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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 reference to an IP address, to a network or a trunk.
		The association 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, the
		implementation of queues was discarded.
	</para>
	</section>
	<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 false
			(negative value).
		</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 false (negative value).
		</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>
	<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 length of the timer interval in seconds. Counted messages are reset
		each timer_interval, therefore the amounts of messages have to be divided
		by this timer_interval value to get the messages per second value. For
		example, if you want to allow an average of 10 messages per second with
		a timer interval of 10 seconds, then the limit value has to be 100.
		</para>
		<para>
		Note: 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.timer_mode">
		<title><varname>timer_mode</varname> (integer)</title>
		<para>
		Control what timer process to be used: 0 - use main fast timer; 1 - use
		secondary wheel timer.
		</para>
		<para>
		<emphasis>
			Default value is 0.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>timer_mode</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "timer_mode", 1)
...
</programlisting>
		</example>
	</section>
	<section id="pipelimit.p.load_fetch">
		<title><varname>load_fetch</varname> (integer)</title>
		<para>
		Control if the module should fetch the load for CPU and network traffic.
		If set to 0, no load is fetched; if set to 1, the load is fetched every
		timer interval.
		</para>
		<para>
		<emphasis>
			Default value is 1.
		</emphasis>
		</para>
		<example>
		<title>Set <varname>load_fetch</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "load_fetch", 0)
...
</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 id="pipelimit.p.clean_unused">
		<title><varname>clean_unused</varname> (int)</title>
		<para>
		Clean unused pipes after this number of timer intervals.
		</para>
		<para>
		<emphasis>
			Default value is 0 (cleanup disabled).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>clean_unused</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("pipelimit", "clean_unused", 10)
...
</programlisting>
		</example>
		<para>
		This value can be modified at runtime using &sercmd;
		</para>
		<example>
		<title> Set <varname>clean_unused</varname> parameter at runtime </title>
		<programlisting format="linespecific">

&sercmd; cfg.set_now_int pipelimit clean_unused 10

		</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 if one with that name doesn't exit. If it exists, no changes
		to algorithm is done and the pipe limit is set to the 'limit' parameter
		value, if this is greater than 0. Algorithm is case sensitive.
		</para>
		<para>	
		The pipe name can be provided via a pseudo variable.
		</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
			per timer_interval.
			</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>RPC Commands</title>
	<section id="pipelimit.r.pl.list">
		<title>
		<function moreinfo="none">pl.list</function>
		</title>
		<para>
		Lists the details of one or all pipes, respectively the attributes
		pipe name (id), algorithm, limit and counter.
		</para>
		<para>
		Name: <emphasis>pl.list</emphasis>
		</para>
		<para>Parameters: <emphasis>name</emphasis> - (optional) pipe name</para>
		<para>
		RPC Command Format:
		</para>
		<programlisting  format="linespecific">
...
kamctl rpc pl.list
kamctl rpc pl.list testid
...
		</programlisting>
	</section>
	<section id="pipelimit.r.pl.stats">
		<title>
		<function moreinfo="none">pl.stats</function>
		</title>
		<para>
		Lists the parameters and variables in the pipelimit module:
		pipe id, pipe load and pipe counter.
		</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 than 0.0 and smaller than 1.0).
			</para></listitem>
		</itemizedlist>
		<para>
		RPC Command Format:
		</para>
		<programlisting  format="linespecific">
...
kamcmd pl.push_load 0.85
...
		</programlisting>
	</section>
	</section>

</chapter>
