tutorials:alias-example - sip-router.org

[ Please fill or disable this placeholder (:wiki:site_notice) ]
You are here: start » tutorials » alias-example
This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
====== An example on how to use add_contact_alias() and handle_ruri_alias() functions ======

===== Introduction =====

The benefits of using add_contact_alias() and handle_ruri_alias() functions instead of conventional NAT traversal solutions are:

  * support for re-use of tcp sessions between proxy and UAs
  * supports for routing of requests to UAs behind NATs so that r-uri is always what UAs expect

In the example below only functions related to signaling are shown.  Proxying of media using either Mediaprxy or RTP Proxy can be easily added.

===== Non-Register Initial Requests =====

Call add_contact_alias() for all non-register initial requests, which
don't come from another proxy (which takes care of its own UAs).
If you know that non-register initial request is going to another
proxy, set TO_PROXY flag before relaying the request.
In cases, where initial request may go to another proxy, but you are
not sure about it, store the number of record-route headers in
incoming request in an AVP that you can then later test in onreply
route and find out, if next hop was a proxy.

<code>
route [NON_REGISTER_INITIAL_REQUESTS] {

    if (!is_present_hf("Record-Route")) {
        route(ADD_CONTACT_ALIAS);
    };
    ...
    if (I_KNOW_FOR_SURE_THAT_NEXT_HOP_IS_ANOTHER_PROXY) {
        setbflag("TO_PROXY");
    };
    if (NEXT_HOP_MAY_BE_ANOTHER_PROXY_BUT_I_DONT_KNOW_FOR_SURE) {
        $avp("rr_count") = $rr_count;
    };
    t_on_reply("REPLY");
    if (!t_relay()) ...
}

route [ADD_CONTACT_ALIAS] {

    if (!add_contact_alias()) {
        xlog("L_ERR", "Error in aliasing contact <$ct>\n");
        send_reply("400", "Bad request");
        exit;
    };
}
</code>

===== Register Requests =====

Call fix_nated_register() on register requests, if registering ua is
behind nat OR is using tcp.

<code>
route [REGISTER_REQUESTS] {
    ...
    if (isflagset(FROM_NATED) || (proto == TCP) || (proto == TLS)) {
        fix_nated_register();
        if (isflagset(FROM_NATED)) {
            setbflag("TO_NATED");
        };
    };
    save("location");
    ...
}
</code>

===== In-Dialog Requests =====

Call add_contact_alias() for all in-dialog requests that don't come
from another proxy.  Call handle_ruri_alias() for all in-dialog requests before
t_relaying them to UAs.  Next hop is an UA if loose_route()
didn't set $du.  If next hop is a proxy, set TO_PROXY flag.

<code>
route [IN_DIALOG_REQUESTS] {

    if (@via[2] == "") {
        route(ADD_CONTACT_ALIAS);
    }
    loose_route();
    if ($du == "") {
        handle_ruri_alias();
        switch ($rc) {
        case -1:
            xlog("L_ERR", "Failed to handle alias of R-URI <$ru>\n");
            send_reply("400", "Bad request");
            exit;
        case 1:
            xlog("L_INFO", "Routing in-dialog $rm from <$fu> to <$du>\n");
            break;
        case 2:
            xlog("L_INFO", "Routing in-dialog $rm from <$fu> to <$ru>\n");
            break;
         };
    } else {
        setbflag("TO_PROXY");
    }
    t_on_reply("REPLY");
    if (!t_relay()) {
        ...
}
</code>

===== Replies =====

Call add_contact_alias() on all replies except the ones that come from
another proxy.

<code>
onreply_route [REPLY] {

    if (!isbflagset("TO_PROXY") {
        if (is_avp_set("$avp(rr_count)")) {
            if ($rr_count == $avp(rr_count) + $rr_top_count) {
                route(ADD_CONTACT_ALIAS);
            };
        } else {
            route(ADD_CONTACT_ALIAS);
        }
    }
    ...
}
</code>

===== Notes =====

Do //not// call fix_nated_contact() on anything, because
add_contact_alias() replaces it.
Trace: • xavp • 2009-07-07
Navigation

Search

Toolbox

QR Code
