Sunday, April 30, 2006

How BROAD is my BAND???!!

Well there is a lot of apparent confusion on the definition of Broadband......what speed qualifies as Broadband?

I frequently get asked this question.

The most important thing to keep in mind is that today Broadband, at best, is a relative term. In technical terms (as applicable to communications theory), broadband is a signal which carries a wide range of frequencies. In this sense multiple signal streams (eg. data) are sent concurrently to effectively increase the rate of data transmission. We can contrast this to baseband where one signal will use the full bandwidth available in a medium. In simple terms, broadband: mutiple signals over one medium which effectively increases the speed, baseband: one signal over one medium.

So how fast is Broadband?

The International Telecommunications Union (ITU) [www.itu.org] Standardization Sector (ITU-T) recommendation I.113 defines broadband as a transmission capacity that is faster than primary rate ISDN (which is 1.5 to 2 Mbit/s depending on American or European implementation).

The Federal Communications Commission (FCC) defines broadband as 200 kbit/s (0.2 Mbit/s) in one direction, and advanced broadband as at least 200 kbit/s in both directions.

The Organisation for Economic Co-operation and Development (OECD) defines broadband as 256 kbit/s in at least one direction.

The OECD definition is probably the most common baseline "broadband speed" around much of the world, but the puritans will likely disagree. Technically speaking an analogue modem operating at > 600 bits/s (that's 0.6kbits/s) is broadband. Higher data rates are obtained by using multiple channels on the same medium, so 2 channels @ 600 baud give 1200 bits/s and 4 channels would give 2400 bits/s and so on. Why is this (in today's terms) low data speed broadband? Because it combines multiple signal streams over the same medium - refer to the definition of a broadband signal above.

Confused? So are the rest of us.........

Unfortunately, there is no specific all inclusive gloablly accepted definition of broadband as evident by the varying definitions above from different organisations around the world. Because of this, in the internet world, ISPs capitalise on this fact and typically market anything above dial-up modem services as "broadband". Generally speaking most regulators/policy makers tend to go by the OECD definition and thus internet broadband is regarded as anything better than 256kbits/s (minimum in one direction ie. usually download speed; upload speeds are generally slower).

A point to note is that most ISPs will typically oversell the backbone bandwidth they have available. This is based on the fact that most users do not use their full link capacity all the time, and it generally works, with users being able to burst up to their link speed most of the time. There is likely to be performance degradation at peak times though if the available ISP backbone capacity is heavily oversold. Also remember that most broadband connections are asymmetric in nature eg. if you subscribe to a 256k package, this will be the maximum download speed, and the upload speed is likely to be 64k or another multiple of 64k.

1 comment:

Franck Martin said...

"Broadband is the bandwidth you can't have"