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The Speed of Broadband

The Speed of Broadband

The Speed of Broadband

This post is intended to be a little timely. Five's Gadget Show have just launched a campaign regarding broadband speeds. The industry uses the terms "up to" such as "up to 8Mbps" for reasons which we'll cover off a bit later. But we'd like to throw down the gauntlet so to speak and ask customers what they think we, and others, should do to better explain the product that is being sold. If the "up to" is seen as problematic or misleading then that makes us uncomfortable at the very least in using this. We have no intention of misleading but do acknowledge how people feel and that some will feel mislead that a service is advertised as "up to 8Mbps" and because of where they live for example they may never see any faster than say 2Mbps. We've put the following text on our signup pages:

"Why 'up to' 8Mb?Broadband is described as 'up to' 8Mb because download speeds will vary depending on your telephone line and location.Actual download speeds can reach a maximum of 7Mb, with an average speed of 5-6Mb. BT Wholesale estimates that 78% of customers will achieve download speeds of 4Mb and above. It is likely that speeds no greater than 2Mb will be achieved at peak usage times due to contention in our network and our suppliers' networks.
Download speeds will vary significantly in the first 10 days after connection and then will become more consistent."

But does that adequately explain the speeds you may see or should it go into more detail. Should we drop or change the "up to" phrasing, or use something else entirely. Please feel free to let us know your thoughts in our Community Forums. So moving along I thought I'd share a bit of experience, cover off some of the factors that will have an effect on speed and broadband performance and also provide some suggestions for improving speeds. Yesterday's Experience First off a bit of a story that I alluded to previously and I'll also include a link to James's excellent diagnosing speed faults post. We've tested some different routers over the last couple of days on a couple of the lines we have in the building. One of these lines sync'd at 8128kbps, the fastest DSLMax will allow and the other sync'd around 6000kbps (it fluctuated a little up and down from that). This was the same using the same router on each line. It's not unusual for two lines in the same building to sync at different speeds but it is a little unusual for there to be that big a difference. Now it may just be because of the way the lines are patched through the building (our internal wiring) or it may be that one line goes half way round Sheffield before getting back to the exchange. The other strange thing is that the line that sync'd at 6000kbps had a solid 5Mbps on speedtests but the one the one sync'd at 8128kbps got less than 2Mbps on a speedtest, sometimes less than 1Mbps (we haven't tried it over night yet). Again this is the same regardless of the hardware (same router and PC) and we've also used the same PlusNet broadband username on both to rule out anything funny with the login details. Looks like either it's a line fault or there's exchange contention kicking in. So what are the factors that can influence broadband speed? Let's first off make sure we're thinking in the same way. The first is quite important to consider the difference between sync speed and throughput speed. Sync Speed The sync speed is the speed that your modem or router will connect to the exchange at. When an ISP quotes the speed of your connection as, for example, up to 8Mbps, it is the sync speed that is being quoted here. On Max the maximum a line can sync at is 8128kbps (or 8Mbps). The sync speed though can actually be anything between 160kbps and 8128kbps. This is where the "up to" in "up to 8Mbps" comes from. The maximum speed is 8Mbps but it could be anything up to 8Mbps depending on a number of factors. This page will show you how to check the sync speed on most ADSL modems and routers and this page on our portal will show you the sync rate to the nearest 500kbps (so 8128kbps will show as 8000kbps for example). The way that Max is designed is that whenever the router connects it will work out the fastest rate that it can connect at (based on certain criteria). The biggest factor that will influence the sync speed is distance from the telephone exchange, or to be more precise, the length of the telephone line itself. ADSL is very much a distance dependent technology, the longer the phone line the lower the speed that phone line will support. It's not too unlike a radio signal (only much shorter distances), in Sheffield I can get perfect reception of Hallam FM but the further away from Sheffield I get the weaker the signal until I get to point where the noise or another radio station drowns it out. With ADSL you'll get the fastest speeds if your phone line is under about 1.5km and then it will generally start to get slower and when you get out to around 6km you may only be able to get a 512kbps or 1Mbps connection. Another factor that can affect the sync speed is "noise" on the phone line. By noise I'm talking about anything that can cause interference on the line. The most common things will be unfiltered or incorrectly filtered devices on the telephone such as a phone, fax machine, Sky box, alarm system or analogue modem. Anything on the line that doesn't have a filter can cause noise that will reduce the sync speed. I've experimented on a good line in the past and just plugging an unfiltered fax machine in caused the sync speed to drop from 8Mbps to 6Mbps. Going back to the radio analogy, if you drive under an electric pylon for example your radio signal will break up because of the noise from the pylon. The basic rule to think about is that everything connected to the phone line should be filtered once and once only. Where possible it's also best to avoid extension cables; a long or damaged cable can be just as bad as an unfiltered device. Because of the way that Max works it's normal for the sync speed to fluctuate, normally this will just be by a small amount but sometimes sync speed can drop by a significant amount. As a one off this could caused by a number of things from the weather, such as thunderstorms, to some of the more unusual things we've seen over the years like electric fences and microwave ovens. Sometimes if the line speed fluctuates a lot and the line is unstable the systems at the local BT exchange that monitor the stability of each line will reduce the speed the line syncs at in order to improve that stability. Some people will therefore notice that over time the speed decreases, or they have a period of instability and then the speed is slower but in turn the line more stable. This is normal behavior, the system is designed to give better stability over speed. If the line remains stable then over time the speed will increase again. Another factor that should be noted is that some customers will be on fixed rate broadband services (either 512kbps, 1Mbps or 2Mbps). The up to 8Mbps speeds have only been around for just over 18 months, any customers getting broadband before this would be have been activated on a fixed rate. The majority of our customers have now been upgraded to Max but we are still processing upgrades for free every week. Any customer that wants an upgrade can request it via this page or this page for Metronet customers. Throughput Speed The throughput speed is the speed at which you can actually download at. The throughput speed is always going to be less than the sync speed (you can't download at a speed faster than you're sync'd at). A certain percentage of the sync rate though will always be taken up by overheads. Whenever any data is transferred across a broadband connection a certain amount of data overhead is needed to ensure that it gets to and from the right place. I guess one way of thinking about it when you send a letter, the letter itself is the data and the address and envelope are your overheads. With an 8Mbps sync rate the maximum possible throughput rate is about 7.15Mbps. Overheads generally make up around about 10% of your sync speed. The next factor that governs your throughput speed, is the BRAS profile. The BRAS profile is a rate limit that BT apply to each ADSL connection at the exchange. The actual rate limit is based on the sync speed. This page has a lot of information about Max including a list of the BRAS profiles and what sync speed they are seen at. The BRAS profile will decrease when the sync speed decreases within about an hour, but it can take up to 5 days to increase if the sync speed increases. It's possible then to see a low throughput speed because of a low BRAS profile even though the sync speed is high. If the connection is unstable sometimes the rate at which the sync speed is decreasing is quicker than the the profile increases. So even though the line may only resync at a low speed for a short period if it does it often enough the BRAS profile will stay at a low rate. You can check what the BRAS (or IP profile) is by running the BT Speedtest, details here about how to do it. With a new activation or upgrade to Max it is also normal for the sync speed, and thus the throughput speed, to fluctuate over the first 10 days as the line works out the stable rate for the line. Another factor that can affect throughput speeds is the MTU and RWIN settings. This is often particularly noticeable on line sync'd at a higher speed but it can affect any line. This help page covers more about tweaking your RWIN. The source of the download can often be a factor, when trying to determine whether a line is fast or slow we would always recommend testing from different sources. There are a number of speedtests that can be used such as the BT Speedtest above, our speedtest or Think Broadband. Sometimes one source can give lower speeds than another, perhaps because it's being heavily used so testing different ones will give a better spread. Testing at different times of the day can also give different results. Over night and early mornings will often give the best speeds whilst Satuday afternoons and Monday evenings the busiest times. Sometimes slowdowns can be seen because the particular local exchange (or part of the equipment at the local exchange is busy). You can check the exchange status at this page to see if there are any known problems (the data can sometimes be a week or two behind so even if it shows as green if the speeds have only recently decreased it may not yet be showing up). That page will also show if there are any known outages at the exchange which is useful to check in the event of a sudden problem. Another factor that could affect speeds is usage. Some broadband accounts have set amounts of usage per month and if you exceed this amount you may see speeds reduced. You can check your usage via the View My Broadband Usage (VMBU) page here. You will also normally receive an email to let you know if you've reached the usage limits. Our network also employs traffic management which gives different priorities to different types of traffic on different account types. When the network gets busier speeds on the lower priority traffic will be be reduced in order to ensure that the higher priority traffic is unaffected. Some traffic will also see rate limits at certain times of the day on some account types. This page shows the priority of each traffic type too and should be used in conjunction with the expected speed page and the network performance graphs to determine whether the speeds that you are seeing are normal (or at least expected) for the time of day and network load at the time. There are other factors that can affect broadband speeds but these are generally the most common. If nothing here helps, or indeed if it does or you have other suggestions that may help others then please feel free to post in our discussion forums. Dave Tomlinson PlusNet Product Team 

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