Zit Seng's Blog

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How Much Network Bandwidth For Off-Site Event

I was recently asked to oversee the Wi-Fi networking requirements of an off-site event. Is the Wi-Fi coverage adequate? Is the network bandwidth sufficient? Well, you know what, it’s never enough. Not when you have to pay. Unless, of course, you have limitless budget, in which case, money is not an issue, it’s like you don’t have to pay.

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So, as you can imagine, I provided some feedback. Feedback like, you know, that the subscribed bandwidth was perhaps not really great. Not great at all, in fact. I tried to be polite. When polite suggestions and political correctness did not work, it was time to be blunt.

Network bandwidth, as you know, can be quite elastic. Or compressible. Who’s to say that 10 Mbps cannot work for 5 users? Why not 25 users? Or 50 users? Sure, it will work. It’s simply a test of your patience. If something barely works, does it count as working or not working? If it is tolerable for a webpage to timeout several times before finally loading completely 5 minutes later, then of course, 10 Mbps can be quite plentiful for a big chunk of users.

It’s difficult to appreciate the intricacies of network engineering. I was motivated to write this post because, well, an issue arose about sizing network bandwidth requirements.

You see, some people like to look at averages. There are times the network is more heavily loaded, and at other times it is lesser used. Hence, if you look at average bandwidth consumption, it seems like you don’t need a whole lot of bandwidth.

In real life, averages don’t work. Let’s say you are running a conference. There are times when everyone wants to use the network at the same time. For example, at the start of a keynote speech, there may be lots of photo-taking, followed by uploads to social media. Network usage may settle down a little once the talk gets underway. Unless of course it’s quite boring, in which case people may go back to their smartphones. At break times, you may find the network usage climbs up again.

There are peaks, and there are troughs. The peaks can be very very high. At those instances, don’t you need enough bandwidth to cater to usage demand? If you don’t, you will get complaints about network slowness. Lots and lots of complaints, because many people are using the network. No one bothers about the troughs. The few people using the network at the lull times are happy, but surely their compliments, if any, will be completely overshadowed by complaints during the peaks. People complain louder than they compliment, if they compliment at all.

The concept of averages does not work. Unlike a typical stable office environment, network usage at special events spike a lot.

My bandwidth sizing formula is like this, for an off-site sort of event, something like a conference cum exhibition at a convention centre.

First, let’s establish some basic parameters.

  • An average webpage is about 1.2 MB big. Of course, some are smaller, while others are bigger. This 1.2 MB figure comes from a 2013 report. For the record, the Straits Times homepage today weighs in at over 7 MB.
  • For satisfactory web experience, users expect webpages take no more than four seconds to load. This is reported in a 2015 article, though the figure appears to be partly based on data from an Akamai survey in 2006. But that’s alright, we’ll just go with this figure.
  • Generally, users stay no more than 15 seconds on a webpage, according to this TIME article in 2014. That means to say, users will be loading a new page every 15 seconds.

Let’s digest these numbers a little bit. To load 1.2 MB content from the Internet within four seconds, you’d need a network speed of 2.4 Mbps. 15 seconds later, you’d want to load another webpage. In the meantime, 3.75 other users (15/4) can use your idle time to load other webpages. That means to say, the 2.4 Mbps network bandwidth can be shared by 4.75 users (1 + 3.75). In other words, effectively, each user needs about 0.51 Mbps of bandwidth.

Now, consider an event that has 1000 users. Not everyone will use the network at the same time, even at the peak of peaks in network demand. What percentage of those 1000 users would be actively engaged on the network at the same time? This will certainly vary somewhat, depending on the type of event the kind of industry it involves. At Apple’s WWDC, during the keynote speech, particularly as Tim Cooks or some other Apple executive reveals some exciting news, perhaps over 90% of the people will be excitedly tweeting and posting updates in real time. At a more academic oriented conference, but something that still involves IT and hence filled with tech-savvy individuals, perhaps that percentage may only be 70% at the peak.

I don’t have a simple answer on how to arrive at that percentage figure. You’ll need to figure that out based on your knowledge of each event and the kind of people who go there.

Considering that we now live in a very technology-infused world, where smartphones are so prevalent, and many people are always connected on the Internet, this figure will never be small. However, another twist to this is that some users may already have their 3G or 4G connectivity, and therefore don’t depend on Wi-Fi provided by the event. On the other hand, some users who already have 3G/4G connectivity may still want to leech on free Wi-Fi, because there’s a quota on their 3G/4G data usage. I think, basically, this comes down to your understanding of your own event and the people who go to it.

Moving on, let’s pick a figure of 50% for purpose of this example. That means out of 1000 people, 500 will possibly be actively engaged on the network simultaneously. Therefore, at 0.51 Mbps per user, we’re looking at a peak network demand of 255 Mbps.

Logic and math got us this number. It may sound like a lot, particularly to the person controlling budget, but it is not a number plucked out of thin air. Can you make do with less? Of course you can, at the expense of user satisfaction of course. I can appreciate that 255 Mbps could cost a bomb at a hotel or from a business service provider, but to put things in perspective, compare this with how you get 500 Mbps or 1 Gbps fibre broadband you get at home, and which may not even be enough for some people? (That’s right, we also have 2 Gbps fibre broadband services in Singapore!)

To recap, this is the essential bits you need to work out:

  1. You need 0.51 Mbps per user.
  2. Know how many people you will need to serve (i.e. total users).
  3. Determine the percentage of users, at the peak of peaks, who will want to actively use your network at the same time.
  4. From there, you just work out the math, and arrive at the total bandwidth you need.

This is what I’d refer to as minimally acceptable experience.

I can just picture your financial controller protesting at the cost of whatever you’ll be proposing. You’ll want to make them understand what cutting costs will mean. Is it alright to have disgruntled users at the peak of peaks, at the biggest highlight of the event? You want to protect yourself, in case you get blamed for signing-off or endorsing a provisioning that is inadequate for the needs.

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