How to... migrate between 802.11 variants

Wireless networking, particularly the IEEE 802.11b standard, is now a mass-market concept and so more and more organisations are adopting it in their corporate networks. Unfortunately, it has many of the same problems as the early versions of Ethernet – it’s a shared-media concept and it’s slow (that is, a number of computers share a single 11Mbit/s link). How, then, do you make the switch from 802.11b to one of its faster siblings?

The choice of where to go is fairly simple, as there are only two options – 802.11a (which we’ll call “a”) and 802.11g (“g”). Both run at 54Mbit/s, but there are two key differences. First, “a” runs on a faster carrier wave than (and uses different modulation techniques from) “g”. So, although the two are the same speed today, “a” has the potential to go faster in the future. Second, because “g” is really just a souped-up version of “b”, the two are interoperable – “a” is out on its own and won’t work with either “g” or “b”.

Despite the existence of two apparent tangents in the way the technology is developing, the interoperability issue needn’t be a great hardship. In the mobile phone market, where there are three GSM standards (900MHz and 1800MHz in Europe, and 1900MHz in the USA) some of the phone manufacturers produced phones that could work with two, sometimes all three variants. In the wireless LAN market, the likes of Cisco and NetGear have started to produce dual-frequency access points than can talk to the 802.11a and 802.11b/g at the same time.

Access points
Step one in the update process is to upgrade the access points – the devices that are bolted to the wall/ceiling, which are cabled into the corporate LAN and which the client PCs talk to over the airwaves. It makes sense to do some analysis on the loading of the various access points, because you often find that some areas are very busy (so it makes sense to move to 54Mbit/s) and some are perfectly fine with their existing 11Mbit/s rate. Because there are two possible migration paths (802.11b/802.11g, both at 2.4Gbit/s, or 802.11b/802.11a, on a more expensive dual-frequency basis) you’ll want to consider the cost versus scaleability. Given 802.11a’s likely expansion beyond 54Mbit/s (something 802.11g is unlikely to do) you should be asking yourself whether you’re likely to want to go further and thus whether the extra cost will be worthwhile.

Shifting things around
You’ll probably have learned something about your building since you installed the first wireless units – namely where the signal is lousy and where it’s good. All wireless LAN technologies run at a range of speeds (11Mbit/s and 54Mbit/s are really just the maxima for the various alternatives). By design the data rate degrades in favour of error-correction as signal strength drops, due to distance between endpoints or intervening bits of building. You should therefore take the opportunity to either move the access points or perhaps add external antennas if a highly-populated area is seeing sub-optimal throughput.

If your existing access points aren’t upgradeable, and you therefore have to replace them completely with faster ones, you might consider devices that use Power Over Ethernet (PoE) instead of powering them from the mains – particularly if you’re planning to re-site some of them to get a better signal. PoE is the difference between employing one contractor (a data guy) or two (a data guy and an electrician) and although there’s a slight increase in cost at the cabled LAN, PoE quickly pays for itself.

Peripheral technologies
When you’re deciding the brand of equipment to buy, you’ll want to think about the peripheral technologies that have appeared in the wireless market – not least standards for authenticating with existing LANs and for encrypting the wireless signals. Actually, when we say “standards” some of them aren’t yet. So if you’re happy that WEP (Wired Equivalent Privacy, the security standard supported by all wireless hardware we’ve come across) is sufficient then you have a wide choice of vendors. If, on the other hand, you think there’s more to life than WEP, you may choose to go down a proprietary path such as Cisco EAP/LEAP – security will be better than WEP, but you’ll be restricting your choice of equipment vendor.

Data cards
Once you’ve upgraded the access points, you’ll probably need to replace the cards in your desktops. If you’ve chosen a dual-speed network, this is a simple migration process – you upgrade the ones who need the extra speed first, and the rest later – if at all. Why upgrade something that doesn’t need it? Changing the data cards is no different from when you migrated your 10Mbit/s Ethernet to 100Mbit/s (remember that?) – just pull out the old one, stuff in the new one, install the driver and reboot.

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