ADSL FAQs

Here are answers to questions which people often ask about broadband internet access:

• What is ADSL?
• What speeds does ADSL run at?
• 8Mbps ADSL
• What about broadband over cable?
• What is 21CN?
• ADSL2+
• What is contention ratio?
• What is rate-adaptive?
• What are the download and upload speeds for ADSL?
• Why is the download speed faster than the upload speed?
• What is ALT ?
• What type of phone line is required for ADSL service?
• Is ADSL available everywhere?
• How can I find out about my local BT exchange?
• What is NAT/No-NAT?
• Do you get a fixed IP address?
• What is IPv6?
• What equipment to I need?
• What is a microfilter?
• We have just got broadband, When we have used our computer in the past, we have always closed it down and then turned it off at the wall. My husband says that now we are on broadband and a router, we can close it down, but not turn it off at the wall. Is this correct?
• I have an ISDN2 line. How do I get ADSL?
• Can I still get dial-up access without a broadband contract?
• Want to know more about broadband?

 

What is ADSL?

ADSL (Asymmetric Digital Subscriber Line) is always-on broadband service delivered over a standard BT PSTN analogue line. ADSL uses different frequencies on the line which means you can make phone calls and use the Internet at the same time.

It is Asymmetric because the download speed is different from the upload speed.

BT supplies the service via its telephone exchanges but wholesales its service via Internet Service Providers (ISPs) who package the service in different ways or offer additional services to the end user.

What speeds does ADSL run at?

ADSL based on BT lines or other local loop telephone providers:

 ADSL is usually sold as a Max or Max Premium service providing UP TO 8Mbps download speed. But be aware that the actual speed achieved depends on the distance from the exchange and the quality of the lines installed. The achievable speed depends on these and other factors. The exchange and router will try to find the best speed to achieve a reliable connection. This is referred to as "rate-adaptive".

Upload speed is also "rate-adapted" and can be UP TO 448Kbps (Max products) or 832Kbps (Max Premium products).

It is possible to provide higher speeds download and upload by aggregating traffic across two or more ADSL connection using managed bonding.

ADSL circuits are shared services and are subject to a contention ratio.

Old style:

Traditionally ADSL was offered at the following speeds:-

• Download: 512kb Upload: 256kb
• Download: 1Mb Upload: 256kb
• Download: 2Mb Upload: 256kb

These are known as classic services or non-rate adpative and are still available is some places. May be beneficial if at the desired location the speeds obtainable from Max rate adaptive products is low or unreliable.

Cable services:

Cable TV providers - in most of the UK now only Virgin Media (who swallowed up NTL and Telewest) - offer broadband through the same cable which is installed to run the TV. This is usually a pretty stable service with speeds available up to 20Mbps. You don't have to have a BT phone line for this service and in fact they offer a phone service bundled with the broadband. So if you don't have a BT line already or don't need or use one very much it is a good choice.  However, check the phone tariffs available - they are not the same as BT tariffs and may not be as advantageous depending on who you phone and when. 

8Mbps broadband

BT is well on its way in rolling out its higher speed "Max" services. Of 5583 exchanges over 5350 have already been upgraded. The service offers speeds of up to 8Mbps (megabits per second). This service is also available from ISPs such as ENTAnet who use the BT exchange infrastructure.

It is important to note that the Max products are "Rate Adaptive" product which could offer DSL line rates of UP TO 8Mbps, dependent on length of the line from the BT exchange and line conditions. As line conditions will vary, so the line rate will vary, and may deteriorate over time. Other factors can contribute i.e end user hardware, wiring and the incorrect/non use of microfilters.

Max services are asymmetric i.e. the download speed is much faster then the upload speed, and this needs to be considered when ordering services for inter-branch communications.

What is 21CN? 

21CN is the name given to BT's next generation network programme, under which it is creating an IP-based national fibre network to enable communication in a range of formats and support the demand for voice and data convergence. One of the most significant benefits of the network is the flexibility of choice and control that customers will gain in the way they use the connectivity services made available . 21CN will enable you to provide faster and more stable broadband at ADSL2+ speeds as well as Quality of Service (QoS) options for customers who wish to be able to prioritise traffic.

BT is enabling its exchanges for 21CN on a roll-out programme starting June 2008. Not all new services will be available right away from all exchanges. Existing ADSL customers shouldn't notice any difference to service.

Note that those who have been migrated to 21CN exchanges are not automatically upgraded to ADSL2+. They shouldn't notice any difference and indeed most customers have not been aware of the change in technology providing their broadband.

What is ADSL2+

ADSL2+ is an enhanced version of ADSL. Its principal characteristics are increased performance in terms of improved stability and data transfer speeds.

While ADSL provides speeds of 'up to 8Mbps', ADSL2+ is capable of delivering speeds of 'up to 24Mbps'. Furthermore, while ADSL provides a maximum upstream speed of 448Kbps (832Kbps in the case of ADSL MAX Premium), ADSL2+ allows an uncapped upstream experience, potentially up to 1.4Mbps.

However, like traditional ADSL, it should be noted that ADSL2+ is a rate adaptive product whose speed performance is dependent on factors such as the distance of customer premises from the exchange and the quality of the line connecting them to the exchange. Customers currently experiencing speeds of over 4Mbps on ADSL MAX should see an increase in speed. This isn't going to help customers who are located far from exchanges. It will offer better facilities for the lucky ones who get reasonable speeds already. Also only a few exchanges are ADSL2+ enabled at the moment. It's going to widen the gap even further between the broadband haves and have-nots.

It will provide additional features such as the facility to prioritise types of traffic on a QoS (Quality of Service) basis which is going to be more and more important with the convergence of voice and data and the availability of low-cost VOIP systems.

ADSL2+ services, under the banner of 2Plus Broadband, are available from ENTAnet via resellers like Realcom.

What is a contention ratio?

Contention is basically sharing. With ADSL you are sharing the resource with a number of other users. Most of the time the sharers are not using it at the same time but in theory you don't actually get all the bandwidth.

To buy internet access with no contention - effectively a leased line - costs several thousand pounds a year.

Contention ratio refers to the maximum number of users you could be sharing your bandwidth with. There are 2 contention ratios in general use: 50:1 (home) and 20:1 (business / office / premium). If you have a 50:1 contention ratio then in theory another 49 users could be competing for the 2Mb bandwidth you have. In practice this very rarely happens and even on the slowest ADSL product users typically see a 10x improvement over a 56k modem.

However, with the new Max services contention is more complex but also less definite. Contention for service occurs at the BT exchanges and various points in their network and also at the ISP. Different ISPs may implement contention ratios in different ways. In general, remember your ADSL connection is a shared service and the performance may go up and down depending on how busy the various connections in the service are.

Why is the download speed greater than the upload speed?

ADSL is Asymmetric which means it runs at different speeds for upload and download.

There is also a service called SDSL (Symmetric Digital Subscriber Line) which runs at the same speed for both upload and download with a contention ration of 10:1. (If you are interested in this service please send an email with your post code and we will check availability)

 

What is ALT?

ALT (Anti-Loss Tool) is an traffic management tool that was created by ENTAnet to maximise performance for all users and to ensure latency and packet loss is kept to a minimum at times of stress on the network. Read more about how this works in ENTAnet's Customer FAQ document >>

What type of phone line is required for ADSL service?

A standard BT PSTN analogue line is required for ADSL. Certain BT services and/or configurations are NOT compatible with ADSL, these include:-

• PBX Switchboard
• ISDN 30(PRI)
• Surftime
• BT Data Stream
• BT Video Stream
• Non-BT Telephone Line e.g supplied by cable co.
• Certain Redcare Alarm Monitoring - although mostly OK now
• Pulse Metered Line
• Coin/Pay Phone

It is possible to convert a ISDN 2/2e, Business Highway and Home Highway service into ADSL. This does however mean that the ISDN service is lost as the line has to be converted back to a single analogue line. Most ISDN/Highway circuits have 3 phone numbers attached, please note that the 2 additional numbers that came with the ISDN/Highway will be lost. This is a consideration if any of the additional numbers are in use and well known (i.e. Fax Number). more info>>

Is ADSL available everywhere?

ADSL is available in nearly all of BT Exchanges. However, the distance from the exchange must be less than a certain figure and quality of wiring and connections can affect connectivity and speed. Email us with your post code and if possible the telephone number you wish to use (see stipulations above) and we will check it out for you, or try the availability checker at Samknows.

If ADSL is not available at your location there are other options for broadband e.g. cable modem from NTL or Telewest and satellite but these services are not always suitable for business use.

How can I find out about my local BT exchange?

There are nearly 5600 BT exchanges in the UK, each in a different phase of upgrade and with different facilities. Nearly all can provide basic ADSL, some host equipment for other ISPs, some have already been upgraded to 21CN. To check out your exchange try Samknows exchange search.

What is NAT/No-NAT?

NAT (Network Address Translation) is a technology that allows you to share a single IP address assigned by a ISP among a number of computers or pieces of apparatus (e.g. printers/cameras) on a LAN. Most ADSL hardware supports NAT out of the box.

NO-NAT means that instead of having a single IP address to share you get a subnet of 8 or 16 IP's that are routable and can be assigned to your computers. Please note that because a subnet is assigned it means you do not have access to all the 8 or 16 IP addresses. On a 8 IP connection 5 IP addresses are available to you and on a 16 IP connection 13 IP addresses are available. This is because a IP is reserved for the network address, broadcast address and router respectively.

Do I get a fixed IP address?

All ENTAnet ADSL accounts come with a fixed IP address on both NAT and No-NAT. There are low-cost options for additional IP addresses. Some ISPs don't offer this - so if you need it e.g. for VPN access then make sure you ask before placing the order.

A fixed IP address is required if you are using ADSL for inter-branch communications, if you have home-workers who need to access your company systems, VOIP and is useful for remote troubleshooting and support.

What equipment to I need?

Apart from a BT analogue telephone line you will need an ADSL router if you wish to connect a server or several computers on a LAN to the internet or an ADSL modem - usually a USB connection - if you just have a single PC to connect. Routers come complete with a small switch for connecting other PCs and printers in the office with Cat5e cables and a wireless hub which will connect PCs, printers and lap-tops with compatible wireless interface cards.

Routers provide better performance than USB modems and don't impact on performance of the PC. A Router also includes a firewall.

For example, Zyxel 660HW

• Embedded Firewall
• Up to 100M Wireless
• NAT and DHCP
• Supports PPPoE, PPPoA and RFC1483
• 4-Port Ethernet 10/100Mbps Switch
• Easy web-based configuration and management

What is a microfilter?

A microfilter is an adapter that plugs into the telephone socket the ADSL service is provided on. The microfilter separates the ADSL signal from the voice signal. You plug your phone and your ADSL hardware into the microfilter and the microfilter into the BT phone socket.

An alternative is a "splitter" which doesn't have a "tail" but this can be awkward to fit if the phone socket is close to the floor.

Note: if you have more than one BT extension you must put a microfilter or splitter on each one and run the phone from that even if you aren't running a data device from that extension. ADSL will not work if you don't do this.

I used to turn off the computer

We have just got broadband. When we have used our computer in the past, we have always closed it down and then turned it off at the wall. My husband says that now we are on broadband and a router, we can close it down, but not turn it off at the wall. Is this correct?

Your husband is talking about the communications connection, i.e. modem & phone socket, rather than the power. When you used a dial-up internet connection you may have wanted to disconnect the modem from the phone socket when you closed down your computer, especially if you were using a single phone line for internet and for voice. Then you could use the line for ordinary telephone and also you can be confident that the internet connection has finished and you are not being billed for time you were not really using.

With broadband you get two connections on the same phone line - one for ordinary telephone and the other for the internet connection. You don't get charged for the time you use on the internet - just for the connection (although some service providers charge if you do a large amount of downloading). The router takes care of the connection and you don't have to do anything when you have finished your internet session or close down your computer. Actually, it is not a good thing to turn the power off your router because it will take a few minutes to "find" the connection again when powered on again. When you have your router set up correctly just leave it powered on. It won't matter if you turn the power off your computer - when you turn it on again it will connect to your router and thence to the internet automatically.

If you have broadband from your television company - e.g. NTL / Virgin - you will have a different kind of router but the story is the same - just leave the router powered on and it will look after your internet connection for you.

I have an ISDN2 line. How do I get ADSL?

ADSL works over PSTN (analogue) lines. Your ISDN2 line must be converted back to PSTN for ADSL to be installed.

An ISDN line will normally have 2-3 line numbers allocated to it. ADSL runs over a PSTN line which only has one number associated with it. You will only retain the line number that is specified in the ADSL order, the other numbers will be lost. Bear this in mind if you need to have a separate number for incoming faxes.

It is necessary for a BT engineer to visit to remove the ISDN and convert this to a PSTN, ADSL will then be put on the PSTN line the same day (unless circumstances dictate otherwise)

The lead time for an ISDN conversion is two weeks approx, BT will charge the a nominal fee on your BT phone bill for the conversion work.

If the you miss the BT appointment or turn the engineer away BT may make a charge.

Can I still get dial-up internet access?

Yes. You can get an old-style dial-up service using an 0845 number. You will be charged for the time you are on-line based on the rate your telephone provider charges for an 0845 number. There is no contract so this is ideal for casual, back-up or emergency use - but remember the speed will be a lot slower than broadband and you will need a modem. Sign up for a dial-up account >>

What is IPv6?

Since 1984 IPv4 (Internet Protocol version 4) addresses which consist of four groupings of numbers (e.g. 123.49.61.34) have been used to access the Internet. Twenty five years on and unsurprisingly the 4.3 billion addresses originally available with that scheme of numbering are now running out. A new scheme is being implemented and rolled out now alongside the old. IPv6 as it is known uses hexadecimal format and more numbers and will keep the world going for a while longer.

Entanet's network is enabled to support IPv6. However, their DSL, colocation and leased line services are set to use IPv4 as default to ensure that customers' setup is correct prior to adopting IPv6, for example in terms of having IPv6 supporting hardware and firewalls in place. If ENTAnetr customers would like to upgrade to IPv6 you can do so easily and for no extra charge by emailing IPv6@enta.net

Want to know more about ADSL & broadband?

Visit the ADSL Guide "How it works"

Also check out www.thinkbroadband.com and www.samknows.com/broadband/

 

If you have any further questions or would like to discuss your requirements and internet access options please telephone our office on the number below or email sandra@realcom.co.uk

Realcom is an ENTAnet reseller for ADSL & SDSL broadband, leased lines and VOIP.
Email sales@realcom.co.uk for more information or a quote

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