AAF workshop Measurement Session MICNET 2009 Best-Case WiBro Performance for a Single Flow Shinae Woo † , Keon Jang † , Sangman Kim † Soohyun Cho * , Jaehwa Lee * , Youngseok Lee ‡ , Sue Moon † † Computer Science Department, KAIST ‡ School of Computer Science and Engineering, Chungnam National University * KT Central R&D Laboratory Nov 23, 2009 1
What is WiBro (Mobile WiMAX) ? • Provides high-bandwidth mobile data service • Served by KT and SKT in Korea • Being deployed in US, India and Japan Han River Population 20,000,000 Seoul WiBro users 200,000 Inchen Korea Airport Service Area 2
Market Positioning of WiBro (Mobile WiMAX) • Speed : Cellular networks < WiBro < WiFi • Mobility : WiFi < WiBro < Cellular networks Speed 144Mbps WiFi WiBro 35.44Mbps HSPA 14.4Mbps GSM Mobility 120km/h 300km/h 3
Characteristics of WiBro (Mobile WiMAX) • IP-based packet-switching in the core • Uses 2.3GHz frequency, OFDMA - Multiple users can access same time • Uses TDMA for up/downlink b/w allocation • 5 QoS classes implemented, only BE used now 4
Outline Background Motivation Experiment Environment Analysis Basic characteristics of WiBro TCP Performance over WiBro Conclusion 5
Motivation • Experiments on commercial network - Hard to pinpoint major factors affecting performance • To know the baseline of WiBro performance - Focus on the performance of a single flow - Assume no competition and interaction between flows 6
Experiment Set-up KREONET GPS WiBro GPS 1Gbps link Network Server Client KT’s IP Network 7
Experiment Set-up KREONET GPS Link speed = 1Gbps WiBro GPS Network Server Client KT’s IP Network KT – KREONET MRTG graph (26 April, 19:40:14) 8
RTT by the Hop RTT (ms) Hop number 9
RTT by the Hop RTT (ms) Wireless link dominates e2e performance Hop number 10
Experiment Environment Architecture of Our GPS System GPS module U-blox LEA-5 LAN cable NMEA data 1 PPS USB RS232 11
Experiment Environment Clock Synchronization in Our GPS System GPS signal per second by PPS Packet sent or arrival event CPU clock ck time GPS UTC time 12
Analysis Overview Basic Characteristics of WiBro • How different is WiBro from WiFi and cellular networks? • We use UDP to measure min and max one-way delay - Min one-way delay = best-case w/o queuing - Max one-way delay = represents queue size TCP Performance over WiBro • Do we get theoretically maximum 35.44 Mbps over WiBro? - Vary send and recv window sizes 13
Basic Characteristics of WiBro Minimum one-way delay • Definition : delay without queuing = transmission delay + propagation delay + scheduling delay (at ACR ) • Measurement methodology Send 40 byte packet every 40ms • Measurement outcome: - Downlink: 14ms 100ms - Uplink: 14
Bandwidth and Queuing Delay of WiBro • We saturated link with UDP traffic Downlink 10 Mbps Large queuing delay Uplink 2.5 Mbps 15
Basic Characteristics of WiBro Queue Size of WiBro links • Queue size decides the queuing delay!! • With full queue, Queue size = (max. one-way delay) * (bandwidth) • Measured queue size in each direction, - Downlink 961ms * 9603Kbps = 1126 KB - Uplink 417ms * 2628Kbps = 137 KB If bandwidth temporarily decreases to 1 Mbps, queuing delay can increase up to 10 s !!! 16
TCP performance over WiBro How Does the Buffer Size Affect TCP Bandwidth? • WiBro link has high bandwidth-delay product • TCP need socket buffer size of at least bandwidth-delay product ex) Window XP’s default TCP socket buffer size, 17KB, is not enough to utilize the WiBro link fully 17
TCP performance over WiBro How Does the Buffer Size Affect TCP Bandwidth? Bandwidth (Mbps) Window Size(KB) 64KB 5 Mbps with Windows XP’s Min 128 KB buffer size can default socket buffer size fully utilize the link 18
TCP performance over WiBro Auto-tuned TCP Socket Buffer in Ubuntu TCP get the same bandwidth with UDP Auto-tuned buffer works well in WiBro 19
TCP performance over WiBro One-way Delay of Downlink TCP Traffic Increase with queuing Decrease with piggybacking Window Size (KB) 20
Our Contributions • Developed cheap GPS module with sub-millisecond accuracy • Showed that WiBro is high bandwidth-delay network Down Up High Bandwidth 10 Mbps 2.5 Mbps Long Min Delay 14 ms 100 ms Big Buffer Size 1126 KB 137 KB • To fully utilize WiBro network, min 128KB or more TCP buffer size is needed - Windows XP’s default size without TCP 1323 extension option is only 64KB 21
Thank you!! GPS LAN cable USB RS232 22
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