PlusNet Broadband capacity planning and traffic management 2008
The aim of this blog is to cover off some of our plans for traffic management and for the capacity of our broadband network over the next year. We will take a look at some of the factors that influence how our approach to traffic management changes, as well as what governs the amount of capacity that we require. Firstly, we'll look at capacity. When you look at a broadband network there are a several places where you can measure capacity but the most important part, and most expensive, is the central pipe capacity that transfers data between our network and BT's network and ultimately on to the customer via their local telephone exchange. We won't go into the costs here, but instead link to an earlier blog that details how a UK ISP is charged for providing a broadband service. How we determine the amount of capacity is required is a fairly complex process, but I'll try and simplify it a little. The biggest determining factor is the number of customers, essentially the larger the number of customers the more capacity is needed. But that has a caveat - you also have to take into account the type and mix of customers. For example, business customers are more likely to make use of their connections Monday to Friday, between 8am to 6pm. These graphs show the usage patterns of our Business customers over the last two days last week (Wednesday and Thursday) and the previous week: Whilst residential customers are more likely to make use of their connections after 4pm on weekdays and at weekends (there's more file downloads going on overnight and the day on residential accounts but the interactive types of traffic like browsing are used more in the evening and weekend). The graphs below show the usage on Broadband Premier Option 1 over 2 days and the previous week: Of course not every customer fits that kind of pattern (plenty of businesses work in the evenings and weekend) but when you are talking about several thousand customers you can see these kinds of trends. Therefore, if you have a mix where almost all of your customers are business customers you'd need more capacity during the day than if they were half business and half residential. Similarly you'd need more capacity in the evenings and weekends if they were all residential. You also have to take into account the type of users there are. We sell different broadband products with different usage allowances, Broadband Your Way Option 1 comes with 1GB by default, BBYW Option 4 comes with 40GB. As such you would probably expect the average BBYW Option 4 customer is going to be a higher user than the average BBYW Option 1 customer; so you need to provision more capacity for each BBYW Option 4 customer than BBYW Option 1 customer. But, there's another factor, whilst your BBYW Option 4 customers may be higher users than the Option 1 customers, their usage may be more evenly spread out across the week while you might find that the Option 1 customers tend you use their connections at the same times, such as Monday and Tuesday evenings between 8 and 10pm, and mainly using similar types of traffic (such as web browsing, email and streaming). This graph shows the usage on BBYW Option 1 over the last 3 months between 8 and 9pm per protocol. Mainly web traffic but streaming is on the increase. So doing the analysis on a per product per hour basis you may well find that BBYW 1 customers use as much as BBYW 4 in some hours of the week but when you at the week or month in total BBYW 4 will come out higher. For example, for a single hour on a weekday evening we may see that the average BBYW 1 customer using streaming uses the same as the average BBYW 4, but that overall the BBYW 4 average is higher. From there we've built up an idea of the capacity that is required based on the customer numbers and the account types they are on. We also need to consider extra pre-pay and PAYG usage. On each BBYW product you can choose to pre-pay for additional usage should you wish or if you reach the usage allowance to pay for additional usage on a PAYG basis. The extra usage translates into additional capacity; a BBYW Option 1 customer with 3GB is likely to use more than a BBYW Option 1 customer with 1GB, and of course at the same time is spending more and thus contributing more to the bandwidth costs. We also need to look at the type of traffic that is being used, whether usage is increasing and by how much, what type of customers are seeing growth in usage and when that usage is being used. Over the past few weeks we've seen huge increases in streaming traffic, by and large this is all down to the BBC's iPlayer and when you look at the data there's growth in streaming of between about 20% and 70% for just about every product we offer and for each hour of the week. What we are seeing is that something like iPlayer, coming from a trusted name like the BBC, is appealing to just about every sort of customer. Those that are used to downloading or watching TV and video on the Internet are using it in addition to or as a replacement for other sources and those new to online video are starting to use it too. It always helps when the BBC are doing such a good job of promoting it. But it's something like iPlayer that can make a big shift in the overall usage because it can turn the lightish users who do say 1-2GB per month into customers that do say 3-4GB per month. If you look at the usage figures for January if all the customers in the 31-40% and 41-50% brackets increased their usage by 2GB each, that's roughly an extra 80TB of data (based on 200,000 customers). Over a month a 155Mbps segment can transfer roughly
(155 + 76.5) / 8 * 60 * 60 * 24 * 30 / 1000 / 1000 = 75.6TB
(assuming it is maxed out up and down 24/7). Chances are though that the extra usage isn't so evenly spread and is weighted more towards download than upload. So what looks like a fairly small shift in usage actually has a very big impact on capacity planning. Again though that's where BBYW comes into play, because a lot of those 1 and 2GB customers that were on BBYW 1 that become 3 and 4GB customers are either spending more on extra pre/post pay usage or are upgrading to BBYW 2 or Pro. Same with the BBYW 2 customers that were 6-8GB and are now becoming 9-10GB. With the legacy products like Broadband Plus and Premier it's a slightly different case (PAYG fits alongside BBYW quite well in planning stakes). We haven't sold these products in almost a year now so the number of customers on them is declining. Customers on Broadband Plus who used to fit quite well into the 4GB usage allowance will generally find that upgrading to BBYW Option 2 works out quite well for them (not just because of the 4GB extra usage but the overnight free period allows you to download more via P2P and Usenet in less time than on Broadband Plus because of the rate limits that are set on this type of traffic). Premier customers on the other hand may find similar by switching to Broadband Your Way 3 (or Pro in some cases). We do though have to keep a very close eye on the off peak usage in particular because half of off peak on Plus and Premier is part of the chargeable period for BBYW and also, as mentioned above, the time when business customers use their connections the most. Which leads us nicely into traffic management. It is through the traffic management systems that we can have the level of detail on what our customers are doing that we do. Without it we could see how much customers were using but it would be difficult to tell how they were using their connections and where the growth really was occurring. It also allows us to further differentiate the products by setting different priorities and rate limits on different products and at different times of the day. It gives that different level of quality of service across each account type. We could just sell one broadband product with one level of experience but then you end up with one group of customers subsidising another. For those customers that are light users and perhaps don't want to use much P2P or Usenet BBYW Option 1 works out quite well. For someone that wants to use P2P and Usenet but doesn't mind scheduling it overnight BBYW 2 and 3 are fine. For the heavier use there's BBYW 4 and BBYW Pro if you want the best speeds on all types of traffic in the evening. The overnight free usage period also allows lower prices; it encourages customers to schedule large downloads overnight so we see less P2P and Usenet traffic in the day and evening spreading the overall usage out better across the full 24 hours of the day. We also apply rate limits at certain times of the day; these are designed to ensure a fairer spread of the available bandwidth. If you imagine there's say (made up figure) 6Mbps of capacity available for Usenet and 2 customers are trying to use it at the same time. If one customer is downloading using 10 threads and the other 2 threads then each thread should get 0.5Mbps and thus the first customer downloads at 5Mbps and the second 1Mbps. But there's another issue, the available 6Mbps may not be constant and you might find that the first person is downloading at 5.1Mbps and the second 1.1Mbps. 6.2Mbps of traffic doesn't go into a 6Mbps space, at this point our network buffers the extra traffic for a few milliseconds and then tries to resend it, if it goes through then the worst issue is a little extra latency (which is fine for a Usenet download but not for gaming). If it can't resend it after a certain amount of time then the traffic gets dropped. If in this case you apply a 3Mbps rate limit to Usenet traffic, then assuming the second customer can get 3Mbps they both download at 3Mbps each. Because we've rate limited the traffic to a maximum of 3Mbps there's never more than 6Mbps when it gets to the central pipes. We also have weightings on each queue of traffic to ensure that a certain minimum amount of each type of traffic will always be allowed when the network is busy. In our simple example this may be that it always allows a minimum of 6Mbps of Usenet traffic (bronze), but there will be more allowed to be downloaded when the network is quieter. The rate limits are also designed to be adaptable depending on how busy the network is, in the example above 3Mbps works when there are two customers, if a third starts downloading the ideal rate limit would be 2Mbps and if the available capacity increased to 9Mbps the ideal rate limit would then be 3Mbps again. The aim is to ensure that available capacity is split as fairly as possible between the customers using that type of traffic, maximising the available capacity with the least amount of dropped traffic. So for example on a Friday and Saturday evening some rate limits will be relaxed because the network is quiet. Over Christmas and New Year there was a lot of spare capacity that meant that virtually all the rate limits we have were removed or relaxed. Unfortunately the rate limit changes don't work as intelligently as they could but that's something we are working on. Looking to the future, one of the biggest issues we have, and was touched on in our cost of broadband blog is predicting the future. We have all kinds of historical data; we can look at what our customers have done per hour, per product and per protocol. We can see how many are using each protocol in each hour and for each product and how much they've uploaded and downloaded. We can trace that back in detail for a fair way now as we've been doing this for a while now. Therefore, we know certain trends and patterns; we know that certain days of the week and times of the year have specific characteristics. Monday for example is usually the busiest evening of the week with the highest number of people online, Saturday evening the least. Sunday evening tends to see more gaming than other evenings, Friday afternoon more streaming than other afternoons while school holidays bring more web and gaming traffic in the afternoons. Warm summer evenings mean people are outside more and in contrast cold winter evenings there are more inside on the PC. Microsoft patch Tuesday can cause big spikes on Tuesday evenings and Wednesday mornings and can carry on for a couple of days after, while big events on the TV, particularly the terrestrial channels (England football games on the BBC for example), cause dips in usage (you can see a visible dip in usage on the Wednesday on the graph to the left which was taken from when England played Croatia last year shown on BBC1). In planning the capacity required for our network and the day to day running we therefore need to take into account as many factors as we possibly can. We need to look at the usage trends over the past few days, weeks and months to see what's being used and when. We need to take into account the regular events that happen like patch Tuesday and also the one off events like the football games and then from there look at what's around the corner, what could be the next big bandwidth application (think iPlayer or YouTube). For 2008 specifically we've obviously just entered the iPlayer world and there are already plans from the BBC for some improvements (including higher quality streams which will no doubt increase streaming usage further). Down the line expect Project Kangaroo, which I guess at the moment the best way to think of it is iPlayer but with the BBC, ITV and Channel 4 all in one. There are also developments on the way for iTunes, the BBC have just launched on there and the number of shows available is expected to grow, plus Apple are also expected to launch movie rentals including High Definition films. Some of the video sharing sites like YouTube and DailyMotion are also planning (or already have available) streaming HD video clips too (Apple's movie trailers are also available in HD). Joost has been pretty popular in the USA but we've not seen the same levels of traffic over here, but it's another to keep an eye on especially if they get the right content. Another thing we expect to rise this year is gaming. Mario Kart Wii could be the biggest game on the Wii so far and will be playable online. There's also the latest Grand Theft Auto game on the way in April, Gran Turismo 5 at some point and lots more. But this gives us two aspects to keep an eye on. First there's the usage but second there's identifying the games for our traffic management database. Each game requires a signature in the traffic management database to identify it as gaming. Fortunately a lot of games (particularly console games) look the same so don't require any work to add them in. We post a list of known games in our forums but this will be incomplete and not listed every game in the database, simply because some games are matched against another. We have rules for PS3 games or Xbox Live that pick up most of the Playstation and Xbox games and there's no need to list each individual game. (As an aside I intend to write another blog over the next couple of weeks going into more detail about the process of adding games into the database.) We try and keep on top of games as and when they come out but it's not always possible to have every game included in the database before release date so we often need help from our customers. Same goes for other applications such as VPN or other remote access tools, we can try and get as much in as we can but sometimes we need help. As mentioned above another part of traffic management is planning how much capacity is required. We've recently updated how we work out the capacity that is required to work in a far more granular way. Previously we allocated a kilobit per second value to each account type based on three periods of the day - midnight to 8am (night), 8am to 4pm (day) and 4pm to midnight (evening) and calculate the amount of capacity based on the day and evening figures (and the custumer numbers) and the amount of extra bandwidth purchased. Now we are looking on a more hour by and protocol-by-protocol basis which, combined with the extra bandwidth gives a better handle on the forecasting. With something like iPlayer going from a fraction of 1% to approximately 5% of the total network capacity in only a matter of weeks the forecasting needs to react to changes in usage at the very least on a weekly basis. And that really best sums up the plans for 2008. We have ideas on some of the things that going to drive usage and what some of the content providers have in store. But ultimately what we are doing is keeping a very close eye on what customers are doing and what's changing. We knew iPlayer would be big, but we didn't know exactly how big, we suspect that without the Flash version it wouldn't have seen as large a take-up as it has, and certainly not as big without the promotion it's been getting. Same with iTunes movie rentals, if that takes off it could easily account for similar levels of traffic as iPlayer and so could a number of others. We shall just see; it's one of those interesting rides. Dave Tomlinson PlusNet Product Team
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