So we looked at the things that could happen at your end to make things slower and how you might look to resolve them. Now lets look at what your provider may be doing and what could happen on their network. We will be focusing on Cable and Telephone delivered services here (ADSL/VDSL). For those of you that work on these networks there is a level of simplification here. Yes I know there are other steps but they are of little if any concern to the end customer.
So we have two main categories here to look at. Deliberate decisions by the provider and ones they have no control over.
Deliberate decisions include over subscription, capping, bandwidth management, backhaul insufficiency and under investment. Now if you are going with a low end or monopoly provider all of these are likely to be bigger factors. So lets look at them….
Over subscription, the single biggest cause of slow downs and issues. Bandwidth is a finite resource and despite the technical differences both cable and phone delivered services use the same model with the only difference being where your connection gets merged with the rest. With VDSL and Cable this happens at your local cabinet and ADSL at your exchange. With the latter your connection goes to a local cabinet or mode. Once it’s here it is combined with everyone else’s and send on to providers facility. What you need to note here is that if you use VDSL you’ll be getting stuffed in with everyone else no matter who the provider is unless you are very lucky and use a provider with their own network. From the exchange out to the cabinets and on you you BT Openreach own ALL of this and you are on their network, even if you use Sky, Plustnet or Kcom for example. In some areas its even the case that Virgin traffic flows on these lines. So at this stage for 99% of the UK you are on the Virgin Network or the Openreach network. Each cabinet is normally supplied by a fibre and includes either the Virgin Headend or BT DSLAM. There is another small difference in that smaller Virgin cabinets feed into the “master” cabinets so one Virgin master cabinet may serve thousands of properties. These then connect to the Virgin fibre network and everyone’s traffic gets blasted down the same fibre. A BT DSLAM tends to service around 300 properties.
The backhaul, the fibre that goes to the next stop for your connection, has to carry everything and bandwidth on a fibre is again, finite. Multiple pairs can be used but there is a realistic upper limit on this. Right away you can see that 300 32Mbit connections isn’t going to be the same issue as say, 3000 100Mbit connections. ADSL, although slower, is actually installed at the same location as most BT connections end so it’s less of an issue here. The number of properties you share this fibre with is your contention ratio. This was a headline figure years ago when fibre was slow and many hundreds of ADSL connections were connected to low speed fibre. Nowadays it still plays a huge part but no one mentions it.
This all relies on one really big assumption, all of the customers arent going to be online using all of their bandwidth at once. Traditionally this works well but with the massive uptick in people staying at home or home working, it isn’t working so well and has been a source of constant issues and failure. This is where over subscription, selling connections based on a theoretical traffic model rather than actual traffic comes in. Virgin has way more scope to add users past what is sensible than Openreach as the DSLAM units are physically restricted in terms of connections.
One way providers try and manage this is use of traffic or bandwidth management. Although your connection speed doesn’t slow, the provider artificially slows the traffic on your connection to free up more bandwidth. This is a process many use and has drawn a lot of bad press. Thankfully it is falling out of favour. Lower cost providers or those with heavily congested networks often resort to this. As the data has to be paid for by the provider to BT many will use this as a cost reducing exercise. Incidentally traffic management is also VERY common on 3.5G and 4G mobile networks. As an end user this will show up as loss of performance despite your connection showing a normal speed. This will often happen at the same time every day and most end any management after midnight.
Under investment is the last part. All carriers are guilty of this one. Much of the network is old and in some cases bits of the Openreach network just cant support the speeds people want, this is particular bad on some industrial sites where older aluminium cables are installed. Large chunks of the Virgin network are as Nynex/Videotron/CW left them in the early 90s and this leads to some of the issues we will look at next.
There are any number of things that can cause issues on the network of providers. Some obvious, some less so. There are of course the really obvious ones, damage to infrastructure from road works, road traffic accidents, tress and lightning and to be fair, there is little anyone can actually do about these. It wasn’t long ago our local FTTC cabinet was flattened by a car.
The cable network is pretty resilient, it’s almost exclusively underground and bar someone taking a cabinet or cable out its rare to have issues related to weather. Most cables in the network are point to point, so your cable goes to the cabinet in one go meaning its a long, uninterrupted run. Phone lines however run all over the place, the infrastructure is often quite old and lines are frequently merged and connected underground or in exposed locations leading to frequent issues with water ingress and/or flooding. Failing cables overhead can cause issues in winds and in icing conditions and are frequently treated to lightning strikes. Flooded ducts and open junction boxes are common causes of issues and the sight of an Openreach engineer in a cabinet or up a pole strikes fear into many customers.
Some sections of the Openreach network do use microwave links. Mostly these are remote villages or locations it’s hard to get fibre to. These installations can be affected by the weather in particular heavy rain, snow and fog.