In earlier posts, The Big News in WLANs: 802.11n and Is Pre-Standard 802.11n a Safe Bet?, I’ve described the technology and standards issues surroundingthe new 802.11n wireless LAN radio interface. Make no mistake, this will be a major boon for mobile unified communications, but let’s start with a quick review of the facts. The basic story is th at this new radio link can potentially deliver a five-fold increase in transmission capacity, and the standards are such that it is now safe to take the plunge.

The first thing to recognize is that the raw transmission rate that’s advertised is only one factor in the real network throughput you will experience. The maximum data rates for 802.11n are 289 Mbps using the same 20 MHz channels we have with 802.11a and g, or 600 Mbps with a 40 MHz double-channel. Those data rates assume you are using a 4- transmit chain MIMO system, and none of our initial products have that capability; the current maximum is 3-transmit chains. It’s important that you understand factors like that when shopping for products.

Of course, the effective throughput of a WLAN is about half the raw transmission rate, and that ratio should be about the same with 802.11n. Finally, while you can intermix 802.11n devices with legacy 802.11a/b/g devices on the same channel, the extra overhead required greatly reduces the effective throughput for the end devices.

That’s the basic stuff. However, moving to 802.11n will involve more than just an equipment swap. There is a whole range of issues you will have to think through.

1. Equipment Upgrades: The first requirement is that you will have to upgrade all of your WLAN access points and client devices; this is a whole new radio system, so 802.11n involves a hardware, not a software, upgrade. Given the importance of 802.11n, access point vendors are jumping on the bandwagon, but you will also need 802.11n compatible clients. The side benefit of upgrading just your access points is you will get some improvement in legacy 802.11a/b/g networks as a result, but for the full impact, you have to do 802.11n at both ends.
   
2. Network Design: The 802.11n MIMO transmission results in a different coverage pattern that what we see intraditional access points. Legacy 802.11a/b/g access points produce a coverage pattern that is characteristically round, though it can be misshapen by thick walls or other obstructions. The use of MIMO-impacted 802.11n results in a coverage pattern with a completely different shape based on the environment in which it is used. That means a new site survey, either manual or computer-assisted, will also be required to optimally locate your n-access points.
   
3. Wireless Intrusion Detection System Upgrades: If you are using Wireless Intrusion Detection/Prevention Systems (WIDS/WIPS) to detect unauthorized WLANs in your facility, thosesystemsmust be upgraded to detect 802.11n transmissions. Your users can buy 802.11n access points at Best Buy toady, and your existing WIDS or WIPS will not be able to see those networks. This is something that security conscious firms should jump on pronto.
   
4. Wired Network Changes: The 802.11n radio link can now support data rates above 100 Mbps, so a 100 Mbps connection to the wired network will no longer be adequate. All 802.11n access points will all require 1 Gbps wired network connections as a minimum.
   
5. Power over Ethernet (PoE): The other big change on the wired infrastructure will be power, in particular, Power over Ethernet. We typically install access points on the ceiling to improve the propagation pattern, and use Power over Ethernet (IEEE 802.3af) to power them. The first generation 802.11n access points required more than the nominal 15.4 W provided with 802.3af. That meant we either had to use a vendor-proprietary PoE solutionor start installing AC power receptacles in the ceiling. Siemens recently announcedthe first 802.11n AP that could operate on standard 802.3af PoE, though you should look carefully at any other capabilities you might be giving up to use standard PoE.

Unfortunately, that’s just the easy stuff. The real decisions will center on how you plan and manage your wireless LAN network going forward. We noted that 802.11n can operate in either the 2.4 GHz or 5 GHz bands, so which will you use? The knee-jerk response from many consultants has been to leave your existing b/g devices in the increasingly congested 2.4 GHz band, and use the 5 GHz band with its 23 available 20 MHz channels for n-devices.

Unfortunately, many customers were looking at deploying WLAN voice services in the 5 GHz band using 802.11a handsets; we don’t expect 802.11n-capable voice handsets for a few years at least. Should we change our voice deployment plan to use 2.4 GHz for voice and migrate our legacy data devices to 802.11n in the 5 GHz band, or should we divide our 5 GHz channels between 802.11a voice devices and high-capacity 802.11n devices?

Conclusion

Mobility is one of the key developments in unified communications, and the wireless LAN is one of the primary vehicles for providing it. The introduction of 802.11n will increase the range of capabilities we can extend to that mobile user, but only if we do it right.