Sorry for the late reply, I have clients with 'down' Sure Signals and it is becoming a headache.
There are two reasons in my experience for Sure Signals giving problems. With the first generation SS units, the Power Supply would not give a full current charge and as such would either drop service all together or would simply end up in a permanent start-up mode.
The second is to do with bandwidth. This is amuch harder issue to address as you are dealing with smoke and mirrors once you leave your home. BT Infinity works two ways for the "last mile". Cabinet-based users pretty much get what they had with the original copper-based broadband, however, if you have fibre coming to the premises, things get very much harder to identify.
Assuming you are on copper between you and the cabinet, I will go on.
Over night several things happen that can cause the 'apparent' speed and the 'real' speed to be poles apart. I have first hand experience of this whereby in the daytime I will get over 30Mbps down and around 10Mbps up, but over night the download speed drops to around 4Mbps. Now BT's internal test program shows that there is no problem, but external testers such as Ookla's Speedtest show significantly different speeds - around 90% different to be exact.
SS devices need around 1Mbps minimum to operate. However, just because your speed is good, does not mean that this is what is being available in server land (as you know). The C21 network (BT's fibre network) is currently being rolled out nationally and this is going to place some very high bandwidth consumers on limited pipes between the exchange and the main backbone. Trace route data does not take this into account, but you only need to have a the equivalent of a bandwidth brown out which lasts a few seconds for the SS to lose its VPN pipe and have to retrain. This will be seen at Vodafone as a restart, not necessarily a reset. If the attempted retry cannot be completed for whatever reason, the SS goes into what I call a 'panic' mode and simply stops trying to restart the VPN pipe.
The C20 network (BT's copper system) is still hugley over-subscribed in some places and my initial thought when I read your original post is that the exchange is running 'hot' which would account for adegradtion in service. Getting that verified is almost impossible as no one in Openreach would make that assertion publicly.
My advice is to run speedtest over the weekend and see what you are getting at night. Try running the test from her: http://www.thinkbroadband.com/download.html and see what you get in terms of results. Let me know how you get on.
Wherever I lay my '@', that's my 'ome.
