PyCon 2009 Wireless Network

By Sean Reifschneider Date October 28, 2009

Also see my related articles on networking set up for PyCon 2008 2010 , and and 2012

It's been a long time coming, for a variety of reasons, but I have gotten the statistics collected from the 2009 PyCon back in March and have pretty graphs to show. I had hoped to write this up shortly after the conference, but it took months for my router boxes to get back to me, and I didn't have local copies of those systems (with their stats) available as I did in 2008.

This year was largely successful with the exception of people with Netbooks. We did had a surprise with the hotel network infrastructure, but were able to work that out. The big news is that we had way more 802.11a users than 802.11g, and almost no 802.11b users. At one point we ran out of DHCP leases, but that was a minor issue as I had more IPs ready and just had to configure the NAT for them and turn them on in the DHCP configuration.

Lessons Learned



Leave money in the budget to deal with unanticipated issues such as having to light a dozen strands of fiber.

Public IPs was just not worth it.

Netbooks have terrible wireless cards in them.

Terrestrial wireless backhaul is good stuff.

Get wired ports out there for people to use.

Too many access points is almost enough. The PyCon attendees are a great group of people to provide networking to.

We were running mostly with public IPs given out to attendees, but we were fairly limited in the number of public IPs we could get from them.

Upstream Bandwidth

Read on for more details.

This year we had two locations, one for the main conference and a different one for the sprints. This is why the two graphs above.

We again used Business Only Broadband for the upstream link, and we had 100mbps at the main hotel and 50mbps at the Sprints hotel. In both cases the bandwidth was very much overkill. But it's better than the reverse situation.

Wireless

BoB performed very well, just as expected. We had absolutely no problems with the upstream.

The equipment last year wasn't able to give us statistics about the usage of the wireless, so I have to go back to 2007 for comparison. This year we had a peak of around 600 wireless users connected. Note the graphs are incomplete because I didn't have the statistics collection set up right away.

In 2007 we had mostly 802.11g users connected (200 out of 340), with about half that many using 802.11a and half again using the dusty old 802.11b.

This year most people by far were using 5.2GHz 802.11a, with less than half more using 802.11g and few people using 802.11b. At the sprints it was more even between the a and g users, which I am a little surprised at. I guess the sprinters aren't the technophiles that I expected...

My records indicate that we had 24 APs at the main venue. They were configured as before, with 802.11bg running at the lowest power on channels 1, 6, and 11, 802.11a running at high power but using all channels and channel duplication spread as far apart as possible.

At the sprints I had set up basically one AP per room. As I had reports of networking problems I went around and added additional APs to cover the problem areas. By this time we had switches from the main hotel over at the sprints hotel, so I was able to give out wired connections also. Each room had only one jack, so putting a second AP in place involved putting in a switch and connecting the two APs to it, so some wired ports became available as well. We ended up with 10 APs deployed for the sprints.



Someone came to me saying they were getting disconnected from the network.

I would add another AP, putting it right next to their laptop.

I would make a joke about hoping that they didn't want to have children. Their networking problem was solved.

802.11n

Networking problems at the sprints had this workflow:

We didn't use any 802.11n equipment this year, largely because of budget. The APs we have are great for our needs, being dual radio, having control over output power, and working with my existing software for pulling statistics out of the APs. And on top of this they're "cheap", between $100 and $200 each.

The Netbook Problem

I may get a couple of 802.11n APs to try out for 2010, but mostly I expect that we will be using the same gear as 2009.

Netbooks just basically did not work at the conference on wireless. And we just didn't have the gear to do wired ports. I had both a ThinkPad T61 and a Eee 901 with me. I tested the network with the Eee, and everything worked fine. But once significant numbers of users started showing up, my connection would drop around 30 seconds after it got established.

My theory is that the wireless cards that are going into $200 to $300 computers are just not that good, and they can't cope with the high levels of interference.

As I said, I had a Eee 901 with me and just could not get a reliable connection while I was there. I tried a number of different settings including locking on to a single AP, adjusting the rate, modifying the RTS, nothing really helped. Even going into the speakers ready room, which was somewhat isolated from the rest of the wireless, just didn't give a reliable connection...

Discussing this with others I heard stories of people replacing the network cards in their Netbooks with nice Intel cards and getting much improved wireless, but also getting worse battery life.

In the end I just gave up and decided that next year we'd get some wired ports available. I don't think there's anything we can do about this.

The Venue Problem: Hyatt Regency

So, if you plan to take a netbook to a big conference, you may want to consider going armed with a USB wireless dongle, particularly an 802.11a-capable one.

The Hyatt Regency had been telling us that they would just give us Ethernet handoffs in each of the wiring closets that we needed to make connections in, with those being on a VLAN dedicated to our use.

The reality when we showed up was that they refused to let us use their existing infrastructure, and instead required that we use their "dark fiber" infrastructure for connecting between the closets.

The good news is that I had some experience with doing fiber because of some recent changes to our tummy.com hosting service, so I was able to fairly quickly and inexpensively light the fiber.

It was more challenging than it should have been because their fiber infrastructure was poorly labeled, and their guy that really knew the fiber infrastructure was not available. One of the ports was wired the reverse of what it should have been, so after spending a pile of time trying to figure out why this link wasn't coming up, I had to cut apart our fiber connector so I could swap the two fibers. These were the SC ends which are designed so that they only work one way. Impossible to connect reversed, unfortunately this is exactly what I needed to do in this case.

The Venue Problem: Crowne Plaza in Rosemont

The labeling problem also resulted in their staff not being able to find one of the fiber runs we needed, which resulted in their registration system getting knocked off the network, apparently for a significant amount of time. Worse, this was apparently not the first time this had happened, and even so they hadn't corrected the labeling.

On the other hand, the Crowne Plaza went very smoothly. Their network was exactly as promised, and was labeled correctly. The only problem we had with bringing that up was fairly weird...

The run from the uplink to the main patch panel was flaky. We could connect directly into it at the radio end, but if we connected the cable running to the patch panel we would get link but no traffic.

If I put a different switch in between the cable to the patch panel, and the cable to the radio gear, it started working just fine. That took a while to figure out.

The Leases Problem

The Crowne Plaza was a joy to work with after the problems we had run into at the Hyatt Regency.

This was the other significant problem, we just ran out of DHCP leases in the public space. I had already allocated some private IPs, so when this report came in I just had to bring up another interface on the firewalls, add a NAT rule, and modify the DHCP configuration. I had hoped to bring this up before we ran out of public IPs, but I had just been occupied by other things.

An easy fix, but I was disappointed that I hadn't prevented it before it happened.

About Public IPs

The above graph shows the number of leases. Again, the graph is blank because I didn't get it set up until later in the conference.

We had, mostly at previous sprints, had a few requests for public IPs for demo severs or file shares for groups of developers, etc... I figured that plus the elimination of any NAT traversal problems for people running VoIP or other programs might make things go more smoothly.

I don't recall anyone mentioning that the public IPs were a benefit, nor do I recall more than one or two people at previous PyCons asking for public IPs or saying there were problems with the NATed IPs.

I'm not sure this was worth the effort, small as it was, because it lead to running out of leases as explained in the above section. When we've used private IPs, we've always had plenty of them available, so leases were just never an issue.

The PoE Problem

It reminds me of a previous year when someone came up to me and suggested that we drop the lease time from, I think I had it set to 24 hours or more, so that IPs would be re-used more quickly and we wouldn't run out. "Well, we have 4,000 IPs available and are only using 1,000 of them..."

Ok, this wasn't really a problem... But only about half of our APs supported Power Over Ethernet. I had gotten several switches that would do PoE, because in previous years we had some problems with APs getting disconnected from power, or worse APs getting disconnected from Ethernet but still being connected to power and broadcasting their ESSID.

Going Forward

The down side to this was that I had several reports of APs that had been disconnected from power, because they only had an Ethernet connection. Part of this was because the LEDs for the AP you couldn't really see unless you bent down and "looked it in the eye". Despite the reports, we didn't have any APs that were disconnected from power this year.

I think the biggest thing I would do in the future is to get wired ports available for people to use. I have a line item in the budget for next year to get switches for end user connections. I'd love to get some that are managed to the level of reporting the number of active links, but I think we probably want to spend the money on ports rather than management. But it would be nice to know how many people are using the wired ports. Maybe I'll use a different network for the wired ports, and just count based on the number leases we have in that network...

In Conclusion

The other thing I think I'll probably adjust for is not using public IPs. It was an interesting experiment, but ultimately I don't think it was worth it.

Shameless Plug

Using many small independent APs continues to work well for our needs. The network this year was well received, though having wired ports for attendees is necessary.

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