SIP phone problems

[Rev+Mark]

Hi - hoping desperately that someone can help me with this. I work from work with ultra fasat fttp... I have for several years now connected a number of SIP phones to my router and had no difficulty whatsoever.

(My voip service provider is IRISH VOIP)

A couple of weeks ago two of the handsets that I was using suddenly ceased to be registered

They were a YEALINK T48G and a FANVIL X6

I have used both phones successfu;;y for about two years, both are simply programmed and extremely reliable.

I also have 2 x GIGASET GIGASET DX800A which I have also used for a couple of years without any kind of problems. They have both been configured to work on TWO lines. I have changed no settings whatsoever. However suddenly this week both phones have displayed a message NOT REGISTERED Broadband in all respects seems to be working perfectly. I have done factory resets on ALL my phones but still cannot connect. Please can anyone give me an explanation of what might be going on?

[mae-3]

@Rev+Mark 

SIP port 5060/5061 must be responsive from the SIP provider, and DNS and NTP must be working with your internet provider if these fail or are blocked by Sky then the phone won't work.

[TimmyBGood]

@Rev+Mark 

On the Q and Sky Broadband Hubs I believe there's a setting to toggle SIP-ALG clamping which may be worth a try.