[Kamailio-Devel] [Kamailio-Users] Dispatcher hash algorithms.

[Alex Balashov]

samuel wrote:
> The Call-ID hash is used to send all requests of the same dialog to the 
> same endpoint (proxy,application server,gateway,whatever...).  The 
> reason after this behaviour is not to have these SIP endpoints sharing 
> the status of all the dialogs (not many applications out there share 
> this status and therefore you are required to send all within-dialog 
> messages to the same SIP instance).
> 
> simple: to send the BYE to the same gateway you sent the INVITE...
> 
> This does not guarantee fare load distribution....that's why depending 
> on what you are dispatching you can hash on several headers (if you 
> don't have to keep dialog state,...)

Yes, but is that not a relatively minor use case that applies to 
situations in which stateful transaction forwarding (TM module) is not 
used?

Meaning, if I t_relay() an INVITE to a gateway selected by dispatcher, 
subsequent provisional responses and in-dialog requests will be passed 
between the original endpoints without further intervention.

If it didn't work that way, round-robin and random wouldn't work as 
algorithms because the next message would be sent to another server.

So, stateless forwarding aside (why would you want to do that in a 
dispatcher load balancing or failover scenario?), why do these hash 
algorithms make any sense to use?

-- 
Alex Balashov
Evariste Systems
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