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1.1. Overview

   This module implements rate limiting for SIP requests. In
   contrast to the PIKE module this limits the flow based on a
   per SIP request type basis and not per source IP. The MI
   interface can be used to change tunables while running
   openSER. Currently supported requests are INVITE, REGISTER and
   SUBSCRIBE.

   The module does not implement any actions on blocking - it
   just simply reports that there is a high traffic; what to do,
   is the administator decision (via scripting).
     _________________________________________________________

1.2. Use Cases

   Limiting the rate messages are processed on a system directly
   influences the load. The ratelimit module can be used to
   protect a single host or to protect an openSER cluster when
   run on the dispatching box in front.

   A sample configuration snippet might look like this:
...
        if (is_method("INVITE|REGISTER|SUBSCRIBE") {
                if (!rl_check()) {
                        sl_send_reply("503", "Service Unavailable");
                        exit;
                };
        };
...

   Upon every incoming request listed above rl_check is invoked.
   It returns an OK code if the current per request load is below
   the configured threshold. If the load is exceeded the function
   returns an error and an administrator can discard requests
   with a stateless response.
     _________________________________________________________

1.3. Rate Limiting Algorithms

   The ratelimit module supports two different algorithms to be
   used by rl_check to determine whether a message should be
   blocked or not.
     _________________________________________________________

1.3.1. Tail Drop (TD)

   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
   rl_check returns an error.

   The downside of this algorithm is that it can lead to SIP
   client synchronization. During a relatively long interval only
   the first requests (i.e. REGISTERs) would make it through.
   Following messages (i.e. RE-REGISTERs) will all hit the SIP
   proxy at the same time when a common Expire timer expired.
   Other requests will be retransmissed after given time, the
   same on all devices with the same firmware/by the same vendor.
     _________________________________________________________

1.3.2. Random Early Detection (RED)

   Random Early Detection 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) SER will
   return errors to the SER 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
   SER might drop messages although the limit might not be
   reached within the interval. Decrease the timer interval if
   you encounter this.
     _________________________________________________________



Regards,
Ovidiu Sas

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>Comment By: Daniel-Constantin Mierla (miconda)
Date: 2008-01-15 23:23

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You should have write access to SVN. Please report otherwise.

Once the module is imported, just close this item. The enhancements done
in opensimscore do look interesting, when time allows you, would be nice to
import.

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Comment By: Ovidiu Sas (osas)
Date: 2008-01-15 02:55

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New src tarball updated.
File Added: ratelimit.tar.gz

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Comment By: Ovidiu Sas (osas)
Date: 2008-01-15 00:49

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Hi Daniel,

Yes, I noticed the missing free in destroy.  I will fix them up and when I
have time, I will import the openims extensions.
I would be happy to maintain the module.


-ovi

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Comment By: Daniel-Constantin Mierla (miconda)
Date: 2008-01-15 00:34

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I took a quick look at the module, and for a clean shut down, all
variables allocated in share memory in mod init should be freed in mod
destroy. Make sure they are initialized to NULL and you check their value
before freeing, to avoid crashes when there are errors in config and
openser shut downs before the module is initialize.

I assume you want to maintain the module on svn repository.

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Comment By: Ovidiu Sas (osas)
Date: 2008-01-14 15:09

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> Does this also includes the extensions from openims?

No.  It is the port of the version that is in the SER cvs.
I will backport the openims extensions later.


Regards,
Ovidiu

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Comment By: Klaus Darilion (klaus_darilion)
Date: 2008-01-14 12:37

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Does this also includes the extensions from openims?

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