[Serusers] Re[5]: [Serhelp] third part session control

Jiri Kuthan serhelp at lists.iptel.org
Wed Dec 4 18:50:41 CET 2002

At 03:57 PM 12/4/2002, Igor Vasiliev wrote:
>Does it mean that some request(e.g. depends on caller name)
>I can redirect to B2BUA?

Yes. You can proxy SIP servers in long chains, in which each
element adds some value. A proxy server in the middle of 
a chain can decide what the next hop for a request would be.
For example, you can make such a SIP-routing decison with SER:

# prefix for germany -- route over b2bua.germany.bar
if (uri="^sip:+49[0-9]*@foo.bar) t_relay_to("b2bua.germany.bar", "5060");
# anything else is routed using userloc database
else {
  if (!lookup("location")) {
        sl_send_reply("404", "Not Fond");
   } else {
       # forward to the destination in UsrLoc database

SER is then acting as a "switch", switching by request URI.

>Is such scenario correct?
>caller --->SER --->B2BUA ----> callee

Such a scenario can be correct to. How you construct the chains
depends mainly on how you want to concatenate values added
by each element in the path. One element can add authentication,
another one user location, yet another firewall control, etc...
Alternative, all the functionality can be merged in a single
server. That is the freedom of choice when building SIP 

>> >Could I use B2BUA without SER(and without any SIP proxy)?
>> Yes. There is BTW many other things which you can do without
>> any SIP proxy -- skiing, playing chess
>I just mean, could caller send INVITE directly to B2BUA?


Yes -- a B2BUA could be certainly built in such a way, which
delivers all features a proxy server does.


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