As the 802.11n standard gets closer to final ratification, Enterprises are beginning to wonder how this may impact on their Wireless LAN strategy in the coming year and beyond. For organisations that may choose to deploy 802.11n, it will have serious upgrade implications for both the infrastructure and the client side, so businesses will need to decide if it's worth the upgrade and they need to understand what kind of 802.11n technology to deploy.
What is 802.11n?
802.11n is the next standard within the 802.11 Wireless LAN family following 802.11a, 802.11b, and then 802.11g. Unlike 802.11a, b, or g, 802.11n will not be limited to either the 2.4GHz range or the 5GHz range and it is up to the specific product to implement different levels of backward compatibility.
Table of various 802.11 standards:
| Standard | Peak data throughput * | Peak signalling rate ** | Radio Frequency | Downward compatibility |
|---|---|---|---|---|
| 802.11b | 6mbps | 11mbps | 2.4GHz | |
| 802.11a | 23mbps | 54mbps | 5GHz | |
| 802.11g | 23mbps | 54mbps | 2.4GHz | 802.11b |
| 802.11n 20MHz channel | 60mbps | 124mbps | 2.4 or 5GHz | 802.11b/g, possibly 802.11a depending on implementation. |
| 802.11n 40MHz channel | 90mbps | 248mbps | 2.4*** or 5GHz | 802.11b/g, possibly 802.11a depending on implementation. |
* This is the actual data throughput that you get with real equipment under IDEAL conditions. Real world performance is lower than this if and when noise is introduced. This is also shared bandwidth among wireless clients. When 2 devices use the same Access Point, the bandwidth is typically divided in two though it's possible some clients will hog more of the bandwidth than others.
** This is the performance number that's actually quoted by marketing and on the retail packaging. It's absolutely worthless to home and enterprise consumers and is actually quite deceptive.
*** The chances of 2.4 GHz 40 MHz mode being permitted to function are next to zero in the urban or suburban environment. Since 802.11n draft 1.10, any sign of neighbour Wireless LAN activity will force 20MHz operation.
State of 802.11n draft products -- Infrastructure side:
Early draft 1.0 implementations of 802.11n made a mockery out of the standard by annihilating any neighbouring 802.11 b/g devices in range with the use of "channel-bonding" which occupied 40MHz instead of the normal 20MHz. Fortunately, the 802.11n draft 1.1 specification put a stop to that nonsense by banning dual-channel 40MHz operation if it detects the slightest amount of traffic from neighbouring Wireless LANs.
Unfortunately, early and current 802.11n draft implementations only supported single band operation in the 2.4GHz range which is a very scarce and overpopulated band compared to the 5GHz band. This is because it's expensive to create an Access Point that supports both 2.4 and 5GHz operation at the same time and simultaneous dual-band operation is required on the infrastructure side. Since the vendors had to make a choice and be backwards compatible to 802.11b/g, they completely gave up on 5GHz operation. Buffalo announced the only simultaneous dual-band 2.4/5GHz 802.11n product at Comdex 2007. Apple's latest Airport Extreme wireless router is unfortunately an either/or device that supports either 2.4 or 5GHz operation but not both at the same time since it only has a single set of radios.
On the Enterprise infrastructure side, there are currently no Enterprise-class Wireless Access Points that support 802.11n draft 1.1 or 2.0 mode. Most of the Enterprise vendors have announced the intention to eventually support 802.11n but it hasn't happened yet. IT departments should avoid purchasing any 802.11n Access Point that doesn't support simultaneous dual-band 2.4/5GHz operation.
State of 802.11n draft products -- Client side:
On the client side, simultaneous operation in the 2.4 and 5 GHz band isn't required but it needs to be able to flip between the two bands. Early draft products were unfortunately 2.4 GHz only and they should be avoided at all cost. Intel's latest draft 802.11n product (Intel 4965agn PCI-Express mini card at US$49 is also one of the cheapest client adapters available) supports 802.11 a/b/g/n operation which is ideal. Intel would likely provide decent "upgradeability" to the official 802.11n standard based on their past level of driver and firmware support for all of their older Wireless LAN products. At this stage in the draft game, it's very unlikely that Intel would commit to a design that won't be upgradeable to the official standard when it comes out.
So long as your laptop is new enough to have a PCI-Express mini slot along with at least two antennas, you'll be able to upgrade it using the Intel 4965agn adapter. Three antennas would be the preferable antenna configuration but two is the minimum. If you're ordering a new laptop, dual-band operation is an absolute must. Even having 802.11a support is very nice because almost no one uses it and if you can find a hotspot that supports 802.11a 5GHz, you're in luck because it's like the first class line with 2 people waiting while there might be 50 people in the 2.4GHz line. Enterprises should considering purchasing 802.11 a/b/g/n capability for newer laptops especially when they don't add much to the cost of the notebook. Again if it doesn't support dual-band operation, avoid it. Note that simultaneous operation isn't a requirement on the client side.
Potential negative implications on Access Point density:
In the Enterprise Wireless LAN, individual peak throughput isn't nearly as important as spectrum capacity. The use of channel-bonding and 40MHz operation would have a severe impact on spectrum capacity. The 5GHz band in the Americas normally has 8 channels available in the 5.3GHz range and 4 channels in the 5.8GHz range (additional US Federal Communications Commission (FCC) requirements for 5.8GHz operation) which means there's a potential of 12 normal 20MHz wide channels. Note that many 5GHz digital spread spectrum cordless phones use the 5.8GHz band so that can interfere with 5.8GHz 802.11 operation.
Utilizing 40MHz bonded channels would slash the number of available channels in half which would cut Access Point density in half. Since channel-bonding doesn't deliver double the performance or anything close compared to single-channel 802.11n operation, it simply isn't worth using 40MHz wide channels in the 5GHz band unless you intend to implement a low-density architecture.
Huge benefits in wireless Ethernet bridging:
For Wireless LAN bridging applications where we're concerned about maximum aggregate speeds from a single Wireless LAN bridge link, then it might be wise to use two of the 5GHz channels in 40MHz mode to maximise the throughput of that Wireless Ethernet bridge. If you're using two pairs of bridges in EtherChannel (802.3ad) configuration, then you'll get more bandwidth per channel using 20MHz mode. If you can spare four 5GHz channels, then by all means use 40MHz on both bridge links. With the potential of 802.11n based Ethernet bridges, it can begin to threaten the high-speed domain of FSO (Free Space Optics) solutions.
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