[SR-Users] Using path with DMQ to send calls to origin SBC - not sure when to modify destination URI

[Rhys Hanrahan]

Hi Everyone,

I am trying to add DMQ for redundancy of registrations and USRLOC, and I’m trying to send calls to the correct SBC that is the original registrar for a handset. I’ve been using the thread here where Charles gave some guidance on how to use path to store and use the original SBC: https://lists.kamailio.org/pipermail/sr-users/2018-February/100246.html and  https://lists.kamailio.org/pipermail/sr-users/2013-September/079736.html

I am struggling with when to decide to modify the destination URI. My testing shows this is required otherwise some handsets will ignore the invite, but right now I am doing it in a blanket form, right before SIPOUT (which is where the origin SBC handles the invite instead of LOCATION). I am sure this is being too heavy-handed though and there are some cases where I won’t want to set this, but I am not sure which?

        # record routing for dialog forming requests (in case they are routed)
        # - remove preloaded route headers
        remove_hf("Route");
        if (is_method("INVITE|SUBSCRIBE")) {
                record_route();
        }
…
        xlog("Setting du according to path. Current du is $du\n");
        xlog("Current route header: $(hdr(Route))\n");
        xlog("Current route: $(hdr(Route){uri.host})\n");
>>>        $du = $(hdr(Route){param.value,received});
        #xlog("New du destination uri is: $du\n");

        # dispatch requests to foreign domains
        route(SIPOUT);

In the linked threads, Charles mentioned that only the last-hop registrar should make this change, but what’s the best way to determine if I am on the last-hop registrar?

As per the snippet above, I tried using the {uri.host} transformation to extract the origin SBC’s IP from the route header. My plan is to then compare this against “myself” but I am struggling to extract the right info from the route header. And I am not even sure if this is the right general approach?

The route header looks like this: <sip:ORIGIN_SBC_IP:5060;received=sip:UAC_WAN_IP:2048;lr>

Any guidance or examples would be appreciated.

Thanks!

Rhys Hanrahan | Chief Information Officer
e: rhys at nexusone.com.au<mailto:rhys at nexusone.com.au>

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