We are all used to having unbelievably powerful computers – none of us would go back to systems that we had 10 years ago. And, just as you can never have a too fast processor, or too much RAM, or too bib a disk, you can never have too much bandwidth.
Before we go into details, let’s go back to basics. The PSTN (Public Switched Telephone Network) for many years was analogue, the conversion to digital technology was completed in the late 80’s. Or at least mostly digital. The “last mile” to the home (the “local loop”) was always left analogue due to the cost up upgrading everyone’s home phone.
Come the PC. Computers are of course digital. They work in binary – one’s and zero’s. On or off. To network these digital devices over an analog network means that the digital signals need to be converted to analogue at one end, then reconverted back to digital at the other end. Devices called modems were created for this job. Modem is a made up word, standing for MOdulation and DEModulation – these simply take the digital signals coming out of the PC, converted then to analog for the local loop section, created a connection through the network to the receiving end where the process is reversed.
A number of characteristics that we all became familiar with:
1) The “dial up” process and associated horrible noise (this noise being the audio “analogue” equivalent of the digital data being transmitted)
2) Slow speeds of connection
3) No one could call you unless you had a second line
Speed of connection. Bandwidth is measured in bits per second – that’s the number of one’s and zero’s transmitted in a second. The size of a file, or volume of data, is measure in bytes. A byte is generally made of 8 bits – a combination of 8 one’s and zero’s representing something, such as a digital image. Only you’d never get enough information into 8 bits for a whole image – a single photo image might be 500Kbytes – 500,000 bytes (that’s 500,000 x 8 bits = 4 million bits!)
When I were a lad, modems were working at 300bps and we got very excited about new modems that worked at 1200bps!! Modems reached a peak of 56kbs using a technical standard called V92. But this wasn’t the whole truth as this speed referred to the download speed only – the upload speed was slower at 48kbs. Those naughty marketing folk…
This may sound really technical, but it’s really just basic maths. Here’s how it works.
Remember we said that 8 bits make a byte? And that modems convert digital signal to analogue and analogue back to digital? This conversion is done in real time – the analogue signal is “sampled” (or photographed if you like) 8,000 times a second. Each sample, or photograph, generates 8 bits or one 8-bit-byte.
So a second generates 8(bits) x 8,000 (samples) = 64,000 bits per second or 64Kbps. This is the fundamental building block of telecommunications – telecommunications DNA as it were.
A digital telephone line used for one telephone call will work at 64Kbs. But the modem maxed out at 56Kbs upstream – what happened to the missing 8Kbps? These were used by the network for control signalling.
Phew! Hope you’re still with me – it’s important to get these basic building blocks understood so that you can understand what’s going on in the world of broadband and why not all broadband is the same.
Broadband as offered by most service providers in the UK is based on a family of digital network technologies called DSL or Digital Subscriber Line. The most common DSL family member that’s used is ADSL. The A stands for Asymmetric. DSL was designed in the days when bandwidth was scarce and expensive and the general view was that people would download more than they would upload, so it made sense to have a technology that optimised the strained network resource in that way. For many folk at the time, the concept of “youtube” was unimaginable.
DSL is digital. There’s no modem required. This means that once connected to the network, there’s no need to “dialup” or reconnect. The service becomes “always on”. This transforms the way in which the internet is used – it becomes much more casual and informal – and just as convenient to use as a television.
So the Asymmetric nature of ADSL means that download speeds are faster than upload speeds. ADSL was designed as an 8Mbps service – that’s 8 million bits per second. So if you have an 8Mb (eight million bytes) file how long will it take to transmit? If you said a second, you got it wrong! Remember size is Bytes, speed is bits. Assuming 8 bits per byte there are 8 x 8 million bits in an 8Megabyte file (64 million bits) so it’ll take 8 seconds at 8Mbps to transfer the file.
This 8Mbps refers only to the download speed – the upload speed as defined in the relevant standards, is 1Mbps. You’ll notice of course that service providers emphasis the larger of the two numbers – it’s those naughty marketing folk at it again!
However you may not have an 8Mbps service, despite it being designed and defined as an 8Mbps technology. When “broadband” was introduced to the UK the service providers throttled back the bandwidth so that their infrastructure was less stressed and upgrading it would be less stressful to their own cash flow. You could also argue this strategy maximised their profits whilst keeping their costs to a minimum, though that might be uncharitable.
This throttling back of bandwidth resulted in a tiered structure for bandwidth services. We’ve gradually been upgrading up to the full 8Mpbs service over the last few years. But even if you do take an 8Mbps contract, you may still not get this amount. Why?
Well first of all physical infrastructure just may not be able to deliver it. Speed is affected by distance, quality of copper, joints etc etc.
Also, the concept of contention has been implemented. Contention, or sharing, is known in other industries as “over booking”. Airlines and hotels use this principle. They know that statistically a percentage of passengers or guests won’t turn up, so to ensure all seats and rooms are full, they’ll sell more than the plane or hotel actually has. Telecoms companies know that not all people will want to transmit files or download files at the same time so they can afford to overbook bandwidth at the local exchange.
Typically residential are shared among 50 people – the contention ratio here is 50:1. Small business packages are contented less at 20:1. The results of this are:
• Your 8Mps is shared with 49 other people
• As more people use the service, performance (actual throughput) will decrease
It is possible to take an uncontended ADSL service, but they are few and far between and it’s a premium service and you’ll have to be prepared to pay a premium price.
Another source of bandwidth restriction lies further back in the service providers’ network – if the pipe connecting the exchange to the internet isn’t big enough to handle the total aggregated bandwidth of all subscribers, then this will also impact service delivery.
Another tactic service providers are using to reduce the impact of all of this on their infrastructure is to impose another form of limit on users – that of volume. Remember, volume of data is measured in bytes, speed in bits per second. You may take out an 8Mbps service but that may have a data volume limit of 2Gigabytes. This means that once you’ve downloaded a total volume of data of 2Gigabytes, you’ll bump into this limit.
Quite what happens next is service dependant. It could be that your bandwidth speed drops to a lower level, unless you upgrade, or theoretically it could be completely stopped, unless you upgrade. Or bandwidth speed could carry on, but you pay a premium for the remainder of the period. This form of limit is often found in cheap broadband offers – you never get something for nothing and a headline speed-for-price is only part of the story. Don’t base your purchasing decision on this factor alone.
You may have seen very high speed broadband services – 24Mbps. This uses another DSL technology called ADSL2+. This is designed to give 24Mbps downstream and 3Mbps upstream but does mean that the service provider offering it not only has to install the necessary special ADSL2+ equipment, they’ll also have to significantly upgrade their own backhaul network to accommodate the extra bandwidth usage. After all, if the backhaul network is sufficient to handle 50 x 8Mbps users, it stands to reason that 50 x 24Mbps users will need much more bandwidth in the backhaul.
However, laws of physics will intervene here – the higher speeds means that the service travels over a shorter distance. As there are no known plans to significantly increase the exchange density, this higher bandwidth service will be available to fewer people.
OK so you’ve now got all broadbanded up – what next? There’s more to it than just the service over the wire – you’ll need to have some sort of customer premises equipment (CPE) installed in your home. First of all you’ll need a “splitter”. This is a small white box that plugs into your broadband-enabled telephone socket. Its job is to separate voice from data onto different frequencies – this means that you can make and receive telephone calls whist surfing away, which is very handy indeed.
You’ll also need to connect your computer to the broadband connection. Your best bet by far is to use a combined WIFI/Ethernet/ADSL Router (don’t use a USB one, these are rubbish, in my opinion). We’ve dealt with the ADSL bit. A router is a piece of networking technology that uses something called IP – internet protocol – to move your data across a network, the internet itself is made of a gazzilion of these things. Ethernet is yet another networking technology, typically used in an office for a Local Area network (LAN). LANs use “Cat5″ cabling and if you don’t want to run miles of this stuff around your house then you need WIFI (WIreless FIdelity).
WIFI is marketed as Centrino on Windows machines and as Airport on Apple Macs. It’s all the same stuff, which is handy as both Macs and PCs can share a WIFI network. Of course there are different versions WIFI, just to keep you on your toes. There’s 802.11b that runs at 11Mbs. Then there’s 802.11a or g – this runs at 54Mbps and is the most usual on new systems today. And just coming in is 802.11n – which offers an enticing 270Mbps. These speeds by the way are theoretical max, not the actual throughput, figures for this are 6Mbps-ish, 35Mbps-ish and 74Mbps-ish respectively. Those pesky marketers…
But why would you want a LAN, whether wired or wireless? It means that multiple computers, and other devices, can share resources. When I first got broadband and wifi, I posted an article June 2004 on Ecademy asking “Where are all the network applications?” Here’s what goes on in my house to day:
1) The laptop I am using is WIFI’d to the internet now. I can surf the web and email, make and receive regular telephone calls
2) As it’s on the same network as my printer I can print without getting up from my armchair
3) Ben, No 2 son, can do the same from his iMac upstairs
4) We can Skype for free phone calls
5) We can video conference using iChat
6) We can chat to any instant messenger user (MSN, Yahoo, iChat etc) by using Adium
7) Both he and I can share files from computer to computer (very handy in a multi-computer office set up)
8) Visitors – Mac or PC users can share my network
9) Until it was nicked, my spare laptop had all my CDs in iTunes and was connected to my HIFI using an Airport Express box – any track could be played on any computer or hifi system at anytime. Thieving scum.
10) Podcasts are downloaded into iTunes and from their I can play them on my TV using an AppleTV box
It’s easy enough to protect data on a wifi network – just add a password. The range of which will depend on factors such a speed of connection, location of CPE, number of aerials.
• ADSL is finally starting to deliver 8Mbps, even though it’s shared
• ADSL2+ delivers higher speeds, but to fewer people
• Virtually all services are shared – check out what the contention ratios are
• If you take a bargain basement service don’t be caught out by any data volume limits (I wouldn’t use such a service)
• Broadband allows you to make and receive telephone calls whiles surfing
• WIFI is a good thing and brings the internet to life with a home network.
All of this sounds fantastic, and I suppose it is, but until all the restrictions and limits on ADSL are lifted, we’ll always be hobbled in our usage of the internet – in fact, until the copper is replaced with fibre we’ll face fundamental limitations on how this new medium can be used.
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