[Kamailio-Users] help understanding kamailio.cfg and processing call flow

[Klaus Darilion]

1. read the confige file from sipwise.com - IMO it is very self explanatory.

some comments below:

Fabian Borot schrieb:
> hello
> 
> Register with Auth:
> 
> 1- user sends REGISTER request w/o the encripted credentials
> 2- kamailio answers with 401 and sends the challenge
> 3- the uac sends the REGISTER again, this time with the right 
> credentials and after verifying kamailio sends 200 OK
> 4- if the user is behind a NAT we can fix the contact info before saving 
> it to the location db.
> 
> 
> With the help of the forum and the tutorials I have found in the 
> internet I have been able to accomplish it with these
>  commands:
> 
> route{
>     if (uri==myself) {
>         if (method=="REGISTER") {
>                 xlog("L_INFO","mylog: starting to process 
> REGISTER.Info.\n");
>                     if (!www_authorize("", "subscriber")) {
>                         xlog("L_INFO","mylog: REGISTER came without 
> auth, sending challenge.\n");
>                             www_challenge("", "0");
>                             exit;
>                     };
>                     if (nat_uac_test("1")){
>                         xlog("L_INFO","mylog: REGISTER-Device behind 
> NAT.\n");
>                             fix_nated_register();
>             }
>                     force_rport();
>                     save("location");
>                     xlog("L_INFO","mylog: save-location successful.\n");
>                     exit;
>     }
>     route(1);
> }
> route[1] {
>         if (t_relay()) {
>                 xlog("L_INFO","mylog: Route 1 section. Method [$rm].");
>         } else {
>                 sl_reply_error();
>                 xlog("L_INFO","mylog: Route 1 section. T_Relay failed. 
> Method [$rm].");
>         };
>         exit;
> }
> 
> but here come the first questions:
> 1- when the uac sends the first REGISTER, the function www_challenge() 
> is the one that actually sends the "401" message?

Yes, it sends 401 and exits immediately. Thus the exit after 401 would 
not be needed, but it is good to have it there as it eases reading the 
config script.

> or the "exit" just exit out the "if" block and the script will continue 
> with route(1) which in turns executes "t_relay()?
> 
> ++from the doc, www_challenge() function++++
> The function challenges a user agent. It will generate a WWW-Authorize 
> header field containing a digest challenge, it
> will put the header field into a response generated from the request the 
> server is processing and send the reply.
> +++++++++++++++++++++++++++++++++
> 
> 
> 2- the "exit" after the save("location") function I assume would stop 
> the execution of the script and at that point kamailio
> responds with "200 ok"? or just exit out the "if" block, the script then 
> reaches the "route(1)" section and the "t_relay()"
> sends the "200 ok"?

save stores the record and send back 200 OK. But it does not stop 
processing. Thus, you MUST have an exit after save().

> 
> ++ from the doc, core-cookbook, exit() function+++++++
> Stop the execution of the configuration script – it has the same 
> behaviour as return(0). It does not affect the
> implicit action to be taken after script execution.
> ++++++++++++++++++++++++++++
> 
> 3- the "t_relay" function: does that function creates and sends the 
> approriate response for each request?
> ex1: an INVITE is received, does t_relay() "know" that it can send "100 
> trying" automatically?

t_relay() sends automatically 100 trying to the caller (except you call 
it with some special flags (see README of tm module)) and forwards the 
request to the next destination.

> ex2: a "200 OK" is received as a response to an INVITE, does t_relay 
> knows that it has to send an "ACK"?

No. The proxy does not send ACK. The proxy forwards the response to the 
caller. Then the caller will send the ACK which will be forwarded by the 
proxy to the callee. For successful call setups the proxy wont send 
ACKs. The proxy will send ACK to the callee by itself only if a call 
gets cancelled.

> 
> ++++++from the doc, t_relay() funcion ++++++++++
>  From user's perspective, the major function is t_relay(). It setup 
> transaction state, absorb retransmissions from upstream,
>  generate downstream retransmissions and correlate replies to requests.
> +++++++++++++++++++++++++++++
> 
> 
> 4- why do I see ";" even after a "}", is it needed sometimes?

  };
is the same as
  }

choose the syntax you like

> 5- is "exit" the same as "exit()"?

I don't know - I always use exit;
Probably exit() is just an alias.


regards
klaus



> 
> 
> These may sound like dumb questions for some of the experienced users, 
> but for a newbie they are not. Also, if this sounds like "
> hey, code my config file for me" I assure you that that is not the 
> intended purpose.
> I would appreciate any help and thank everybody in advance.
> 
> 
> Fabian
> 
>  
> 
> 
> 
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