In early October 2011 we received a call from a local primary school. They were ‘having trouble with their wireless system’ and someone suggested they call us.
On our first visits we were able to see first hand some of the challenges faced by the school. We saw how these challenges seriously affected teaching and learning. Use of ICT in the school was very unreliable and the major investment they had recently made in laptops was causing concerns.
As an example – a very well specified laptop was trying to access Espresso – which was running on a server within the school. After five minutes of trying to start with Espresso the link dropped. Apparently, that was a typical situation.
As I was saying
At the TeachMeet in Lutterworth earlier in the year, I gave a presentation on the ‘ISO Seven Layer Stack’ and where to troubleshoot. This was exactly the procedure we took.
The performance of the wireless linked devices was so poor that simple tests were failing to give any clues. Walking through the school helped.
The network was installed during the NGfL supply years – where every school was given a broadband access. In this schools’ case they were supplied with an internet connection through a Cisco Router which is connected to a Cisco VLAN switch.
The switch is set up using a facility generally known as ‘router on a stick’. This means that the Cisco switch was configured so some ports were linked to the office network (on one IP numbering scheme), some ports were linked to the curriculum network (on another numbering scheme).
The VLAN switch is then linked to the router – this allows the office to get to the internet and the curriculum to get to the internet, but blocks the office and curriculum users from accessing each other. But The VLAN switch had enough capacity to handle 4 or 5 PCs using the internet. Now, the school has a 2008 server, a networked laser copier, the Espresso system and nearly 70 PCs in total. All connected to the VLAN switch.
It gets better
On further investigation the 3 domestic grade wireless access points (yes three) were connected via 4 port switches to the VLAN switch. Like so -
These were not actually fed directly to the VLAN switch, but endured the following route -
That’s a Cisco Fast Hub 100. In its day it was wonderful. There is a place for these – but not here.
Catalyst 2950 Backplane – 4.8Gbps (a measure of how much data can be pushed between the ports of the switches)
Netgear 5 port switch backplane – 1Gbps
Cisco FastHub 100 Series Backplane – 100Mbps (it’s a hub). This was a very, very serious choke point.
A simple sketch can hopefully give a few ideas -
And the icing on the cake?
This came when we discovered that the 3 domestic grade wireless access points were all set to different SSIDs. This meant that if a laptop was moved out of range of one point you had to try to manually connect it to a different SSID. Later, we also discovered that the Wireless Access Points had been left with the default admin log-ins and passwords – handy points for drive by hacking or free internet for anyone else nearby.
Why is the internet so unreliable on our laptops?
The numbers indicate the paths taken as data is requested from the internet.
Pupil goes on the internet – this starts the following
- The laptop links to the domestic grade (it’s okay for home or very small office) wireless access point
- Wireless access point links to domestic grade (see above) switch
- Domestic switch links to hub (now it all slows down)
- Hub sends DNS info. request to server (via domestic grade switch)
- Server receives DNS request (along with shared file access requests etc.)
- Server provides DNS info for internet provider back via domestic grade switch
- DNS info sent back to hub
- DNS info and web request data sent from hub to VLAN switch
- DNS info and web request data sent from VLAN switch to router
- Request eventually sent to the internet
- Internet supplied data returned to router
- Internet supplied data returned to VLAN switch
- Internet supplied data sent to hub
- Internet supplied data sent to domestic grade switch
- Internet supplied data sent to domestic grade wireless access point
- Internet supplied data sent to laptop
- (Not shown) Pupil has left the building
This circuitry looks complex. It’s only part of the story. Ethernet uses a traffic management system called CSMA/CD. This doesn’t actually help things.
The teeth are fine but the gums have to come out
In an ideal world with infinite time and budget to sort this we could have a wonderful time. We discovered the FastHub 100 series on the Monday of half term. Ideally we would network points throughout the school straight away and build from there. You may have seen some information related to cost savings in schools in the press recently.
‘Do what you can with what you have – where you are and now’ – Theodore Roosevelt
We had to add a few bits to make a huge difference.
(Click here for this webpage as a pdf)