W&M 2009 – 802.11n - The Good The Bad The Ugly?


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  • An overview of how the various modes apply to frequency band, the number of channels available, and the expected data rates and throughput.
  • This slide helps to explain the first two 802.11n innovations with a picture. Channel bonding is analogous to taking two pipes of the same diameter, and making one pipe that has twice the diameter of the original ones. The bigger the pipe, the more water can flow. Similarly, by taking two channels and “bonding” them into one channel that’s twice as wide results in much greater speed. The price to be paid for higher speed is less unique, distinct channels. The 2.4GHz example here shows how 3, 20 MHz channels reduce down to 1, 40MHz channel and 1 remaining 20MHz channel. So… higher speed per channel, but less channels overall. The mixed-mode effect is seen next. If only “new” .11n clients are allowed to operate in the bonded 40MHz channel, then the maximum throughput of 802.11n is possible. However, as soon as “old” .11g devices are allowed to mix with the n devices, the throughput can drop to as little as a quarter of before. The same phenomenon happens in 20MHz channels. The bottom line: understand what clients you will need to support and in what band. Channel bonding and legacy support, in isolation, are a good thing. In practice, in a system context, things may not be so clear.
  • W&M 2009 – 802.11n - The Good The Bad The Ugly?

    1. 1. 802.11n – The Good, the Bad and the Ugly <ul><li>Phil Belanger </li></ul>© 2009
    2. 2. What is 802.11n? <ul><li>A new IEEE 802.11 standard for high throughput wireless LANs. </li></ul><ul><li>The biggest change in wireless LANs since the first Wi-Fi. </li></ul><ul><li>The only 802.11 standard to change both the MAC and PHY. </li></ul><ul><ul><li>11n changes everything - modulation, framing, antennas... </li></ul></ul><ul><li>The official IEEE standard has not yet been published. </li></ul><ul><ul><li>the official standard is now expected in 2010 </li></ul></ul><ul><ul><ul><li>huge changes and a bureaucratic process led to a very long development </li></ul></ul></ul><ul><ul><li>the technical debate has been over for years </li></ul></ul><ul><ul><li>draft 11n chipsets are widely available </li></ul></ul><ul><li>Wi-Fi Alliance is certifying interoperability for 802.11n Draft 2 </li></ul><ul><ul><li>interoperability has been good </li></ul></ul><ul><ul><li>this effectively creates a pre-standard version that is standard </li></ul></ul><ul><ul><li>the formal standard will include backwards compatibility with Draft 2 </li></ul></ul>© 2009
    3. 3. What is 802.11n? Features <ul><li>MIMO - Multiple Input/Multiple Output </li></ul><ul><ul><li>multiple radios and multiple antennas for receive and transmit </li></ul></ul><ul><ul><li>signal processing that combines the inputs from multiple antennas to improve signal </li></ul></ul><ul><ul><ul><li>multipath reflections previously cause errors, now 802.11n MIMO uses multipath as an advantage </li></ul></ul></ul><ul><ul><li>Draft 2.0 enterprise products are typically 3 receive and 3 transmit </li></ul></ul><ul><li>Spatial multiplexing </li></ul><ul><ul><li>supports multiple simultaneous streams of data on same channel </li></ul></ul><ul><ul><li>Draft 2.0 equipment must support at least 2 streams </li></ul></ul><ul><li>Improved modulation </li></ul><ul><ul><li>better OFDM achieves 65 Mbps in a single stream 20 MHz channel </li></ul></ul><ul><li>Channel bonding </li></ul><ul><ul><li>two 20 MHz channels can be combined to form a single 40 MHz channel that delivers twice the data rate </li></ul></ul><ul><li>Frame Aggregation, Block ACK, Short Guard Interval </li></ul><ul><ul><li>more efficient protocol which provides higher effective throughput </li></ul></ul><ul><li>More spectrum available </li></ul><ul><ul><li>802.11n supports both bands - 2.4 GHz and 5 GHz </li></ul></ul><ul><ul><li>802.11h opens up more channels in 5 GHz band through DFS </li></ul></ul>© 2009
    4. 4. The Promise of 802.11n <ul><li>Speed - High Throughput </li></ul><ul><ul><li>Current Draft 2 products can achieve 300 Mbps raw data rate </li></ul></ul><ul><ul><ul><li>160 Mbps of actual throughput </li></ul></ul></ul><ul><ul><ul><li>Under ideal conditions, when configured properly </li></ul></ul></ul><ul><ul><ul><li>All of the enhancements must be enabled, only 11n products on channel </li></ul></ul></ul><ul><ul><ul><li>40 MHz channel, 2 streams </li></ul></ul></ul><ul><ul><li>Six to eight times improvement in performance </li></ul></ul><ul><li>Improved Range and Coverage </li></ul><ul><ul><li>much better range for most clients </li></ul></ul><ul><ul><li>twice the range? </li></ul></ul><ul><ul><li>What is coverage? </li></ul></ul><ul><li>Perfect backwards compatibility </li></ul><ul><ul><li>can support legacy 802.11 products on the same system </li></ul></ul><ul><ul><li>11n clients can operate in legacy mode on older networks </li></ul></ul>© 2009
    5. 5. Reality of 802.11n <ul><li>Consumer success </li></ul><ul><li>Works great </li></ul><ul><ul><li>Great speed and great coverage </li></ul></ul><ul><ul><li>Perfect backwards compatibility </li></ul></ul><ul><ul><ul><li>802.11n clients work with legacy infrastructure and perform as well as the best 802.11g or 802.11a client </li></ul></ul></ul><ul><ul><ul><li>802.11n APs also support legacy 802.11g or 802.11a clients </li></ul></ul></ul><ul><li>Built into many devices </li></ul><ul><ul><li>Mature chipsets, second or third generation 802.11n </li></ul></ul><ul><ul><li>Still priced higher, but prices of 11n declining at the device level </li></ul></ul><ul><li>Just starting in the enterprise... </li></ul><ul><ul><li>802.11n Draft 2 products are stable </li></ul></ul><ul><ul><li>There is no reason to wait from an interoperability point of view </li></ul></ul><ul><li>Single 11n AP and a few clients in the home works great! </li></ul><ul><li>Can 802.11n scale up to multiple AP systems in the enterprise? </li></ul><ul><ul><li>Yes - but it takes careful planning. </li></ul></ul>© 2009
    6. 6. Enterprise WLAN 11n Challenges <ul><li>Wireless Network Challenges </li></ul><ul><ul><li>Full speed requires channel bonding which reduces available channels </li></ul></ul><ul><ul><li>Lack of 40 MHz channels in 2.4 GHz band, few 40 MHz channels in 5 GHz </li></ul></ul><ul><ul><li>MIMO makes channel planning impractical </li></ul></ul><ul><ul><ul><li>Unpredictable coverage increases interference and creates coverage gaps </li></ul></ul></ul><ul><ul><ul><li>More range forces larger spacing between same-channel APs </li></ul></ul></ul><ul><ul><ul><ul><li>which consumes more channels or leaves coverage gaps </li></ul></ul></ul></ul><ul><ul><ul><li>legacy planning tools do not work </li></ul></ul></ul><ul><li>Wired Network Challenges </li></ul><ul><ul><li>Each AP needs at least a gigabit Ethernet uplink </li></ul></ul><ul><ul><li>Dramatic bandwidth improvements on the wireless network may require wired network upgrades </li></ul></ul><ul><ul><li>802.3af PoE power budget may be insufficient for some multi-radio 11n APs </li></ul></ul><ul><li>Wireless Client Challenges </li></ul><ul><ul><li>Legacy 802.11b/g clients are not going to disappear </li></ul></ul><ul><ul><li>There will be a variety of 802.11n clients with different capabilities too… </li></ul></ul>© 2009
    7. 7. 802.11 Speeds and Feeds... © 2009 Mode Operating Band Channel Width Raw Data Rate Useful Throughput Non-Overlapping Channels 802.11b 2.4 GHz 20 MHz 11 Mbps 5.5 Mbps 3 802.11g 2.4 GHz 20 MHz 54 Mbps 20 Mbps 3 802.11a 5 GHz 20 MHz 54 Mbps 24 Mbps 24 with DFS Mode Operating Band Channel Width Raw Data Rate Useful Throughput Non-Overlapping Channels 802.11n 2.4 GHz 40 MHz 300 Mbps 160 Mbps 1 802.11n 2.4 GHz 20 MHz 150 Mbps 80 Mbps 3 802.11n 5 GHz 40 MHz 300 Mbps 160 Mbps 3 without DFS 11 with DFS 802.11n 5 GHz 20 MHz 150 Mbps 80 Mbps 24 with DFS
    8. 8. The Effect of Channel Bonding and Backward Compatibility <ul><li>Today’s 3 non-overlapping channels collapse down to 1 x 40 MHz and 1 x 20 MHz channel in the 2.4 GHz band </li></ul>© 2009 160 Mbps ‘ n’ devices only 80 Mbps n & g devices in mixed mode 38 Mbps? 19 Mbps? 2402 2407 2412 2417 2422 2427 2432 2437 2442 2447 2452 2457 2462 2467 2472 2484 MHz Today 802.11g/n 40MHz 20MHz Ch 1 Ch 6 Ch 11 Ch 2 Ch 7 Ch 12 Ch 3 Ch 8 Ch 13 Ch 4 Ch 9 Ch 14 Ch 5 Ch 10 802.11g (Japan)
    9. 9. Unpredictable Coverage <ul><li>The techniques that bring greater range and better coverage to 11n also make coverage unpredictable. </li></ul><ul><ul><li>Very sensitive to the environment since MIMO leverages RF reflections </li></ul></ul><ul><ul><li>Different depending on client capabilities </li></ul></ul>© 2009 802.11 b/g/a 802.11 n
    10. 10. Impractical Cell Planning <ul><li>Cell planning attempts to insure continuous coverage but minimize overlap to reduce co-channel interference between APs. </li></ul><ul><li>With each AP having erratic coverage, hard to avoid coverage gaps. </li></ul><ul><li>11n has great range, but interference range is greater too! </li></ul><ul><ul><li>11n will generate more co-channel interference that 802.11a/b/g </li></ul></ul><ul><li>How to minimize coverage gaps while avoiding co-channel interference? </li></ul>© 2009 802.11 b/g/a 802.11 n
    11. 11. Variety of Clients <ul><li>Legacy clients </li></ul><ul><ul><li>802.11b/g and 802.11a clients </li></ul></ul><ul><ul><li>Mixed mode protocol slows down 802.11n clients dramatically </li></ul></ul><ul><li>New 802.11n clients with different capabilities </li></ul><ul><ul><li>High power 3 x 3 MIMO supporting 2 streams with beamforming </li></ul></ul><ul><ul><li>Low power, 2x2 MIMO, single stream </li></ul></ul><ul><ul><li>Very low power, no MIMO, single stream </li></ul></ul><ul><li>The AP coverage pattern will be different for each client type </li></ul><ul><ul><li>Makes the AP cell planning even more difficult </li></ul></ul>© 2009
    12. 12. Wired Network Challenges <ul><li>The increased bandwidth of 802.11n APs may move the network bottleneck. </li></ul><ul><ul><li>In legacy WLAN systems bottleneck was always in the wireless access edge </li></ul></ul><ul><ul><li>802.11n may create enough bandwidth to move the bottleneck back to the wired network </li></ul></ul><ul><li>A dual band 802.11n AP could generate 320 Mbps of traffic load for the wired Ethernet. </li></ul><ul><ul><li>10 indepndent APs is 3.2 Gigabits! </li></ul></ul><ul><ul><li>Gigabit Ethernet backbones may no longer be sufficient. </li></ul></ul><ul><ul><li>A big centralized WLAN controller may not be the best architecture </li></ul></ul><ul><ul><ul><li>creates too much traffic back to the network core </li></ul></ul></ul><ul><ul><ul><li>routing at network edge is more efficient </li></ul></ul></ul><ul><ul><ul><li>Upgrade to 10 gigabit Ethernet core? </li></ul></ul></ul><ul><li>New wired and wireless architectures may be required to get the most out of 802.11n in the enterprise. </li></ul>© 2009
    13. 13. Enterprise 802.11n Design Considerations <ul><li>Applications and Devices </li></ul><ul><ul><li>What applications will be supported? </li></ul></ul><ul><ul><li>What device types will be supported? </li></ul></ul><ul><ul><li>What percentage of the users will use legacy devices? </li></ul></ul><ul><li>Network Architecture </li></ul><ul><ul><li>Does the wired network have enough capacity? </li></ul></ul><ul><ul><li>Where shall the wireless network connect? </li></ul></ul><ul><li>Wireless Network Architecture </li></ul><ul><ul><li>Which bands will be used? Shift 802.11n users to 5 GHz? </li></ul></ul><ul><ul><li>Centralized WLAN controller or switch? </li></ul></ul><ul><ul><li>Routing at the edge? Fat APs? </li></ul></ul><ul><li>Implementation Approach </li></ul><ul><ul><li>Gradual introduction or re-start? </li></ul></ul><ul><ul><li>Wireless layout redesign needed? </li></ul></ul><ul><ul><li>Impact to current cabling? </li></ul></ul><ul><ul><li>Required powering scheme? </li></ul></ul>© 2009
    14. 14. Summary <ul><li>802.11n is a significant upgrade to the 802.11 standard. </li></ul><ul><li>It is great technology that delivers excellent performance. </li></ul><ul><ul><li>higher data rates and better throughout </li></ul></ul><ul><ul><li>better range and more robust coverage </li></ul></ul><ul><ul><li>perfect backwards compatibility with legacy Wi-Fi equipment </li></ul></ul><ul><li>Getting all of the 802.11 benefits in multiple AP enterprise deployments can be challenging. </li></ul><ul><ul><li>careful planning is required </li></ul></ul><ul><ul><li>new tools and new network upgrades may be needed </li></ul></ul><ul><ul><li>new network architectures may be required to deliver the full benefit </li></ul></ul><ul><ul><li>wireless and wired </li></ul></ul>© 2009
    15. 15. Thank You © 2009
    16. 16. Extricom 802.11n Channel Blankets <ul><li>Practical deployment of 802.11n. </li></ul><ul><ul><li>Multiple APs on same channel form a contiguous blanket of coverage </li></ul></ul><ul><ul><li>Overlapping AP coverage is good in the Channel Blanket, more diversity </li></ul></ul><ul><ul><li>Simpler planning, Channel Blanket works well with unpredictable coverage of 802.11n APs </li></ul></ul><ul><li>Full-performance for both 11n and 11b/g devices in the 2.4 GHz band. </li></ul><ul><ul><li>11n and 11b/g in separate blankets allows 11n clients to run full speed in “greenfield mode” </li></ul></ul><ul><ul><li>1 40 MHz channel for 11n and 1 20 MHz channel for 802.11g </li></ul></ul><ul><li>Channel Blanket provides system level diversity for 802.11n. </li></ul><ul><ul><li>Excellent complement to device level diversity of 802.11n MIMO system </li></ul></ul><ul><li>Smooth migration from legacy 802.11 a/b/g to full performance 802.11n </li></ul>© 2009 2.4 GHz ‘n’ 2.4 GHz ‘b/g’ 5 GHz ’n’ 5 GHz ‘a’ A separate Channel Blanket for each client type Optimized for IEEE 802.11n