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What are DSL, xDSL, ADSL etc?
How does ADSL work?
What is broadband?
What is ADSL?
How fast is it?
How does it work?
What can ADSL be used for?
Will telephone calls be charged separately?
What quality of service is provided?
What recommended specification of computer is required for ADSL?
What standard does our ADSL modem adhere to?
Can I use my own ADSL Modem?
How does ADSL speed compare to other access technologies?
What are the key benefits of ADSL for end users?
What are 'Upstream' and 'Downstream?
What is Citynet Broadband Fair Use Policy?
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What are DSL, xDSL, ADSL, etc?
Digital Subscriber Line, or DSL, is a broadband technology. It transforms a normal telephone line into a high speed broadband connection.
xDSL is a generic term used to refer to the family of DSL technologies. There are several different forms of DSL with different capabilities suited to different markets including:
- ADSL (Asymmetric DSL)
Provided over an existing telephone line (one copper pair), ADSL converts it to a high speed digital line up to 40 times faster than a traditional modem. It is asymmetric because it provides more bandwidth in one direction than the other.
- SDSL (Symmetric DSL)
Similar to ADSL, but it offers the same bandwidth in both directions. It is suited to situations where the user needs to send and receive large amounts of data.
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How does ADSL work?
ADSL operates over a normal telephone line. This means that there is no need to dig up any roads to install it. The ADSL signal is carried by two modems - one in the home or office premises and the other in the telephone exchange. These modems exploit the physical transmission capabilities of the copper line to achieve much higher data rates. A 'splitter' separates the telephony signal from the ADSL signal so phone calls can be made at the same time that data is being sent or received, without interference.
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What is broadband?
Broadband refers to services that provide high-speed communications, usually to access the Internet. There is no common definition of broadband, but typically, when people talk about 'broadband', they mean a service that provides:
- Faster speed
e.g. A peak bandwidth of at least 500Kbps, which is 10 times the speed of a 'normal' connection.
- Always on connection
i.e. You do not need to 'dial up'. Instead, the broadband line is always connected, like your water supply or electricity.
- Flat rate charge
i.e. You pays a monthly fee and can be online all day, every day for no extra charge.
For home users and small/medium businesses
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What is ADSL?
ADSL stands for Asymmetric Digital Subscriber Line. It transforms the standard telephone line between a local telephone exchange and a customer's telephone socket into a high-speed digital line. It is called 'asymmetric' because it moves data more quickly from exchange to customer than from customer to exchange. This makes it particularly suitable for applications where customers expect to receive more data than they transmit such as use of internet surfing, receiving digital audio-visual material and working from home over corporate intranets.
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How fast is it?
These speeds are between about 10 to 40 times faster than today's typical modems.
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How does it work?
ADSL enables your normal phone line to operate as though there were two cables. You can receive phonecalls whilst surfing the net at the same time. Your line is converted to ADSL by sending two different frequencies down the line. One frequency is for voice calls the other for the computer. A splitter/microfilter is added to the phone socket of the ADSL enabled phone line. The splitter/microfilter has two sockets, one for the phone cable connection and one for the cable that connects to the ADSL modem or router that you would need to use for this service.
If you have more than one phone socket connected to the ADSL enabled phone line then you will need a microfilter for each one. The extra phones can be plugged into the correct socket of the microfilter, the other socket of the extra microfilters, where you would normally attach the modem/router cable, can remain empty. If you run an extension cable from the microfilter that is attached to the master socket to another phone then you do not need a microfilter at the end of this extension.
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What can ADSL be used for?
ADSL's higher bandwidth has the potential to improve access to existing online services and applications and to stimulate the development of new ones:
- Internet access
The access speeds available with ADSL make it practical for web sites to carry more feature-rich information such as embedded video clips, animations and good quality audio. The virtually instant downloading of internet pages significantly enhances the online experience.
- Intranet access
Fast access to a corporate Intranet (internal communications network) makes teleworking a realistic proposition for businesses as well as their employees, bringing benefits to both the organisation and the individual.
- TV based services
ADSL can be used to deliver interactive applications to the TV, such as email and net surfing, movies and TV on demand, music and internet radio and home shopping and banking.
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Will telephone calls be charged separately?
Yes. Normal telephone rental and call charges will still apply.
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What quality of service is provided?
We aim to provide excellent service quality. Contractual terms and conditions govern the broadband services that we offer.
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What recommended specification of computer is required for ADSL?
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Windows 95, 98, 2000, NT, ME, XP, Apple Mac and Linux .
- 32Mb RAM (Depending on OS) .
- CD-ROM drive (Depending on modem type).
- USB port (Depending on modem type)
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What standard does our ADSL modem adhere to?
Discrete Multi-Tone (DMT), which uses interleaving to achieve good error performance and has become the international standard.
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Can I use my own ADSL Modem?
If you have a Router/Modem it will work with 2U ADSL Broadband. You will simply need to re-configure it with your 2U ADSL username and password etc.
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How does ADSL speed compare to other access technologies?
Speed comparisons are very hard to make since there are a number of influencing factors - the design of the network, host server speed, international bandwidth constraints etc.
- Technology Limits
- Dial-up modem 28 kbps 56 kbps
- ISDN 64 kbps 128 kbps
- ADSL 0.5 Mbps 2 Mbps
- Cable modems 0.5 Mbps 15 Mbps
- Leased lines Huge, only limited by cost
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What are the key benefits of ADSL for end users?
A faster connection to the Internet - at least 10 times the speed of a normal connection. Web sites with feature rich pages will download virtually instantly, compared to a 'normal' dial up connection.
- An always on connection - so no need to waste time 'dialing up'.
- Flat rate tariff - no call charges for the time spent online, so you have a predictable price for unlimited access.
- Simultaneous phone usage - you can surf and talk at the same time. The ADSL service runs over your existing telephone line, so there is no need to pay for an extra phone line to be put in. (Note that normal telephone rental and call charges will still apply though)
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What are 'Upstream' and 'Downstream'?
'Upstream' describes the flow of information (data) from your equipment to the exchange. 'Downstream' describes the flow of information from the exchange to your equipment.
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What is Citynet Broadband Fair Use Policy?
To ensure everyone gets a fair share of our High Performance we have implemented a 'Fair Use' policy with a fair quota per month Peak Time transfer allowance – this applies to data transferred between the hours of 9am and Midnight, seven days a week. Once the allowance is hit, users will still be able to connect – but limited to 64Kbps transfer rate. Any data transferred between Midnight and 9am does not count towards the Data Transfer Allowance.
Why have one?
Well it's designed to make sure your broadband service is fast and reliable whenever you use it.Some of our broadband customers use file sharing software and download large files like music and videos. This uses up lots of network capacity leaving less available for you. If they're doing this at peak times, it could mean that the speed of your broadband service will be affected.
Am I likely to be affected by the Fair Use Policy?
If you don't use file sharing software or download large files from the Internet it's unlikely you'll ever be affected by this policy. If you do, all we ask is that you do so considerately, perhaps by downloading outside the peak hours of 9am to 12pm.
What will happen if my use is very high?
If you only occasionally have very high usage, we're unlikely to be concerned unless it becomes a regular occurrence. If this does happen then we'll get in touch to help you find ways to reduce your usage.
If your usage continues to be very high, we'll get in touch again. Ultimately, if your usage still remains excessive despite our attempts to help you reduce it, we may have to suspend your service and possibly close your account.
We don't want to do that, and with your support and goodwill we'll work with you to see if we can avoid this happening.
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