P.S. There is a dispatcher-oriented example config in the package that can help get you started:

http://git.sip-router.org/cgi-bin/gitweb.cgi?p=kamailio;a=blob;f=modules/dis...

But the central idea is really quite simple:

1. Load the 'dispatcher' module:

loadmodule "dispatcher"

2. Configure 'dispatcher' to load a list of hosts, either from a database (db_url), or else from a flat text file:

modparam("dispatcher", "db_url", "DB_DRIVER://DB_USER:DB_PASSWORD@DB_HOST/DB_NAME") modparam("dispatcher", "table_name", "dispatcher") modparam("dispatcher", "force_dst", 1) modparam("dispatcher", "flags", 2) modparam("dispatcher", "dst_avp", "$avp(s:d_dst_set)") modparam("dispatcher", "grp_avp", "$avp(s:d_grp_set)") modparam("dispatcher", "cnt_avp", "$avp(s:d_cnt_avp)") modparam("dispatcher", "ds_probing_mode", 0)

3. In your initial request route, pick a host from the dispatcher set, based on the round-robin strategy (algorithm #4):

if(!ds_select_domain("1", "4")) { # This should only happen if the route set is empty.

sl_send_reply("503", "Out of Gateways");

xlog("L_ERR", "[R-DISPATCHER-INITIAL:$ci] !> " "No gateways available!\n"); exit; }

xlog("L_INFO", "[R-DISPATCHER-INITIAL:$ci] -> " "Selected gateway: $rd:$rp\n");

t_on_failure("DISPATCHER_ROLLOVER");

4. If that gateway should fail to respond or to accept the call, catch that event in a failure_route and pick the next gateway from the set:

failure_route[DISPATCHER_ROLLOVER] { if(t_is_expired() || t_is_canceled()) exit;

if(!ds_next_domain()) { # This should happen when we are out of gateways/have tried # the last one in the route set.

xlog("L_ERR", "[R-DISPATCHER-ROLLOVER:$ci] !> " "No more gateways in route set\n");

t_reply("503", "Out of gateways"); exit; }

xlog("L_INFO", "[R-DISPATCHER-ROLLOVER:$ci] -> " "Attempting relay to new gateway: $rd:$rp\n");

t_on_failure("DISPATCHER_ROLLOVER"); t_relay(); }

And repeat recursively until you run out of gateways.

5. The timeouts due to non-response of the gateway are regulated by the transaction state module (TM):

modparam("tm", "fr_timer", 3000) # 3 seconds modparam("tm", "fr_inv_timer", 90000) # 1.5 minutes.

You can read more about these values here:

http://kamailio.org/docs/modules/4.1.x/modules/tm.html#fr_timer http://kamailio.org/docs/modules/4.1.x/modules/tm.html#fr_inv_timer

-- Alex

On 02/04/2014 06:25 AM, Alex Lake wrote:

That's very useful, thanks. Your guess as to my assumption was 100% correct. I presume, therefore, that the Kamailio community have no ambitions to become more "app"y. To be honest, I can quite sympathise with that.

Well, yes and no. :-)

On the one hand, the essence of Kamailio's flexibility and its power comes from its rather low-level nature. And, there are plenty of open-source and commercial platforms built on top of Kamailio that do wrap and abstract a lot of its complexities into higher-level presentation, and, like any project that has spawned such an ecosystem of third-party software, we'd be reluctant to steamroll over it by co-opting or absorbing the functionality into the project core.

From the beginning, the intent of SER/OpenSER/Kamailio was to provide a really good toolbox, and I think that's the core competency of the project. It's been implemented at the corresponding level of abstraction for a toolbox from the ground up. I don't think that is going to change.

On the other hand, like any other project, obviously we would like to grow our ecosystem, promote the project, encourage wider adoption and understanding of it ("mindshare"), etc. There are varying opinions as to whether the best strategy to achieve this is by focusing on sophisticated operators who stand to benefit the most from Kamailio's technical nuances, or whether to focus on packaging Kamailio in a way that appeals to a wider mass-audience.

With regard to the latter, the project has actually evolved. The documentation has seen a lot of improvements in recent years. The stock config file that ships with Kamailio, which most novice to intermediate users base their installations on, has become more templated, with lots of options to enable and disable certain out-of-the-box features, and it does a lot more than it used to. Daniel-Constantin Mierla/ASIPTO are about to release a brand new, up-to-date Kamailio Admin book.

It may still feel "user-unfriendly" to new users, but trust me, it used to be even more so. :-)

-- Alex