Broadband pricing

Monthly Exc VAT. See VAT Inc.

Up to:	8Mb/s	8Mb/s	24Mb/s*
Tariff	Std	Prem	ADSL2+
A	£16.16	£26.38	£14.46
C	£22.97	£33.19	£22.13
D	£29.78	£40.00	£27.23
E	£39.99	£50.21	£32.34

Setup £51.06 Full tariff list The package Max *ADSL2+ trial Extra charges

Monthly Inc VAT. See VAT Exc.

Up to:	8Mb/s	8Mb/s	24Mb/s*
Tariff	Std	Prem	ADSL2+
A	£18.99	£31.00	£16.99
C	£26.99	£39.00	£26.00
D	£34.99	£47.00	£32.00
E	£46.99	£59.00	£38.00

Setup £59.99 Full tariff list The package Max *ADSL2+ trial Extra charges

Migrate Bonding CUG Line+ADSL

Availability

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UK-wide high-speed broadband internet

ATM and IP rates for Max

There are many rates quoted, such as "up to 8Mb/s" and so on. However, the rates are measured at different points and so can cause some confusion.

Line rate

The rate you may see on your router settings is the line rate. This is the raw rate of the data on your ADSL line. The line rate includes ATM overheads so the rate at which IP packets can be sent is lower.

IP rate

The IP rate is the rate at which IP packets are transferred. This can be worked out from the ATM rate, but it is not a simple ratio. The IP rate is about 12% less than the ATM rate. The problem is that it depends on the exact size of the IP packets. Different sizes fit better or worse in to ATM cells and so may have more overhead.

TCP rate

The TCP rate is what you are likely to see reported on a download on your PC. This has to take in to account IP and TCP overheads. These are around 2.5% of overhead, but again depend on packet sizes.

However, it is important to realise that all the rates we have been talking about are based on bits per second, and most applications will report file transfer speeds in bytes per second. The byte per second rate is one eighth of the bit per second rate.

BRAS rate limiting

BT impose rate limiting within their network. This is a normal part of the way they provide the link to us. The rates set for Max are one of a number of specific rates at (mostly) ½Mb/s levels (at IP rates). This can mean, for example, that a line could sync at 1120Kb/s which works out at around 0.99Mb/s at IP rates, yet only get ¾Mb/s at IP rates. See below for a table of BRAS rates and ATM rates. See Max magic and myths for more details.

Contention

The internet is a shared resource - the total speed of all links to the internet is way more than the internet itself can handle! This is no different to any other shared utility (e.g. if everybody ran their water taps at full speed then they would all slow to a trickle).

This makes it impossible to define a speed that you will get for any specific download for any point on the internet. This can cause some concern - people with an 8M/s line expect to get 8Mb/s downloads! As we can see, this in itself is not realistic as even a perfect 8.128Mb/s ADSL line would allow a 7.15Mb/s IP rate which is under 7Mb/s with IP and TCP overheads. However, even that is slightly unrealistic because of contention within BT and the rest of the internet.

It is increasingly likely with higher speeds that the TCP/IP stack on either end may have difficulties keeping up, or recovering from any packet loss. There are web sites dedicated to fine tuning the TCP settings on windows machines to get the best performance.

In practice, people can expect that there will be times when they will get lower speeds than the maximum their line can handle. This could be contention within BT, or contention at the serving end (where the web site is, etc), or aspects of the TCP stack on the server of the machine doing the download. What we can assure customers is that we aim not to be the bottle neck. We aim to ensure we have routers and links that are more than capable of handling the normal load and have plenty of spare capacity.

How to get more speed

There are several ways to increase speeds

• Better router: This can increase the actual sync speed of the line. Some routers are better than others. We have found that generally the Voyager 210 is much better than routers using the conexant chipset, for example
• Better TCP/IP stack: Fine tuning settings in your TCP/IP stack (particularly on windows machines) can help make the most of the bandwidth available. There are many web sites explaining this.
• Max Premium: BT say that the Premium service has higher priority than the Standard service, and the figures they quote suggest twice the priority. So, for extra money you can buy a bigger share of the bandwidth.
• Multiple lines: You can have multiple lines. We will bond them together for faster download. This means you may well hit limits of backhaul bandwidth in BT. E.g. some smaller exchanges may only have 10Mb/s of backhaul, so two 7.15Mb/s Max lines are not going to ever get more than 10Mb/s combined in that case. However, whatever there is, if you have two lines you will get twice the share, as well as the added redundancy that two lines offer.

Uplink rates

Uplink rates are 448Kb/s or 832Kb/s capped (Standard or Premium) and have the same ATM and IP overheads as downlink. This means a maximum of 400Kb/s or 750Kb/s (Standard or Premium) at the IP level. These are not capped at the BRAS and not rate limited. Also, whilst your line may be asymmetric, the links within BT and the internet are not, so generally uplink has no issue running at full speed whenever you want. You can bond multiple lines for faster uplink using suitable equipment (such as the FireBrick).

The following table shows the IP rate you can expect for each ADSL sync rate (as reported by your router)