Technology Primer

This page will help you distinguish your bits from your bytes.

For more technology definitions, see our Jargon Buster.

What is broadband?

When broadband first appeared in the UK in the late 1990s, it was characterised by two things:  it was always on, allowing customers to surf the internet and make phone calls at the same time, and the speed of data transfer was faster than that of dial-up modems.  Today the term broadband has become synonymous with always-on access to the internet, regardless of the technology used.

One caveat: although the term broadband is becoming increasingly diluted, it usually refers to the affordable internet access offered to consumers and small businesses; not to bespoke, high-capacity internet connections for the enterprise market.

What is superfast broadband?

Superfast broadband originated as a marketing term without a strict definition, but Ofcom is now using it to describe broadband speeds greater than 24 Mbps.  The significance of 24 Mbps is that this is currently the maximum possible speed for broadband over existing copper telephone lines.  However, it's worth noting that BT is marketing all of its fibre-based broadband products as "superfast", with a lower speed limit of just 5Mbps.

What is next-generation access?

The majority of homes and small businesses in the UK currently receive broadband services through the access network that connects them to their local telephone exchange via a twisted-pair copper cable.  The term next-generation access (NGA) describes a significant upgrade to the access network.

In NGA networks, some or all of the copper in the network has been replaced with fibre.  Since fibre is capable of sustaining much higher data transmission speeds over longer distances than copper cable, NGA is the key enabler for faster broadband.

It is generally accepted that NGA includes fibre-rich infrastructure and technologies such as fibre-to-the-cabinet (FTTC), fibre-to-the-home or premises (FTTH/FTTP) and upgraded cable TV networks.

There has been some confusion about the difference between broadband and NGA.  Broadband is a service that allows a connection to the internet; NGA is the physical cables and equipment to deliver the service.

Bandwidth, bits and bytes

The performance of a broadband connection is most often described by its speed, or bandwidth.  This is the amount of digital data that can be transmitted in a given time, measured in bits per second.  A bit is the smallest unit of information, either 0 or 1, in the digital language of computers.

Dial-up modems connected at 56 kilobits per second (kbps).  Today the average download speed of broadband connections in the UK is nearly 100 times faster at 5.2 million bits per second (megabits per second or Mbps), according to a study carried out in May 2010 by Ofcom with technical partner Samknows.

The total quantity of data, like hard disk capacity, is measured in bytes rather than bits, where a byte equals eight bits.  A typical email is just a few thousand bytes (kilobytes or kB), while standard quality BBC iPlayer requires a continuous 800kbps of throughput, so watching a 30 minute programme would consume 180 million bytes (megabytes or MB) of data.

A number of internet service providers (ISPs) in the UK have introduced bandwidth allowances, which place an upper limit on the total amount of data consumed during the month, typically 10 billion bytes (gigabytes or GB) for any entry-level broadband account.  Consumers exceeding their allowance may incur penalties, such as a surcharge on their bill or “throttling”, where the speed of the connection is reduced for a period.

A 10GB data allowance will allow hundreds of hours of basic web browsing, but it is not particularly generous for streaming video.  Future applications are likely to make heavier use of video.  For example, streaming a little over eight minutes of HD-TV at 16Mbps would consume a massive 1 GB.

Broadband speeds explained

Advertised speed is the speed that ISPs use to describe the packages they offer to consumers.  They are usually expressed as “up to” speeds because they are only a guide to the speed the ISP can provide. Few subscribers (if any) can get the “up to” speed of service advertised by internet providers, something that is the source of consumer dissatisfaction and much debate in the industry.

Line speed is usually the maximum speed a customer’s telephone line can support, which depends on factors such as distance to the telephone exchange and line quality.  The line speed will always be slightly higher than the speed the customer actually experiences because 10-15% of transmitted bits are protocol overheads to manage the connection.

Throughput speed is the actual speed a consumer experiences at any particular moment when they are connected to the internet. This figure is dependent on many factors, including the ISP’s traffic management policy, the number of subscribers sharing the connection (contention), congestion across the core of the internet, and the speed of the target website’s connection to the internet.  Poor in-home wiring and old computer equipment can also reduce the throughput speed.

An ISP doesn't have control over all of the factors affecting your broadband speed.  The ISP can tell you exactly what your line speed should be, and also controls the "contention ratio" in the backhaul, which determines the amount of capacity allocated per user in the connection between the telephone exchange (or equivalent) and the internet.


This article was originally published in the "Beyond Broadband" booklet.