Carrier routing

The carrierroute module picks an outbound carrier for a call based on the dialled number. Routing rules live in a tree keyed by a carrier and a domain, where each entry matches a prefix of the request user and rewrites the destination. It is the usual way to build least cost routing or to spread traffic across several upstream providers with weights and failover.

Configuration

Rules are read from a database table rather than from the config file, so the module needs a db_url and a default tree to fall back on:

loadmodule "db_mysql.so"
loadmodule "carrierroute.so"

modparam("carrierroute", "config_source", "db")
modparam("carrierroute", "db_url", "mysql://openser:1234@localhost/openser")
modparam("carrierroute", "carrierroute_table", "carrierroute")
modparam("carrierroute", "default_tree", "default")
modparam("carrierroute", "fetch_rows", 2000)

Setting config_source to file instead reads the rules from a plain text tree, which is easier for a small static set of prefixes but requires a reload to change.

Lookup in the routing logic

kamailio_carrierroute.cfg exposes the lookup as a redirect service: a request carrying the header X-ROUTE: LOOKUP is answered with a 302 pointing at the carrier chosen for the dialled number, rather than being relayed.

if (is_method("INVITE") && $hdr(X-ROUTE)=="LOOKUP") {
    if (!cr_route("default", "default", "$rU", "$rU", "call_id", "$avp(s:route_desc)")) {
        sl_send_reply("604", "Unable to route this call");
        exit;
    } else {
        avp_pushto("$ru/username", "$avp(s:route_desc)");
        sl_send_reply("302", "$rd");
        exit;
    }
}

The arguments to cr_route() are the carrier, the domain, the number to match, the user part to rewrite, the hash source used to distribute traffic across equally weighted rules, and an AVP that receives the description of the rule that matched. Using call_id as the hash source keeps all requests of a dialog on the same carrier.

To relay instead of redirecting, drop the sl_send_reply("302", ...) and call t_relay() after cr_route() has rewritten the request URI.

Notes

• mpath in this configuration points at /opt/kamailio/lib64/kamailio/modules/; change it to match your installation, commonly /usr/lib/x86_64-linux-gnu/kamailio/modules/ on Debian.
• The example listens on udp:127.0.0.1:5062 and disables TCP, so it can run beside another Kamailio instance while you test the routing tree.
• mi_fifo is used for the control interface here. On Kamailio v5.x prefer jsonrpcs with kamcmd, see the kamcmd notes.

View this page’s source on GitHub