h1. Load-balancing for SIP

!load_balancing_sip.gif!

_Server1_ performs a role of a load-distributor for _Carrier1_.
Its functions:

* incoming calls authorization
* signalling stream redirection to _Server2_ and _Server3_ using message SIP "302 Moved Temporarily"
* configuring of [[Web-interface]]
* periodic actions ([[Invoice generation]] etc) 

This method works only for SIP protocol.

*Server2* and *Server3* act as SBC (Session Border Controller).
Their functions:

* [[Routing]];
* [[Billing]], [[Online billing]] and [[Balances|Balance maintenance]];
* signalling protocols translation
* when a call is connected, signalling session maintenance with Carrier2 and Carrier3;
* media streams proxying
* media streams translation;
* [[VAS]] (if enabled);

The function distribution is approximate.
In the example below we assume, that resource spending on signalling handling from all customers are approximately equal to resources spendings to other functions ([[Billing]], [[VAS]], etc).
Maximal capacity of such a scheme is defined by maximal capacity by load-distributor *Server1*.
Therefore in example above it's shown how to maximally offload it.
In case if proportions will be different, it's possible to move some of functions from SBC to load-distributor.

[[Распределение нагрузки для SIP|Русский перевод]]