802.11n promises faster speeds, closing the performance gap between wired and wireless networks. However, not too long ago, the question on everyone`s lips was do we wait for the standard to be ratified or is it worth it to invest in `pre-n` compliant products. With 802.11n Draft 2.0 ratified, adoption of these products is increasing. The burning question is what impact will this have on pre-n and legacy WLAN equipment?
Draft 2 products that have been approved by the WiFi Alliance since June 2007 contain all the major features expected in the final standard and it is expected that compatibility with the final standard will be maintained. Indeed, the undertaking by vendors to ensure this compatibility is driving greater uptake of these products. However, pre-n products, like the previous versions of the standard - ie 802.11 a/b/g - may have some limitations. To reach the full throughput and functionality that Draft 2 and the final 802.11n standard products promise may require an upgrade.
While organisations that acquired the pre-n products to fill a need have certainly in most cases gained some benefits, an evolutionary approach is in general expected to be taken to attaining the full functionality of the new standard. The existing investment made by enterprises in wireless networks may well be leveraged for another three years or more, depending on the requirements of the organisations. Implementing 802.11n Draft 2 products in the enterprise and gaining the full benefits of these products will thus require network administrators to evaluate a number of deployment considerations. These include operational modes, frequency band selection, power management, the AP wired Ethernet port, use of WLAN controllers and network management.
A recent white paper released by the Burton Group in association with the WiFi Alliance puts these considerations into perspective. According to Paul de Beasi of the Burton Group, 802.11n improves the performance of existing wireless applications that currently operate using 802.11a/b/g and it enables more applications to use a wireless LAN that currently requires wired Ethernet. Point-of-sale transactions, voice over wireless LAN, and Internet browsing will all benefit from the increased performance, coverage and robustness of 802.11. In addition, 802.11n enables applications such as wireless backup, video conferencing, and medical imaging to operate over a wireless LAN. However, managers that take time to evaluate enterprise deployment considerations, within the context of their enterprise needs and constraints, will improve their ability to achieve a successful 802.11n deployment.
The key advantages of 802.11n, according to Burton Research, include many new features that improve throughput, robustness, and range. These include:
* Frame aggregation, where a half duplex, shared, media access control layer allows the aggregation of several packets into a single packet to avoid the wasted overhead between frames;
* Multiple input, multiple output, a signal enhancement technique that makes a channel more spectrally efficient by increasing the baud rate/hertz ratio;
* Channel bonding, which bonds the single 20 MHz channel used by 802.11a/g to form a 40 MHz channel, boosting throughput; and
* Greater throughput and range, approximated by manufactures at five times faster throughput than 802.11g at an equivalent distance and a 50% better range.
Performance can be limited by a number of factors, however. The design of the system and the network, configuration and environmental interference all need to be taken into consideration. Administrators also need to take care of the basics when combining legacy and 802.11n equipment.
This includes ensuring APs are configured to operate in `mixed mode` to enable different devices to interoperate on the same wireless LAN. The problem is that legacy WLAN devices in the network transmit at a slower rate than 802.11n devices and are bandwidth hungry. Thus they can slow the performance of 802.11n devices.
Legacy equipment also generally operates in the 2.4 MHzchannel, which has numerous overlapping channels (and so more interference) and doesn`t allow for channel bonding, according to the Burton Group white paper. Since the 802.11n technology offers dual band, administrators need to consider use of the 5GHz band where possible for the greatest flexibility and for better throughput.
Power management is another consideration as 802.11n APs with all features enabled will likely exceed the power rating of 802.3af POE equipment - an IEEE standard that specifies Power over Ethernet. It is advisable to use APs that comply with the POE rating as it will simplify installation and assist to ensure functionality does not degrade.
Vendors are assisting by taking a number of approaches to this problem. For example, wall-outlet-powered APs, APs with multiple Ethernet connections, and APs that are engineered to not exceed the POE rating are now all available, says the Burton Group white paper.
Other considerations include the upgrading of Fast Ethernet switches and cabling to Gigabit Ethernet since 802.11n data rates exceed the 100Mb per second capacity of Fast Ethernet used by legacy devices. Users will also need to ensure WLAN controllers, which centralise control of APs, are upgraded to support multiple Gigabit Ethernet connections.
A final consideration is network management. Various tools, such as spectrum analysers, WLAN monitors, site planning and configuration management tools are being used. These too will need to be upgraded to manage 802.11n networks.
The new WLAN standards will continue to evolve and along with it enterprise networks. As with any technology, understanding the limitations and how to maximise existing architectures will assist administrators and organisations to leverage these benefits.
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