Saturday, 11 January 2014

The need for speed

So, the latest BT advert had someone streaming music, and it keeps stalling. They are selling FTTC as a fix for that.

So, let's try and understand this shall we. A streaming audio can be of the order of 200kb/s. But the slowest broadband lines, even on old 20CN exchanges, are rarely as low as 250kb/s. Under 2% of A&A BT circuits have a sync under 300kb/s at present. Audio can stream at lower rates.

So, basically, any working ADSL line will be able to stream audio without pauses.

But that is not the only possible issue. The streaming can be stalling for several other reasons

  • The line is filled with other data at the same time (downloading email, web pages, torrenting, etc). This issue applies regardless of speed, and even an 80Mb/s FTTC can be full of traffic causing streaming audio to stall. In fact, you need some sort of QoS stuff (like the way A&A prioritise small packets) to fix that, something a normal BT FTTC would not provide. So that can't be the reason as FTTC would not be a valid fix.
  • The far end could have capacity issues, or some peering link in the Internet could be full. Again, this would not be fixed by FTTC, so not the issue.
  • The back-haul over the BT network could be congested. This is usually at the ISPs control. It is, again, not something that is fixed by changing to FTTC. If the ISP has full links that cause that level of congestion, a solution is to move to an ISP that does not. FTTC is not the fix.
  • The line could have some sort of fault with lots of loss or some such. The fix is not FTTC, it is fix the fault.
Basically, unless that example is an incredibly long line with 250kb/s DSL trying to run a higher bit rate down it, then FTTC will be no help. Sadly, such long lines are normally in remote villages which don't have FTTC. Even so, that would be an obscure example to pick for an advert.

I'm not saying FTTC is bad, no. It is good. What I am saying is that raw line speed is not always at all relevant to the issues you are trying to fix. This is a perfect example - it is really unlikely that the line speed is the cause of the broken audio.

All this advert does is propagate the myth that speed is all that matters. What is often more important than speed is lack of congestion in back-haul and over the Internet, low and consistent latency, and lack of packet loss on the line. Even OFCOM don't actually bother measuring these.

Even the government is hung up on speed, but with arguments about ensuring people have access to government services via the Internet, e.g. on-line VAT returns, etc. These are things that don't need speed, but they do need connectivity.

There are speed milestones, levels where completely new services become possible. At a few Mb/s it possible to have streamed video in real time. Below that you can have downloaded video. At higher rates you can have multiple streamed video in real time, and very high resolution video. There may, some time, be yet more speed milestones for some new services we have not invented. That said, entertainment is the main use of high bandwidth, and that comes down to how many bits/sec of useful information can a person consume (eyes, ears, touch, etc), and we are hitting that sort of limit with TV higher resolution than we can see, and sound higher fidelity than we can hear, so entertainment is not likely to push the limits a lot more than it does now. So higher speeds are useful, but far from the only factor.

Everyone is just concentrating on speed!


  1. Speed is at the heart of my issues. But the BT advert isn't aimed at me, since it's going to be a couole of years at least before I can get FTTC.

  2. No different to EE claiming you need 4G to stream video.

    I wonder if such adverts ever work.. Surely everyone just says 'well my connection already does this, so I don't need their product"

    1. They rely on the idea of selective memory. Your 3G connection will pause and buffer video 1 time in 20/50/100 due to situations completely unrelated to the technology (as in Rev's arguments).

      People remember these rather than the 19/49/99 times it works and think moving to 4G will solve the remembered issues

    2. The interesting one is if 4G deals better with congestion than 3G as with 3G/HSPA if the cell is congested you often get nothing at all.

  3. 4G deals with congestion like anything else. If there isn't the capacity to get the bits to the terminal, they will all be expelled through a little pipe that comes out of the base station.

  4. Not sure that OFCOM doesn't measure packet loss. They might not publish it.

    I'm on the samknows/OFCOM monitor panel/program (basically a small WRT router their own test code) and have access to my data. Packet loss is measured (both "normal" and RTP) as well as RTP jitter, DNS response time (ISP published DNS server), latency, speed, etc..

    1. Maybe they have more clue than they let on then, good. Loss and latency is massively important as a measurement, and indeed, relates directly to speed and reliability and usability.

  5. I think they were overcooking the "audio" aspect in the ad, possibly loosely based on the fact that a lot of people listen to songs via youtube which can include video content.
    When the reality is I can listen to an internet radio station over a 56K modem and anything above narrowband can usually handle streaming audio so well that it's often the streaming server/routing that causes buffering rather than local bottlenecks.
    Maybe I'm wrong, maybe i'm giving BT more credit than they deserve!

  6. Current HD TV is 1080p - ie 1K pixels vertically - online streaming (eg. iplayer) doesn't really do that, I think, if memory serves, it's 720 at most. 2K TVs are becoming more common and people are demonstrating 4K displays too. The level of detail you get in a 4K picture is pretty awesome - its like being able to zoom in on detail on the screen as you would when looking at a real scene and actually see the detail happening, rather than zooming having to happen with the camera.

    So, while I agree with your general point (I do completely loathe the current BT adverts), the need for more bandwidth will increase for many more years, as streaming catches up with the capabilities of the displays more and more of us are using to watch Film/TV (and, for example, multiple people in the same household wanting to stream different things at the same time)

    1. Note that 2K and 4K are horizontal sizes, whereas 1080p and 720p are vertical sizes. In pixels, a 720p display is 1280x720. A 1080p display is 1920x1080. A TV 2K display is also 1920x1080 (it's just a rebrand of 1080p); a cinematic 2K display is 2048x1080; a TV 4K display is 3840x2160, while a cinematic 4K display is 4096x2160.

      So, lots of people have 2K TVs - they're just the good old Full HD displays of yore under a new name.

    2. Dang - you're right! resolution fact fail :D Still, they are bigger, so I might still have a point ;)