Monday, 23 December 2013

I don't usually do telephone vectors

A very busy day, and being one of only three staff who made it in I was landed with the scheduled jobs this morning. Now let me just say that all our voice and telephone specialists were off and the instructions and documentation they left consisted of the following sentenance (and nothing else): 'Change the opening hours on table 5 and 7 for the Students' Union box office and welcome desk'.

Well that's easy, the box office is closed...

However, when removing all the opening times from the service-hours-table and placing a test call you get a message saying your call will be answered shortly (then nothing).


Okay, no problem, let's look at the call routing...

Ahh, it looks at a holiday table. Yay! So... to get to the message saying the box office is closed, the closure dates need to be in the holiday table. No problem. So I will change the closure dates to reflect the days it is closed.

Test call... perfect, "The box office is now closed, please call back..." etc...etc

[A little later...]

Oh S**t

It seems, though, that some bright spark has decided to use the SAME HOLIDAY TABLE FOR EVERY VECTOR. That means changing the holiday table for one number, in this case the box office, also changes it for the University switchboard, the helpdesk, student services, registration, the welcome desk, and on and on...

So thanks to me large parts the University didn't receive any calls this morning (when, in the most part, it should be open until 6pm Christmas Eve).

Now I have created seperate holiday tables for different departments and phone lines so one can be closed while another is still open.

I'm not sure how it was supposed to work (no documentation). Do they usually keep people on hold until they realise nobody is going to answer the call on days when they are closed? In my opinion this is not good service and, fingers crossed, people ringing in should now get the correct messages for the correct services at the correct times.

Probably best if I stay off the voice system now until the University opens in the new year.

Thursday, 12 December 2013

Transmit Power Control - Wireless tips (No. 1)

You may have seen on your enterprise access points that the power level can be moved up and down. You may also see, in most cases, that the power levels are numbered 1-7 or 1-8. So what do these numbers mean?

If you are using a controller-based solution, you will see something like the above screenshot in your access point settings. If you don't use a controller then these settings should be on your interfaces of your AP. At first glance you might take a look at that and go "hang on, is 1 the highest or is 7 the highest"?

The table below shows the meanings of the power level on our access points. The reason they are numbered like this is because you can have different maximum power levels in different countries, and setting the country code determines what it is, rather than vendor having to write a different config page for each country.

The dBm and mW conversions are much easier to work out if you remember the 3's and 10's rule. This rule simply states that:
  • Adding 3dBm doubles the power in mW
  • Removing 3dBm halves the power in mW
  • Adding 10dBm adds ten times the power in mW
  • Removing 10dBm removes ten times the power in mW
So you can see now, looking at the table, that as the power level drops one 'level' the transmit power goes down 3dBm and the mW of power is reduced by half.

As another example, if you were to reduce the power level from 20dBm to 10dBm (so you have removed 10dBm), you would have gone down to one-tenth the power in mW, 100mW to 10mW. This rule is especially handy when working out antenna gain.

So why would you want to reduce power?

Where do I start? There are a whole host of reasons, which mainly involve interference. Say you've got your AP on 'full whack' for best coverage and you're leaking onto the floors below in a shared building or into a neighbor's building. Firstly, that's not good etiquette, but say they have their own wireless network, and they have a protection mechanism that will send deauth packets to rogue AP's. Now they're going to kick all your users off your AP.

Now, if you have more than one AP. Say, for example, you are having a conference of 400 people. You're probably going to need more than the 3 x 2.4GHz channels you would normally deploy but the access points are all in the same room, so you're going to want to reduce the power to prevent the AP's interfering with each other.

My third example (I could go on) is, say you have an access point in a lecture theatre turned up too high, somebody who can authenticate with your network walks past outside. They are not using wireless, but have their device switched on. It automatically associates and now every device in the lecture theatre has to share airtime. Worse still, say the device connects using 802.11b. The protection mechanisms will be switched on and you have lost 50% of throughput (Source).

I hope this has given some idea about power settings on wireless access points.

Monday, 9 December 2013

Catch up

Well it's been 3 months since my last post and, inspired by my friend's posts about his days working in school, I thought it was about time I put something on the blog.

It's been a busy few months and one of the reasons is I have sat and passed my CWNA. I am now a certified wireless administrator, and as a result it seems I have a lot more responsibility at work... but not more pay sadly.

We also have a number of new buildings coming online at the same time and the usual departments moving over Christmas (and expecting the magical elves to come in when the University is closed and set up their machines, phones, faxes and so on to be ready for the day they return to work). As a result a few of us have been working weekends to get all the equipment set up and ready, but even then some of the timescales are ridiculous. Not sure how we are supposed to set stuff up when the sites are locked for Christmas (?).

Wireless access points going in the Graduate School

Over 30 switches going in 3 cabinets in the Grad School

75 IP phones to be deployed

As well as the Graduate School, that is due to be completed 6th January, we also have a training centre that should have been handed over already but is still not finished. We have two cabs in there we are waiting to be cleaned before installing a further 19 wireless access points, almost as many switches and media gateways.

We are upgrading our main student study building to gigabit port switches and will soon also be trialling 802.11ac in there. We have been reducing the number of patched ports and saving money on the amount of kit required and the power that is used. This has involved some early morning work to avoid disruption as best as we can (this is a 24 hours a day, 365 days a year open building).

The Student Union has just had a £20million refurbishment that involved installing two new data cabinets and wireless throughout. After numerous problems with contractors we may nearly be there on completing the install for this one.

That almost brings us up to date, with the exception of all the normal day to day faults and jobs going on. However, we had an 'interesting' day last week. When the Union's decided to call a strike so we were short of staff the students, as a sign of solidarity, decided to occupy one of the main buildings on campus, forcing all staff to relocate and causing us to urgently network empty buildings and providing phone services, laptops, PC's and wireless.

I was also informed that the project to install wireless 'everywhere' by summer 2015 was actually expected, by some of our department heads, to be completed by the start of the next academic year. September 2014. It will probably involve deploying around 2000 more access points, installing at least another 2 controllers and somehow finding the time to survey every room and space on campus over the next few months.

Well, at least they're keeping us busy. I wouldn't want to be bored.

Forgive me if, over the next term, I don't post as often as I would like. For more frequent updates I can be found on Twitter.