Following on from Your broadband speed - the basics this guide explains the some of the terminology used in more detail.
- Broadband Products
- Sync Speeds
- IP Profile
- Throughput Speed
- Dynamic Line Management
- Banded Profiles
- Blip Logic
1. Broadband Products
Our broadband is supplied over the BT Wholesale network. The products on offer are split into two categories:
20th Century Network (20CN)
Available in most UK exchanges. 'IPStream Connect' (IPSC) technology is used to provide speeds up to a theoretical maximum of 8Mb via ADSL1
21st Century Network (21CN)
Available in a growing number of UK exchanges, 'Wholesale Broadband Connect' (WBC) technology is used to provide:
Note: We often refer to our ADSL1/2+ products as 'Standard broadband' to help differentiate them from FTTC products.
2. Sync speed
Also known as: Sync rate, Downstream rate or DSL Connection rate
This is the 'physical' speed of the connection between your router (or modem) and your local telephone exchange. It's determined by the characteristics of your line e.g. line length and quality.
Your sync speed is not fixed and can change each time you reboot or switch on your router.
While it should remain stable for the majority of the time, small changes are normal for most users. You should only ever see significant changes in the event of a problem (see Dynamic Line Management for more on this).
You can find out what your current sync speed is by running a BT Speedtest or logging in to your router (ADSL 1 & 2 only).[Top]
3. IP Profile
Also known as: BRAS profile
This a speed limit applied by equipment in your telephone exchange.
The IP Profile is designed to stop us from sending more data down your phone line than it (or your router) can physically handle. As such, it represents the maximum speed you can achieve whilst also receiving a stable connection.
The way an IP Profile is calculated depends on the broadband product:
- 21CN products: the IP profile will always be 88.2% of the sync rate
- 20CN products: the IP profile is assigned according to the table below:
|Sync speeds between||IP Profile||Sync speeds between||IP Profile|
|288 to 415kb/s||250 (up to 0.25Mb/s)||3424 - 3999kb/s||3000 (up to 3Mb/s)|
|416 - 575kb/s||350 (up to 0.35Mb/s)||4000 - 4543kb/s||3500 (up to 3.5Mb/s)|
|576 - 863kb/s||500 (up to 0.5Mb/s)||4544 - 5119kb/s||4000 (up to 4Mb/s)|
|864 - 1151kb/s||750 (up to 0.75Mb/s)||5120 - 5695kb/s||4500 (up to 4.5Mb/s)|
|1152 - 1439kb/s||1000 (up to 1Mb/s)||5696 - 6239kb/s||5000 (up to 5Mb/s)|
|1440 - 1727kb/s||1250 (up to 1.25Mb/s)||6240 - 6815kb/s||5500 (up to 5.5Mb/s)|
|1728 - 2015kb/s||1500 (up to 1.5Mb/s)||6816 - 7391kb/s||6000 (up to 6Mb/s)|
|2016 - 2271kb/s||1750 (up to 1.75Mb/s)||7392 - 7967kb/s||6500 (up to 6.5Mb/s)|
|2272 - 2847kb/s||2000 (up to 2Mb/s)||7968 - 8095kb/s||7000 (up to 7Mb/s)|
|2848 - 3423kb/s||2500 (up to 2.5Mb/s)||8096 - 8128kb/s||7150 (up to 7.15Mb/s)|
If the profile on our website and the BT Speed test don't match
BT Wholesale send profile change reports several times a day, so our system should update within 24 hours. If you end up waiting longer than this, please contact our Support Team through the Help Assistant.[Top]
4. Throughput Speed
Also known as: Download Speed or Data Rate
This is the actual speed you're able to download data. In normal conditions this will be close to but never higher than your current IP Profile.
Throughput speeds can vary due to contention (other broadband customers) at your telephone exchange and Traffic Management. Our broadband service is provided over a shared network. This means we have to manage traffic to make sure our customers receive a quality and sustainable broadband service.
All traffic is prioritised according to type, broadband account and the time of day. Read our Traffic management guide to find out how and why this is implemented.[Top]
5. Dynamic Line Management (DLM)
DLM is an automated system that manages the performance of your broadband service.
For 10 days after broadband activation, DLM will test your line to find the best balance between speed and reliability. Speed during this time can vary and your broadband may drop out occasionally (it should return immediately).
After 10 days, small changes in speed can occur (as DLM reacts to changing conditions) but your line speed should remain relatively stable.
In the event of problems (e.g. line errors or frequent disconnections), DLM will reduce your sync to a level that allows for a stable connection. This allows you to continue using your broadband during problems, albeit at a lower connection speed.
Once the problem is fixed, your sync speed should return to normal quickly. When your sync speed returns the IP profile youll receive depends on the broadband product:
- 21CN products: the IP Profile is calculated each time your line syncs
- 20CN products: the IP Profile will be recalculated after your line is deemed stable (up to 3 days without disconnection)
BT send us reports of profile changes several times a day, so speeds should return to normal once we've updated our system with the new profile (usually within 24 hours).
DLM is the main reason that we advise you to leave your router switched on, as turning it off frequently can cause DLM to think there's a problem and reduce your speed.
Remember: DLM reacts to problems on your line rather than fixing them. If your IP profile or sync speed fluctuate regularly, there may be a line fault or something causing interference. See our Broadband speed tips guide for help tracking down the problem.[Top]
6. Banded Profiles
ADSL2+ and FTTC only
When first activated, your line is 'fully rate adaptive'. This means there's no upper limit to your sync speed (within the capabilities of your broadband product).
If your line drops frequently, has a high error rate or severe noise problems, a banded profile can be applied to aid stability.
This will force your line to sync within the range of an assigned band and is used to limit the sync rate when it's not stable above a certain rate.
The table below shows the bands used on ADSL2+ products. Details of the bands used on FTTC products has not yet been published by BT Wholesale.
|160kb/s - 288kb/s|
|288kb/s - 576kb/s|
|576kb/s - 1152kb/s|
|1152kb/s - 2272kb/s|
|1472kb/s - 3072kb/s|
|2272kb/s - 4544kb/s|
|3328kb/s - 6656kb/s|
|4864kb/s - 9728kb/s|
|7168kb/s - 14336kb/s|
7. Blip Logic
20CN products only
Some customers have very stable lines, but for one reason or another can occasionally see a one-off sync rate at a lower speed. The use of 'Blip logic' means if a stable line, (one that hasn't seen a IP profile decrease in the last 14 days), experiences a short drop in sync rate and then goes straight back up again, it won't result in a wait for the IP profile to catch up, although a second drop would lower the IP profile.[Top]
Interleaving is a form of error correction that can help reduce the number of 'errors' on a line.
This is activated by default on new broadband services and where a fault has previously been reported. It helps to stabilise a line that might otherwise suffer frequent disconnections.
One drawback is that in some cases, Interleaving can increase latency. In most cases the effects are minimal and unlikely to be noticed by the majority of people but this can cause ping times to increase slightly while playing games online.
Whilst we'd recommend against it, we can switch off Interleaving for you. To do this, use the Help Assistant to raise a Question. Follow the path - My Broadband Connection > Interleaving.[Top]
This page last updated 29th May 2013