can be used from REQUEST_ROUTE|BRANCH_ROUTE|FAILURE_ROUTE|ONSEND_ROUTE.
		</para>
		<example>
		<title><function>pl_drop</function> usage</title>
		<programlisting format="linespecific">
...
	if (!pl_check("one")) {
		# send back a "503 - Server Unavailable"
		# with a "Retry-After: 5"
		pl_drop("5");
		exit;
	}
...
</programlisting>
		</example>
	</section>
	</section>

	<section>
	<title>MI Commands</title>
	<section id="pipelimit.m.pl_stats">
		<title>
		<function moreinfo="none">pl_stats</function>
		</title>
		<para>
		Lists the parameters and variables in the pipelimit module.
		</para>
		<para>
		Name: <emphasis>pl_stats</emphasis>
		</para>
		<para>Parameters: <emphasis>none</emphasis></para>
 		<para>
		MI FIFO Command Format:
		</para>
		<programlisting  format="linespecific">
		:pl_stats:_reply_fifo_file_
		_empty_line_
		</programlisting>
	</section>
	<section id="pipelimit.m.pl_set_pipe">
		<title>
		<function moreinfo="none">pl_set_pipe</function>
		</title>
		<para>
		Sets the pipe parameters for the given pipe id.
		</para>
		<para>
		Name: <emphasis>pl_set_pipe</emphasis>
		</para>
		<para>Parameters:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>pipe_id</emphasis> - pipe id.
			</para></listitem>
			<listitem><para>
			<emphasis>pipe_algorithm</emphasis> - the
			algorithm assigned to the given pipe id.
			</para></listitem>
			<listitem><para>
			<emphasis>pipe_limit</emphasis> - the limit
			assigned to the given pipe id.
			</para></listitem>
		</itemizedlist>
		<para>
		MI FIFO Command Format:
		</para>
		<programlisting  format="linespecific">
		:pl_set_pipe:_reply_fifo_file_
		2
		RED
		10
		_empty_line_
		</programlisting>
	</section>
	<section id="pipelimit.m.pl_get_pipes">
		<title>
		<function moreinfo="none">pl_get_pipes</function>
		</title>
		<para>
		Gets the list of in use pipes.
		</para>
		<para>
		Name: <emphasis>pl_get_pipes</emphasis>
		</para>
		<para>Parameters: <emphasis>none</emphasis></para>
		<para>
		MI FIFO Command Format:
		</para>
		<programlisting  format="linespecific">
		:pl_get_pipes:_reply_fifo_file_
		_empty_line_
		</programlisting>
	</section>
	<section id="pipelimit.m.pl_set_pid">
		<title>
		<function moreinfo="none">pl_set_pid</function>
		</title>
		<para>
		Sets the PID Controller parameters for the Feedback Algorithm.
		</para>
		<para>
		Name: <emphasis>pl_set_pid</emphasis>
		</para>
		<para>Parameters:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>ki</emphasis> - the integral parameter.
			</para></listitem>
			<listitem><para>
			<emphasis>kp</emphasis> - the proportional parameter.
			</para></listitem>
			<listitem><para>
			<emphasis>kd</emphasis> - the derivative parameter.
			</para></listitem>
		</itemizedlist>
		<para>
		MI FIFO Command Format:
		</para>
		<programlisting  format="linespecific">
		:pl_set_pid:_reply_fifo_file_
		0.5
		0.5
		0.5
		_empty_line_
		</programlisting>
	</section>
	<section id="pipelimit.m.pl_get_pid">
		<title>
		<function moreinfo="none">pl_get_pid</function>
		</title>
		<para>
		Gets the list of in use PID Controller parameters.
		</para>
		<para>
		Name: <emphasis>pl_get_pid</emphasis>
		</para>
		<para>Parameters: <emphasis>none</emphasis></para>
		<para>
		MI FIFO Command Format:
		</para>
		<programlisting  format="linespecific">
		:pl_get_pid:_reply_fifo_file_
		_empty_line_
		</programlisting>
	</section>
	<section id="pipelimit.m.pl_push_load">
		<title>
		<function moreinfo="none">pl_push_load</function>
		</title>
		<para>
		Force the value of the load parameter. This command is useful
		for testing the Feedback algorithm.
		</para>
		<para>
		Name: <emphasis>pl_push_load</emphasis>
		</para>
		<para>Parameters:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>load</emphasis> - the forced value of load
			(it must be greater then 0.0 and smaller then 1.0).
			</para></listitem>
		</itemizedlist>
		<para>
		MI FIFO Command Format:
		</para>
		<programlisting  format="linespecific">
		:pl_push_load:_reply_fifo_file_
		0.85
		_empty_line_
		</programlisting>
	</section>
	</section>
	
	<section>
	<title>RPC Commands</title>
	<section id="pipelimit.r.pl.stats">
		<title>
		<function moreinfo="none">pl.stats</function>
		</title>
		<para>
		Lists the parameters and variabiles in the pipelimit module:
		pipe id, pipe load and pipe couter.
		</para>
		<para>
		Name: <emphasis>pl.stats</emphasis>
		</para>
		<para>Parameters: <emphasis>none</emphasis></para>
 		<para>
		RPC Command Format:
		</para>
		<programlisting  format="linespecific">
	kamcmd pl.stats
		</programlisting>
	</section>
	<section id="pipelimit.r.pl.set_pipe">
		<title>
		<function moreinfo="none">pl.set_pipe</function>
		</title>
		<para>
		Sets the pipe parameters for the given pipe id.
		</para>
		<para>
		Name: <emphasis>pl.set_pipe</emphasis>
		</para>
		<para>Parameters:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>pipe_id</emphasis> - pipe id.
			</para></listitem>
			<listitem><para>
			<emphasis>pipe_algorithm</emphasis> - the
			algorithm assigned to the given pipe id.
			</para></listitem>
			<listitem><para>
			<emphasis>pipe_limit</emphasis> - the limit
			assigned to the given pipe id.
			</para></listitem>
		</itemizedlist>
		<para>
		RPC Command Format:
		</para>
		<programlisting  format="linespecific">
	kamcmd pl.set_pipe 2 RED 10
		</programlisting>
	</section>
	<section id="pipelimit.r.pl.get_pipes">
		<title>
		<function moreinfo="none">pl.get_pipes</function>
		</title>
		<para>
		Gets the list of in use pipes.
		</para>
		<para>
		Name: <emphasis>pl.get_pipes</emphasis>
		</para>
		<para>Parameters: <emphasis>none</emphasis></para>
		<para>
		RPC Command Format:
		</para>
		<programlisting  format="linespecific">
	kamcmd pl.get_pipes
		</programlisting>
	</section>
	<section id="pipelimit.r.pl.set_pid">
		<title>
		<function moreinfo="none">pl.set_pid</function>
		</title>
		<para>
		Sets the PID Controller parameters for the Feedback Algorithm.
		</para>
		<para>
		Name: <emphasis>pl.set_pid</emphasis>
		</para>
		<para>Parameters:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>ki</emphasis> - the integral parameter.
			</para></listitem>
			<listitem><para>
			<emphasis>kp</emphasis> - the proportional parameter.
			</para></listitem>
			<listitem><para>
			<emphasis>kd</emphasis> - the derivative parameter.
			</para></listitem>
		</itemizedlist>
		<para>
		RPC Command Format:
		</para>
		<programlisting  format="linespecific">
	kamcmd pl.set_pid 0.5 0.5 0.5
		</programlisting>
	</section>
	<section id="pipelimit.r.pl.get_pid">
		<title>
		<function moreinfo="none">pl.get_pid</function>
		</title>
		<para>
		Gets the list of in use PID Controller parameters.
		</para>
		<para>
		Name: <emphasis>pl.get_pid</emphasis>
		</para>
		<para>Parameters: <emphasis>none</emphasis></para>
		<para>
		RPC Command Format:
		</para>
		<programlisting  format="linespecific">
	kamcmd pl.get_pid
		</programlisting>
	</section>
	<section id="pipelimit.r.pl.push_load">
		<title>
		<function moreinfo="none">pl.push_load</function>
		</title>
		<para>
		Force the value of the load parameter. This command is useful
		for testing the Feedback algorithm.
		</para>
		<para>
		Name: <emphasis>pl.push_load</emphasis>
		</para>
		<para>Parameters:</para>
		<itemizedlist>
			<listitem><para>
			<emphasis>load</emphasis> - the forced value of load
			(it must be greater then 0.0 and smaller then 1.0).
			</para></listitem>
		</itemizedlist>
		<para>
		RPC Command Format:
		</para>
		<programlisting  format="linespecific">
	kamcmd pl.push_load 0.85
		</programlisting>
	</section>
	</section>
	
</chapter>
