[Serusers] Re: INVITE timeout

[Jiri Kuthan]

I agree variable Final-reply timer is a good thing for the scenario you
mentioned as well as for the scenario of user-defined "number of rings"
before voicemail hits.

We actually used to have it, it just turned out to be a performance 
concern and I removed it. The problem is the variable length may 
escalate CPU consumption. With fixed timer, we have fixed cost of appending 
a new element to timer list. With variable timer, we need to insert, i.e., 
seek proper position first. Needless to say, if CPU consumption escalates 
with load you would make server more vulnerable to stressful situations 
such as DoS.

So I think we need to reimplement the timer in a way which is both fast
and variable. A way is to maintain two timer lists, one for fixed-length
fast timers, another for those who use variable timer no matter what it
costs. This would get the variablity without penalty to those who don't
need it. Other way would be some kind of hash table. 

Also other alternative would be just to give up on performance and do
it the way you did. 

I need to digest this first.

-jiri

At 05:34 PM 2/8/2004, Greg Fausak wrote:
>I'm thinking about a timer variable.  Something like:
>
>in h_table.h, add this:
>
>typedef struct cell
>{
>        /* linking data */
>        struct cell*     next_cell;
>        struct cell*     prev_cell;
>
>        ....omitted.....
>
>        unsigned int inv_timer;
>}
>
>Then, in tm.c, something like (with the appropriate hooks):
>
>inline static int w_t_inv_timeout( struct sip_msg* msg, char *go_to, char *foo )
>{
>        struct cell *t;
>        t = get_t();
>        if (!t || t==T_UNDEFINED) {
>                LOG(L_CRIT, "BUG: w_t_on_negative entered without t\n");
>                return -1;
>        }
>        t->inv_timer = (unsigned int)(long)go_to;
>        return 1;
>}
>
>Then, in timer.c, create a new function set_timer_val()
>which is exactly like set_timer() except the timeout
>value is passed to it:
>
>void set_timer_val( struct timer_link *new_tl, enum lists list_id,
>       unsigned int timeout )
>{
>        struct timer* list;
>
>        if (list_id<FR_TIMER_LIST || list_id>=NR_OF_TIMER_LISTS) {
>                LOG(L_CRIT, "ERROR: set_timer: unkown list: %d\n", list_id);
>#ifdef EXTRA_DEBUG
>                abort();
>#endif
>                return;
>        }
>
>        list= &(timertable->timers[ list_id ]);
>
>        lock(list->mutex);
>        /* check first if we are on the "detached" timer_routine list,
>         * if so do nothing, the timer is not valid anymore
>         * (sideffect: reset_timer ; set_timer is not safe, a reseted timer
>         *  might be lost, depending on this race condition ) */
>        if (new_tl->timer_list==DETACHED_LIST){
>                LOG(L_CRIT, "WARNING: set_timer called on a \"detached\" timer"
>                                " -- ignoring: %p\n", new_tl);
>                goto end;
>        }
>        /* make sure I'm not already on a list */
>        remove_timer_unsafe( new_tl );
>        add_timer_unsafe( list, new_tl, get_ticks()+timeout);
>end:
>        unlock(list->mutex);
>}
>
>
>Then, in t_reply.c, something like:
>
>int reply_received( struct sip_msg  *p_msg )
>{
>....omitted.....
>        /* update FR/RETR timers on provisional replies */
>        if (msg_status<200) { /* provisional now */
>                if (t->is_invite) {
>                        /* invite: change FR to longer FR_INV, do not
>                           attempt to restart retransmission any more
>                        */
>                        
>                        set_timer_val( & uac->request.fr_timer,
>                                  FR_INV_TIMER_LIST, t->inv_timer );
>                }
>.....
>
>
>Then, in your ser.cfg file you would do:
>
>t_inv_timeout(120);
>t_relay();
>
>this would override the global, ie:
>
>modparam("tm","fr_inv_timer",25)
>
>What do you think?  I think I can get it to work.  It is in
>the tm module. Is this desirable?  I think it would solve
>my problem.  Also, I think it would allow for some other neat
>things, like user controllable timeout before voicemail is
>called.
>
>---greg
>        
>
>Greg Fausak wrote:
>
>>I have an INVITE timeout problem.
>>My SIP layout includes:
>>
>>             +---------------+
>>             | EXTERNAL PSTN |
>>             | SIP SERVERS   |
>>             +---------------+
>>                     |
>>                     |
>>             +---------------+
>>             | MAIN INCOMING |
>>             | SIP SERVER    |
>>             +---------------+
>>               |           |
>>               |           |
>>     +------------+      +-----------------+
>>     | SIP SERVER |      | SIP SERVER      |
>>     | DOMAINA.com|      | OtherDom.com    |
>>     +------------+      +-----------------+
>>         |                     |
>>         |                     |
>>     +----------+             +---------+
>>     | customerA|             |otherCust|
>>     +----------+             +---------+
>>I hope the ASCII drawing worked!
>>Calls come in from the top down.
>>The MAIN INCOMING server uses internal ENUM
>>to deliver the call to the correct domain
>>server.   Once delivered to that server,
>>if the customer does not answer his phone before
>>an INVITE timeout occurs the call is forwarded to
>>voicemail.
>>This works great when the call is from an external PSTN
>>server.  It also works great if a user in DOMAINA.com calls another
>>user in DOMAINA.com.
>>I am experiencing difficulty when a user in DOMAINA.com
>>calls a user in OtherDom.com.  The SER at DOMAINA.com
>>recognizes that INVITE is going to a foreign domain, and it
>>t_relays() the INVITE to the MAIN INCOMING SER.  It then gets
>>t_relayed() to OtherDom.com where the call is delivered.
>>The problem is both use the same INVITE timer, so the TIMEOUT
>>on DOMAINA.com occurs *before* the TIMEOUT on OtherDom.com, which
>>means that the call is not delivered to voicemail.
>>Any ideas?
>>---greg
>>
>
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--
Jiri Kuthan            http://iptel.org/~jiri/