ADSL

Asymmetric digital subscriber line. In plain english, a way to access the internet using a conventional phone line - See PSTN below.

Asymmetric means that upload speeds and downloads speeds are not the same. Download, for example watching movies on iPlayer, is normally much faster than upload, such as sending an email.

It's popular for domestic use because you can use it to make a phone call at the same time as accessing the internet.

ADSL can send and receive data at much faster rates than modems, but is slower and less expensive, than SDSL.

Find out about First Line's single ADSL service and our Bonded ADSL service.

Contention ratio

The 'contention ratio' of an ADSL connection means the maximum number of organisations that share that connection.

It's quite normal for domestic ADSL to offer contention ratios of 50:1. So you could be sharing your connection to the internet with up to 49 other houses at any one time. Commercial ADSL tends to be more expensive than domestic, but typically offers better contention ratios at around 20:1.

If you're not getting the speed you expect it can be due to the contention ratio. But it could be down to many other factors such as the capacity of the website you are accessing, or the quality of your phone line and the distance you are from the local BT exchange.

Read about First Line's low contention ratio ADSL service.

SDSL

Symetric digital subscriber line. In plain english, a way to access the internet using a conventional phone line - See PSTN below.

Symetric means that upload speeds and download speeds are the same. SDSL is a lot faster and more expensive than ADSL.

Another difference between ADSL and SDSL is that SDSL cannot share a phone line with a telephone - it needs its own.

ISDN

Stands for integrated services digital network - not exactly a helpful acronym, then. What it means is a single telephone line that can have two seperate phone conversations going over it at the same time.

PBX

Short for private branch exchange, a PBX is a private telephone network used within a company. Users of the PBX share a certain number of outside lines for making telephone calls external to the PBX.

Most medium-sized and larger companies use a PBX because it's less expensive than connecting an external telephone line to every telephone in the organization. In addition, it's easier to call someone within a PBX because the number you need to dial is typically just 3 or 4 digits.

With First Line Telecoms' FeaturePlus system, you no longer need a PBX, as the exchange is hosted online. So you get all the benefits of having your own internal exchange, without having to buy or make physical space for the hardware.

PSTN

Stands for public switched telephone network. In other words, a bog-standard domestic phone line. Only allows you to have one phone conversation over it at a time, but you can run ADSL broadband over it, (but not SDSL).

The next level up from PSTN is ISDN