802.11n: Beyond the Hype

802.11n: Beyond the HypeVersion: 1.0, Jul 05, 2007

AUTHOR(S):Paul DeBeasi([email protected])

TECHNOLOGY THREAD:

Wireless and Mobility

Conclusion802.11n is an emerging Institute of Electrical and Electronics Engineers (IEEE) wirelessstandard that significantly improves throughput and range compared with older 802.11standards. 802.11n is the only 802.11 standard that operates in either the 2.4 GHz and 5 GHzfrequency bands, and it is the first to standardize the use of multiple input, multiple output(MIMO) antenna design. 802.11n is backward compatible with 802.11b/g/a, which means thatan 802.11n device can communicate and interoperate with legacy 802.11 devices. 802.11n mayeventually become the dominant enterprise local area network (LAN) technology.

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Table Of Contents

Synopsis.......................................................................................................................................................................... 4Analysis...........................................................................................................................................................................5

What Is 802.11n?........................................................................................................................................................ 5The 802.11n Performance Boost.................................................................................................................................5Wireless Spectrum Choices........................................................................................................................................ 6

Dual-Band WLAN.................................................................................................................................................. 7Single-Band WLAN................................................................................................................................................7

802.11b/g/a Protection Mechanisms........................................................................................................................... 8Standardization and Certification................................................................................................................................8Power Consumption..................................................................................................................................................10AP Backhaul............................................................................................................................................................. 10System Impact...........................................................................................................................................................10

Intrusion Detection Systems................................................................................................................................. 10Network Management Systems............................................................................................................................ 11WLAN Systems.................................................................................................................................................... 11

Market Impact........................................................................................................................................................... 11Impact on Ethernet Switching Vendors................................................................................................................ 12Impact on Independent WLAN Vendors.............................................................................................................. 13Impact on Enterprise VoWLAN Market...............................................................................................................13

Recommendations.....................................................................................................................................................14Only Buy Products That Are WFA Certified........................................................................................................14Consider Draft-N, WFA-Certified Products for Production.................................................................................14Deploy 802.11n in 5 GHz Band............................................................................................................................14Use 40 MHz Channel Bonding............................................................................................................................. 14Use Dual-Band 802.11n Stations.......................................................................................................................... 14Use Dual-Band, Dual-Radio 802.11n APs............................................................................................................14Make Sure That Gigabit Ethernet Is Available for AP Backhaul......................................................................... 14Upgrade Intrusion Detection Systems Now..........................................................................................................15Prepare for 802.11n APs That May Exceed the PoE Power Budget.................................................................... 15Avoid Mixing 802.11b and 802.11n Stations on the Same 2.4 GHz Band.......................................................... 15

The Details.................................................................................................................................................................... 16802.11n: Major Features........................................................................................................................................... 16Multipath...................................................................................................................................................................17MIMO....................................................................................................................................................................... 18Throughput and Range..............................................................................................................................................19The 2.4 GHz and 5 GHz Bands.................................................................................................................................19Modes of Operation.................................................................................................................................................. 20Transmit Beam Forming........................................................................................................................................... 20Frame Aggregation................................................................................................................................................... 21Reduced Inter-Frame Spacing...................................................................................................................................22Power Save Modes....................................................................................................................................................22IEEE 802.11n Ratification Timeline.........................................................................................................................22

Conclusion.................................................................................................................................................................... 23Notes............................................................................................................................................................................. 24Author Bio ....................................................................................................................................................................25

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Synopsis

802.11n is an emerging Institute of Electrical and Electronics Engineers (IEEE) wireless standard thatsignificantly improves throughput and range compared with older 802.11 standards. Although the standard willnot be ratified until the first quarter of 2009 (at the earliest), expectations are that 802.11n will provide over 100Mbps of packet throughput and up to twice the range of 802.11g.

The higher throughput speeds will be quite adequate for most enterprise applications. The extended wireless rangemeans that fewer 802.11n access points (APs) can achieve the same coverage as current 802.11g/a APs, therebysaving enterprises money. Conversely, enterprises that share facilities with other tenants may find that aneighbor's 802.11n AP causes co-channel interference with their enterprise network.

802.11n is different from previous 802.11 standards because it is designed to operate in both the 5 GHz and the2.4 GHz frequency bands, enabling 802.11n to provide backward compatibility for 802.11b/g/a devices. However,beta tests of pre-standard 802.11n APs show that backward compatibility may degrade network performance byup to 25%. In addition, many pre-standard 802.11n APs will exceed the Power over Ethernet (PoE) power budget.

The Wi-Fi Alliance (WFA) will certify interoperability of Wireless Fidelity (Wi-Fi) products based upon 802.11n,draft 2.0, beginning in June 2007. This first-phase certification program will ensure interoperability betweendraft-N products. A future second-phase certification program will be based upon the final 802.11n standard.Therisk that first-phase certified products, based upon draft 2.0, will not be interoperable with second-phase certifiedproducts, based upon the final standard, is low.

802.11n will enable pervasive wireless deployment in the enterprise and may eventually become the dominantenterprise local area network (LAN) technology. As this happens, the growth of the Ethernet switching marketmay begin to slow due to wireless local area network (WLAN) substitution resulting in the acquisition of WLANsystem vendors by traditional wired Ethernet switching vendors. Pervasive 802.11n deployment will alsoaccelerate the growth of the enterprise Voice over WLAN (VoWLAN) market.

Enterprises should consider the following recommendations.

• Only Buy Products That Are WFA Certified

• Consider Draft-N, WFA-Certified Products for Production

• Deploy 802.11n in 5 GHz Band

• Use 40 MHz Channel Bonding

• Use Dual-Band 802.11n Stations

• Use Dual-Band, Dual-Radio 802.11n APs

• Make Sure That Gigabit Ethernet Is Available for AP Backhaul

• Upgrade Intrusion Detection Systems Now

• Prepare for 802.11n APs That May Exceed the PoE Power Budget

• Avoid Mixing 802.11b and 802.11n Stations on the Same 2.4 GHz Band

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Analysis

By virtually any measure, the Institute of Electrical and Electronics Engineers (IEEE) 802.11 wireless local areanetwork (WLAN) standards have achieved tremendous international success. More than 250 million 802.11chipsets were sold in 2006 and many more will be sold in 2007. In addition, the IEEE 802.11 committeecontinues to evolve the standard to improve performance, security, manageability, ease of use and deployment.See the Network and Telecom Strategies report, “Wireless LANs Standards: Where Are We Now?” for additionalinformation.

This report is the first of two reports on 802.11n. It introduces the reader to 802.11n and focuses on technicalissues such as throughput, range, compatibility, power, and spectrum. The second report will analyze how802.11n will change the way that enterprises architect their wireline and wireless networks.

Throughout this report the following terminology is used:

• A wireless station refers to a user system such as a laptop or phone.

• A wireless access point (AP) connects wireless stations to the wired network.

• A wireless device refers to a wireless station and/or AP.

What Is 802.11n?802.11n is an emerging IEEE wireless standard that significantly improves throughput and range compared witholder 802.11 standards. Although the standard will not be ratified until the end of 2008 (at the earliest),expectations are that 802.11n will provide 100 Mbps of packet throughput and up to twice the range of 802.11g(see the “Throughput and Range” section of this report).

802.11n is the only 802.11 standard that operates in both the 2.4 GHz and 5 GHz frequency bands. Mostenterprises have deployed 802.11b/g stations and APs, so therefore they are using the 2.4 GHz frequency band.However, the dual-band operation of 802.11n presents enterprises with a unique opportunity to revisit theirprevious spectrum decision (see the “Wireless Spectrum Choices” section of this report).

802.11n is backward compatible with 802.11b/g/a, which means that an 802.11n device can communicate andinteroperate with legacy 802.11b/g/a devices. For instance, an enterprise could choose to deploy 802.11n APs inthe 2.4 GHz band and those APs would interoperate with 802.11b/g stations. Conversely, an enterprise couldchoose to deploy 802.11n APs in the 5 GHz band and those APs would interoperate with 802.11a stations (see the“802.11b/g/a Protection Mechanisms” section of this report).

802.11n includes many new features that improve throughput, range and efficiency (see the “802.11n: MajorFeatures” section of this report). For example, 802.11 can take advantage ofchannel bonding to boost throughput.And, in an interesting change of character, 802.11n uses multiple input, multiple output (MIMO) technology toturn a wireless propagation problem, calledmultipath, into a throughput enhancing solution.

The 802.11n Performance Boost802.11n is expected to provide at least 100 Mbps Internet Protocol (IP) packet throughput and up to twice therange compared to 802.11g (see the “Throughput and Range” section of this report). The increase in throughputwill enable enterprises to use wireless for more data intensive applications. Figure 1 compares the averagethroughput per user versus the number of simultaneous users per AP. Figure 1 assumes maximum AP throughputrates of 25 Mbps for 802.11g/a and 100 Mbps for 802.11n. If the WLAN is designed to accommodate up to tenusers per AP, then each user will receive 10 Mbps, on average, and could achieve burst speeds that are well over50 Mbps. Although the throughput per user is far less than a Gigabit Ethernet wired connection, 802.11n providesthroughput speeds that are quite adequate for most enterprise applications.

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Figure 1: 2.4 Average Throughput per User: 802.11n vs. 802.11g/a

The extended wireless range can be viewed positively or negatively, depending upon your point of view. Theextended wireless range means fewer 802.11n APs can achieve the same coverage as 802.11g/a, thereby savingenterprises money. This can be especially important for enterprises that desire broad wireless coverage but havemoderate bandwidth needs. On the other hand, the fact that 802.11n has a different coverage map than 802.11g/ameans that enterprises will need to carefully deploy 802.11n APs so as to minimize co-channel interference withexisting 802.11g/a APs. Finally, enterprises that share facilities with other tenants may find that an 802.11n APdeployed by their neighbor causes co-channel interference with their enterprise network.

Wireless Spectrum ChoicesAll previous 802.11b/g/a standards operate in a single frequency band, either 2.4 GHz (or 802.11b/g) or 5 GHz(for 802.11a). However, 802.11n is different because it is designed to operate in both the 5 GHz and the 2.4 GHzfrequency bands. So 802.11n presents a unique opportunity for enterprises to reconsider which frequency band touse. See Table 1 for a summary of the major spectrum considerations and tradeoffs.

Considerations

Tradeoff

Regionalregulations

Regional authorities regulate the 2.4 GHz and 5 GHz bands and may restrict frequency bandchoice.

Station-APinteroperability

Many stations are equipped with dual-band, 802.11b/g/a cards that can interoperate withbackwards-compatible 802.11n APs using either frequency.

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Radiofrequency(RF)interference

802.11 competes with many other technologies in the 2.4 GHz band (e.g., Bluetooth,microwave ovens, portable phones). The 5 GHz band is less crowded.

Range Lower frequency (longer wavelength) 2.4 GHz signals are better able to penetrate obstaclesthan 5 GHz signals and can therefore achieve 20%+ greater range.

Number ofnon-overlappingchannels

The 2.4 GHz band has only three non-overlapping channels (60 MHz). The 5 GHz band has upto 23 non-overlapping channels (460 MHz) and can therefore provider much greater aggregatenetwork performance.

Opportunityto use 40MHz channelbonding

The 5 GHz band can easily accommodate 11, 40 MHz channels, effectively doubling channelthroughput. The 2.4 GHz band can accommodate a single 40 MHz channel. 802.11n mustrevert back to a 20 MHz channel when it encounters an 802.11b/g/a device operating in one ofthe two 20 MHz channels.

Table 1: 2.4 GHz vs. 5 GHz Considerations and Tradeoffs

The 5 GHz band enables 802.11n to achieve the best possible wireless network throughput. The large number ofnon-overlapping channels in the 5 GHz band enables enterprises to take full advantage of channel bonding.Channel bonding is possible in the 2.4 GHz band but the limited number of non-overlapping channels seriouslyrestricts its usage. Channel bonding is important because it doubles the channel capacity, which boosts overallwireless throughput.

However, the installed base of 802.11b clients drove many enterprises to select 802.11g to ensure interoperabilitywith their previous investment. Therefore, most enterprises are using the 2.4 GHz band, not the 5 GHz band.

So, does that mean that once an enterprise has deployed a 2.4 GHz network they are stuck with 2.4 GHz forever?The answer is no. There are two approaches an enterprise can use to evolve their network to use the 5 GHz band:a dual-band approach and a single-band approach.

Dual-Band WLAN

Many early adopters of 802.11 have a mix of 802.11b, 802.11b/g, and 802.11b/g/a legacy stations. It is importantfor these enterprises to maintain backward compatibility while they migrate the network forward to 802.11n. Oneapproach is to operate a dual-band WLAN. Enterprise 802.11n APs will contain two radios. One of the radios canbe configured to support 802.11b/g (using the 2.4 GHz band) and the other can be configured to support 802.11n(using the 5 GHz band). Two different service set identifiers (SSIDs) can be used to ensure that legacy stationsonly connect to the AP using 802.11b/g, and that new 802.11n stations only connect to the AP using 802.11n.Over time, 802.11b/g/a stations and APs can be replaced with 802.11n stations/APs, respectively.

The benefit to this approach is that 802.11n stations can take full advantage of the high performance features of802.11n without competition from the legacy 802.11b/g/a stations. For example, all of the 802.11n stations canoperate using double-wide 40 MHz channels. In addition, the enterprise can fully utilize its investment in legacy802.11b/g/a stations. The drawback to this approach is that the enterprise must operate and maintain two wirelessnetworks. This is because the legacy stations/APs continue to operate at 2.4 GHz until they are replaced with new802.11n stations/APs.

Single-Band WLAN

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Several years ago, most stations were single band—in other words, most stations supported either 802.11b/g andcould only operate in the 2.4 GHz band, or they supported 802.11a and could only operate in the 5 GHz band.However now, most enterprises deploy 802.11b/g/a dual-band stations that can operate as either 802.11b/g or802.11a. So an enterprise that has an installed base of dual-band stations can choose to deploy 802.11n APs in the5 GHz band and still maintain a high degree of interoperability with its installed base of 802.11b/g/a stations byconfiguring them to use 802.11a.

With the single-band approach, the enterprise configures its existing 802.11b/g/a APs to use 802.11a, and thusoperates the AP in the 5 GHz band. New 802.11n APs are also configured to operate in the 5 GHz band. Legacy802.11b/g/a stations will use 802.11a in order to communicate with the old 802.11b/g/a APs and the new 802.11nAPs. Note that legacy 802.11b/g stations must be replaced by new dual-band 802.11g/a/n stations.

The benefit to this approach is that it maximizes the return on investment (ROI) of installed 802.11b/g/a stationsbecause all of the old 802.11b/g/a stations can use the new 802.11n network. The drawbacks to this approach arethat 802.11b/g stations must be upgraded to 802.11g/a/n, and 802.11b/g/a stations cannot take advantage ofchannel bonding and will thus degrade the performance of 802.11n stations that try to use 40 MHz channels.However, over time newer 802.11n stations will replace older stations thus reducing contention and improvingoverall network performance. Eventually, the entire network will operate using 802.11n running at 5 GHz.

802.11b/g/a Protection Mechanisms802.11n is designed to operate with backward compatibility for 802.11b/g/a devices—a method of operation thatis calledmixed mode. 802.11b/g/a, on the other hand, does not have forward compatibility with 802.11n.Therefore 802.11n must protect 802.11b/g/a stations from 802.11n transmission that may be interpreted asinterference.

The 802.11n protection mechanism for 802.11g and 802.11a stations is straightforward. This is because all threestandards use the orthogonal frequency-division multiplexing (OFDM) Physical Layer (PHY) and, morespecifically, share a similar physical layer convergence procedure (PLCP). Thus, at the most basic level, 802.11ndevices can communicate with 802.11g/a devices in order to ensure protection. 802.11n adds only 8 microsecondsof extra information in the preamble for protection. So, in theory, the 802.11g/a protection mechanism should bevery efficient and should have very little impact on overall network performance. However, beta tests of pre-released 802.11n APs show that mixed mode operation can degrade network performance by 25%. EnterpriseWLAN system vendors are working with the semiconductor vendors to reduce this performance degradation.Enterprises can avoid the 802.11g performance degradation entirely if they operate 802.11n in the 5 GHz band.

802.11b, on the other hand, uses the direct sequence spread spectrum (DSSS) or Complementary Code Keying(CCK) PHY. Therefore, it is not possible to use the same PLCP to protect 802.11b stations. Instead, much lessefficient medium access control (MAC) layer frames must be used. 802.11n must send a Request to Send (RTS)frame to the 802.11b station and wait for a Clear to Send (CTS) response frame from the 802.11b station. Afterthe RTS/CTS exchange the 802.11n station is free to transmit. This is a very inefficient mechanism and will havea significant impact on network performance. Enterprises can avoid the 802.11b performance degradation entirelyif they operate 802.11n in the 5 GHz band.

Standardization and CertificationDevelopment of the 802.11n standard has been anything but a smooth process. MIMO pioneer Airgo Networks(acquired by QUALCOMM) built the first MIMO-based, commercial, off-the-shelf chipset. It demonstrated thatMIMO could significantly improve 802.11 throughput and range, and that MIMO was the next great innovationfor 802.11. Airgo was an enormous threat to the current 802.11 chipset leaders (Atheros Communications,Broadcom, and Marvell), and set in motion a very public technical and political battle.

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The battle line was drawn between two warring camps. The TGn Sync group included Atheros, Agere Systems,Marvell, and Intel, while the World-Wide Spectrum Efficiency (WWiSE) group included Airgo, Broadcom,Conexant Systems, and Texas Instruments. Both camps created similar proposals and waged bitter battles at IEEEworking-group meetings. At stake was the future of 802.11 and the winner would reap enormous financialrewards. Both sides dug in for a long fight over seemingly irreconcilable differences, thus bogging down theformation of a single, 802.11n draft specification.

Then in October 2005, 27 vendors announced the formation of the Enhanced Wireless Consortium (EWC). TheEWC included vendors from both camps, including Atheros, Broadcom, Intel, and Marvell—but not Airgo. TheEWC specification was submitted to the IEEE, and in January 2006 the IEEE members voted unanimously toaccept the EWC proposal as the official 802.11n draft 1.0 specification.

The draft 1.0 specification was a huge step in the right direction, but many issues remained. However, these issuesdid not prevent vendors from delivering draft-N APs to market in 2006. Many independent tests uncoveredproblems, including poor performance, lack of vendor interoperability, and lack of backward compatibility.Undeterred, these vendors promised that their draft-N products would be software upgradable to the finalstandard.

According toIn-Stat, there could be more than 50 million draft-N products on the market by the time the standardis ratified. With vendors claiming draft-N compliance (whatever that means!), how will customers determinewhich products are interoperable, and which products will be software upgradable to the final standard? Itappeared that the 802.11n market was devolving into a chaotic free-for-all.

Then on August 2006, the Wi-Fi Alliance (WFA) announced plans to certify interoperability of Wireless Fidelity(Wi-Fi) products based upon a draft of the 802.11n standard in the first half of 2007. This certification is calledthe first-phase certification program. In addition, a future second-phase certification program will be based uponthe final 802.11n standard. The goal of the draft-N certification program is to ensure interoperability betweenproducts based upon a subset of the draft 2.0 standard (which was approved in early 2007). In addition, the WFAexpects first-phase certified products to be interoperable with future products certified during the second phase.The second-phase certification will be introduced at approximately the same time that the final standard is ratified(it is currently planned for March 2009; see the “IEEE 802.11n Ratification Timeline” section of this report forfurther details).

First-phase WFA testing will focus on the major features in 802.11n, such as:

• 2.4 GHz and 5 GHz operation

• Double-wide 40 MHz channels (5 GHz only)

• Mixed-mode operation (2.4 GHz and 5 GHz)

• Two spatial streams

• MIMO power save

First-phase testing will be a subset of the second-phase testing. This means that some features of 802.11n (e.g.,the use of 40 MHz channels in the 2.4 GHz band) will not be certified until the second phase. Whether or notuncertified features implemented in first-phase certified products will be fully interoperable with second-phasecertified products remains an unanswered question.

On the other hand, every 802.11n vendor interviewed for this report said it was very confident that a softwareupgrade will enable its first-phase certified products to be interoperable with second-phase certified products. Inaddition, there is tremendous business pressure on 802.11n vendors to make their products software upgradable tothe final standard. Therefore, the risk that first-phase certified products based upon draft 2.0 will not beinteroperable with second-phase certified products based upon the final standard is low.

The WFA has performed pre-standard certification in the past. In April 2003, the WFA began testing the Wi-FiProtected Access (WPA) security certification. WPA was based upon draft 3 of the IEEE 802.11i securitystandard. When the IEEE completed ratification of 802.11i, the WFA revised the WPA test suite to be compliantwith the final 802.11i standard, and created a new certification mark called WPA2.

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Power Consumption802.11n APs will likely consume more power than 802.11b/g/a APs. This is because of the use of multiple radios,higher power digital signal processors (DSPs), and higher-power central processing units (CPUs). In addition,power consumption is highly correlated to traffic rate. The more traffic that an AP is transmitting and receiving,the more power the device consumes.

Legacy APs have a maximum power draw that is very close to the IEEE 802.3af,1 Power over Ethernet (PoE),maximum of 15.4 watts (12.95 watts with cable losses). For example, the Cisco Aironet 1200 series has amaximum power draw of 13 watts. Therefore, because 802.11n APs will likely consume more power than legacyAPs, most 802.11n APs will likely exceed the power rating of 802.3af PoE equipment.

Enterprise AP vendors will address this problem in several ways. First, all vendors will support use of wall-outlet-powered APs, and thus will be able to draw all the power they need. Secondly, some vendors will design their802.11n APs with multiple Ethernet connections, thus enabling the AP to be powered by two PoE connections.Finally, many PoE-powered 802.11n APs will still continue to operate—albeit with degraded functionality—inorder to stay within the PoE power budget. An example of degraded functionality is the use of a single transmitterrather than multiple transmitters, resulting in reduced system throughput.

The IEEE is working on a new PoE standard—IEEE 802.3at, commonly called PoE Plus. PoE Plus will make useof all four pairs of Ethernet twisted pair cable (802.3 used two of four pairs of Category 3, 5, 5e, 6, or 6A cable).PoE Plus will likely provide up to 56 watts of power. Some 802.11n APs will support pre-standard 802.3at.Unfortunately, PoE Plus will not be ratified before 2008.

AP BackhaulLegacy 802.11b/g/a APs used Fast Ethernet uplink ports to communicate traffic onto the wired network. Becausethe 802.11n data rate will exceed the 100 Mbps capacity of Fast Ethernet (especially when using 40 MHzchannels), most new APs will use Gigabit Ethernet for uplink communication. Gigabit Ethernet provides morebandwidth than any 802.11n AP can generate over a backhaul connection.

System Impact802.11n will have an impact on existing 802.11 systems. This section analyzes its affect on intrusion detectionsystems, network management systems, and WLAN systems.

Intrusion Detection Systems

To monitor the WLAN for security violations, many enterprises have deployed, or are considering deployment of,wireless intrusion detection systems (WIDSs). These tools use hardware sensors to capture data from the RF link,perform analysis on that data in a central server, and provide alerts and reporting related to security of the WLANin a portal or console view. Monitoring for rogue APs and unauthorized devices, maintaining policy adherence inthe air and on the APs, and looking for anomalous or unexpected behavior on the WLAN are a few of the servicesa WIDS offers.

Rogue APs can attempt to join the network, lure unsuspecting users to their own network, disrupt traffic, orinterfere with the RF signal. 802.11n presents a new challenge because existing hardware sensors, withoutsoftware and/or hardware updates, may not be able to recognize N or draft-N APs. In addition, an 802.11n deviceconfigured forGreenfield mode could be used to launch a denial of service (DoS) attack on legacy 802.11nnetworks.

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Independent IDS vendors such as AirTight and AirDefense announced product support for 802.11n in 2006.WLAN system vendors have also developed product upgrades for 802.11n. It is important for an enterprise toupdate its wireless IDS, regardless of whether or not it plans to deploy 802.11n.

For more information on WIDSs, see the Security and Risk Management Strategies report, “Wireless LANIntrusion Detection Systems: Something's in the "Air".”

Network Management Systems

WLANs are significantly different than wired networks. For instance, the 802.11 MAC layer is a shared, half-duplex connection and the three-dimensional (3D) nature of RF allows the signal to pass through walls andceilings, rendering it susceptible to interception, interference, and unpredictable performance. Given theincreasing deployment of WLANs, network managers have found a way to address these differences using avariety of network management tools (e.g., spectrum analyzers, WLAN monitors, site planning, and configurationmanagement tools).

802.11n introduces, at the PHY and the MAC, changes that impact all of these tools. For example, spectrumanalyzers must be able to both recognize MIMO spatial streams, and visually communicate network behavior tothe user. WLAN monitors need to be able to perform packet capture at much higher speeds, and must be able todecode MAC layer frame aggregation. In addition, configuration management tools need to be able to manage themany new features in 802.11n.

For more information on 802.11 network management tools, see the Network and Telecom Strategies report, “Wireless LAN Management Tools: Filling the Gaps.”

WLAN Systems

The term WLAN system is used to represent any device that implements centralized management and control ofmultiple lightweight APs. With WLAN systems, the network manager configures a controller, and the controllerconfigures the individual APs. The primary benefit is improved manageability, because instead of hundreds orthousands of individual APs, the network manager could direct one or more controllers. This approach helped toscale network management as WLANs proliferated. Many enterprises now recognize the value of WLANsystems, and have migrated their networks to use controller-based architectures.

WLAN system vendors that centralize the data-forwarding function in the controller must backhaul all wirelesstraffic across the wired network, where the controller can make forwarding decisions, perform quality of service(QoS) queuing, and perform virtual LAN (VLAN) tagging. In some cases, the wired network must double switchthe traffic. However, in the past this double switching did not matter because 802.11a/b/g speeds were muchslower than wired LANs. But 802.11n APs will generate significantly more traffic at higher rates than the olderAPs, and they will have much more of an impact on the wired network and the WLAN system controller thanprevious generations.

See the Network and Telecom Strategies report, “Wireless LAN Systems: Ready for the Future?” for moreinformation.

Market Impact

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There is very strong demand for 802.11n products (see Figure 2). The fact that the installed base of draft-Nproducts will be more than 50 million units by the time the standard is ratified shows just how strong the demandfor improved wireless performance really is. Most of this demand comes from the consumer market, which has amuch higher tolerance for pre-standard products than the enterprise market. The strong consumer demand willaccelerate the learning process for chipset vendors and original design manufacturers (ODMs). As more devicesare deployed, these vendors will gain real-world experience. This real-world experience will benefit the WLANsystem vendors because many of them use off-the-shelf chipsets and ODM reference designs in their enterpriseproducts.

Figure 2: 802.11n Market (Adapted from: Dell'Oro Group)

In addition, the upcoming IEEE standards—802.11k, 802.11v, and 802.11r—will improve 802.11 reliability andpredictability. Thus 802.11n, along with these emerging standards, will make WLANs much more like a wiredLAN, and they will ultimately have a significant market impact. See the Network and Telecom Strategies report, “Wireless LANs Standards: Where Are We Now?” for additional information on these emerging standards.

Impact on Ethernet Switching Vendors

According to Infonetics Research,2 the wired Ethernet switching market is forecasted to grow 20% per year (from2006 to 2009), reaching $18.6 billion in sales by 2009. Conversely, the WLAN equipment market is expected to

reach $4.3 billion by 2010.3 Although the WLAN market is less than one-quarter of the size of the wired Ethernetswitching market, the fact that these forecasts aggregate the consumer and enterprise markets conceals anemerging trend in the enterprise market: 802.11 is slowly becoming the preferred technology for enterprisenetwork access. The emergence of 802.11n, and related 802.11 standards, will accelerate that trend so that802.11n may eventually become the dominant enterprise LAN technology. As this happens, the growth of theEthernet switching market may begin to slow due to WLAN substitution.

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Ethernet switching vendors that rely upon an original equipment manufacturer (OEM) partner—includingExtreme Networks (Siemens OEM), Foundry Networks (Meru Networks OEM), and 3Com (NextHopTechnologies OEM)—are vulnerable to losing their partner through acquisition. For example, when CiscoSystems acquired Airespace in 2005, Nortel Networks had to scramble to find a new OEM partner. The samething could happen to other wired Ethernet switching vendors. Although this vulnerability existed before, 802.11nwill make the stakes much higher because it will be pervasively deployed throughout the enterprise. Ethernetswitch vendors must ensure continuous wireless product delivery or else risk losing market share in one of thebiggest growth markets in the networking industry.

802.11n is also a more complex technology than earlier versions of 802.11. When a customer calls customersupport with a tricky wireless interference problem, will a wired-Ethernet-switch vendor be able to handle theproblem? Probably not. The Ethernet switching vendors are at a competitive disadvantage because they rely upontheir OEM's wireless expertise rather than their own core competency.

Finally, as 802.11n controllers become more embedded in traditional Ethernet switching products, it will becomemore difficult to separate wired and wireless products. This means that Ethernet switching products will evolve tobecome converged wired-wireless products. Ethernet switching vendors will need to integrate wireless into theirentire solution portfolio, including their network management systems, consulting services, and customer support.

Impact on Independent WLAN Vendors

Enterprise acceptance of WLANs has been slower than consumer acceptance. This is due to a number of factors,including security concerns, lack of a standard QoS mechanism, and poor performance. The ratification of the802.11i and 802.11e standards addressed the need for security and QoS, respectively. The 802.11n standard willsignificantly improve WLAN performance and will accelerate the demand for WLAN products.

As the saying goes, “a rising tide raises all boats.” Similarly, an expanding market benefits all vendors. Thegrowing WLAN market, driven by 802.11n, will help the independent wireless vendors grow their revenue too.But, the trend toward integration of wired and wireless solutions will make it increasingly difficult forindependent wireless vendors to grow market share. In addition, Voice over WLAN (VoWLAN) and fixed mobileconvergence (FMC) solutions will require the integration of handsets, WLAN equipment, IP private branchexchanges (IP-PBXs), and software. Larger vendors with an integrated equipment portfolio will have anadvantage over the smaller, wireless-only vendors. See the Network and Telecom Strategies report, “Fixed MobileConvergence: Aggregation or Aggravation?” for additional information.

The acceptance of 802.11n technology will increase the urgency for a wired Ethernet Switch vendor to expand itscore competence to include WLAN technology. The fastest way to do this is through merger and acquisition(M&A). Independent WLAN vendors will increasingly be the target of M&A activities. The recent initial publicoffering (IPO) of Aruba Networks may have priced it out of the market in the near term. However, if Arubastumbles and experiences a significant fall in market capitalization, it could become a viable M&A target.Vendors such as Meru, Trapeze, and Colubris Networks have sufficiently mature products that they are likelytargets. Xirrus and Extricom are relative newcomers but are sufficiently differentiated from the other WLANvendors that they may also become M&A targets.

Ultimately, WLAN products will be integrated into broader product portfolios. Therefore, any WLAN vendorsleft standing when the M&A music stops may find themselves relegated to the “other” category in future marketshare reports.

Impact on Enterprise VoWLAN Market

Voice over IP (VoIP) running over a wired LAN has begun to take hold in the enterprise. The benefits of using asingle network for both data and voice traffic are now recognized. However, running VoIP on a WLANexacerbates the issues surrounding use of VoIP on a wired LAN. See the Network and Telecom Strategies report,“Voice-Enabled WLANs: Is the Network Ready?” for additional information.

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However, the broad deployment of 802.11n in the enterprise will facilitate widespread in-building coverage—aprerequisite for pervasive VoWLAN support. In addition, support for emerging standards 802.11r/k/v, will createa reliable, manageable, and predictable wireless network. Therefore, 802.11n will accelerate the growth of theenterprise VoWLAN market.

Recommendations802.11n is a more complex WLAN technology and is not yet standardized. Enterprises should consider thefollowing recommendations.

Only Buy Products That Are WFA Certified

During most of 2007 and possibly into 2008, WLAN vendors will sell draft-N WLAN equipment that is not WFAcertified. These products can be used for lab testing, but only WFA-certified products should be used forproduction deployments. Watch for third-party test results in order to evaluate interoperability and performance.

Consider Draft-N, WFA-Certified Products for Production

Draft-N, WFA-certified (i.e., first-phase) products will be available in the fall of 2007. Although the IEEEstandard is not yet ratified, the risk that draft-N, WFA-certified products will be incompatible with final 802.11n,WFA-certified (i.e., second-phase) products is low. Enterprises should consider using draft-N, WFA-certifiedproducts for large-scale deployment of production networks.

Deploy 802.11n in 5 GHz Band

Enterprises should deploy 802.11n in the 5 GHz frequency band. The 5 GHz band has many more channels thatcan be used for double-wide, 40 MHz channels. In addition, the 5 GHz frequency is less crowded, so WLANtraffic will be subjected to less interference than in the 2.4 GHz band.

Use 40 MHz Channel Bonding

Use 40 MHz channel bonding in order to achieve the best possible WLAN throughput. This will not be possiblewith legacy 802.11 devices or when adjacent channels are already in use.

Use Dual-Band 802.11n Stations

Use dual-band stations. They provide the greatest deployment flexibility because they can be used either in the 2.4GHz or the 5 GHz bands.

Use Dual-Band, Dual-Radio 802.11n APs

Enterprises should use dual-band, dual-radio 802.11n APs because they can operate in either the 2.4 GHz or the 5GHz bands. In addition, dual-radio APs can be configured to have one radio operate as an 802.11g/a AP, and theother radio operate as an 802.11n AP. Network managers can use this configuration to implement adual-bandWLAN.

Make Sure That Gigabit Ethernet Is Available for AP Backhaul

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802.11n APs need Gigabit Ethernet backhaul connections. Make sure that Gigabit Ethernet is available for APbackhaul.

Upgrade Intrusion Detection Systems Now

Intrusion detection systems (IDSs) must be upgraded now in order to detect draft-N (and eventually standardizedN) rogue APs and mobile devices.

Prepare for 802.11n APs That May Exceed the PoE Power Budget

802.11n APs may exceed the power budget for PoE. Enterprises must prepare to power 802.11n APs either byusing 2 PoE connections, a power brick, or pre-standard (i.e., higher-power) PoE Plus.

Avoid Mixing 802.11b and 802.11n Stations on the Same 2.4 GHz Band

802.11n stations are backward compatible to 802.11b devices. However, that compatibility comes at a severeperformance penalty. Therefore avoid mixing 802.11b and 802.11n stations on the same 2.4 GHz band, either byeliminating 802.11b mobile devices or by operating 802.11n at 5 GHz.

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The Details

This section details many of the innovative new features of 802.11n as they relate to earlier wireless local areanetwork (WLAN) standards such as 802.11 a/b/g.

802.11n: Major Features802.11n defines many features that improve throughput, range, transmission efficiency, and channel reliability. Inorder to achieve backward compatibility, 802.11n must support the three physical layer modulation techniquesused by the older standards: direct sequence spread spectrum (DSSS), Complementary Code Keying (CCK), andorthogonal frequency-division multiplexing (OFDM).

802.11a

802.11b 802.11g 802.11n

Standard approved July1999

July 1999 June 2003 Not yet ratified

Maximum data rate 54Mbps

11 Mbps 54 Mbps 600 Mbps

Modulation OFDM DSSS orCCK

DSSS or CCK orOFDM

DSSS or CCK orOFDM

Radio frequency (RF)band

5 GHz 2.4 GHz 2.4 GHz 2.4 GHz or 5 GHz

Number of spatialstreams

1 1 1 1, 2, 3, or 4

Channel width 20MHz

20 MHz 20 MHz 20 MHz or 40 MHz

Table 2: Primary Institute of Electrical and Electronics Engineers (IEEE) 802.11 Specifications (Source:Broadcom)

802.11n is the first 802.11 standard to standardize use of multiple input, multiple output (MIMO) antenna design.MIMO can significantly improve throughput and range. 802.11n also incorporates many other features in order toachieve superior performance:

• Orthogonal frequency-division multiplexing (OFDM): 802.11n improves the OFDM physical layer that isused in 802.11a/g. These improvements increase the raw data rate for a single stream from 54 Mbps to 65Mbps. Only 802.11n devices can take advantage of the 65 Mbps speed.

• Channel bonding: Previous 802.11 standards used a single 20 MHz channel, but 802.11n can bond togethertwo channels to form a double-width 40 MHz channel. Channel bonding doubles the channel bandwidth, so it isa very important feature of 802.11n.

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• Space-division multiplexing (SDM): 802.11n devices can split a transmission stream into four separatetransmission streams (called “spatial streams”). Each spatial stream is transmitted through separate antennas.More spatial streams provide greater throughput because more information can be transmitted on the samechannel. See the “MIMO” section of this report for more details.

• Beam forming: Beam forming is a technique that focuses the radio signals directly onto a target antenna.When radio signals are focused, the receive antenna receives more signal energy.Beam forming improves bothrange and interference sensitivity.

• Frame aggregation:Frame aggregation enables a transmitting 802.11n station to pack several frames togetherinto a single larger frame. This improves transmission efficiency in amixed-mode network by increasing thepercentage of time that an 802.11n device uses the channel, as compared to a legacy device.

• Multiple input, multiple output (MIMO) power save:MIMO power save reduces power consumption bytemporarily using only a single antenna.

• Reduced inter-frame spacing (RIFS): RIFS enables a station to burst frames by gaining greater access to thechannel.

MultipathGuglielmo Marconi (1874–1937), the Italian radio researcher, performed the first tests in 1896 that demonstratedthat radio waves could travel beyond the horizon. The initial discovery of non-line of sight (NLOS) transmissionled to extensive research on multipath communication. Multipath (see Figure 3) is an RF propagationphenomenon that occurs when RF signals reflect off of objects within the transmission channel between thetransmitter and the receiver.

Figure 3: Multipath

Multipath causes interference, fading, and phase shifting of the original signal. For many years, the effects ofmultipath (see Figure 4) were viewed as sources of signal degradation that had to be taken into affect whendesigning a wireless system.

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Figure 4: Effects of Multipath (Adapted from: Cisco)

In 1993, to counter the effects of multipath transmission, Arogyaswami Paulraj and Thomas Kailath proposed theconcept of spatial multiplexing using MIMO antenna design. Then in 1996, 100 years after Marconi's originaltests, Greg Raleigh (a Stanford PhD student) and Gerard J. Foschini (a Bell Labs engineer) separately refined newapproaches to MIMO technology, ultimately laying the foundation for 802.11n.

MIMOMIMO is a technology that uses multiple antennas at the transmitter and the receiver (this is why MIMO issometimes referred to as “smart antenna” technology). MIMO exploits the fact that RF signals often reflect off ofobjects in their path, causing a phenomenon calledmultipath. MIMO uses a technique called spatial multiplexingthat transmits multiple data streams at the same frequency but over different spatial channels. In an interestingtwist, spatial multiplexing takes advantage of the multipath phenomenon to increase effective channel capacitywithout consuming additional spectrum. In effect, MIMO takes multipath transmission and converts it from asignal impairment into a signal enhancement. MIMO makes a channel more spectrally efficient because spectralmultiplexing increases the (baud rate)/(hertz) ratio.

MIMO terminology assumes the antenna's perspective of the antenna/radio interface—rather than the antenna/airinterface (see Figure 5). Therefore, the “multiple-input” part of the MIMO name means that a WLAN devicesimultaneously sends two or more radio signals from the radio into multiple antennas. The “multiple-output” partof the MIMO moniker means that two or more radio signals are coming out of multiple antennas and entering theradio.

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Figure 5: Multi-Input/Multi-Output System (Source: Atheros Communications)

Throughput and RangeWireless performance is often characterized using a throughput-versus-range curve. Throughput is usually plottedon the y axis, and range on the x axis. Throughput will decrease as the receiver moves away from thetransmitter—thus increasing range. Figure 6 shows throughput-versus-range curves for three access point (AP)configurations: 802.11g (light grey), 802.11n with 2x2 MIMO (dark blue), and 802.11n with 3x3 MIMO (lightblue). The curves show that throughput decreases with distance, and they also show the relative throughput foreach of the three configurations.

Figure 6: Throughput vs. Range (Source: Adapted from Atheros)

Chip manufacturers expect that 802.11n throughput will be at least five times faster than 802.11g, and will have atleast twice the range of 802.11g. However, it is very important to note that real-world performance is highlydependent upon many factors, including environmental interference, system design, network design, and buildingconstruction. Therefore the performance of an 802.11n network can vary from enterprise to enterprise, building tobuilding, and even floor to floor. Given these caveats, the previous curves should be used as guidelines only.

The 2.4 GHz and 5 GHz Bands802.11n can operate in either the 2.4 GHz band or the 5 GHz band. Table 3 provides specific frequency-bandranges, and describes usage and regional allocation.

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Frequencyband

Usage and regional allocation

2.403–2.483GHz

802.11b/g, 802.11n, Bluetooth, microwave ovens

ISM band in the United States, available in most of the world

5.150–5.250GHz

802.11a, 802.11n, 802.16 fixed/mobile

United States (Unlicensed National Information Infrastructure [U-NII]), Canada, Europe,Japan, China

5.250–5.350GHz

802.11a, 802.11n, 802.16 fixed/mobile

United States (U-NII), Canada, Europe, China

5.470–5.725GHz

802.11a, 802.11n, 802.16 fixed/mobile

United States (U-NII), Canada, Europe, Central and Latin America, Middle East, Asia Pacific

5.725–5.825GHz

Cordless phones, 802.11a, 802.11n, 802.16 fixed/mobile

U-NII band in the United States

Table 3: 2.4 GHz vs. 5 GHz Frequency Bands

Modes of OperationAn 802.11n device can be configured to operate in three operational modes: legacy mode, mixed mode, andGreenfield mode. Legacy mode configures the station to operate as an 802.11a or 802.11g device. In this mode,the 802.11n station appears to an 802.11a/g device as another 802.11a/g device. This mode could be used when anenterprise buys a new 802.11g/a/n device but does not yet want to turn on 802.11n operation.

Mixed mode configures the station to operate as an 802.11n device but it must co-exist with older 802.11 deviceson the same channel. When configured for mixed mode, the 802.11n must provideprotection for the older 802.11devices. The 80211.n preamble looks like an 802.11g preamble. The preamble contains a tiny data field thatcontains that data rate and indicates how long the transmitter is going to be transmitting. The 802.11g deviceshave to respect that information by waiting for the 802.11n device to finish transmitting before they use thechannel. This mechanism is very efficient because only 8 microseconds of extra information is added to the802.11n preamble for 802.11g compatibility.

Greenfield mode assumes that only 802.1n stations operate on the network, so no protection is necessary.Greenfield mode offers the highest possible performance, but only incrementally higher than mixed mode.Stations can freely use double-wide channels without accommodating older devices that can only use a single-wide channel. The concern with Greenfield mode is that, if a non-802.11n device wanders into range of an802.11n device that is operating in Greenfield mode, then the 802.11n device will not protect the traffic from theolder device and will stomp on the legacy packets.

Transmit Beam Forming

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Most antennas used by enterprise and consumer APs are omni-directional antennas, and they radiate energyequally in all horizontal directions. Conversely, a directional antenna focuses most of the energy in one direction(see Figure 7).

Figure 7: Radiation Pattern from a Directional Antenna (Source: Spectrum Signal Processing)

Transmit beam forming (TBF) is a technique using directional antennas to improve the range of a wireless systemand indirectly improve throughput. TBF uses an array of transmit antennas with the same signal except that themagnitude and phase are adjusted at each transmitter such that a focused beam is generated. If a priori informationabout the location of the target receiver is known, TBF would point its focused beam in that direction. TBF

focuses energy, and thus improves range by increasing average received signal power.4

Frame AggregationLegacy 802.11 stations (e.g., those using 802.11b) take much longer to transmit a frame of equal size than an802.11n station because the legacy station transmission rate is much slower than an 802.11n station. This resultsin the legacy station consuming an inordinate amount of time on the wireless channel compared to an 802.11nstation. The 802.11n standard attempts to compensate for this by allowing 802.11n devices to aggregate severalframes into single frame (see Figure 8).

There are two types of aggregation: payload aggregation and packet aggregation. Payload aggregation combinesseveral Internet Protocol (IP) packets into a single 802.11n frame with a single medium access control (MAC)layer Cyclical Redundancy Check (CRC). Packet aggregation combines several individual 802.11n frames into asingle aggregated 802.11n frame. Each of the individual 802.11n frames maintains their individual CRC.

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Figure 8: Frame Aggregation (Source: Broadcom)

Reduced Inter-Frame SpacingReduced inter-frame spacing (RIFS) shortens the delay between frame transmission and increases efficiency inOFDM-only networks. RIFS enables a station to retain control of the wireless channel in order to transferadditional frames. RIFS is a technique for bursting frames.

Power Save ModesThere are two types of power save modes in a MIMO system. MIMO power save reduces power consumption byusing only a single MIMO transmitter. This mode conserves power because it turns off one or more MIMOtransmitters. MIMO power save is different from the 802.11 Unscheduled Automatic Power Save Delivery (U-APSD) power save mode. U-APSD is used primarily by Wireless Fidelity (Wi-Fi) phones. U-APSD turns off alltransmitters and receives at a predetermined time interval. During the U-APSD sleep mode, the AP must bufferframes that are destined for the station. When the station wakes up, the AP transmits the buffered frames to thestation.

IEEE 802.11n Ratification TimelineThe IEEE 802.11n ratification timeline can be found at http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm.

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http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm

Conclusion

802.11n is an emerging Institute of Electrical and Electronics Engineers (IEEE) wireless standard thatsignificantly improves throughput and range compared with older 802.11 standards. 802.11n is the only 802.11standard that operates in either the 2.4 GHz and 5 GHz frequency bands, and it is the first to standardize the use ofmultiple input, multiple output (MIMO) antenna design. 802.11n is backward compatible with 802.11b/g/a, whichmeans that an 802.11n device can communicate and interoperate with legacy 802.11 devices. 802.11n mayeventually become the dominant enterprise local area network (LAN) technology.

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Notes

1 “Power over Ethernet.” Wikipedia. Accessed online 20 Apr 2007. http://en.wikipedia.org/wiki/Power_over_Ethernet.

2 “Cisco passes $10B in enterprise switch sales in 2006; 1G, 10G, PoE ports growing strong.” InfoneticsResearch. Accessed online 28 Apr 2007. http://www.infonetics.com/resources/purple.shtml?ms07.sw.4q06.nr.shtml.

3 “Wireless LAN switch market up 27%, 802.11 adoption continues to ramp up in 2006.” Infonetics Research.Accessed online 28 Apr 2007. http://www.infonetics.com/resources/purple.shtml?ms07.wl.4q06.nr.shtml.

4 Winston Sun. “MIMO Architecture: The Power of 3.” Atheros Communications, Inc. May 2006. http://www.atheros.com/pt/whitepapers/MIMO_Pwr3_whitepaper.pdf.

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http://en.wikipedia.org/wiki/Power_over_Ethernet

http://www.infonetics.com/resources/purple.shtml?ms07.sw.4q06.nr.shtml

http://www.infonetics.com/resources/purple.shtml?ms07.wl.4q06.nr.shtml

http://www.atheros.com/pt/whitepapers/MIMO_Pwr3_whitepaper.pdf

Author Bio

Paul DeBeasi

Senior Analyst

Emphasis: Wireless and Mobility

Background: Over 25 years of experience in the networking industry. Previously, founded ClearChoice Advisors, awireless advisory firm, and was the VP Product Marketing at Legra Systems, a wireless-switch provider.

Primary Distinctions: Led product management for Cascade Communication's Frame Relay business unit,contributing to revenue growth of more than $160M over two years. Launched networking startups Legra Systems,IPHighway, and ONEX Communications into highly competitive markets as VP Product Marketing. Developedprofitable networking products as a senior engineer at Bell Laboratories, Prime Computer, and ChipcomCorporation. He frequently speaks at Networld+Interop, Next Generation Networks Enterprise Networks, InternetTelephony, and several other conferences. Holds a BS degree in Systems Engineering from Boston University and aMaster of Engineering degree in Electrical Engineering from Cornell University.

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802.11n: Beyond the Hype

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