Broadband contention ratio explained

Broadband services are shared services. This is true whether its simple ADSL broadband, super-fast (FTTC), or ultra-fast (FTTP). It’s just how broadband works – and really, what makes it affordable. By sharing a main connection into a building, industrial estate, or a particular part of a town, city or rural area, the service provider can use less infrastructure to support more connections.

This is also why broadband speeds are always quoted as giving you “up to” a certain speed. If the shared part of the connection is being used by a lot of people at the same time, there will be congestion – which they call “contention’ in the broadband world. As a result of the congestion, the traffic will have to slow down, and you won’t get the maximum theoretical speed.

It really is just like a busy road complex. If it’s empty, you will sail through without any delays. If there’s a lot of traffic on the road, there will be hold-ups and delays.

And just like a road network, there are times that are always busy and times when it’s quiet. What broadband providers try to do is set contention ratios and make bandwidth available to maximise performance for everyone. If they do this well, most customers will get good performance most of the time.

While downstream speeds are always higher than upstream speeds – broadband is designed that way because most of the time you will be sucking down a lot more into your connection (web pages, images, videos etc), than you will be sending (often just a web address or a few emails) – there is still potential for traffic jams in both directions. The upstream road is a lot narrower, so it can get clogged up if excessive strain is placed on it by any single user or a small group of users.

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What is broadband contention ratio?

The contention ratio is the number of connections that are on a shared main broadband line. Generally speaking. the faster and more expensive your broadband connection, the lower the contention ratio will be. It might be as low as 8:1 on a high-speed FTTP connection, for example, but as high as 32:1 or even higher on a standard ADSL2+ service

Oddly though, having a higher contention ratio does not mean that you will necessarily experience slower speeds – but the chances of the service slowing down will be higher. Part of the reason you will be paying a higher price for a broadband service is that there are fewer “tails” or endpoint connections sharing the same main broadband line, and there will thus be a much smaller chance of a any traffic jams.

Contention can still happen though, even on the fastest services. As all broadband connections are shared, there is always the possibility that everyone will try to use a lot of bandwidth at the same time. The assumption (or hope) of course, is that this won’t happen – at least, not too often.

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Can the contention ratio affect my business broadband speeds?

Yes. If everyone on your shared connection tries to use a lot of bandwidth at the same, you will experience a loss in performance. It is impossible to say by how much, as it depends entirely on what kind of traffic is being used.

Video is quite bandwidth-hungry, so if other connections are running HD streaming services, or using video conferencing, that could cause contention and slow things down. Downloading and uploading or large files or backups could also affect speeds. Using cloud services can also take up a lot of bandwidth and of course, more people are now working at home and connecting into the network remotely

All this can put added strain on bandwidth – both for businesses and for home users – and result in contention issues.

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How does contention ratio affect my broadband?

When contention occurs, the Internet Protocol (IP) – the set of rules that governs how devices connect over the Internet, starts to exert control on the traffic flow of traffic in an effort regulate the speeds for everyone. It basically does this by slicing up streams of traffic into smaller packets and allowing then through in turn. Put simply, it sets up a set of traffic lights at the junction to the main connection to ensue that all traffic can get through and everyone is treated fairly.

This is absolutely fine as long as one connection in particular is not “hogging” the bandwidth i.e., trying to receive or send so much data that it slows broadband services down for everyone else. Internet Services Providers (ISPs) are monitoring traffic all the time, so they can see when this is happening and act if they feel it’s required. The best thing though would be to persuade that user to upgrade to a faster service i.e., one with a lower contention ratio.

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Can I influence the contention ratio?

You can’t change the contention ratio on your broadband – but you can choose to upgrade to a faster service – in other words, one that has a lower contention ratio. But that will, of course, cost more.

If you can’t afford to do that or don’t want to for whatever reason, the only other option is to try and reduce your own bandwidth. In areas where there is low bandwidth (where the connection point is a long way from the green junction box), users will sometimes experience jittery performance on their broadband line when using video conferencing services like Zoom or Teams.

This is because video requires as much bandwidth upstream as it does downstream to run effectively. If there is contention on the line, it won’t work properly. Just switching off the video and using voice only will usually help.

Ultimately, if you want guaranteed downstream and upstream bandwidth, you need to subscribe to a dedicated or leased line service. This is often the option a business will take if its connection is of critical importance.

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Which providers offer the best contention ratio?

It’s not really possible to say which providers offer the best contention ratios as the performance you get will depend on many other factors. However, they generally don’t advertise their contention ratios up-front, so it is worth making a point of asking them the question – and what measures the take to monitor and manage any contention issues. The level of service you can expect should be detailed in your service level agreement (SLA).

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