This article is the second of two that describe the 802.11n wireless standard and the issues you must consider before deploying the new technology.
Even though final acceptance of the IEEE 802.11n standard is more than a year away, wireless network and laptop vendors have announced -- and have begun shipping -- equipment based on the draft specification. Further, the Wi-Fi Alliance plans to certify interoperability among products based on the draft during the first half of 2007. The hope is that any differences between the current draft and the final standard can be addressed via software upgrade without requiring a hardware change.
Before jumping into a deployment of pre-standard equipment, you must understand the risks involved. Chances are good that no hardware change will be required, but if it is, you could end up replacing everything you've bought. If you need to replace your existing network or build a new one and do not want to invest in soon-to-be-outmoded 802.11g equipment, try to wait until after the Wi-Fi Alliance completes its interoperability tests. At that time, you will be able to choose among a selection of manufacturers' equipment that -- though it may not match the final standard -- will at least interoperate.
IEEE 802.11n's throughput increase will affect your entire network, not just the wireless portion. A 100 MB Ethernet was sufficient to carry traffic from 802.11g access points (APs), but 802.11n will require a gigabit connection. The need to upgrade to handle the higher data rate will ripple throughout your entire network.
Most current wireless networks consist of "thin" APs, with most of the intelligence centralized in a switch. All data traffic from all of the APs travels to a central wireless switch. The switch offloads from the APs the processing required to authenticate users, encrypt and decrypt data, and coordinate roaming among APs.
Trapeze Networks and Colubris Networks have recognized that a successful archit
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ecture for 802.11n networks will require intelligence and processing power in the AP. Both have announced plans for products to deal with the data rates that 802.11n will bring.
"It only takes some simple math to show that a first-generation switch with 1 GB/s interfaces simply cannot function in an 802.11n world," said Carl Blume, director of marketing at Colubris. "A switch currently supporting 50 access points with 20 Mb/s throughput will only be able to support 10 access points at the 100 Mb/s or more of throughput offered by 802.11n."
Colubris centralizes wireless management in a controller, but data travels from APs into the network infrastructure without passing through the controller or through a wireless switch. APs negotiate authentication, interfacing directly with RADIUS servers. Encryption and decryption are also handled in the AP, which communicates each user's authentication and QoS parameters and encryption keys to the controller. The controller then passes these parameters to physically adjacent APs to eliminate the need to re-authenticate when the user roams into the territory of an adjacent AP.
Co-existence with existing wireless networks will require careful analysis. Most 802.11n products will provide compatibility with 802.11g equipment operating on the same channel by reducing speed to the level of 802.11g. The speed reduction will affect the entire wireless network, not just the 802.11g equipment.
If you are currently using all three channels at 2.4 GHz, be sure to select 802.11n products that will operate at 5 GHz. If you are using two channels at 2.4 GHz, you will not be able to take advantage of 802.11n's ability to utilize a 40 MHz channel.
Some 802.11n APs may include two radios, one supporting existing 802.11g networks at 2.4 GHz and another operating at 5 GHz with full 802.11n speed. Be sure to consider how existing equipment will be supported before selecting an 802.11n vendor.
IEEE 802.11n will certainly be widely deployed. It will enable high-bandwidth applications currently limited to wired networks to migrate to wireless. It will improve wireless VoIP reception.
But jumping in too soon and with insufficient analysis can mean trouble in the future. Delay, if possible, until the final specification is approved and equipment based on it is released and tested. Understand the impact throughout your network. Finally, create your plan with an understanding of all the redesign needed and all of the equipment that must be upgraded.
Go back to part one, IEEE 802.11n: Looking ahead to the next wireless standard.
About the author:
David B. Jacobs of The Jacobs Group has more than 20 years of networking industry experience. He has managed leading-edge software development projects and consulted to Fortune 500 companies, as well as software startups.
