WHAT IS CONTENTION ?

At Green ISP we aim to provide you with the best service that is possible - our connectivity is taken from major backbone providers to provide as direct (and therefore fast and reliable) a connection to the Internet.

However, 'in the real world' you are unlikely to achieve the types of figures which are stated in our packages (512kbps/1Mbit/2Mbit for example) consistently due to some of the following factors:

Contention Ratios - this is probably the single most important thing to affect your download speed. The HOME ADSL 512k, 1Mbit and ADSL 2Mbit HOME services are contended at 50:1 whereas the ADSL 500 BUSINESS, ADSL 1000 BUSINESS and ADSL 2000 BUSINESSservices are contended at 20:1. The lower ratio of the business services means less other people are 'sharing' the overall link speed resulting in generally higher and more consistent performance.

This contention is applied within the BT network - both locally with other users on your telephone exchange and within the BT network as it connects into our network.What this means in the 'worst case' is that you could be sharing a 1Mbit connection with up to 49 other users. So if they were all using it at the same time 'theoretically' you would only get 22 Kbit/s (not very fast at all - in fact quite a bit slower than a normal modem).However, 'in reality' this scenario is very, very unlikely to happen and you should usually find it to be far far faster than a modem connection (at least 50-60% of stated speed when fully contended).

ADSL relies on individual users not making unreasonable traffic demands on the network to provide fast access speeds for all.Remember if you are not getting the speed you expect it can be due to the contention ratio but also to many other factors including the capacity of the remote site you are accessing, the quality and length of your telephone line from the local BT exchange.

OTHER FACTORS TO TAKE INTO ACCOUNT !

Remote Site Speed - the actual site you are downloading from may be busy and unable to supply the download at full speed. In addition some sites will actually use 'traffic shaping' to restrict the speed at which single users can download from their site to help ensure a fair level of service for all their users. Network Congestion - sometimes the interconnecting networks are unable to cope with the levels of traffic at peak times causing some slowdown.

Other Applications - you may be running other applications (for instance checking your mail etc.) at the same time which can degrade download performance.

Other Users - if you have more than one computer through your broadband connection (for instance if you are using a router or you are on a network), then it will cause your download to be slower than you might expect.

ADSL Link Distance - if you are a long way from the exchange it is possible that BT have installed your circuit using RADSL - this technology is used to extend the maximum range for broadband services. However, it 'can' be a cause of degrade in performance especially on upload speed. Unfortunately there is very little that can be done as without it you would not be able to receive broadband services at all!

ADSL Equipment -

ensure you are using the latest drivers for your ADSL equipment and operating system. We have seen this to be important most frequently with ADSL modems connected via USB. Also with USB modems you are best not to use unpowered USB hubs - instead connect direct to your computer or via a powered USB hub.

BT would regard the speed ranges shown below as normal service:

For 500kbps End Users speeds between 100 - 500kbps.
For 1000kbps End Users speeds between 200 - 1000kbps.
For 2000kbps End Users speeds between 400 - 2000kbps

 

 

 ADSL MAX INFORMATION.

The following table represents the maximum possible throughput speeds for the different sync speeds you might see.

Sync speed Throughput speed
from 288kbps up to 0.25Mbps
from 576kbps up to 0.5Mbps
from 1152kbps up to 1Mbps
from 1728kbps up to 1.5Mbps
from 2272kbps up to 2Mbps
from 2848kbps up to 2.5Mbps
from 3424kbps up to 3Mbps
from 4000kbps up to 3.5Mbps
from 4544kbps up to 4Mbps
from 5120kbps up to 4.5Mbps
from 5696kbps up to 5Mbps
from 6240kbps up to 5.5Mbps
from 6816kbps up to 6Mbps
7392kbps up to 6.5Mbps
7968kbps up to 7Mbps
8128kbps up to 7.15Mbps

Fluctuating Throughput Speeds?
It is perfectly normal to see throughput speeds that change from day to day, from hour to hour, even from minute to minute. A Max connection in the late afternoon would likely see variable speeds due to exchange-side contention. The same download at 4am when the network is very quiet might give a very steady download speed.

Broadband works as it does, and at the low prices we as customers pay, because it works on a shared network. The available capacity on the network is shared out amongst all the customers that are using the Internet at that time. This means that at busy times, when more people are using the Internet, each person gets a smaller share of the bandwidth and so lower speeds than when the network is quiet. As different people use the Internet in different ways and have different usage patterns, this can mean that the speed you see can be constantly going up and down, especially when it is busy.

As a general rule so long as your throughput speeds fit within the following bands it is considered to be normal.

Sync Speed Performance Threshold
Up to288kbps 50-250kbps
from 288kbps to 576kbps 50-500kbps
from 576kbps to 1152kbps 100-1000kbps
from 1152kbps to 2272kbps 200-2000kbps
from 2272kbps to 8128kbps 400-7150kbps


The ADSLMAX service was launched on 31st March with 99.9% of BT exchanges enabled to provide the higher bandwidth services.
Please use the broadband availability checker to check the status for your local exchange.

What sort of speed might I expect?
For many users ADSL Max will provide an increase in line speed. However, MAX is a rate adaptive service and the actual speed that a user will experience will be dependent on the line length and the line quality. It is quite possible for users in close geographical proximity to receive services with different speeds.
MAX provides download service at up to 8Mb/s. Although some users may experience line speeds at or close to this rate, the majority are likely to receive line (sync) rates around 6.5Mb/s

Actual data throughput speeds will also depend on contention in the external networks and the performance of the remote server etc. Many users report actual throughput at around 50% of downstream line rate. Please note that it is highly likely that different speed tester servers/applications will report widely differing results and at different times.

BT do advise that IPstream aDSL MAX is delivered over a 'best efforts' network and that no guarantee is given that the line rate seen by End Users will result in throughput above that of the IPstream Home/Office fixed rate services (IPstream Home/Office 2000). Outside of busy periods, services may take advantage of any reduction in the core bandwidth utilisation which may be seen by End Users as an increase in throughput.

Will there be an immediate increase in speed?
Note: Regrades will take up to 5 working days from order to provision. There will then be a minimum 10 day period whilst the maximum line rate is determined.
When a user upgrades/orders ADSL Max the system will attempt to synchronise the user modem/router and the BT exchange DSLAM to determine the maximum stable rate (MSR). ADSL Max is rate adaptive - the BT system will record upper and lower line rates. Data will be collected for a MINIMUM of 10 DAYS before the lower line rate is rounded down and to become the MSR. The Fault Threshold Rate (FTR) will be set at a level 30% below MSR. There is likely to be some alteration to the line speed whilst the BT system undergoes 'training' to find the MSR. Once the MSR is set this will be the benchmark level for the lifetime of the connection.