1. Dobby@mmlab.snu.ac.kr An Empirical Study on 3G Network Capacity and Performance INFOCOM2007 Wee Lum Tan, Fung Lam and Wing Cheong Lau Chinese University of Hong Kong

2. Dobby@mmlab.snu.ac.kr  1. Introduction  2. Measurement Methods  3. Measurement Results  4. Conclusion Outline

3. Dobby@mmlab.snu.ac.kr  1. Introduction  2. Measurement Methods  3. Measurement Results  4. Conclusion

4. Dobby@mmlab.snu.ac.kr  “UMTS”  Universal Mobile Telecommunications System WCDMA as underlying air interface Based on GSM infrastructures (3GSM) Standardized by the 3GPP Combined with TD-CDMA/TD-SCDMA 1. Introduction HSDPA(Korea), HSUPA, HSPA+ TD-CDMA, TD-SCDMA(China) Japan 04/24

5. Dobby@mmlab.snu.ac.kr  Three 3G Network Operators in HK Service combining of GSM/GPRS/UTMS(WCDMA)  - New World Telecom  - Pacific Century Cyber Works Ltd.  - Hutchison Global Comm. Ltd. 1. Introduction Later They are denoted as X,Y, Z… 05/24

6. Dobby@mmlab.snu.ac.kr  Capacity of 3G Network  The maximum number of simultaneous users that can be supported, while satisfying the service quality requirements (data rate, bit error rate) of each user  Acquire realistic statistical data… 1. Introduction System-level analysis and modeling Empirical measurements and experiments Improving Performance 06/24

7. Dobby@mmlab.snu.ac.kr  1. Introduction  2. Measurement Methods  3. Measurement Results  4. Conclusion

8. Dobby@mmlab.snu.ac.kr  Measurements for investigation:  To measure the performance of 3G networks using a mixture of data, video and voice traffic. 2. Measurement Methods Data, video/voice capacities of 3G networks. Tradeoffs between data and video/voice traffic. 3G user experience under light-load scenarios. Tradeoffs between video and voice traffic. 08/24

9. Dobby@mmlab.snu.ac.kr  Measure Setup:  Nokia 6680 (video call capable)  JAVA for clients & server program  TCP Reno with TCP SACK enabled  Methods:  1. a cell is saturated with data calls, then video/voice calls are made increasingly  2. a cell is saturated with video calls, then voice calls are made until network saturated  3. other normal measurements under fully- loaded/lightly-loaded cell condition 2. Measurement Methods 09/24

10. Dobby@mmlab.snu.ac.kr  Saturation Point  Calls are made one by one until the aggregate throughput reaches the upper-boundary.  “Trial-and-Error” method to find the optimal number of calls to saturate the network  Stability  Stability of saturated cell is not so good  Sometimes, all connections suddenly dropped in all X, Y, Z, when the network is saturated  Make more tests longer repeatedly… 2. Measurement Methods 10/24

11. Dobby@mmlab.snu.ac.kr  1. Introduction  2. Measurement Methods  3. Measurement Results  4. Conclusion

12. Dobby@mmlab.snu.ac.kr  A. Performance in Saturated 3G Nets  Downlink Measurements Results: A cell is saturated with data calls, then video/voice calls are made more and more Video calls reduce DL aggregate throughput significantly –Video~64kbps / Voice~12kbps 3. Measurement Results Figures from X,Y,Z are nearly the same… Operators reserves some minimum BW resources for data calls 12/24

13. Dobby@mmlab.snu.ac.kr Individual throughput of each mobile client –Significantly drop if additional video/voice calls into the data- saturated cell –X works fairly, all data calls are allocated the same BW »Raise together, reduce together… –Y&Z allocate different BW resource to different calls »based on call-in time, occupied time, and some parameters 3. Measurement Results 3DL 12 Video calls 24 Voice calls 13/24

14. Dobby@mmlab.snu.ac.kr  Uplink Measurements Results: –In X, after 8 video calls, total number of data calls dropped from 14 to 7, then more attempts get failed. »Becase of BW data-min, some data calls can be protected –In Y network, when saturated, once data uplinks are ongoing, no preemption by new video/voice calls »No more calls is admitted, to guarantee admitted ones 3. Measurement Results For Y, there are upper limits on the number of data/video/voice calls that can be admitted. Also minimum services for admitted calls are guaranteed & protected 14/24

15. Dobby@mmlab.snu.ac.kr  B. Performance in light-load 3G Network Average RTT value to local websites through light- load 3G network is around 350ms –RTT value to same websites by network provider is 50ms Substantial internal processing and queuing latency (>300ms) are imposed in 3G network system 3. Measurement Results 15/24

16. Dobby@mmlab.snu.ac.kr  C. Percentages of TCP retransmissions X – 1% ( 6% the most) –X uses low threshold value for SNR to achieve higher transmission BW, therefore X generally has higher data capacity but with a little more transmission errors Y & Z – 0.1%~0.9% –Y&Z use RLC ACK mode to lower TCP retransmission but capacity is relatively reduced 3. Measurement Results 1.0% 0.1% 0.6% 0.2% 0.9% 16/24

17. Dobby@mmlab.snu.ac.kr  D. 3G Network Capacity Results  Obviously, uplink BW is lower than downlink BW  Number of voice calls equivalent to 1 video call Y allocates video call more resource & higher priority. 3. Measurement Results Data Video Voice 17/24

18. Dobby@mmlab.snu.ac.kr  Capacity region – A generalized representation Most of data points from trade-off tests are distributed near the linear line generated by the two intercepts A plane in 3D coordinates, with axis-intercept values equal to the maximum capacity for corresponding single-service types: 3. Measurement Results 18/24

19. Dobby@mmlab.snu.ac.kr  E. Repeated measurements  Even under the same condition, e.g. same place, same SNR value, same devices, … measurement results always differ by more than 10%, even ~50% as time changes…  So, 4 months 170 sites Repeatedly 3. Measurement Results 19/24

20. Dobby@mmlab.snu.ac.kr  1. Introduction  2. Measurement Methods  3. Measurement Results  4. Conclusion

21. Dobby@mmlab.snu.ac.kr  First paper on large scale and a long time empirical study of 3G networks  Key Findings:  A. Substantial additional processing and queuing latency (>300ms) are imposed, and it will be >1sec in fully-loaded network.  B. TCP retransmission probability varies from <<1% to 1~6%, because different operators configure different SNR thresholds, then different error rates, and different BW. 4. Conclusion 21/24

22. Dobby@mmlab.snu.ac.kr  C. Under saturated condition, higher priority video/voice calls always make data calls dropped. Data services is and should be guaranteed minimum BW.  D. Multi-service capacity region of a cell can be conservatively bounded by a plane in 3D coordinates, with axis-intercept values equal to the maximum capacity for corresponding single- service types, e.g. data BW, max number of video/voice calls 4. Conclusion 22/24

23. Dobby@mmlab.snu.ac.kr  E. 3G operators extensively customized the configurations in a cell-by-cell manner in order to cope with the projected traffic demand of individual sites and neighborhood  …  Useful for both: Network planners –To plan enough capacity to support new data applications –To make more scalable resource allocation method Application designers –To design control scheme to handle the bandwidth variability –To optimize applications to highly utilize network resource 4. Conclusion 23/24

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