1. Best-Case WiBro Performance for a Single Flow 1 MICNET 2009 Shinae Woo †, Keon Jang †, Sangman Kim † Soohyun Cho *, Jaehwa Lee *, Youngseok Lee ‡, Sue Moon † Nov 23, 2009 † Computer Science Department, KAIST ‡ School of Computer Science and Engineering, Chungnam National University * KT Central R&D Laboratory AAF workshop Measurement Session

2. 2 Provides high-bandwidth mobile data service Served by KT and SKT in Korea Being deployed in US, India and Japan What is WiBro (Mobile WiMAX) ? Seoul Han River Inchen Korea Airport Service Area 50km Population 20,000,000 WiBro users 200,000

3. 3 Speed : Cellular networks < WiBro < WiFi Mobility : WiFi < WiBro < Cellular networks Market Positioning of WiBro (Mobile WiMAX) WiFi Mobility Speed WiBro HSPA GSM 300km/h120km/h 144Mbps 35.44Mbps 14.4Mbps

4. 4 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 Characteristics of WiBro (Mobile WiMAX)

5. 5 Background Motivation Experiment Environment Analysis Basic characteristics of WiBro TCP Performance over WiBro Conclusion Outline

6. 6 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

7. 7 KT’s IP Network KREONET Server GPS WiBro Network Client GPS Experiment Set-up 1Gbps link

8. 8 Experiment Set-up KT’s IP Network KREONET Server GPS WiBro Network Client GPS KT – KREONET MRTG graph (26 April, 19:40:14) Link speed = 1Gbps

9. Hop number RTT (ms) 9 RTT by the Hop

10. Hop number RTT (ms) 10 Wireless link dominates e2e performance RTT by the Hop

11. 11 Architecture of Our GPS System GPS module U-blox LEA-5 LAN cable USB RS232 Experiment Environment NMEA data 1 PPS

12. 12 Clock Synchronization in Our GPS System GPS UTC time CPU clock time GPS signal per second by PPS Packet sent or arrival event Experiment Environment

13. 13 Basic Characteristics of WiBro TCP Performance over 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 Do we get theoretically maximum 35.44 Mbps over WiBro? - Vary send and recv window sizes Analysis Overview

14. 14 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 - Uplink: 100ms Basic Characteristics of WiBro

15. 15 Bandwidth and Queuing Delay of WiBro Downlink10 Mbps Uplink 2.5 Mbps Large queuing delay We saturated link with UDP traffic

16. 16 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 !!! Basic Characteristics of WiBro

17. 17 TCP performance over WiBro 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 How Does the Buffer Size Affect TCP Bandwidth?

18. 5 Mbps with Windows XP’s default socket buffer size 18 How Does the Buffer Size Affect TCP Bandwidth? TCP performance over WiBro 64KB Min 128 KB buffer size can fully utilize the link Window Size(KB) Bandwidth (Mbps)

19. TCP get the same bandwidth with UDP  Auto-tuned buffer works well in WiBro 19 Auto-tuned TCP Socket Buffer in Ubuntu TCP performance over WiBro

20. 20 One-way Delay of Downlink TCP Traffic Decrease with piggybacking Increase with queuing TCP performance over WiBro Window Size (KB)

21. Developed cheap GPS module with sub-millisecond accuracy Showed that WiBro is high bandwidth-delay network 21 Our Contributions DownUp Bandwidth10 Mbps2.5 Mbps Min Delay14 ms100 ms Buffer Size1126 KB137 KB High Long Big 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

22. 22 Thank you!! GPS LAN cable USB RS232