pipelimit Module

Daniel-Constantin Mierla

Hendrik Scholz

Edited by

Ovidiu Sas

Edited by

Daniel-Constantin Mierla

Table of Contents

1. Admin Guide
1. Overview
1.1. Algorithms
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Parameters
3.1. hash_size (int)
3.2. db_url (string)
3.3. plp_table_name (string)
3.4. plp_pipeid_column (string)
3.5. plp_limit_column (string)
3.6. plp_algorithm_column (string)
3.7. timer_interval (integer)
3.8. reply_code (integer)
3.9. reply_reason (string)
4. Functions
4.1. pl_check(name [, algorithm, limit])
4.2. pl_drop([ [min ], max ])
5. RPC Commands
5.1. pl.stats
5.2. pl.set_pipe
5.3. pl.get_pipes
5.4. pl.set_pid
5.5. pl.get_pid
5.6. pl.push_load

List of Examples

1.1. Set hash_size parameter
1.2. Set db_url parameter
1.3. Set plp_table_name parameter
1.4. Set plp_pipeid_column parameter
1.5. Set plp_limit_column parameter
1.6. Set plp_algorithm_column parameter
1.7. Set timer_interval parameter
1.8. Set reply_code parameter
1.9. Set reply_code parameter at runtime
1.10. Set reply_reason parameter
1.11. Set reply_reason parameter at runtime
1.12. pl_check usage
1.13. pl_drop usage

Chapter 1. Admin Guide

1. Overview

This module implements traffic limiting for SIP requests.

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.

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.

1.1. Algorithms

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.

Tail Drop Algorithm (TAILDROP)

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.

Random Early Detection Algorithm (RED)

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.

Network Algorithm (NETWORK)

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.

Feedback Algorithm (FEEDBACK)

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).

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.

2. Dependencies

2.1. Kamailio Modules

The following modules must be loaded before this module:

  • database connection module.

  • sl: Stateless Request Handling.

2.2. External Libraries or Applications

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

  • None.

3. Parameters

3.1. hash_size (int)

Used to compute the number of slots for the internal hash table, as power of 2 (number of slots = 2^hash_size, aka 1<<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).

Default value is 6 (64 slots).

Example 1.1. Set hash_size parameter

modparam("pipelimit", "hash_size", 10)

3.2. db_url (string)

URL of the database server to be used.

Default value is mysql://kamailio:kamailiorw@localhost/kamailio.

Example 1.2. Set db_url parameter

modparam("pipelimit", "db_url", "dbdriver://username:password@dbhost/dbname")

3.3. plp_table_name (string)

Name of DB table where data definition for pipes is stores.

Default value is pl_pipes.

Example 1.3. Set plp_table_name parameter

modparam("pipelimit", "plp_table_name", "mypipes")

3.4. plp_pipeid_column (string)

Name of 'pipeid' column.

Default value is pipeid.

Example 1.4. Set plp_pipeid_column parameter

modparam("pipelimit", "plp_pipeid_column", "name")

3.5. plp_limit_column (string)

Name of 'limit' column.

Default value is limit.

Example 1.5. Set plp_limit_column parameter

modparam("pipelimit", "plp_limit_column", "name")

3.6. plp_algorithm_column (string)

Name of 'algorithm' column.

Default value is algorithm.

Example 1.6. Set plp_algorithm_column parameter

modparam("pipelimit", "plp_algorithm_column", "name")

3.7. timer_interval (integer)

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.

IMPORTANT: A too small value may lead to performance penalties due to timer process overloading.

Default value is 10.

Example 1.7. Set timer_interval parameter

modparam("pipelimit", "timer_interval", 5)

3.8. reply_code (integer)

The code of the reply sent by Kamailio while limiting.

Default value is 503.

Example 1.8. Set reply_code parameter

modparam("pipelimit", "reply_code", 505)

This value can be modified at runtime using kamcmd

Example 1.9.  Set reply_code parameter at runtime

kamcmd cfg.set_now_int pipelimit reply_code 505

3.9. reply_reason (string)

The reason of the reply sent by Kamailio while limiting.

Default value is "Server Unavailable".

Example 1.10. Set reply_reason parameter

modparam("pipelimit", "reply_reason", "Limiting")

This value can be modified at runtime using kamcmd

Example 1.11.  Set reply_reason parameter at runtime

kamcmd cfg.set_now_string pipelimit reply_reason "Limiting"

4. Functions

4.1.  pl_check(name [, algorithm, limit])

Check the current request against the 'name' pipe.

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.

The pipe name can be provided via a pseudo variabile.

The method will return:

  • -2 if no pipe was found

  • -1 if pipe limit was reached

  • 1 if pipe limit was NOT reached

  • 2 if pipe has NOP algorithm

Meaning of the parameters is as follows:

  • name - the string or pseudovariable with the pipe name.

  • algorithm - 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.

  • limit - the integer or pseudovariable with the limit value.

This function can be used from ANY_ROUTE.

Example 1.12. pl_check usage

	# perform pipe match for current method
	if (!pl_check("one")) {
	# 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");
	case -1:
		xlog("L_ALERT","pl_check(\"$var(p)\") drop\n");
	case 1:
		xlog("L_INFO", "pl_check(\"$var(p)\") pass\n");
	case 2:
		xlog("L_ALERT","pl_check(\"$var(p)\") pass -NOP algorithm\n");
		xlog("L_ERR","pl_check(\"$var(p)\") dropping \
with unexpected retcode=$var(check_result)\n");
	# perform pipe match for authenticated user
	$var(limit) = 20;
	if (!pl_check("$au", "TAILDROP", "$var(limit)")) {
	# perform pipe match for INVITE
	if (is_method("INVITE")) {
		$var(invlimit) = 10;
		if (!pl_check("$si", "TAILDROP", "$var(invlimit)")) {

4.2.  pl_drop([ [min ], max ])

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 max parameter is given, the reply will contain a "Retry-After: max" header. If both min and max params are given, the reply will contain a "Retry-After: random" header with random being a random value between the given min and max.

Meaning of the parameters is as follows:

  • min - the minimum value of "Retry-After" header.

  • max - the maximum value of "Retry-After" header.


Example 1.13. pl_drop usage

	if (!pl_check("one")) {
		# send back a "503 - Server Unavailable"
		# with a "Retry-After: 5"

5. RPC Commands

5.1.  pl.stats

Lists the parameters and variabiles in the pipelimit module: pipe id, pipe load and pipe couter.

Name: pl.stats

Parameters: none

RPC Command Format:

	kamcmd pl.stats

5.2.  pl.set_pipe

Sets the pipe parameters for the given pipe id.

Name: pl.set_pipe


  • pipe_id - pipe id.

  • pipe_algorithm - the algorithm assigned to the given pipe id.

  • pipe_limit - the limit assigned to the given pipe id.

RPC Command Format:

	kamcmd pl.set_pipe 2 RED 10

5.3.  pl.get_pipes

Gets the list of in use pipes.

Name: pl.get_pipes

Parameters: none

RPC Command Format:

	kamcmd pl.get_pipes

5.4.  pl.set_pid

Sets the PID Controller parameters for the Feedback Algorithm.

Name: pl.set_pid


  • ki - the integral parameter.

  • kp - the proportional parameter.

  • kd - the derivative parameter.

RPC Command Format:

	kamcmd pl.set_pid 0.5 0.5 0.5

5.5.  pl.get_pid

Gets the list of in use PID Controller parameters.

Name: pl.get_pid

Parameters: none

RPC Command Format:

	kamcmd pl.get_pid

5.6.  pl.push_load

Force the value of the load parameter. This command is useful for testing the Feedback algorithm.

Name: pl.push_load


  • load - the forced value of load (it must be greater then 0.0 and smaller then 1.0).

RPC Command Format:

	kamcmd pl.push_load 0.85