[SR-Users] Dispatcher module with call load balancing

[Daniel-Constantin Mierla]

Hello,

On 12/15/11 12:06 PM, Mino Haluz wrote:
> Hi,
>
> I would like to use the dispatcher module with algorithm 10 - call 
> load balancing. But there are multiple things that are a bit unclear 
> to me. I have multiple gateways that can serve different maximum 
> number of calls.
>
> 1) Can I somehow set the maximum calls count for each dispatcher 
> gateway, so that it can fairly distribute the calls? I know it is 
> stateless module, but how could I solve this?
it is not stateless module - dispatcher has nothing to do with the 
states, it just selects the destinations. Then, if you relay with tm you 
make the routing transaction stateful and if you forward() then it is 
stateless routing.

The algorithm does selection of the least loaded destination. There is 
another algorithm for weight based distribution (iirc 9), might suit 
better your need.
> 2) Is there any method how can I get the current number of calls for 
> each gateway from the dispatcher module?

Not yet.

> 3) What is the expiration timer in the dispatcher module for dialogs 
> if the dialog is canceled uncleanly ?

http://kamailio.org/docs/modules/stable/modules_k/dispatcher.html#id2498263

> 4) Imagine I will restart kamailio, it will lose the call count and 
> the distribution will be incorrect. Maybe it could nice, that kamailio 
> would offer MI command to set these values.
Some enhancements can be done, of course, it is a matter of time and 
interest for developers, the fastest way to get something is to 
contribute, it is open source greatest benefit.

Personally I haven;t invested much in enhancing this algorithm lately 
because it does not bring relevant benefits comparing with round robin. 
The actual load on a server is not a matter only of the number of active 
calls, but also the content of the media stream and its processing 
(e.g., 10 calls on hold consume less resources than 3 active and verbose 
conversations). The most of the calls are in the average duration of a 
business type, thus simple round-robin is keeping pretty fair load 
balancing of the active calls -- from experience, with round-robin none 
of the destinations got more than 10% load than the average.

Regarding the restart, yes, there can be coding to make it more 
accurate, but if it is call load balancing, practically a restart cannot 
get a destination to have more than 1 call than it should have, which I 
think it is not something critical.

But again, any contributions in this regard will be considered and 
accepted when they bring benefits.

Cheers,
Daniel

-- 
Daniel-Constantin Mierla -- http://www.asipto.com
http://linkedin.com/in/miconda -- http://twitter.com/miconda