[SR-Users] Problem with worst case scenario of accessing 15 gateways over the DISPATCHER module - MAX_BRANCHES is reached

[Klaus Feichtinger]

> On Sunday 03 July 2011, Klaus Feichtinger wrote:
>>  I have a problem in my scenario where I use the dispatcher module for
>> (round-robin based) distribution of incoming calls to 15 (!) different
>> gateways. In idle case (= all gateways are up and running or just a
>> couple of them does not accept calls) my solution is working fine. The
>> solution is very primitive and based on the example of the dispatcher
>> module's ReadMe. However, when e.g. 12 of 15 gateways are out of
>> service (in detail: rejecting the call with "480 - Temporarily
>> Unavailable") and only the 13th would be okay, I can not reach that
>> gateway. This is because the TM module is interrupting the
>> distribution with an error message indicating that the maximum number
>> of branches (per transaction) is reached (ERROR:tm:add_uac: maximum
>> number of branches exceeded)....
>>
>>  My first idea for solving this problem was/is in manipulating the
>> definition of the "max_branches" constant in the config.h file.
>> However, I prefer using the precompiled Debian packages. Therefore
>> that solution is not optimal. I have not found a method for decreasing
>> the destination_set on an easy way... Does anybody know an alternative
>> solution / workaround?
>
> Hi Klaus,
>
> did I understand it correctly, you trying sequential 15 gateways in your
>  setup? E.g.,
>
> - try GW 1
> - on error try GW 2
> - ...
> - up to GW 15?
>
> Normally I'd expect that you restrict the number of tries to something
> smaller, that you don't run into this max_branches issue and also don't
> have a  that long call setup time for the user. And I also would think
> that you would  notice that you running at a few percent of your
> capacitiy via some other  alarms, and just fix the gateways?
>
> With regards to your question, you could make the max_branches number
> configurable with a patch, at the moment its just a define.
>
> Best regards,
>
> Henning


Hi Henning,

the described scenario is not a standard scenario. This would be realistic
in emergency situations only (e.g. so many calls are coming in and the
gateways are busy => e.g. responding with "486 Busy Here" ). Also the time
delay would not be very high, because the fr_timer variable is set to a
value of 750ms before relaying the call to the dispatcher-targets
("t_set_fr([...]))") - this is just for a scenario when the target is
unreachable.

In case that the dispatcher-target is responding with a negative response
code (as it was until now), all targets are sequentially addressed within
a time of lower than 1 second until the error message of the TM module is
interrupting that process.

However, if there is no alternative to changing the define value of
MAX_BRANCHES I will use your recommendation for limiting the number of
gateways that will be addressed over the failure_route. My Question now
is: how can I count the number of branches / rejections (from the
failure_route)?
I've tried using the pseudo_variable $branch(count) (according description
of the WIKI page), but the value is "0" all the time => not useful. I
could create a private table and use the sqlops module. Do you have any
easier alternative recommendation how the number could be limited?

Thanks in advance!

Best regards,
Klaus

P.S. an excerpt of the current situation of Kamailio 3.1.4 in the scenario
- the <names> are representing different [failure]routes

kamailio: INFO: -<|XLOG|>-:  <route> an incoming call to a virtual ID with
R-URI sip:225201@<ipaddr-Sip-Srv>
kamailio: INFO: -<|XLOG|>-:  <DISTGWY> is reached for target
sip:225201@<ipaddr-Sip-Srv>
kamailio: INFO: -<|XLOG|>-:  <DISTGWY> relay to R-URI:
sip:225201@<ipaddr-Sip-Srv> with DS: <null> and AVP: sip:10.180.38.76:5060
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 100
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <REPLYDISTGWY> is reached with Reply-Code 480
From: sip:123456@<ipaddr-vgw> To: sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-:  <FAILDISTGWY> is reached with Code 480 from
sip:123456@<ipaddr-vgw> for sip:225201@<ipaddr-sip-srv2>
kamailio: INFO: -<|XLOG|>-: <FAILDISTGWY> ds_next_dst was executed
successfully with DS <null> and AVP <null>
kamailio: ERROR: tm [t_fwd.c:651]: ERROR: add_uac: maximum number of
branches exceeded
kamailio: ERROR: tm [t_fwd.c:1528]: ERROR: t_forward_nonack: failure to
add branches
kamailio: ERROR: tm [tm.c:1368]: ERROR: w_t_relay_to: t_relay_to failed
kamailio: WARNING: -<|XLOG|>-:  <FAILDISTGWY> t_relay for GWYs failed.