Broadband Glossary

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Glossary of Broadband Terms


Third generation mobile data technology with connection speeds similar to early ADSL fixed-line broadband. Launched in 2003.


Fourth generation LTE / LTE-A mobile network technology launched in 2012, now with widespread coverage and far higher data speeds than its predecessor along with lower latency. Supports voice calls with VoLTE resulting in enhanced call quality.


Next-generation mobile data technology. At present little more than a ratified standard for the next generation and unlikely to be in any kind of use or integrated into new devices until around 2020.


Asymmetric Digital Subscriber Line. Technology that allows a standard telephone line to carry digital broadband signals. Downstream is faster than upstream, hence the ‘asymmetric’ element of the name


First generation ADSL with a maximum downstream speed of 8 Mbps.


Second generation ADSL Technology with a maximum downstream speed of 12Mbps.


An enhancement to ADSL2, which by doubling the frequency range increases maximum downstream speed to 24Mbps.


The maximum data throughput of a network connection.


A high-speed, always-on data internet connection.

Broadband speed

The maximum data transfer speed of a broadband connection expressed in Mbps (Megabits per second) or Kbps (kilobits per second).


A generic term often used in relation to broadband to describe fibre-optic networks – even more generically; a length of conductor carrying any electrical connection between two points, regardless of specific purpose.


Limiting a broadband connection – either in terms of line speed or data allowance.


Multiple users sharing the same available bandwidth.

Contention Ratio

The ratio of users sharing the same bandwidth – for example, a common contention ratio used with ADSL domestic broadband is 50:1 where 50 users would be vying for a share of the total available bandwidth.


Receive data from a source – typically used to describe the process of saving files from the internet, although it can be applied to any downstream data transfer.

Download Speed

The speed at which data flows towards the client from the source. Often used as a maximum possible rate for a given connection.

DNS (Domain Name System)

Essentially a constantly updated phone book that allows devices to convert human-readable URLs (domain names, web addresses) to machine-readable IP addresses and then use that data to locate the target on the internet and display that content to the user. When a DNS failure occurs, a device would find it impossible to locate a given resource such as a web site on the internet.


Digital Subscriber Line. An umbrella term for any ADSL, SDSL, VDSL etc broadband connection.


The direction of flow of data towards the user.


A building where all of the copper phone lines are aggregated and where calls and data are routed to the provider’s backbone.

Fair Use Policy

A common type of ‘small print’ employed by service providers to protect themselves from users who abuse their systems or consume excessive amounts of data. These are typically used alongside ‘unlimited broadband’ packages to allow the provider to take action against anyone who they deem to be unfairly using their network. This may result in capping, traffic management or service termination.

FTTC (Fibre to the Cabinet)

A fibre network which runs all the way from the provider to a central location near the end user. This is typically in the form of an on-street communications cabinet. The connection from the cabinet to the end user it then either a plain old copper telephone line or a more modern coaxial copper cable. The vast majority of the fibre broadband available in the UK is FTTC.

FTTH (Fibre to the Home)

A fibre network which runs all the way from the provider to the end user. Capable of extreme speeds and reliability levels.

Gigabit (Gb)

1,000,000,000 bits.

Gigabyte (GB)

1,000,000,000 bytes.

Headline Speed

The ‘up to’ speed used in marketing for a given connection. This often differs from the actual speed – sometimes significantly.

IP Address

A machine readable address format used by devices to locate resources on a network. Both IPv4 and IPv6 addresses are in common use.

IPTV (Internet Protocol Television)

The transmission or streaming of television programmes over Internet Protocol.

ISDN (Integrated Services Digital Network)

A standard for the transfer of voice and data over the telephone network typically used by larger organisations on the voice side.  On the data side, it was used to provide ‘high speed’ internet access before ADSL was available – by combining (or ‘bonding’) 2 64k ISDN channels, it was possible to achieve a whopping 128Kbps!

ISP (Internet Service Provider)

A company proving internet connectivity.


Latency or ‘lag’ variation. Can be used as a measure of stability for a given connection.


A conventional telephone line connected by a fixed cable.


The time taken for one packet of data to travel from the user to a given server and back again. This is expressed in milliseconds and is sometimes referred to as ‘lag’ and the value often referred to as ‘ping’ or ‘ping time’.

Leased Line

A permanent, dedicated communications connection between two points.

MAC (Media Access Control) Address

A unique identifier assigned to a network device. Usually assigned at production and often unchangeable.

Maximum Speed

The highest possible speed deliverable over a given connection.

Mbps (Megabits Per Second)

Used to indicate the amount of data transferred per second, or the ‘bit-rate’. 1Mbps = 1000 Kbps.


Commonly 1 million bits, although technically actually 1,048,576 bits.


Commonly 1 million bytes, although technically actually 1,048,576 bytes.

Modem (actually MODEM, from MOdulate, DEModulate)

A device that carries out modulation and demodulation – essentially an analogue to digital / digital to analogue converter that allows digital devices to converse over analogue telephone lines.

Modem Sync Speed

The speed at which the line speed is negotiated between the ISP and the MODEM depending on line conditions.

SDSL (Symmetrical Digital Subscriber Line)

Similar to ADSL, however both downstream and upstream speeds are the same. The connection operates with the same maximum upload and download speeds.


Any program or device that responds to requests to provide data to a client. This can be on a local network or more commonly over the internet. Servers are typically assigned a specific task, such as web server, mail server etc – in practice one machine often fulfils multiple server roles.


Making use of data while it is still in transit – as opposed to downloading and then using a completed file. Data is transferred to the client application and as long as the downstream speed is sufficient, it can be used without having to wait for a download to complete. 

Sync Speed

See Modem Sync Speed.


To transfer data to a remote device. In the case of consumer broadband, to transfer data from the user’s device to another device, typically a server on the internet.

Upload Speed

The speed at which data flows from the client to the remote target device. Often used as a maximum possible transfer rate for a given connection.


Away from the user – the reverse of Downstream.

URL (Uniform Resource Locator)

A human-readable and easily-remembered web address – for example

VOD (Video On Demand)

Selecting and accessing video at a desired time as opposed to accessing broadcast television in line with a published schedule. Netflix, Amazon Prime and Now TV are examples of VOD.

VoIP (Voice over Internet Protocol)

Any service allowing voice calls to be made over the internet instead of traditional telephone infrastructure. A voice-only Skype call would be an example of a VoIP call.

Wi-Fi (Wireless Fidelity)

A form of network connectivity eliminating cables and instead using Ethernet protocols over radio signals.