Rohan Murty Harvard University Jitendra Padhye, Ranveer Chandra, Alec Wolman, and Brian Zill Microsoft Research.
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Rohan Murty Harvard University Jitendra Padhye, Ranveer Chandra, Alec Wolman, and Brian Zill Microsoft Research 1 Increased adoption and usage [Forrester] Culture of mobility: Users tend to use Wi-Fi even when wired connections are available [Gartner, Forrester, Economist] Move towards an all wireless office Users want wire-like performance from wireless networks 2 Corporate WLAN Study: 12 users < 1 Mbps each 3 Focus on coverage Fewer APs than clients Clients talk to APs far away; worsens rate anomaly Clients pick APs to associate with Use RSSI of beacon packets Agnostic to channel load at APs Lack adaptive behavior No load balancing; fixed channel assignments Congestion and hotspots worsen 4 Focus on capacity Lots of APs; densely deployed Clients can talk to APs near by; mitigates rate anomaly Infrastructure picks client-AP associations Global view of network conditions (channel load, interference, etc.) Adaptability Load balance associations; Dynamic channel assignment Redistributes load away from local hotspots 5 No client modifications Works with legacy clients Changes limited to the infrastructure Easy to deploy Self-managing 6 Interface with clients Send summaries to DC DenseAP Nodes (DAPs) Commands Summarized Data Wired Network Commands to DenseAP nodes Associations Channel Assignments Load Balancing Summarized Data from DenseAP nodes DenseAP Central Controller (DC) 7 Controlling Associations Mechanisms Policy Dynamic Channel Assignment Mechanism Policy Load Balancing Mechanism Policy 8 ACL ACL 00:09:5B:5A:1F:4F ACL 9 Probe Request MAC = 00:09:5B:5A:1F:4F RSSI = 30 ACL Probe Request MAC = 00:09:5B:5A:1F:4F RSSI = 42 ACL 00:09:5B:5A:1F:4F ACL Probe Request MAC = 00:09:5B:5A:1F:4F RSSI = 40 10 ACL Probe Response ACL Accept Client 00:09:5B:5A:1F:4F ACL 00:09:5B:5A:1F:4F Client only sees one DAP at any given time 11 Overall goal: Associate client with a DAP that will yield good throughput What is the quality of a connection between a client and a DAP? (rate) How busy is the medium around each DAP? 12 Available Capacity (AC) (Mbps) = Expected Transmission-Rate (Mbps) X Free Air Time (%) 13 DAP DAP Free Free RSSIRSSIEx. AirAirTxTime Time Rate RSSI = 10 DAP1 DAP1 0.35 0.35 20 20 18 Free air Probe Request DAP2 time = 0.22 DAP2 DAP2 0.22 0.22 10 10 6 DAP3 0.45 0.45 30 30 48 DAP3 Probe Request Probe Response AC 6.3 1.32 21.6 Accept RSSI = 30 Client DAP3 Free air time = 0.45 DAP1 RSSI = 20 Free air time = 0.35 14 Correlation between RSSI of Probe Request packets Avg. throughput between a DAP-client pair Rough approximation ordering of DAPs Online profiling method that builds RSSI to datarate estimates Average Throughput (Mbps) 20 18 16 14 12 10 8 6 4 2 0 Upload 0-9 Download 10 - 19 20 - 29 30 - 39 RSSI Values 40+ Upload and RSSI correlation = 0.71 Download and RSSI correlation = 0.61 15 Estimate how busy is the medium around at a DAP Technique similar to ProbeGap* Measure time taken to finish a packet transmission Estimates match up closely with offered traffic load 100 Estimated Load (%) 80 60 40 20 0 0 50 Actual Load (%) 100 *Lakshminarayan et al., 2004 *Vasudevan et al., 2005 16 Integrated into the association process DAPs not discovered by clients don’t need channels A DAP is assigned a channel only when it goes from being passive (no clients) to active (services at least one client) Central controller assigns channel with least load 17 So far, associations when a new client joins the network No association is perfect Client traffic demands change Local hotspots created 18 Central controller monitors load on every DAP When channel load on a DAP crosses a certain threshold Client causing most load is determined Moved to less loaded DAP nearby Ensure client continues to get at least as much available capacity at the new DAP Load balancing achieved via handoffs Use association control; manipulate ACLs on DAPs 19 20 1 Corp AP (0,0) 3026 3026 3028 3028 24 DAPs 3048 DCR 3048 3046 DESNEY 3046 3044 3044 3042 V-JWING 3042 3131 3131 3106 GREGSMI 3106 3030 3030 3153 3153 3151 3151 3116 MATTU 3116 3118 BROWN 3118 3120 SWINDER 3120 3134 STEEDLY 3134 3035 V-DOAVEL V-JONAHA V-TEDKAO 3035 3380 3380 3377 3377 3001 3001 3354 ZHAO 3354 3338 JELSON 3338 3336 LIUJ 3336 3334 PADMANAB 3334 3320 PADHYE 3320 3318 HELENW 3318 3371 3371 3316 SAGARWAL 3316 3314 HOWELL 3314 3312 RICHDR 3312 3181 3181 3307 DMALTZ 3307 3329 3329 3305 MZH 3305 3331 3331 3333 3333 3303 3303 3306 BZILL 3306 3300 3300 3304 JDUNAGAN 3304 3302 JGEMMELL 3302 3215 3215 3239 3239 3237 CYL 3237 UP STR32 STR32 DN 3242 3242 3244 JFAY 3244 3246 GEORGP 3246 3248 SDRUCKER 3248 3252 WONG 3252 3180 3180 3205 3205 3161 3161 3159 3159 3325 3325 3240 3240 3203 3203 3210 3210 3235 BODHIP 3235 3230 3230 3234 V-AVD 3234 3209 3209 3217 BLINN 3217 3206 KENTOY 3206 3179 3179 3222 3222 3219 3219 3208 ANANDAN 3208 3110 3110 3138 3138 3351 3351 3308 DANSIMON 3308 3309 3309 3330 3330 3347 T-ANDRES 3347 CH33 CH33 3204 3204 3160 3160 CH32 CH32 3213 3213 3207 3207 3165 3165 3340 3340 3360 3360 3211 3211 3321 3321 3323 3323 3343 RANVEER 3343 3341 3341 3002 3002 CH31 CH31 3145 3145 3141 3141 3339 SUMANN 3339 3363 RATUL 3363 3006 3006 3021 3021 3167 3167 3163 3163 3143 3143 3136 SBKANG 3136 3356 3356 3379 3379 3005 3005 3022 3022 3149 3149 3139 T-LUCASK 3139 3114 NURIA 3114 3372 LORCH 3372 3310 3310 3201 3201 802.11 a/bg 3374 BAHL 3374 3359 JOHNDO 3359 EL 31 EL 31 3125 3125 3112 SZELISKI 3112 3376 ALECW 3376 CI32 CI32 3004 3004 3130 3130 3108 BRIANME 3108 3378 BOLOSKY 3378 3019 EMREK 3019 3037 3037 3140 3140 3123 3123 3012 SHUOCHEN 3012 EL 32 EL 32 3147 3147 3100 3100 3014 ARUNKU 3014 3040 3040 3103 3103 3104 GGR 3104 3033 3033 3039 3039 UP 3102 MARYCZ 3102 3016 CHADV 3016 3020 3020 3032 MFORNEY 3032 DN STR31 STR31 24 Clients 3018 BRADDAN 3018 3000 3000 3034 RAMANC 3034 3052 3052 3024 YMWANG 3024 3233 3233 3232 3232 3220 3220 3154 MCOHEN 3154 3156 ERUDOLPH 3156 3172 LARRYZ 3172 3174 A-HGOOD 3174 3176 PETERJ 3176 3178 CRAIGVI 3178 3200 3200 3212 LORIMAC 3212 3214 CLOOP 3214 3216 MARCEL 3216 3218 3218 3224 HHOPPE 3224 3226 JOHNSNY 3226 3228 BGUENTER 3228 (98,32) 21 Performance Density Channels Intelligent Association Load Balancing 22 Per-Client Througput (Mbps) 20 18 16 14 12 10 8 6 4 2 0 DenseAP Corporate Corporate WLAN WLAN Gains due to •More channels 1250% gain •DAP density •Intelligent associations Why? 2 4 6 8 Number of Clients 10 12 23 Put all DAPs on the same channel Factors out Channels Intelligent Associations: same load on all DAPs Single out impact of Density 24 Avg. Per-Client Throughput (Mbps) 20 Corporate WLAN DenseAP - 1 Channel 15 10 5 0 1 2 3 4 Number of Clients 5 6 Higher density provides better performance 25 Is intelligent association control necessary? 26 Client-Driven Disable intelligent association control Let clients pick DAP to associate with (conventional WLANs) Compare with DenseAP Factors out Channels Density Single out impact of Intelligent association 27 Per-Client Throughput (Mbps) 20 18 16 14 12 10 8 6 4 2 0 Client-Driven DenseAP 160% gain 2 4 6 8 Number of Clients 10 12 Intelligent association policy is necessary 28 29 Throughput (Mbps) 25 Client 1 improves 20 15 Clients 2 & 3 improve 10 Client 1 moved 5 Client 2 moved Client 3 Client 1 Client 2 0 0 50 100 150 Time (s) 200 250 300 30 Load balancing algorithm and mechanism Mobility Performance Fewer DAPs Fewer channels 802.11g ….. Scalability 31 Plenty of prior work on static channel assignment, power control and associations Each studied each aspect in isolation Require client modifications [Ramani and Savage, Infocom 2005] SMARTA [Ahmed et al., CoNext 2006] Examines channel and power control Increase overall network capacity Does not consider associations, load balancing MDG [Broustis et al., MOBICOM 2007] Identified tuning channel, power and associations Studies the order in which these knobs must be tuned Requires client modifications 32 Practical system How do density, intelligent association, and more channels affect capacity? Adaptive system Future directions Impact of hidden terminals Heterogeneous mix of client traffic patterns Other backhauls: e.g. Wireless, powerline 33