Wifi: not as easy as you might think

Why is managing wifi on a large scale so tricky? Matthew Seymour explains.

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Netflix would need more than 23 days to buffer
an episode of Game of Thrones (1)

For those who remember a time before wifi, when internet access was via a slow modem and viewing videos an impossible dream, it often seems amazing we can move so much data, so quickly, without wires.

Wifi is now everywhere, almost... It's such an ubiquitous technology that we just expect it to be there, we rely on it and make the mistake of thinking it's an easy thing to implement.

The impression of simplicity is understandable because on a small scale, wifi is pretty easy. Scaling it up to a large building and campus is a different story.

There’s always a place to escape from wifi (2)

To understand why wifi gets tricky for big networks it's helpful to know a little bit about how it works and one crucial way in which it's very different to a modern wired network. So here's a tiny bit of history.

Most computer networks are built with Ethernet. It was designed in the early 70s and has seen a lot of development over the years. In its early days all computers on an Ethernet segment shared the wire with everything transmitted on the network visible to all machines.

Because it was a shared wire, only one computer could talk at once and part of what made Ethernet so successful was the simplicity of the system for handling this. If two computers talked at the same time, both detected the resulting collision on the wire almost immediately. They'd both stop, then wait a random amount of time before trying again and hoping for the best. This is really effective, up to a point.

Network switches - loved by network technicians and kittens alike (3)

As you might imagine, as you increase the amount of data traffic you can reach a point where collisions become so frequent that all the machines spend most of their time waiting to try again. A previously fast Ethernet network could be brought to its knees by excessive collisions caused by too many computers, too much traffic or even a faulty computer belching out rubbish onto the wire.

Fast forward a few years and we no longer use a shared wire, each computer connects to a network switch capable of two-way communication and collisions are (or at least should be) a thing of the past.

But what has this got to do with wifi?

If I tell you that wifi uses a shared medium (the air) and that only one station can talk at a time… does that sound familiar? Because we haven't yet found a way to provide a separate universe for each wifi user to occupy, this time there's no option but to share the air.

How different wifi devices use the network affects this shared air time. Older devices that connect at a slower speed therefore take up more air time. They talk more slowly, and while they’re doing so nobody else can get a word in. But even the latest, super fast Macbook with AC wireless will drop to a slow connection speed if the signal level isn't so good, or there's a lot of interference. What people do is even more significant: a single access point might support 150 clients happily if they're just doing email and a bit of web browsing; bursty traffic works well on a shared medium. The same setup might only support two clients streaming Netflix, which requires a reliable high speed connection.

Wifi design for Ainsty Court, Halifax College

Looking at the building in 3D shows that we don't have
enough channels to avoid overlap

Just as you begin to see how complex the picture is, there's a whole other challenge presented by the shared medium: wifi works in three dimensions.

Imagine our wifi network is a group of people sitting around a table. We know only one can speak at a time without words colliding into garbled nonsense that nobody understands, but it works because everyone's polite.

Now another meeting has started up next door. Because both groups can hear each other the number of people who can cause a collision by talking at the same time is increased.

Then another meeting kicks off in a room above. Because all three groups can hear each other, collisions become even more likely but worse still some of the people upstairs can't hear some of the people downstairs and vice-versa so collisions become almost guaranteed.

Wifi segments the network by using different channels so our three meetings could all take place on separate, non-interfering channels. But it's rare to have enough channels to go round, so for wifi to cover a whole building there's going to be some channel re-use going on across different access points between floors and they'll be in range of each other. This is known as channel contention.

Not only is wifi design challenging, it's also an iterative process because nothing stays the same. Not that long ago most people had one wifi device (laptop) now it's common to have a smartphone, laptop, tablet, console… and maybe throw a desktop into the mix too.

The way people use the network has changed dramatically too. More of us stream audio and video to our devices, placing a much greater demand on that shared air time.

As a result we're seeing some areas where a network design that worked really well for a few years starts to struggle as more is demanded from it. Because of the channel contention issue, just installing more wireless access points doesn't work, and often makes the problem worse.

IT Services are working hard and investing a lot of money in wifi but essentially all this boils down to: getting wifi right is hard and even when you get it right, it won't be right for long.

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Image credits:

1. By Ralf Kühne - used under a Creative Commons license
2. By Dushan Hanuska - used under a Creative Commons license
3. By Michael Himbeault - used under a Creative Commons license

How do you solve a problem like the start of term?

Jamie Clark, one of our IT Support Specialists, explains how we made the start of term a more pleasant experience - for students, and for our staff.

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Jamie, in live action mode
Photo by John Houlihan (johnhoulihan.com)

The start of the autumn term is the busiest time of year for the IT Support Office. Last year we were
swamped with new students keen to get their laptops, tablets and phones connected to the university network. We literally had queues out the door for much of the first week and people were having to wait a long time to be seen. Overall, at the start of the academic year 2013/14, we received 1000 more queries than we had in the same period of the previous year, putting the IT Support Office under a great deal of pressure.

We understand that arriving on campus can be a stressful time for new students and we didn't want to make the same mistakes again, which is why in March we formed a Start of Term working group. We wanted to identify the problems from last year and make arrangements to reduce them as much as possible.

One thing working in our favour was that this time postgraduate and undergraduate students would be arriving on separate weekends, unlike last year, when everybody arrived over the same weekend. But we also identified several other areas where we could improve...

Configuring devices for the network

Last year the XpressConnect network setup tool struggled to cope with the amount of users configuring their devices for the university network, resulting in more students needing to visit the IT Support Office to get connected.

This year, thanks to the brilliant work of the Networking team, the XpressConnect setup tool was available off campus, meaning that for the first time new students could configure their devices for eduroam prior to arriving at university. This helped to lessen the load on arrivals weekend and also meant that new students could have one less thing to worry about on move-in day!

IT information for new students

Last year we provided information about IT Services on the University's New students - welcome! page and our own Information for New Users page. IT User Guides were distributed to new students via their departments, with extra copies available at the Library, IT Support Office and Freshers Fair.

This year we wanted to keep those routes, but go one step further. In the first week of September new students were sent an email including details on how to get connected to the university network, where to get IT help and security advice. Further information was made available on our website and linked to in the email.

Completed wireless roll-out by start of term

Last year we had half of all student accommodation covered by the wireless network and we operating a Remote Access Point (RAP) loan scheme to cover areas with no access to wifi.

Fast-forward to this year and the wireless network covers 100% of on campus accommodation, and as such we have retired the RAP loan scheme (relieving both the IT Support Office and the Networking team of an unnecessary administrative burden). We have however kept a stock of Remote Access Points to allow us to quickly deal with wireless issues and black spots as they are reported to us.

Opened for both arrivals weekends on both campuses

Last year the IT Support Office opened for the arrivals weekend to help new students get connected to the network. Unfortunately, we struggled to cope with demand and had queues out the door consistently throughout the first week.

This year for the first time ever we provided support on the postgraduate arrivals weekend as well as the undergraduate arrivals weekend. We set up IT Help Points in the Library foyer and the Ron Cooke Hub on both these weekends - we announced these in the emails sent to new students, and promoted them via colleges and on social media. This was also the first time we’d provided support at Heslington East. We wanted to ensure that residents on both campuses had equal access to help when they first arrived. We had twice the number of staff available on the arrivals weekend as last year too, and overall we found that new students didn't have to wait long to get help.

Assistance for Chinese students

Last year one of the frequent challenges we had was understanding error messages written in other languages (some errors are difficult enough to decipher when they're written in English!) After English, Chinese is by far the most common language we see on devices brought to the IT Support Office.

This year we had help from former student Irene Chen Shen, who worked with us for two weeks across the start of term and was hired to help translate on-screen messages from Chinese to English. However, having worked in IT Support in China during her undergraduate degree, Irene was also able to assist with other walk-in queries and gave us a greatly appreciated extra pair of hands during the busy periods.

Feedback

Hopefully the measures that we put in place made things as easy as possible for all the new students to get up and running upon arrival. We conducted a survey amongst the new students last month and the feedback we received has been largely positive. For example, 88% of respondents said that the email we sent out was useful, and nearly half said they successfully set up their network connection prior to arriving on campus. Moreover, satisfaction sampling for the first two weeks of term showed 98% of customers were happy with how their query was handled.

We also asked the IT staff who worked on the Help Points and in the IT Support Office for their thoughts, and overall the feeling was that things were much less hectic than they had been in previous years. The number of enquiries received during the start of term period was down by 1000 compared to last year, meaning that the numbers returned to the levels seen in 2012. This is especially encouraging when you consider that the wireless network was supporting more than 13,000 concurrent connections this October - more than twice the number seen 12 months earlier.

We're already planning for the start of the next academic year. Whilst we've made some significant steps forward this time around, we don’t want to rest on our laurels. If you've got any feedback for us on our start of term service, you can email us at itsupport@york.ac.uk or fill out our anonymous feedback form.