3.802.11n WLAN 优化.ppt

1、802.11n WLAN 优化,Xie Qing Nov, 2009,802.11n WLAN 优化特性,ClientLink,对 11a/g 客户端的波束成形,什么是 ClientLink?,思科称之为 “Legacy Beam Forming”。区别于 802.11n 标准的“Beam Forming”，只作用于 802.11n 客户端。 通过两个天线指导信号的强度指向客户端的方向 只工作在 OFDM 数据率 只有 802.11a/g 客户端获益 802.11b 客户端不会从中获得任何好处 需要: WLC 6.0 or higher 1250 or 1140 Access Points,思

2、科 ClientLink 技术 保护现有11a/g 设备的投资,802.11n,挑战 #2: 在混合类型客户端设备的网络中提供公平,挑战 #1:延长11a/g 设备的使用寿命,802.11n,300 Mbps,54 Mbps,11a/g devices reaching max. performance but too costly to upgrade,11a/g devices consume valuable “airtime”, reducing the performance of 11n devices,ClientLink 技术提供下列益处： 为11a/g 设备提供一致的高吞吐量

3、 为11a/g 和 11n 设备增加显著的系统容量 在复杂而有挑战性的射频环境中减少覆盖漏洞,802.11a/g,未优化的802.11a/g客户端连接, 产生覆盖漏洞,802.11n,X,现有的 802.11n 解决方案 波束强度没有朝向客户端,ClientLink 技术通过波束成形将无线信号导向客户端， 改善 802.11a/g 设备的性能和覆盖,波束成形,802.11a/g,802.11n,思科 M-Drive ClientLink 技术 思科的创新： 智能的波束成形,射频技术领先：波束成形,什么是波束成形 ? 来自多个发射天线的信号被聚焦到接受客户端: 增加了覆盖面积，提高连接数据率 减

4、少了无线信号的覆盖盲点,用户获益 ? 所有的 802.11a/g 客户端下行速率更快 无线信号在更长的距离内更稳定可靠 极大改善整个无线系统的性能,NO BEAM FORMING,BEAM FORMING,获益 #1: 改善吞吐量ClientLink 技术为11a/g设备提供更高的吞吐量,No Connection without ClientLink,Throughput vs. Distance,Test: 802.11a/g device with 802.11n networkSource: Miercom,高达 65% 的吞吐量增长,13.6%,87.7%,70.4%,89.5%,C

5、lientLink 技术允许客户端以一致的高数据率连接。更快的数据传输，更少的重试 = 整体上更有效的利用射频信道。 11a/g设备更快的处理意味着11n设备可以利用更多的“空口” 时间，同样改善了11n设备的性能。,Test: 802.11a/g device measured at 16 antenna orientations w/ 802.11n networkSource: Miercom,获益 #2: 更大的系统容量 在覆盖区域内提供一致的高吞吐量,高达 27% 的信道容量增长,在16个不同位置测量吞吐量,Channel Util of 74.2%,Channel Util of

6、45.2%,ClientLink Disabled,ClientLink Enabled,Lower Data Rates,Higher Data Rates,Source: Miercom; AirMagnet 6.0 Iperf Survey,获益 #3: 减少覆盖漏洞 ClientLink 技术提供更高的物理层数据率,ClientLink Disabled,ClientLink Enabled,High Retry Rates,Low Retry Rates,Source: Miercom; AirMagnet 6.0 Iperf Survey,获益 #3: 减少覆盖漏洞 (cont.)

7、ClientLink 技术交付更低的数据重试率,ClientLink可以做什么和不能做什么！,可以做什么:,改善802.11a/g 客户端的性能clients 在一定的距离 通过增加下行数据率，减少 802.11a/g 客户端的“空口占用时间” 在混合部署环境间接增加 802.11n 的吞吐量,不能做什么:,近距离改善性能 使 802.11b 客户端受益 直接增加 802.11n 吞吐量,Cisco Internal,ClientLink 可以做什么,波束成型只有在数据率开始 下降时才能改善性能 意味着 - 如果连接质量已经很好 (例如数据率达到 54Mbps) ，没有什么可以改善 可衡量的优

8、势: 在蜂窝边缘增加 信噪比 在蜂窝边缘增加下行 数据率 在蜂窝边缘增加下行 吞吐量,Provides,Provides,Cisco Internal,基本事实流量类型,需要双向流量 通知无线接入点将波束导向哪里 TCP 下行 (TCP ACKs 提供无线射频模块需要的反馈信息) TCP 双向 UDP 双向,Downstream Data,TCP ACK,提供客户端的位置并 更新波束成型表,Cisco Internal,基本事实阀值和扩展性,ClientLink 只在客户端的接收信号强度指示低于某一阀值时才发生作用 对于 802.11a, 阀值为 -60dBm 或更弱 对于 802.11g,

9、阀值为 -50dBm 或更弱 一般在客户端距离无线接入点 40ft 或更远时发生作用 ClientLink 可以对每个射频模块中的 15 个客户端 产生作用 对于双频AP 总计 30 个客户端 当波束成型表满员, 最老的客户端被新的客户端取代 15 并 不 是每个射频模块支持的最大客户端数量，每个射频模块支持的最大客户端数量并不会被波束成型特性改变,Cisco Internal,基本事实每个射频模块 15 个波束成型客户端,15 并 不 是每个射频模块支持的最大客户端数量 例如右图: 15 个波束成型客户端 6 个非波束成型客户端 共 21 个客户端,如何配置Enabled per Netwo

10、rk (11a/n or 11b/g/n),默认为关闭,ClientLink（Beamforming）全局配置,Data Rates need to support client hardware as well as user application requirements.,如何配置Enabled per Radio (11a/n or 11b/g/n),默认在所有 11n 射频模块上打开 The network-level setting overrides the per radio setting,在单个无线接入点上配置 ClientLink（Beamforming）,如何配置通过

11、CLI,For the 802.11a network: (Cisco Controller) config 802.11a disable network (Cisco Controller) config 802.11a beamforming global enable (Cisco Controller) config 802.11a enable network For the 802.11b/g network: (Cisco Controller) config 802.11b disable network (Cisco Controller) config 802.11b b

12、eamforming global enable (Cisco Controller) config 802.11b enable network Show configuration status: (Cisco Controller) show 802.11a 802.11a Network. Enabled 11nSupport. Enabled Legacy Tx Beamforming setting. Enabled,ClientLink 故障排查,SSH/Console into AP when running commands To show that ClientLink i

13、s enabled on a radio: AP#show controllers | inc Beam Legacy Beamforming: Configured Yes, Active Yes, RSSI Threshold -50 dBm Legacy Beamforming: Configured Yes, Active Yes, RSSI Threshold -60 dBm To show that ClientLink is beam forming to a particular client AP#show interface dot11radio 1 lbf rbf RBF

14、 Table: Index Client MAC Reserved Valid Tx BF Aging 1 0040.96BA.45A0 Yes Yes Yes No,Beam Forming is Active,Cisco Internal,ClientLink 故障排查,To show number of beam formed packets: AP#show controllers dot11Radio 1 | beg LBF LBF Indx BfPkts NbfPkts BfTmr PktCnt0016.6fbe.16c6 RIA 1 48384 19059 4 5781,Beam

15、 Formed Packets,Client MAC Address,参考资料（中英文版）,Cisco M-Drive Technology: Simplify 802.11n Adoption Cisco M-Drive 技术：简化 802.11n 的采用 Cisco ClientLink: Optimized Device Performance with 802.11n Cisco ClientLink：通过 802.11n 优化设备性能 Miercom Lab Testing Summary Report for Cisco ClientLink Miercom 关于 Cisco Cl

16、ientLink 的实验室测试总结报告 ,参考资料,思科 11n 部署指南 Cisco Networker 2009 BRKAGG-3012 设计和部署 802.11n 无线网络 bej-filer01bwg-eenterprisemobilityPublished04.SolutionSolutionSlide802.11n_SolutionDesing&DeployBRKAGG-3012 设计和部署 802.11n 无线网络(XieQing)20090619 v2.ppt WNBU TME ClientLink Site Includes a ClientLink test plan, r

17、esults spreadsheet and scripted Iperf package http:/wnbu-,Arubas ARM 2.0 11n Preferred Access,声称: 11n 客户端不会被速度较慢的11a/g 客户端 处罚 漏洞:以牺牲现有的11a/g客户端性能为代价增加11n 客户端的性能。其结果是不公平的空口占用时间。,DownstreamThroughputComparison,Arubas ARM 2.0 11n Preferred AccessResult: Airtime Unfairness,11a Client 5.4Mbps Total 77.3M

18、bps,11a Client 12.5Mbps Total 67.2Mbps,Aruba 提供 15% 的汇聚改善，但是 11a的性能下降 130%,Arubas ARM 2.0 vs. Ciscos ClientLink,11a/g 客户端的性能 下降 11n 客户端获得大量带宽 这只适合所有的客户端是 802.11n 客户端的部署理想场景, 但是理想和现实的巨大差距是11a/g客户端到处都是。 Preferred access 是 airtime unfairness,11a/g 客户端的性能 增加 11a/g 客户端运行在最大的数据率 增强现有客户端的性能并 减少他们空口占用时间，以便将

19、介质交与11n客户端传输。,目标的差异造成结果的不同,Cisco: 最大化 802.11a/g 客户端性能 结果:改善整个系统的性能包括 802.11a/g 和 802.11n 客户端 11a/g客户端获得更高的数据速率消耗较少的空口时间，从而减少与11n客户端的介质竞争，11n客户端同时获得高性能，系统总体也大幅增加。 Aruba: 当 802.11a/g 客户端关联时最大化 802.11n 客户端性能 结果: 只改善11n 客户端性能但是没有改善整个系统的性能 虽然现有的11a/g客户将逐渐被取代，但是他们还将在很长的时间内和11n客户端共存，他们的带宽需求仍然必须兑现。,ClientLi

20、nk Caveats,Clients may roam further with it enabled Based on the implementation of client roaming algorithms Since RSSI is increased, a client roaming based on this metric will roam at a different point,ClientLink Roaming Impact,Iteration 1 ClientLink On,Iteration 2 ClientLink Off,11ft,BandSelect,将双

21、频客户端导向 5GHz 频段,5,2.4,Optimized RF Utilization by Moving 5 GHz Capable Client Out of the Congested 2.4 GHz Channels,802.11n,BandSelectAccess Point Assisted 5 GHz Band Selection,Dual-Band Client Radio 2.4/5GHz,Discovery Probes Looking for AP,Solution,BandSelect directs clients to 5 GHz optimizing RF u

22、sage Better usage of the higher capacity 5GHz band Frees up 2.4 GHz for single band clients,Challenge,Dual-Band clients persistently connect to 2.4 GHz 2.4GHz may have 802.11b/g clients causing contention 2.4GHz is prone to interference,BandSelect in ActionPacket Capture,Client Probes on 2.4GHzInfra

23、structure doesnt respond,Client Probes on 5GHz Infrastructure responds,BandSelectAlgorithm,Probe suppression Identify dual band clients (2.4GHz and 5GHz capable) Suppress immediate probe response on 2.4 GHz channels Wait for dual band clients to scan into 5 GHz channels Do not respond to dual-band c

24、apable client on 2.4 GHz Accommodate 2.4GHz clients and dual band clients that fall back to 2.4GHz Time-out dual-band client 2.4GHz probe response suppression Mark 2.4 GHz only clients and respond with probes,BandSelect Implementation,Distributed algorithm Algorithm runs on AP firmware Configuration

25、 on controller Off by default Global configuration for the algorithm parameters Global On/Off configuration Per WLAN override control Support on 1140 and 1250 Access Points only Implemented in 6.0 release Supported in 6.0 MR1 release,(Cisco Controller) config band-select probe-response enable WARNIN

26、G: Allowing global band-select may impact time sensitive application like VOICE. Continue? (y/N) y (Cisco Controller) show band-select Band Select Probe Response. Enabled Cycle Count. 3 cycles Cycle Threshold. 200 milliseconds Age Out Suppression. 20 seconds Age Out Dual Band. 60 seconds,BandSelectC

27、onfiguration,WLC,BandSelectConfiguration,WLC,(Cisco Controller) config band-select probe-response enable WARNING: Allowing global band-select may impact time sensitive application like VOICE. Continue? (y/N) y (Cisco Controller) show band-select Band Select Probe Response. Enabled Cycle Count. 3 cyc

28、les Cycle Threshold. 200 milliseconds Age Out Suppression. 20 seconds Age Out Dual Band. 60 seconds Client RSSI. -80 dBm,BandSelectConfiguration Parameters,Cycle Count (Default: 2) Number of client probe cycles to wait before marking client as 2.4GHz-only Cycle Threshold (Default: 200msec) How long

29、a client probe scanning cycle is Age Out Suppression (Default: 20 seconds) If any probe from a client is not seen within this time, the client is removed from the BandSelect table Age Out Dual Band (Default: 60 seconds) If a 5GHz probe from the client is not seen within this timeout, the client is n

30、o longer considered dual-band Client RSSI (Default: -80dBm) Minimum client RSSI for probe responses to be sent to client,BandSelectConfiguration Per-SSID Override,WLC,(Cisco Controller) config wlan disable 2 (Cisco Controller) config wlan band-select allow disable 2 (Cisco Controller) config wlan en

31、able 2 (Cisco Controller) show wlan 2 WLAN Identifier. 2 Network Name (SSID). NoBandSelect Band Select. Disabled,Band Select can introduce latency in connecting and roaming situations This latency is harmless for data applications but can negatively impact real-time applications. Recommendation: Dis

32、able band-select for WLANs that handle real-time applications such as voice and video Example Below disable band select for a specific WLAN,BandSelectConfiguration Per-SSID Override Contd,BandSelectViewing Statistics,Navigate to the Monitor tab on the WLC GUI and click Access Points - Radios - 802.1

33、1b/g/n then Detail.,BandSelectViewing Statistics,WLC,(Cisco Controller) show ap stats 802.11b Band Select Stats Num of dual band client . 26 Num of dual band client added. 64 Num of dual band client expired . 38 Num of dual band client replaced. 0 Num of dual band client detected . 0 Num of suppress

34、ed client . 57 Num of suppressed client expired. 4602 Num of suppressed client replaced. 0,BandSelect Caveat Roaming Delay,2.4G band,5G band,No Delay,Some Delay (1.5s),Possible Delay,Data Rate Tuning,优化传输效果,Data Rate Tuning Why?,Frame Size vs. Channel TimeMeasured in Microseconds,Average Beacon Size

35、,Using 12Mbps is 10X more efficient than 1Mbps!,Real World ImprovementChannel Utilization from 40% to 5%,Optimizing Data RatesConfiguration,For 802.11b/g deploymentsDisable: 1, 2, 5.5, 6 and 9Mbps For 802.11g-only deploymentsDisable: 1, 2, 5.5, 6, 9 and 11Mbps For 802.11a deploymentsDisable: 6 and 9

36、 Mbps Ensure one rate is always kept mandatory Higher rates can also be disabled (ex. 12, 18Mbps) dependant on deployment,Tuned 802.11b/g Data Rates:,Optimizing Data RatesCaveats,Data rate changes are global across the controller and unique per frequency band Individual APs cannot be tuned different

37、ly Disabling too many data rates can decrease the maximum range of Access Points Do not disable all 802.11b rates unless you have no 802.11b clients,Load Balancing,将客户端分布到多个无线接入点,New Client Joining Network,Load BalancingConcept,Load,Min,Max,Load,Min,Max,Assoc Req.,Denied,Assoc Req.,Success,Load Bala

38、ncing in ActionPacket Capture,AP is loaded. AssociationDenied,Association Allowed,Load BalancingImplementation,The threshold to start load balancing is configured as a number of clients Association denied (Code 17) frames will be sent to clients who attempt to associate to loaded APs If the client d

39、oes not join a different AP, the “loaded” AP will allow the client to associate after a number of retries (default is 3) Configured on a per-controller basis at a global level Can be overridden for specific WLANs,Load Balancing Configuration,(Cisco Controller) config load-balancing aggressive enable

40、 WARNING: Allowing load balance may impact time sensitive application like VOICE Continue? (y/N)y (Cisco Controller) show load-balancing Aggressive Load Balancing. Enabled Aggressive Load Balancing Window. 5 clients Aggressive Load Balancing Denial Count. 3 Statistics Total Denied Count. 0 clients T

41、otal Denial Sent. 0 messages Exceeded Denial Max Limit Count. 0 times None 5G Candidate Count. 0 times None 2.4G Candidate Count. 0 times,WLC,Load BalancingConfiguration Per-SSID Override,WLC,(Cisco Controller) config wlan disable 2 (Cisco Controller) config wlan load-balance allow disable 2 (Cisco

42、Controller) config wlan enable 2 (Cisco Controller) show wlan 2 WLAN Identifier. 2 Network Name (SSID). NoLoadBalance Load Balancing. Disabled,Load Balancing can introduce latency in the association and roaming process This latency is harmless for data applications but can negatively impact real-tim

43、e applications. Recommendation: Disable load balancing for WLANs that handle real-time applications such as voice and video Example Below disable load balancing for a specific WLAN,Load BalancingCaveats,Load balancing only occurs amongst APs on the same controller Load balancing requires that the cl

44、ient respect the “Code 17” association response and act accordingly Load Balancing only occurs at initial association, not on re-association. Some older clients simply ignore the “Code 17” response and try and associate again. Know clients that load balance correctly: Intel 4965AGN (with 12.1 or lat

45、er drivers) Cisco CB-21AG (with 4.2 or later drivers),Load Balancing Configuration Per-SSID Override Contd,Load Balancing Troubleshooting,(Cisco Controller) debug dot11 load-balance enable *Sep 23 : XX:.:XX Load Balancing mobile XX:.:XX 802.11a minimum users 0, window 5 *Sep 23 : XX:.:XX Load Balanc

46、ing mobile XX:.:XX on AP 00:17:df:a7:cd:50(1) band 2 has 6 users - Bad: rssi (antenna-A -56) (antenna-B -61), snr = 32 *Sep 23 : XX:.:XX Load Balancing mobile XX:.:XX on AP 00:22:90:95:fc:20(1) band 2 has 0 users - Good: rssi (antenna-A -40) (antenna-B -47), snr = 32 *Sep 23 : XX:.:XX Load Balancing

47、 mobile XX:.:XX on AP 00:17:df:a7:bc:c0(1) band 2 has 0 users - Good: rssi (antenna-A -70) (antenna-B -66), snr = 32 *Sep 23 : XX:.:XX Load Balancing mobile XX:.:XX on AP 00:17:df:a7:c3:60(1) band 2 has 13 users - Bad: rssi (antenna-A -40) (antenna-B -55), snr = 32 *Sep 23 : XX:.:XX Load Balancing mobile XX:.:XX on AP 00:19:a9:78:53:10(1) band 2 has 0 users - Good: rssi (antenna-A -69) (antenna-B -78), snr = 32 *Sep 23 : XX:.:XX Load Balancing mobile XX:.:XX could not find acceptable 802.11b candidate - defaulting all *Sep 23 : XX:.:X