[Serusers] SIP & application server

Jiri Kuthan jiri at iptel.org
Mon Jul 7 10:49:48 CEST 2003

At 10:19 AM 7/7/2003, Victor Gamov wrote:
>I'm novice at SIP technology and I have some questions about it.
>When we speak about "application server" in SIP (SER may acts as AS) what does it means? Is it server which siply launch external applications (internal module or fork & exec) to rewrite SIP/SDP packet and forward it to next hop or something else?

We should have possibly avoided use of that term -- "application server" 
is today used in too many contexts by too many marketeers and has no fixed
technical meaning.

Within SER, we use "Application FIFO Interface" for the interface with which
you can access SER internals and initiate some SIP conversations, like
IM paging or click-to-dial. It became mature in 8.11 -- 8.10 was an infant.
It is not a B2BUA though you could use it to build one. Actually we began
to use this interface by applications like voicemail or conferencing, and
possibly a B2BUA will emerge too.

>For example if I want to write application which accept external call, make some decisions on it and then make external call. Is it suitable for SER or I must write something like B2BUA and start it as independed application (as UA from the point of view of SER) ?

That depends on what you exactly want to do. Most cases are perfectly fine
with a proxy server. For example, you look at incoming INVITE, detect it
should be routed to gateway, check it against some access control lists
and forward it then. B2BUA is much more needed if you would wish the server
to guide caller through multiple-stage converstation. For example, such
a session would include first stage with an announcmenet component ("welcome to 
lipetsk.ru"), then converstation with an IVR ("press 1 to talk to CTO")
and eventually forwarding to a SIP telephone.


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