[Kamailio-Users] Proxying media on reinvite

CSB kjcsb at xnet.co.nz
Thu Oct 23 04:46:22 CEST 2008


We have the following scenario:
Nated UAC receives INVITE
Call is established, we proxy audio
Far end sends Re-INVITE (to inform UAC to use UDPTL)
We don't proxy audio so call fails

So I need to understand how the appropriate way to force us to proxy the
audio when the far end of a reinvite is NATed.

Relevant parts of openser.cfg (OpenSER 1.3.2): We're using mediaproxy.

modparam("usrloc", "nat_bflag", 6)

route {
        # -----------------------------------------------------------------
        # Record Route Section
        # -----------------------------------------------------------------
        #If it's an INVITE & client is NATed,
        if (method=="INVITE" && client_nat_test("3")) { 
                #Record-route and specify the record-route header explicitly
                record_route_preset("64.38.1.1:5060;nat=yes"); # insert IP
address
                #xlog("invite and nated so record_route_preset");
        #If not Nated and not REGISTER then normal record-route
        } else if (method!="REGISTER") {
                record_route();
                xlog("not register and not nated so record_route");
        };
        #if (method!="REGISTER") {
        #       record_route();
        #};
        # -----------------------------------------------------------------
        # Loose Route Section
        # -----------------------------------------------------------------
        if (loose_route()) {
                #Ensure we are dealing with a re-INVITE. Only connected
calls have tag=
                #entry in the To header. So if it's loose routed and doesn't
have totag
                #and it's an invite or reply then something's wrong
                xlog("loose_route");
                if ((method=="INVITE"  || method=="REFER") && !has_totag())
{
                        sl_send_reply("403", "Forbidden");
                        xlog("403 in lr");
                        return;
                };

                if (method=="INVITE") {

                        if (!allow_trusted()) {
                                xlog("!allow_ trusted for r-uri <$ru>");
                                if (!proxy_authorize("","subscriber")) {
                                        proxy_challenge("domain.com","1");
                                        return;
                                } else if (!check_from()) {
                                        sl_send_reply("403", "Use From=ID");
                                        return;
                                };
                                consume_credentials();
                        };

                        #check client is nated or that we've already
identified it's nated
                        if (client_nat_test("3") ||
search("^Route:.*;nat=yes")) { 
                                setbflag(6);
                                xlog("Recipient is nated so setbflag 6 and
use mediaproxy: r-uri <$ru>");
                                use_media_proxy();
                        };
                };
                route(1);
                return;
        };
}

route[1] {

        # -----------------------------------------------------------------
        # Default Message Handler
        # -----------------------------------------------------------------

        #Call reply_route(1) to intercept response messages heading to the
client
        t_on_reply("1");
        #Try to relay the message to its destination
        if (!t_relay()) {
                #If it can't and it's an INVITE or ACK end the media
proxying
                log(1,"route[1] !t_relay");
                if (method=="INVITE" || method=="ACK") {
                        end_media_session();
                };

                sl_reply_error();
        } else {
                log(1,"route[1] t_relay");
        };
}
onreply_route[1]

#Handles message that are returned to the sender i.e. response to caller's
original request
{
        xlog("hit onreply_route(1). rs $rs si $si rm $rm ru $ru tu $tu fu
$fu rr $rr");

        if (isbflagset(6)) {
                xlog("flag(6) is set for $fu . We're currently in
onreply_route(1)");
        };
        if (isbflagset(7)) {
                xlog("flag(7) is set for $fu . We're currently in
onreply_route(1)");
        };
        if (status=~"(180)|(183)|2[0-9][0-9]") {
                xlog("status matches for $fu . We're currently in
onreply_route(1)");
        };
        if ((isbflagset(6) || isbflagset(7)) &&
(status=~"(180)|(183)|2[0-9][0-9]")) {

                #Check the SDP payload length. Assume if we have something
we can call mediaproxy
                if (!search("^Content-Length:[ ]*0")) {
                        log(1,"using media proxy in onreply_route(1)");
                        use_media_proxy();
                };
        };

        if (client_nat_test("1")) {
                fix_nated_contact();
        };
}

The re-invite looks like this:
INVITE sip:6422334455 at 58.28.1.1:5061 SIP/2.0
Via: SIP/2.0/UDP 202.180.1.1:5060;branch=z9hG4bK251fed3b;rport
Route: <sip:147.202.1.1;lr=on;ftag=as45a8ade4>
From: "user" <sip:022998877 at 202.180.1.1>;tag=as45a8ade4
To: <sip:022334455 at 147.202.1.1>;tag=4c813866c894f124i1
Contact: <sip:022998877 at 202.180.1.1>
Call-ID: 0818dfa10f1da0f25daa4759332d3c55 at 202.180.1.1
CSeq: 103 INVITE
User-Agent: UAS
Max-Forwards: 70
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Supported: replaces
Content-Type: application/sdp
Content-Length: 349

v=0
o=root 5466 5467 IN IP4 202.180.1.1
s=session
c=IN IP4 202.180.1.1
t=0 0
m=image 4724 udptl t38
a=T38FaxVersion:0
a=T38MaxBitRate:9600
a=T38FaxFillBitRemoval:0
a=T38FaxTranscodingMMR:0
a=T38FaxTranscodingJBIG:0
a=T38FaxRateManagement:transferredTCF
a=T38FaxMaxBuffer:72
a=T38FaxMaxDatagram:72
a=T38FaxUdpEC:t38UDPRedundancy

Our OK looks like this:
SIP/2.0 200 OK
To: <sip:022334455 at 147.202.1.1>;tag=4c813866c894f124i1
From: "user" <sip:022998877 at 202.180.1.1>;tag=as45a8ade4
Call-ID: 0818dfa10f1da0f25daa4759332d3c55 at 202.180.1.1
CSeq: 103 INVITE
Via: SIP/2.0/UDP 202.180.1.1:5060;branch=z9hG4bK251fed3b;rport=5060
Record-Route: <sip:147.202.1.1;lr=on;ftag=as45a8ade4>
Contact: 6422334455 <sip:6422334455 at 58.28.1.1:5061>
Server: Linksys/SPA2102-5.1.9
Content-Length: 265
Content-Type: application/sdp

v=0
o=- 69685 69685 IN IP4 192.168.1.113
s=-
c=IN IP4 192.168.1.113
t=0 0
m=image 16386 udptl t38
a=T38FaxVersion:0
a=T38MaxBitRate:14400
a=T38FaxRateManagement:transferredTCF
a=T38FaxMaxBuffer:200
a=T38FaxMaxDatagram:200
a=T38FaxUdpEC:t38UDPRedundancy

Unfortunately this code doesn't result in the c record of the OK being
updated to the server IP (it is still the private IP of the UAC). In the
loose route section, the re-invite doesn't pass (client_nat_test("3") ||
search("^Route:.*;nat=yes")) so we don't use mediaproxy. In the on-reply
route bflag(6) is not set. I don't understand why bflag(6) is not set since
the r-uri is to a registered user that has bflag(6) set (at least that's how
I understand it).

Could anyone point me in the right direction? 

Thanks

Cameron






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