11n

802 11n FAQ

This document will help answer some of the most common questions related to 802.11n, how 802.11n applies to Enterprise environments, and how 802.11n relates to Xirrus products.

What is 802.11n? What are the benefits of 802.11n?

Q What is 802.11n?
A 802.11n is an IEEE (The Institute of Electrical and Electronics Engineers, Inc) addendum to the base 802.11 standard for Wireless Local Area Networks. 802.11n defines a higher throughput standard for 802.11 wireless networks.

Q What are the main benefits of 802.11n?
A The key benefits of 802.11n include drastically higher data rates, better throughput, more robust connections, and potentially longer range than previous 802.11 wireless standards.

Q What are the new data rates supported in the 802.11n standard?
A Data rates of up to 600Mbps have been defined as part of the new standard. First generation hardware is expected to support data rates of up to 300Mbps. The Wi-Fi Alliance will certify data rates up to 300Mbps.

Q What is the expected range improvement?
A About twice the range is expected at the same data rate as prior standards. The improved range requires 802.11n capable stations and Access Points to achieve this. Note most enterprise environments will not take advantage of the range improvements; rather, they will take advantage of the higher data rates the standard provides.

Q How will 802.11n benefit the Enterprise?
A The key benefits of 802.11n for the enterprise include: support of additional users, support of bandwidth intensive applications, provide more robust connections for end users, and help applications like voice and video that are sensitive to latency and jitter. 802.11n will help fill-in coverage holes and will perform better in large reflective environments such as warehouses, manufacturing environments, and auditoriums.

802.11n Technology

Q What are the major elements defined in the 802.11n standard?
A The main new features of 802.11n used to increase data rates include: higher encoding schemes, Channel Bonding, Spatial Multiplexing (MIMO), Frame Aggregation, Block Acknowledgements, and other MAC enhancements.

Q What is Channel Bonding?
A Normally, an 802.11 radio operates on a single channel. Channel Bonding allows the use of two adjacent channels to be used together to double the amount of bandwidth available that the 802.11n radio can operate on. Channel bonding therefore doubles the maximum data rates available compared to 802.11a or 802.11g radios.

Q What is MIMO?
A MIMO (Multiple-In-Multiple-Out) uses multiple radios and antennas to receive and transmit packets. A MIMO receiver simultaneously listens to incoming signals on multiple antennas. This technique takes advantage of the large differences in signal characteristics as seen by different antennas just a small distance apart. Using multiple antennas, and signal processing techniques "good signals" from each antenna can be combined to enhance the clarity of the original intended signal .This greatly increases ability to correctly receive packets and the overall range at which a radio can receive packets from other stations.

Q What is Spatial Multiplexing?
A Spatial Multiplexing uses multiple antenna and multiple radios (MIMO) to transmit different packet streams out on different antennas at the same time. The 802.11n receiver can distinguish between these separate streams. This technique can double or even triple the amount of data that can be sent over the air at the same time.

Q How many antennas are needed?
A Spatial Multiplexing uses multiple antenna and multiple radios (MIMO). A minimum of two antennas are needed for basic 802.11n transmitting and receiving (referred to as a 2x2 antenna system). Typical first generation 802.11n radios will have two transmit antennas and three receive antennas (2x3). Additional antenna combinations are possible (4x4) for example would be able to transmit up to four separate spatial streams in order to obtain the highest defined data rates of the 802.11n specification. Typically, at least one more receive antenna is needed than the number of transmit antenna in order to reliably receive the multiple spatial streams being sent.

Q What is Frame Aggregation?
A Every 802.11 packet, no matter how small, has a fixed amount of overhead associated with it. Frame Aggregation combines multiple smaller packets together to form one larger packet. The larger packet can be sent without the overhead of the individual packets. This technique helps improve the efficiency of the 802.11n radio allowing more end user data to be sent in a given time.

Q What are Block Acknowledgements?
A Normally, every 802.11 packet sent must be acknowledged by the receiver. The time needed to send and receive each acknowledgement (ACK) can be very time consuming. The 802.11n standard provides for a mode called "Block ACK" whereby a number of packets can be transmitted one right after the other (increasing efficiency) and a single ACK is then returned that lists which packets were good and which packets will need to be resent.

Interoperability with previous 802.11a, and 802.11b/g Standards

Q Will 802.11n work with my existing 802.11a, 802.11b and 802.11g devices?
A Yes, 802.11n was defined to have a number of mechanisms to ensure interoperability with previous 802.11 devices. 802.11n radios are backwards compatible to 802.11a or 802.11b/g and can receive and transmit standard 802.11a or 802.11b/g packets. 802.11n radios will respect transmissions from standard 802.11a or 802.11b/g devices and will not interfere with them. Additionally, 802.11n radios provide "protection mechanisms" for 802.11a or 802.11b/g devices such that 802.11a or 802.11b/g stations will not attempt to transmit when 802.11n radios are transmitting.

Q Will 802.11n Access Points work along side my existing 802.11a, 802.11b and 802.11g Access Points?
A Yes, 802.11n can be mixed with 802.11a or 802.11b/g Access Points. Depending on the channels used, the 802.11n Access Points may have to refrain from using 80211n Channel Bonding mode if such "bondable" channels are being used by other Access Points in range of the 802.11n Access Point.

Q What happens to range and data rates when only one side is 802.11n enabled?
A When only one radio (the access point or the station) is 802.11n capable, 802.11n data rates cannot be used. The two radios will simply use standard 802.11a or 802.11b/g rates. In terms of range, there will not be a noticeable improvement in maximum distance (at any data rate) that the stations can communicate. At shorter distances, there may be some improvement in terms of the distance that higher data rates can be received by the 802.11n enabled station.

How much will it cost?

Q What will the new 11n products cost?
A It is expected that there will at least initially, be a slight premium for 802.11n products versus previous generation products. 802.11n access points will require additional components and processing power to implement the new standard.

Q Is there an upgrade program from Xirrus?
A Yes, Xirrus offers an 802.11n upgrade program at the time of purchase that provides for a future 802.11n radio module upgrade for the Xirrus Array. Please contact a Xirrus sales representative for additional details.

Ratification of the 802.11n Standard

Q When will the final standards completed?
A The final ratification of the 802.11n standard by the IEEE working group is expected to complete July, 2009.

Q What is the 2.0 draft of the standard?
A The 2.0 draft of the IEEE 802.11n standard was chosen as a reasonably "stable" version of the final specification and been adopted by the Wi-Fi Alliance for vendor interoperability certification of Draft 802.11n products. The Wi-Fi Alliance will incorporate the final version of the standard upon ratification.

Q Will the Final Standard work with the draft 2.0 standard?
A While the final 802.11n standard is not yet complete, the vast majority of the features in the 2.0 draft standard should not change. While there is no guarantee, most devices may be software upgradeable to the final standard.

Q What about Pre-N gear?
A A number of vendors have released product dubbed "Pre-N" gear that supports a number of elements of the 802.11n standard (such as channel bonding, or spatial multiplexing). These Pre-N products will interoperate with existing 802.11abg products but there is no guarantee that they will work with the final 802.11n standard, nor is there any guarantee that Pre-N gear will be upgradeable to the final 802.11n standard.

Q When should I buy? Should I wait?
A Xirrus always recommends buying Wi-Fi certified products to guarantee interoperability between different vendor's products. Xirrus also recommends buying infrastructure that is upgradeable. Because 802.11n is backwards compatible, it is acceptable to phase-in either 802.11n client devices, or 802.11n Access Points at any time.

Client Devices

Q Will my 802.11a/b/g stations work with 802.11n Access Points?
A Yes, 802.11n was defined to have a number of mechanisms to ensure interoperability with previous 802.11 devices. 802.11n radios are backwards compatible to 802.11a or 802.11b/g and can receive and transmit standard 802.11a or 802.11b/g packets. 802.11n radios will respect transmissions from standard 802.11a or 802.11b/g devices and will not interfere with them. Additionally, 802.11n radios provide "protection mechanisms" for 802.11a or 802.11b/g devices such that the 802.11a or 802.11b/g stations will not attempt to transmit when 802.11n radios are transmitting.

Q Will my 802.11abg stations work better with 802.11n Access Points?
A Yes, existing stations will typically work better with 802.11n access points up to the maximum rate that the device can support. 802.11n Access Points will have better receiver sensitivity thereby improving the data rate a station can use and reducing the overall packet error rate.

Q What about power consumption for laptops and other mobile devices?
A Most first-generation 802.11n client adapters will use slightly more power than their 802.11a or 802.11b/g predecessors due to the additional transceivers and processing requirements of the 802.11n standard. Many laptop devices have already been shipping with 802.11n-ready adapters for some time now.

Q What should I do today to prepare my existing laptops for 802.11n?
A If plans for 802.11n include waiting until the final standard is ratified, make sure to purchase 802.11abg adapters when refreshing notebooks today. 802.11a-capable adapters will be more compatible with 802.11n in the 5GHz band than 802.11bg will be in the 2.4GHz band.

Network Infrastructure Requirements

Q What should I do to prepare the wired network for 802.11n?
A 802.11n speeds will require Gigabit Ethernet connections to each access point in order to handle the new wireless throughput capabilities.

Q What should I be doing if I am deploying new access points today?
A 802.11n speeds will require Gigabit Ethernet connections to each access point in order to handle the new wireless throughput capabilities. New access points should also support both 802.11a (5GHz) and 802.11b/g (2.4GHz) and a site survey should be done to locate access points for support of both bands (2.4GHz and 5GHz). This way, the same access point locations can be used to upgrade to 802.11n access points.

Q Will Power over Ethernet (PoE) still work with 802.11n access points?
A Most dual-radio 802.11n access points will exceed the 13watt limit of the 802.3af (Power over Ethernet) standard. This will require using A/C power, or a proprietary power over Ethernet solution

Q Does Xirrus have a Power over Ethernet solution for 802.11n?
A Yes, Xirrus has a power injector solution that works over existing Ethernet and Gigabit Ethernet cable.

Q What about my existing investment in Xirrus 802.11abg Wi-Fi Arrays?
A Existing Xirrus 802.11abg Wi-Fi Arrays will continue to provide years of high performance service. Xirrus Wi-Fi Arrays are one of the few platforms that can be upgraded to 802.11n at the end users time of choice.

Existing Access Points and Locations

Q Will I have to change the location of my existing Wi-Fi Access Points for 802.11n?
A The answer depends on how the original network was laid out. If the original wireless network was planned for 802.11a (5GHz) cell sizes then the same existing locations can be used. If the original wireless network was laid out for 2.4GHz (802.11b/g) cells and you are planning to take advantage of 802.11n in the 5GHz band then a new site survey should be completed to determine new placement of 802.11n access points.

What about Different WLAN Architectures?

Q What should I do if I have a system that uses backend WLAN controllers?
A The primary concern will be for the performance of the wireless controller. With new 802.11n speeds of up to 300Mbps for each access point, WLAN controllers may need to be upgraded in order to handle the increased packet and encryption processing required. Additionally, many controllers have built-in Ethernet ports to connect (via cable) to the "thin AP". These Ethernet ports on the controller will need to be upgraded to Gigabit Ethernet, or otherwise become a bottleneck for the network.

Q What should I do if I have a system like the Xirrus Wi-Fi Array, that has an integrated controller?
A Xirrus Wi-Fi Arrays have the controller integrated and have been designed for 802.11n speeds and include line-rate encryption processing. The only item to upgrade is the radio modules and a software upgrade.

Security

Q Does 802.11n define a new security standards or modes?
A No, security remains the same as previously defined in the 802.11i security specification. 802.11i authentication and encryption provide government-grade security. 802.11i is also known as WPA2 (Wi-Fi Protected Access 2) which is the Wi-Fi Alliance specification that certifies interoperability for the major components of 802.11i.

Q What about Wi-Fi Intrusion Detection and Prevention Systems (IDS/IPS)?
A For enterprises using a wireless IDS/IPS system it is recommended that the wireless sensors be upgraded to 802.11n in order to comprehend 802.11n packets. Xirrus' Wi-Fi Array has an embedded Wi-Fi security sensor and is automatically upgraded to 802.11n as part of the standard 802.11n module upgrade.

Management Systems

Q Does 802.11n require a wireless management system update?
A Yes an update to wireless network management systems will be required to correctly comprehend the new 802.11n data rates, modes and statistics. Normally this will be a simple software upgrade to the management platform.

Planning Tools

Q Does 802.11n require new planning tools?
A Yes an update to planning tools will be required to correctly comprehend the new 802.11n physical characteristics in order to correctly predict cell sizes and environmental characteristics that may affect 802.11n. Normally this will be a simple software upgrade.