[sr-dev] recursive calls to failure_route strange behavior

Miklos Tirpak miklos at iptel.org
Fri Nov 20 18:02:50 CET 2009

On 11/20/2009 05:32 PM, Daniel-Constantin Mierla wrote:
> Hello,
> On 20.11.2009 17:04 Uhr, Miklos Tirpak wrote:
>> Hi Daniel,
>> On 11/20/2009 04:38 PM, Daniel-Constantin Mierla wrote:
>>> On 20.11.2009 9:53 Uhr, Miklos Tirpak wrote:
>>>> On 11/20/2009 12:58 AM, Andres Moya wrote:
>>>>> Dear all!
>>>>> Please help. I have problem dealing with recursive call in failure 
>>>>> route.
>>>>> this route happen first time for authentication to external SIP 
>>>>> provider (react on code 401), then it have response 480 i want to 
>>>>> direct traffic to another operator via cr_route.
>>>>> First i relay INVITE and getting 401, then sending authentication, 
>>>>> but provider gives 480. I can see it in a dump of SIP session. But 
>>>>> my failure_route still thinking that reply code is 401 on second 
>>>>> reply. Maybe because i dont understand well how branches concept 
>>>>> work here? Or using kamailio 3.0? ;) Looks like it give me status 
>>>>> code of first reply and ignoring actual code in reply. :( I don't 
>>>>> know if it something with development version or my own 
>>>>> misunderstanding. sorry
>>>> This is correct, the proxy must choose one of the two responses to 
>>>> forward and 401 has higher precedence than 480 (RFC3261, 16.7: 
>>>> "Choosing the best response"). The failure route always works on the 
>>>> selected response as opposed to the last response received.
>>> I think this is wrong imo, if I got it right from your email, because 
>>> the failure route should work on a selected reply from the last set 
>>> of branches in serial forking.
>>> Do you say that if I get 301 with couple of contacts, then in failure 
>>> route I create new branches, relay, all failed because of timeout 
>>> and/or busy, I get back in failure route with the 301?
>> yes.
>>> I cannot drop all replies because maybe the reply I want to be sent 
>>> back to caller is from a previous branch. Think at:
>>> A calls B
>>> B phone gives busy
>>> B has redirect to C in such case
>>> C phone gives timeout
>>> C has now redirect to voice mail
>>> Voice mail returns server failure
>>> If I need to drop the replies then I will send the 500 reply which is 
>>> wrong. If I do no drop replies, then it is hard to implement the 
>>> proper logic for different kinds of redirects:
>>> - no answer
>>> - busy
>> Yes, the above case is quite complicated, by default I think the 408 
>> will be sent back because it is the lowest response code.
>> The priority list is: 6xx > 3xx > 4xx > 5xx.
>> The lowest response wins within the class but 401, 407, 415, 420, 484 
>> are preferred over other 4xx responses.
> also 487 (request canceled) has the highest priority.
>> If this is an issue then we can implement more sophisticated drop 
>> commands that drop only selected branches, for example a single branch 
>> that is being processed in failure route.
> It just looks a bit unpredictable right now, mainly with what happens in 
> failure route because the reply code presented there is not what is 
> expected. So I would add a parameter:
> t_drop_replies("all");
> t_drop_replies("last");

This sounds good!

> It is not hard to implement at all. In SR is a flag to mark the start of 
> last set of branches -- so getting the first branch in the last step 
> would be:
>    for(first_branch=t->nr_of_outgoings-1; first_branch>=0; first_branch--)
>        if(t->uac[first_branch].flags&TM_UAC_FLAG_FB)
>            break;

t_drop_replies("last") may be a bit confusing if it is called from 
failure route, imagine the following case:

1. A calls B
2. B does not answer -> 408
3. B has redirect to C
4. C is busy -> 486
5. reply route is executed with the lowest response code received that 
is 408 in this case.

If t_drop_replies("last") is called in 5) then it will drop the 486 
although 408 is being processed. This means that it is hard to check in 
5) whether to call t_drop_replies("last") because all the conditions 
work on the 408. So "last" means the last branches not the last 
processed by failure route.

Anyway, this may be a corner case, and it is still better than we 
currently have. It may also make sense to drop a reply from reply_route 
because the status code of the reply can be checked without being 
affected by the other replies. Something like t_drop_replies("current")

> But I would do it opposite, to have script simpler (and be K compatible 
> and have uac_redirect and other k modules work as expected :-) ), 
> instead of drop function, have drop by default the replies from last set 
> of branches, and then t_keep_replies() so one ca decide to keep the 
> replies. Probably can be switched one way or another (K or S) but config 
> compatibility mode.

I am fine with this of course, we just need to have the drop capability 
in one or another way.


> Cheers,
> Daniel
>> Miklos
>>> Cheers,
>>> Daniel
>>>> Try to add t_drop_replies() to the failure route block when the 401 
>>>> is processed. This function drops all the existing replies, 401 in 
>>>> your case, hence 401 will not be selected again when 480 is received.

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