Connect Kamailio to TelecomsXchange

Kamailio usually sits in front of your media servers as an SBC or routing proxy. This guide sends calls from it to TelecomsXchange and accepts TelecomsXchange's calls for routes you sell or numbers you bought. For every TelecomsXchange value in one place, see Connect a SIP platform.

Before you start#

• A SIP account with Kamailio's public IP, for example 203.0.113.10, or a VoIP login and password from Edit Account → Add SIP Digest Auth.
• A purchased route and its tech prefix from My Interconnections, for example 80039#.
• Kamailio with the tm, dispatcher, permissions and uac modules available.
• To sell: a route with IP Address:Port set to Kamailio, for example 203.0.113.10:5060, and the values in Interconnect Info.

How do I send calls to TelecomsXchange?#

1. Add TelecomsXchange as dispatcher set 1, and your own media servers as set 2 for inbound calls:

# /etc/kamailio/dispatcher.list
# setid  destination
1 sip:sip01.telecomsxchange.com:5060
2 sip:10.0.0.21:5060

2. Load the modules and set their parameters in kamailio.cfg:

loadmodule "dispatcher.so"
loadmodule "permissions.so"
loadmodule "uac.so"

modparam("dispatcher", "list_file", "/etc/kamailio/dispatcher.list")
modparam("permissions", "address_file", "address.list")   # next to kamailio.cfg
# digest credentials are read from these AVPs in the failure route
modparam("uac", "auth_username_avp", "$avp(auser)")
modparam("uac", "auth_password_avp", "$avp(apass)")
modparam("uac", "auth_realm_avp", "$avp(arealm)")

3. Rewrite the number and relay. 80039# is the TECH_PREFIX from My Interconnections:

route[TO_TCXC] {
    # strip + or 00 so the number is plain E.164
    if ($(rU{s.substr,0,1}) == "+") {
        $rU = $(rU{s.substr,1,0});
    } else if ($(rU{s.substr,0,2}) == "00") {
        $rU = $(rU{s.substr,2,0});
    }
    $rU = "80039#" + $rU;              # TECH_PREFIX + E.164
    if (!ds_select_dst("1", "4")) {
        send_reply("503", "TelecomsXchange unavailable");
        exit;
    }
    t_on_failure("TCXC_AUTH");
    route(RELAY);
    exit;
}

failure_route[TCXC_AUTH] {
    if (t_is_canceled()) exit;
    # digest variant: answer TCXC's challenge with the account's VoIP login
    if (t_check_status("401|407")) {
        $avp(auser) = "VOIP_LOGIN";
        $avp(apass) = "VOIP_PASSWORD";
        $avp(arealm) = $null;          # empty: use the realm from the challenge
        if (uac_auth()) {
            t_relay();
        }
        exit;
    }
}

Call route(TO_TCXC) from request_route for the INVITEs your customers send to international numbers, after your own authentication of those customers.

With IP authentication only, TelecomsXchange doesn't challenge and the failure route is never used for auth; keep it anyway, so adding a VoIP login later needs no script change.

How do I receive calls from TelecomsXchange?#

Calls on routes you sell, and on numbers you bought, come from 174.136.44.213 over UDP, from source ports 5060 to 5072, with the number in E.164 format such as 14165551234.

1. Allow 174.136.44.213 on your firewall for UDP 5060.
2. Add it to the permissions address file as group 10:

# /etc/kamailio/address.list
# group  address         mask  port  tag
10 174.136.44.213 32 0 tcxc

3. Near the top of request_route, before your customer authentication, send TelecomsXchange's INVITEs to your media servers:

if (is_method("INVITE") && allow_source_address("10")) {
    # route sold: E.164 number in $rU, e.g. 14165551234
    if (!ds_select_dst("2", "4")) {
        send_reply("503", "No media server");
        exit;
    }
    route(RELAY);
    exit;
}

4. Reload with kamcmd permissions.addressReload and kamcmd dispatcher.reload.

If your route has an Outgoing Prefix or strips digits (Edit Route → Outgoing Number Translation Parameters), expect the number in that format.

How do I receive calls on numbers I bought?#

Set the number's SIP Endpoint (Primary) in DID Settings to Kamailio, for example sip:14165551234@203.0.113.10:5060. The INVITE comes from 174.136.44.213, matches allow_source_address("10"), and goes to your media servers with the number in $rU.

How do I test it?#

1. Check the configuration: kamailio -c -f /etc/kamailio/kamailio.cfg, then kamcmd dispatcher.list and kamcmd permissions.addressDump.
2. Start a capture: sngrep port 5060.
3. Place a call from one of your customers and check the INVITE to sip01 carries 80039#447700900123 (or 80039%23447700900123) and the reply code.
4. In the portal, watch the call in Live Calls and find its SIP code in Logs → CDR (Voice).

What if something goes wrong?#

References#

• Kamailio dispatcher module
• Kamailio permissions module
• Kamailio uac module
• Kamailio core cookbook: transformations