Hi All,

I managed to solve my need to re-write NOTIFY packets with help from this thread: https://www.mail-archive.com/sr-users@lists.kamailio.org/msg08088.html

This seems to work well. I am re-writing the packets as shown below… I guess my only question is, is this relatively safe/smart to do? I basically copied what our standalone Asterisk PBXes are doing in my captures, so I guess so? But I’m not confident enough to say it won’t cause some weird edge case issues. I can only say it works fine with the Snom and Yealink handsets I am testing with. I’m just concerned because it feels a bit like a hack.

For SUBSCRIBE I re-write:

• Request URI and To header from 101@ sent by the handset to tenant101@ (to match the SIP username of the handset - tenant101@)

For NOTIFY I re-write:

• From and Contact header to remove the tenant prefix, to go back to 101@ to match the BLF key configuration on the handsets.

Any advice would be appreciated on if this is a bad idea, and there’s a better way.

Thanks!

Rhys Hanrahan
Chief Information Officer
Nexus One Pty Ltd

E: support@nexusone.com.au
P: +61 2 9191 0606
W: http://www.nexusone.com.au/
M: PO Box 127, Royal Exchange NSW 1225
A: Level 12 227 Elizabeth St, Sydney NSW 2000

From: sr-users <sr-users-bounces@lists.kamailio.org> on behalf of Rhys Hanrahan <rhys@nexusone.com.au>
Reply-To: "Kamailio (SER) - Users Mailing List" <sr-users@lists.kamailio.org>
Date: Tuesday, 26 March 2019 at 8:56 pm
To: "sr-users@lists.kamailio.org" <sr-users@lists.kamailio.org>
Subject: [SR-Users] Adding presentity_uri prefix for multi-tenanted presence/dialoginfo configuration

Hi Everyone,

I’ve recently just started working with Kamailio – thanks everyone for this amazing software.

Like many people, I’m in the process of trying to put Kamailio in-front of Asterisk to allow it to scale out, and my plan is for Kamailio to take over registrations, usrloc and presence/dialoginfo, as we’ve had issues where handsets are failing to get BLF updates/notifys, so I am hoping a couple of Kamailio boxes can scale better in this regard. DMQ is particularly exciting in how it will allow me to build a truly distributed platform. But I’m struggling to get presence to work the way I need it to.

Our environment is multi-tenanted, but we do not (and can’t really) use multi-domains. Instead, we prefix the SIP usernames with the “tenant name” such as tenanta101 and tenantb101. My problem is that all the BLFs are configured for 101@PBX with no tenant name in the User part of the URI so that internal dialing and call pickup will work. Because in Asterisk we use “subscribecontext” this hasn’t been a problem in the past – Asterisk knows for subscriptions coming from that handset that it belongs to that tenant’s context in the dialplan and they are “isolated”, so having handsets subscribe as 101@ in their request URI was never a problem. Of course, with Kamailio I don’t have subscribecontext, and my main issue is that the “presentity_uri” being stored is 101@ while each of the SIP accounts of the handsets are registered as tenenata101@, and as such, no NOTIFYs are sent by Kamailio because it thinks that there are no watchers for the presentity_uri.

If I change the SIP account username to 101 to match the BLF key, NOTIFYs are sent as expected. But then this breaks call pickup and internal dialing using the BLF keys. I would rather handle this in Kamailio than in Asterisk and having to re-configure the BLF keys for hundreds of handsets.

I need to do something like:

• When a SUBSCRIBE comes in, I need to prefix presentity_uri with the tenant name so the subscription changes from 101@ to tenanta101@ in the active_watchers table.
• When Kamailio generates a NOTIFY, the notify would be built based on presentity_uri and would come out as tenanta101@, but the phone’s BLFs are configured for 101@ so I would need to *remove* the tenant prefix before sending out the notify.

Is there a good, or recommended way to handle this scenario? Maybe something entirely different to changing the presentity_uri?

I’ve written the following config to re-write the request URI and To field in any incoming subscribe requests, and successfully got the active_watchers table to store a presentity_uri containing my tenant prefix. But the problem I am having is that I can’t figure out how to modify the NOTIFY packets before they are sent – and looking at cfgtrace, it seems I might not be able to?

My “standard” presence + dialoginfo configuration was taken from here as a starting point: https://kb.asipto.com/kamailio:presence:k43-blf

Here is what I have so far in terms of trying to make my modifications – any guidance would be greatly appreciated. It feels like there’s probably a better way to do this than re-writing critical headers like To and Request URI?

@@ -466,6 +467,8 @@ request_route {

        # authentication

        route(AUTH);

+       route(REWRITE_PRESENCE);

+

        # record routing for dialog forming requests (in case they are routed)

        # - remove preloaded route headers

        remove_hf("Route");

# Presence server processing

route[PRESENCE] {

        if(!is_method("PUBLISH|SUBSCRIBE")) return;

        if(is_method("SUBSCRIBE") && $hdr(Event)=="message-summary") {

                # Asterisk is our voicemail

                route(TOASTERISK);

                # returns here if no voicemail server is configured

                sl_send_reply("404", "No voicemail service");

                exit;

        }

#!ifdef WITH_PRESENCE

        if (!t_newtran()) {

                sl_reply_error();

                exit;

        }

        if(is_method("PUBLISH")) {

                handle_publish();

                t_release();

        } else if(is_method("SUBSCRIBE")) {

                # See REWRITE_PRESENCE - this should have been executed before we get here.

                handle_subscribe();

                t_release();

        }

        exit;

#!endif

+route[REWRITE_PRESENCE] {

+       if (is_method("SUBSCRIBE")) {

+               xlog("Re-writing subscribe to include tenant prefix\n");

+                # The default presentity_uri needs to be prefixed with

+                # the tenant name

+               # So re-write the To header 

+                route(TENANTINFO);

+                # Now grab the tenant name.

+                $var(subscribe_ru) = "sip:" + $var(tenant_name) + $rU + "@" + $rd;

+               xlog("Re-writing SUBSCRIBE To header as: $var(subscribe_ru)\n");

+                insert_hf("To: $var(subscribe_ru)\r\n", "From");

+               $ru = $var(subscribe_ru);

+               # Force change immediately: 

+               # http://www.kamailio.org/wiki/tutorials/faq/main#why_changes_made_to_headers_or

+                msg_apply_changes();

+       } else if (is_method("NOTIFY")) {

+               xlog("Re-writing NOTIFY to remove tenant prefix\n"); # This code block does not get executed right now.

+               # We are storing the presentity_uri with a tenant prefix

+               # handsets do not expect this, only 101@, 102@ etc... In their BLF configs

+               # So this tenant prefix must be removed when building the reply.

+                route(TENANTINFO);

+               $var(notify_ru) = "sip:" + $(rU{s.substr,$(var(tenant_name){s.len}),0}) + "@" + $rd;

+               xlog("Re-writng NOTIFY to use: $var(notify_ru)\n");

+                insert_hf("To: $var(notify_ru)\r\n", "From");

+                $ru = $var(notify_ru);

+               # Force change immediately: 

+                # http://www.kamailio.org/wiki/tutorials/faq/main#why_changes_made_to_headers_or

+                msg_apply_changes();

+       }

+}

Thanks for your time.

Rhys Hanrahan
Chief Information Officer
Nexus One Pty Ltd

E: support@nexusone.com.au
P: +61 2 9191 0606
W: http://www.nexusone.com.au/
M: PO Box 127, Royal Exchange NSW 1225
A: Level 12 227 Elizabeth St, Sydney NSW 2000