1. An End-to-End Multipath Smooth Handoff Scheme for Stream Media Yi Pan Meejeong Lee Jaime Bae Kim Tatsuya Suda IEEE Journal On Selected Areas In Communications. Vol. 22, No. 4, May 2004

2. Outline Introduction System Architecture Performance Evaluations Conclusion

3. Introduction Streaming media are becoming popular in wireless mobile network Providing smooth handoff between cells is challenging Rerouting packets may results in burst packet loss Heterogeneous cells bandwidth

4. Introduction A number of mobility management techniques have been purposed to provide smooth handoff in homogeneous networks This paper focus on Smooth handoff of stream media in heterogeneous best-effort wireless mobile networks

5. System Architecture Principles Reduce impact of packet loss Establishing multiple paths to the mobile node Transmitting duplicate packets (video layers) over multiple paths Adapt to available bandwidth in new cell Employing probing techniques to estimate available bandwidth in new cell Change transmission rate adaptively

6. System Architecture Path Management Discover and maintain multiple path between sender and receiver Make use of Mobile IP options Simultaneous binding  Allow receiver to register multiple COAs (Care-Of- Address) Route Optimization  Allow sender to be informed about receiver’s COAs registrations

7. System Architecture Rate Control Estimate available bandwidth on paths Make use of TCP friendly rate control (TFRC) Receiver send packet loss ratio report to sender every RTT

8. System Architecture Multipath Distributor Calculate the number of video layers and bitrates Decide the paths to transmit layers Video Layer-Path Adaptation (VLPA)

9. System Architecture Multipath Distributor Video Layer-Path Adaptation (VLPA) r i – Cumulative rate from layer 0 (base) to (and including) layer i r i layer = r i – r i-1 Number of video layers = Number of distinct transmission rates on the paths r i = i th transmission rates (sorted, ascending) on the paths

10. System Architecture Multipath Distributor Video Layer-Path Adaptation (VLPA) If transmission rates on paths are 1, 2, 2, 4 Mbps Number of layers = 3 r 0 = 1Mbps, r 1 = 2Mbps, r 2 = 4Mbps Layer i is transmitted redundantly through all paths whose transmission rate ≥ r i VLPA runs periodically (40ms in simulations)

11. Performance Evaluations Comparison Schemes Single path without packet forwarding Packets in transit to old base station is discarded Single path with packet forwarding Packets in transit to old base station is forwarded to new base station Proxy-based Proxy located in each base station for transcoding New cell’s proxy retransmit last incomplete video frame Assume a centralized controller to inform proxies about the available bandwidth in new cell immediately

12. Performance Evaluations SimulatorOPNET Coverage radius300m Distance between base stations 500m Wireless link802.11b 11Mbps Wireless link BER10 -3 to 10 -5 Wired link155Mbps Wired link BER10 -12 Wired Propagation Delay10μs Packet Size1024bytes Mobile node movementTrajectory model Performance measures are obtained during handoff

13. Performance Evaluation MPATH utilize all available paths as soon as enter the node enters overlapped zone SP_NF, SP_FF and PROXY may not choose to use the link with more available bandwidth due to handoff Bandwidth estimation by TFRC is slow, so SP_NF and SP_FF are slow in acquiring new available bandwidth Bandwidth in old cell = 7.8 Mbps Node speed = 30 mph RTT = 60 ms SP_NF: Single Path No Forward SP_FF: Single Path With Forward MPATH: Multipath Handoff scheme PROXY: Proxy-based scheme

14. Performance Evaluations All, except PROXY, throughput decrease as RTT increases TFRC rate control relies on end-to-end feedback 9.4Mbps6.2Mbps

15. Performance Evaluations All, except PROXY, throughput decrease as node speed increases Node spends less time in overlapped region TFRC rate control performs end-to-end feedback less often Slower to acquire new available bandwidth 9.4Mbps6.2Mbps

16. Performance Evaluations MPATH does not suffer from rerouting loss Node continues receive packet from all base stations MP_Base (Base layer of MPATH) has near zero loss Redundant transmission in all base stations

17. Performance Evaluations (9.4Mbps)(6.2Mbps)

18. Performance Evaluations (9.4Mbps)(6.2Mbps)

19. Performance Evaluations SP_NF and SP_FF has largest packet loss ratio in most cases SP_FF significantly reduce rerouting loss, and thus total loss MP_Base (Base layer of MPATH) has virtually zero packet loss ratio due to redundant transmissions

20. Performance Evaluations Frame rate = 25fps Frame with less than 10% packet loss is considered successfully received Small fluctuation in all schemes in (a) as the new cell has larger bandwidth and, thus, no congestion Large fluctuation in SP_NF and SP_FF in (b) as the new cell has smaller bandwidth and congestion occurs MPATH shows smooth changes in all case, due to rate control and redundant transmissions 9.4Mbps6.2Mbps

21. Performance Evaluations Redundant transmissions of packet lower bandwidth efficiency Different base stations layout affect transmission redundancy

22. Performance Evaluations Transmission Efficiency = number of unique packets to total number of transmitted packets Transmission efficiency decrease as available path increases Largest reduction occurs when all paths have same bandwidth

23. Performance Evaluations Each node is guaranteed to get at least 400kbps Proxy based scheme is used as comparison base MPATH does not significantly impact the number of mobile nodes supported

24. Conclusion Multipath Smooth Handoff Scheme Protect important data (base layer) through redundant transmissions on multiple paths Performance is comparable to proxy-based scheme Overhead is insignificant as size of overlapping area is limited in practice

25. Final Thought Extensive simulation results Reduction in number of supported nodes is indeed large