What speed am I likely to achieve with Zen 8000 Products?
Aim of this article
This article lays out some guidelines for what download speed you are likely to achieve on a Zen 8000 Lite, Active, Pro, Office 8000 or Office 8000 Max account. Using this information you can assess whether your data speed is normal, or whether there could be a problem.
What is the maximum speed that I can get with Zen 8000 Products?
Zen 8000 products will sync at a maximum line rate of 8128 kbit/s and a minimum of 160 kbit/s.
Accounting for ATM overheads this translates to a maximum achievable data rate of 7150 kbit/s (or 893.75 kBytes/s) and a minimum of 145 kbit/s (or 16.87 kByte/s).
The following page allows you to enter your BT line number to obtain an estimate of what speed your line will be capable of supporting:
Get a Line Speed Estimate
If you would like to find out your current line speed please follow the Related Article on how to use the BT Speed checker.
To maximise performance and reliability you should ensure your Broadband ADSL equipment and telephones are set up in the best manner possible. The following setup guide illustrates the best setup:
Broadband Setup Guide
My service has just been activated and I only receive speeds below 2000Kbit/s, why is this?
Within the first three days BT will be monitoring your lines performance before determining the maximum speed it will obtain. Therefore it can take up to three days after the activation date before you see an increase in speed. If after three days you are still seeing speeds below 2000Kbit/s then the factors below may be affecting the maximum speed you are able to obtain.
What are the reasons why I might not achieve a full 7150Kbit/s?
There are a number of technical reasons why you may not achieve this speed, which are explained in detail later in this article. These reasons are listed below:
How does the physical line limit affect me?
ADSL uses your copper telephone line to carry a signal between the ADSL modem at your premises and equipment at the BT telephone exchange. Line length and quality will introduce interference which affects the strength of the ADSL signal and the connection speed the line can sustain.
The level of interference on your line will be proportional to the line length and quality. The quality of a line can be dependent upon age, material (e.g. some lines include a portion of aluminium cabling) and method of provision (e.g.underground or overhead cables).
BT uses a "Dynamic Line Management" system to automatically negotiate a connection speed which gives the best possible performance your line is able to achieve based on the available ADSL signal. This will be a maximum of 8128 kbits/sec, but can vary significantly depending on your line quality. You can usually check what line connection speed has been negotiated by looking at the line statistics information on your router or modem status page.
Because individual lines will differ it is often the case that neighboring premises will see different speeds; with significant differences observed on some occasions.
Often the speed you obtain will be affected by interference caused by internal wiring and extensions within your premises which you may be able to improve:
- Ensure your ADSL router/modem is connected to the BT Master socket.
- We would advise using good quality filters. Avoid filters that look like telephone doublers. The filters that look like small rectangular boxes with a short cable to the telephone socket are generally better. Check that none of your filters are faulty by swapping them out and checking your line statistics.
- Minimise the amount of extension wiring in use. If it is possible to locate your router at the BT master socket for your premises then this may yield improved stability and performance.
- Ensure all your telephony equipment is properly filtered.
The following article provides instructions on achieving the best possible wiring setup to get the most out of your ADSL Broadband service:
Broadband setup guide
How does the BRAS or IP profile limit affect me?
BT's line management systems will limit the speed you can download data across your ADSL line, in relation to your line connection speed, in order to improve stability. Log on to your router or modem and check what speed it is synchronised at, and then use the table below to check what your BRAS profile limit should be.
You can also determine your current IP profile in the customer portal. See the following Knowledge Base article for instructions for accessing this information:
Zen ADSL 8000 Products - Line Data
| DSL connection/sync rate (kbits/s) |
BRAS/IP profile limit (kbits/s) |
BRAS/IP profile limit (kBytes/s) |
| 8128 |
7150 |
893.75 |
| 7968 - 8096 |
7000 |
875.00 |
| 7392 - 7936 |
6500 |
812.50 |
| 6816 - 7360 |
6000 |
750.00 |
| 6240 - 6784 |
5500 |
687.50 |
| 5696 - 6208 |
5000 |
625.00 |
| 5120 - 5664 |
4500 |
562.50 |
| 4544 - 5088 |
4000 |
500.00 |
| 4000 - 4512 |
3500 |
437.50 |
| 3424 - 3968 |
3000 |
375.00 |
| 2848 - 3392 |
2500 |
312.50 |
| 2272 - 2816 |
2000 |
250.00 |
| 2016 - 2240 |
1750 |
218.75 |
| 1728 - 1984 |
1500 |
187.50 |
| 1440 - 1696 |
1250 |
156.25 |
| 1152 - 1408 |
1000 |
125.00 |
| 864 - 1120 |
750 |
93.75 |
| 576 - 832 |
500 |
62.50 |
| 416 - 544 |
350 |
43.75 |
| 288 - 384 |
250 |
31.25 |
| 160 - 256 |
135 |
16.87 |
Any changes to your Line sync rate should be reflected in the BRAS profile within 3 full days.
If your Line sync rate is higher than the BRAS profile you have been assigned it is possible that you have experienced a low Line sync rate event which has resulted in a drop in speed. The Customer Portal should show this event, and the BRAS profile you have been provided as a result. See the Related Article: Zen ADSL 8000 Products: Line Data.
If this is the case then you may need to improve your wiring setup, in a similar manner to how you would diagnose an intermittent connection fault. See the Related Article: Intermittent Connection Faults.
NOTE: Improvements in speed after a low Line sync rate event will typically occur after 3 days. Therefore when carrying out the Intermittent Connection Faults diagnostics you should monitor the effect of changing your wiring setup for a full 3 days.
What is Virtual Path Congestion?
ADSL is a contended product, using shared bandwidth within BT's Network. This means that your bandwidth is shared with other ADSL users at the same telephone exchange. BT state that because of congestion on these Virtual paths you are unlikely to achieve the full theoretical limit for your line at most times of the day. At peak times of the day they state that it may well perform similarly to a Home/Office 2000 line.
The highest/lowest data rates that fall within the product specification can be found in the following article:
Data rates which vary during the day, but never fall outside the acceptable thresholds published above are very likely to be the result of congestion on your contended virtual path.
We can only raise a contention related speed fault with BT if your data rate falls below the minimum published threshold.
In order to raise a speed fault you should log several BT speed tests demonstrating the poor speed, separated by at least 4 hours, and then contact support. Details of how to perform a BT speed test are in the following knowledge base article:
http://www.zensupport.co.uk/knowledgebase/article.aspx?id=10383
