Well, what do you know.... I take it all back.... I looked in my router logs and found this lot:-
Dec 22 14:27:21 home.gateway:sip_SipTransactionManager_?:none: SIP Registration successful for phone 68*****
Dec 22 16:22:19 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:23:22 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:23:54 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:24:56 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:25:28 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:26:30 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:27:02 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:28:04 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:28:37 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:29:39 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:30:11 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:31:13 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:31:45 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:32:47 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:33:19 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:34:21 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:34:53 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:35:55 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:36:28 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:37:30 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:38:02 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:39:04 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:39:36 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:40:38 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:41:10 home.gateway:sip_SipTransactionManager_?:none: SIP Registration Error 1 for phone 68*****
Dec 22 16:41:31 home.gateway:sip_SipTransactionManager_?:none: SIP Registration successful for phone 68*****
Dec 22 16:41:31 home.gateway:sip_SipTransactionManager_?:none: SIP Registration successful for phone 68*****
Dec 22 18:35:34 home.gateway:sip_SipTransactionManager_?:none: SIP Registration successful for phone 68*****
My registration interval is 7200secs (eg 2 hours) and there was 20 min period where the client was refusing to register. I'm not aware of having seen that before (I periodically scan my logs for anomalies), and my other sip client (on other port of the same router with a different VOIP provider) worked right through fine without any errors.
I was planning on reducing my registration time right down to 5 mins or so (once the platform had stabilised again - with offline notifications working properly again). Maybe now is the time to try that reduction... since the email clearly did warn me of a genuine outage!!! (Oh how little faith I had in the warnings, to instantly assume it was a glitch in the reporting!).
Still a bit mysterious as to why my sip client refused to register for those 20 mins, when I clearly still had net access. Maybe there was a problem with nat.plus.net ... who knows!
I'll still try a manual test of turning my sip clients off this evening, to check it again. Hopefully it'll give me another offline notification email. I'll then move myself over to natproxy.plus.net at the same time (whilst offline) and drop my re-registration interval to 300 secs (5mins).
It is starting to look like this has finally been fixed properly! I'll report back tomorrow.
Mike