@george1976
Indeed 100ms isn't a 'normal' ping level but it's a good place to start in terms of identifying the BT infrastructure issue which gave pings way above 100ms. I can't speak for everyone's VDSL quality, whether Wifi is being used and other factors that may affect the end ping level, hence the 100ms would be an upper limit of a potential normal ping while a connection is being saturated or saturated in bursts from streaming. I think BT also used this value in terms of identifying the ping issue.
I know the max ping I see is 60ms with a fully saturated connection but I know I have a good quality VDSL connection, no interleave with minimal errors or retries and a top notch ISP.
Plus of course it depends where you're pinging from and to, someone up north with interleave enabled pinging the bbc.co.uk down London is likely to have 20 to 30 ms base ping before they even get ping spikes, add 50ms to 30ms and you're at 80ms for what might be an acceptable / normal ping, ping anywhere in the US and your ping will be 90+ms, so there's lots of variables. Speak to any ISP , I've spoke to many, not a single one will quote you on what your ping will likely end up being, it's next to impossible to predict with any accuracy. As you say yourself your base ping has doubled with no apparent explanation.
There's no real way to limit a network request in terms of speed, you can only limit it by requesting data less often or by delaying the ACKs if TCP or dropping packets, this boils down to packets per second, if a bunch of Netlfix packets coincide with your gaming packets you'll get a ping spike. So if you in effect spread out streaming packets over a longer period of time, which equates to less average through put you've got less chance of the packets coinciding.
Again there's lots of variables in terms of streaming application, twitch, youtube, disney, iplayer etc, browsers might be different, Windows or Mac or chrome cast or smart TV or smart phone, all will request data more aggressively or not, producing different ping spikes. The upfront buffering will almost always be more aggressive than the steady state buffering, so starting a stream is likely to cause more ping spikes.
Normal QoS where you tag packets for low latency isn't going to help much, you might be able to tag UDP packets for faster processing by your router, the only way I've found is to use queues and limiting bandwidth to give more space for gaming packets to get through. Mikrotik routers with their routerOS has this feature and Ubiquiti Edge routers as well, I've used both. I get no ping spikes at all with other users on my network and them doing all sorts of streaming, you tube, downloading, whatever they like, simply because my connection is never saturated.
I'd say a base ping jumping from 6ms to 14ms sounds very much like an interleave delay, you should be able to see this in your modem / DSL stats.
From my experience modems and routers aren't overly different in terms of adding extra latency, I've tested many modems, all in one setups, separate router modem setups, all fall within a few ms of variation. As said the difference is brought about by what configuration they offer and general overall quality / stability / consistent latency i.e. I've yet to find a modem that shaves any more than 2ms off my ping compared to other models.
