[asterisk-users] Asterisk architecture

[G(P)L]

jezzzz . a écrit :
> Thanks for your response. I'm looking specifically at
> Asterisk in a SIP-only implementation. So no need for
> Asterisk to transfer calls between PSTN and SIP. Is
> there in such a case still a need for a PBX/Asterisk?

As you can see in a typical SIP communication diagram, Asterisk (proxy, 
register, ...) can be useless during the communication (communications 
over RTP). But before having the communication, you must do different 
things :
--> find your correspondant : if you know his IP adress, you can call 
him directly, if no, you need something to find him for you, with 
information you have (generaly his name). It is like DNS on the web, you 
can connect you to a web server if you know its IP adress, but it is 
less comfortable.
--> try to establish a communication to him : with IP adress, you can. 
But if he is busy, or if he does not answer, the communication is over. 
But maybe you want a telephony service (and not only voice service), I 
mean forward to voicemail on busy, forward on voicemail if no answer, 
tell to try 10 sec and then pass to an another phone number, if you want 
the caller listen a message ("Welcome on MegaWorld company, we will you 
connect to the commercial service"), if you want to make the call 
ringing 5 phones in the same time (like call center), ... for all theses 
services, you need something between the two (or more) terminals (User 
Agent). There Asterisk has his place for building a _dialplan_.
--> build a callcenter : make queues, define phone groups, implement a 
CTI, you need Asterisk and its scripting power.
--> have a interactive vocal server : you need Asterisk.
--> you want security : you should want to forbid person to call some 
phones (if you want to call the director from your phone, you will 
directly routed to the secretary. If the call come from the financial 
director the the enterprise director, the call will not be rerouted).
--> ...

You must see Asterisk like an intermediate for adding _telephony_ services :
{phone1} -------- {asterisk} ---------- {phone2}
{UAC}--------{UAS|add service|UAC} -------{UAS}


>>From what I understand, as long as two users know
> eachother's IP addresses there's no need for Asterisk,
> is this correct? I'm talking here about a pure SIP
> implementation.
> 
> so if you have u1 and u2 and they simply wish to
> communicate and they have eachother's IP, do they need
> Asterisk for something? 
> 
> Also, in a pure SIP implementation, what does Asterisk
> offer and what is Asterisk required for?


Finaly, if you want make a simple call, no need to have Asterisk. If you 
want to make simple calls with more comfort (call by name and not by 
@IP), install Asterisk. If you want some _telephony_services_ you need 
Asterisk.

Bye
GL