Tuesday, 30 June 2015

Broadband Speed & other mysteries

Just as I thought we had been completely overlooked by BT, a team arrived and started digging holes in our street.

We have been stuck with 8Mbps download speed for years, but now we seem to have a number of double digit speed choices from Plusnet, our ISP.

But broadband speeds are not what they seem. What is a connection speed, an IP Profile or a Noise Margin?

Bye-bye, it's been good to do business with you!

So this little journey started 10 days ago when my internet service provider sent me an email. This basically said, "...sorry to hear you are leaving us....your service will be disconnected on June 25th...".

This was news to me. I initially chatted to a Plusnet guy on line who thought it was some kind of mix-up, but couldn't do anything about it. So I had to pick up the phone and give their help desk a call.

Having listened to all the hits of the 1970s and drunk my way through two mugs of tea, I finally got through to a human. A few minutes of double-checking resulted in "Dan" explaining that Plusnet were up-grading me to an improved service. This automatically triggered a useless email, normally reserved for customers who wanted to switch service providers!

Little green boxes

Anyway, this at least confirmed that the weeks of road digging and distruption, and the addition of green street boxes in our road was if fact worthwhile. A new age was dawning, and our broadband was about to get a boost.

I noticed right away that the modem connection speed had jumped up from around 7000kbps to over 17000kbps, but in use, the internet still seemed slow. It was time to investigate.

Speed Tests and other data

As Plusnet uses the infrastructure owned by BT, I generally use the BT Wholesale speed checker. Normally this reports download speeds of 6-7Mbps when I connect my laptop via ethernet to my router.

But on this occasion I only clocked a download speed of about 4.4Mbps. Moving on to the diagnostic check, I got a screen like this:-

So the maximum achievable speed is shown as 21Mbps, but I'm getting just over 4Mbps. I like the comment that "...the acceptable range of speeds is 4-21Mbps". Acceptable to who?

Here are some of the important parameters associated with my internet connection:-
  • Plusnet contract: 8Mbps
  • Max achievable speed:    21Mbps
  • Router Connection speed: 17599kbps
  • Broadband IP Profile:    15.87Mbps
  • Download speed:    4.2 - 4.45Mbps over several runs

Its clear that the maximum speed will be limited by my Plusnet contract speed. I'm guessing that the Max achievable speed is some physical limit that BT have deterimed, possibly based upon the connection from my house to the green box.

I'm curious about the IP Profile. The explaination is that this is a limit set to avoid data being sent too fast to my modem. However, the router (modem) negotiates the best speed with the exchange (the router Connection Speed), so why is the IP Profile lower than this?

And why am I getting only 4.4Mbps?

After moving my router from an extention socket to the main incoming BT socket, I see a much better result:-

After some further messing around with cables, line filters and wiring I managed to put the router back on the original extention socket and still maintain 7Mbps. So I'm not really sure what the original problem was.

It seems to me that the line filter just connects the line straight through to the modem, while providing low pass filtering for the phone. Therefore it is unlikely (but possible) to impact on network speed in the event of a fault developing in the filter.

The other parameters worth checking are Line Attenuation and Noise Margin, which you can normally check via your router:-

Apparently a Line Attenuation figure below 20dB is considered to be very good, so the lower the better. Its the opposite for Noise Margin (why don't they say "signal to noise ratio?"). For this, the larger the better.

Keeping my eye on the speed

As I have an 'always on' RaspberryPi web server thingy, I have decided to periodically monitor the download speed and plot the results on an html page. I discovered I could use the SoftLayer speed checker with this Linux command:-

wget -O /dev/null http://speedtest.wdc01.softlayer.com/downloads/test10.zip

This command results in a timed data transfer with a result in kBytes per second, with the full terminal output looking like this:-

--2015-06-30 05:56:33--  http://speedtest.wdc01.softlayer.com/downloads/test10.zip
Resolving speedtest.wdc01.softlayer.com (speedtest.wdc01.softlayer.com)...
Connecting to speedtest.wdc01.softlayer.com (speedtest.wdc01.softlayer.com)||:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 11536384 (11M) [application/zip]
Saving to: ‘/dev/null’

/dev/null           100%[=====================>]  11.00M   815KB/s   in 14s   

2015-06-30 05:56:52 (813 KB/s) - ‘/dev/null’ saved [11536384/11536384]

To convert kB (kiloBytes) to kb (kilobits) just multiply by 8. So 815kB/s = 6520kbps. However, this is presumably the file data transfer rate based upon an 11MB file, ignoring the protocol data. (I can never remember if you are supposed to multiply by something larger than 8 to get the full data rate!).

Either way, it doesn't really matter to me as I'm just looking for a comparative speed reading (e.g. has it dropped from normal for some reason?).

However I need to modify the command to something like this in order to create a log file that I can work with:-

wget -O /dev/null http://speedtest.wdc01.softlayer.com/downloads/test10.zip -o /home/steve/SpeedLog

...which creates a SpeedLog file with a final line like this:-

2015-06-30 17:36:00 (1.66 MB/s) - ‘/dev/null’ saved [11536384/11536384]

So its just a matter of writing a program to extract the sub-string containing "/s)" from this log file. I'll probably write this program in either Gambas or PHP.

Faster, faster

In my earlier discussion with Dan the Plusnet Man, he suggested I might see a small increase in download speed (maybe from 8 to 12Mbps) with my existing service.

Sure enough, by the 30th June the speed had increased, as reflected in the SoftLayer result above.

You can also use:-


...in a web browser and get a graphical result like this:-

I've now signed up for a faster download service, with the nose-bleed inducing speed of 17Mbps!

Rant alert!

We adopted SI Units over 40 years ago, but still people and organisations can't get it right.

Generally, capital letters are used where a parameter is named after someone (e.g. V for Volts {Mr Volta}, W for Watts {Mr Watt})

So K = Kelvin (Lord Kelvin, temperature), k = kilo (a thousand)
...S = Siemens (Spunky Winklemann, electrical conductance), s = seconds

However, some upper case letters are not named after people, but their use should still be clear:-
 M = Mega (very large)
 m = milli (very small)
 B = Byte (quite large)
 b = bit (quite small)

I hope this helps!

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