1. Quality of Service Issues in Multi-Service Wireless Internet Links George Xylomenos and George C. Polyzos Department of Informatics Athens University of Economics and Business Athens 10434, Greece polyzos@aueb.gr http://dias.aueb.gr/~gcp/ Tel.: +30-1-8203-650, Fax: +30-1-8203-325

2. polyzos@aueb.gr2 Outline l Motivation u Wireless systems and Internet applications u TCP throughput degradation u UDP and real-time application issues u Proposed approaches l Flexible Link Layer Internet Protocol (FLLIP) u Multi-protocol, adaptive, QoS/DS aware solution u Goals, architecture, implementation u Implicit and explicit service selection l Conclusion

3. polyzos@aueb.gr3 Modern Wireless Systems l Opportunities and issues u Digital wireless systems n Cellular, PCS, 3G n Wireless LANs n LEO/MEO Satellites, LMDS u Mobility l Internet protocols: designed for networks that were u Wired: low error rate n TCP: loss  congestion u Fixed: no mobility, no handoffs l Physical layer solutions u Inflexible: one size fits all

4. polyzos@aueb.gr4 Internet Applications and Protocols l Conventional data exchange applications u Usually TCP based u Error intolerance u Delay tolerance u Jitter intolerance (TCP) l Interactive and real-time applications u Often UDP based (plus RTP) u Often multipoint (IP Multicast) u Some error tolerance u Delay intolerance

5. polyzos@aueb.gr5 Proposed Approaches l Indirect TCP u violation of semantics (not end-to-end anymore) l Snoop TCP u works well only in the direction towards the mobile l Modifications to TCP u Compatibility: usually both ends need to be updated u End-to-end retransmissions for a local problem u Not multi-protocol: useless for non TCP applications l Conventional link-layer schemes u Inflexible: one service only u Irrelevant for some protocols/applications

6. polyzos@aueb.gr6 Simulation Experiments l One and two wireless link scenarios l Exponential intervals between errors u 0.8-5.9% frame loss rates (1 Kbyte frames) l TCP: 100 Mbyte file transfer l UDP: Voice activated CBR video (1 Mbps) l Each test repeated 30 times PHY LL IP TCP/UDP Wireless Host A PHY LL IP Base Station A 10Mbps 1ms PHY LL IP PHY LL IP TCP/UDP Wireless Host BBase Station B 2Mbps 3ms 2Mbps 3ms TCP/UDP

7. polyzos@aueb.gr7 TCP Performance: Throughput

8. polyzos@aueb.gr8 UDP Performance: Delay

9. polyzos@aueb.gr9 Flexible Link Layer Internet Protocol (FLLIP) l Address the problem at its source u Local solution to a local problem l Compatible with Internet protocols & architecture u IP and higher layers unchanged l Aware of QoS requirements u Implicitly or explicitly l Per stream or class QoS differentiation u Fully or mostly reliable l Dynamic adaptation to stream/class mix u Variable bandwidth allocation l Dynamic adaptation to channel conditions

10. polyzos@aueb.gr10 FLLIP Architecture l Multiple link layer modules l Packet classifier u Protocol, TCP/UDP ports u IP ToS, DS field l Per class load measurements u Incoming bandwidth allocations l Service class specific processing u Isolation between services l Frame scheduler (SCFQ) u Enforces incoming bandwidth allocations

11. polyzos@aueb.gr11 SCFQ Frame Scheduler l Enforces incoming allocations l Protects services l Encourages efficiency l Self-clocked fair queueing (SCFQ) l Efficient, simple, fair l One queue per class l Heap sort

12. polyzos@aueb.gr12 TCP Performance: Throughput with FLLIP

13. polyzos@aueb.gr13 UDP Performance: Delay with FLLIP

14. polyzos@aueb.gr14 Service Selection l Implicit QoS specification u Assigns applications to services u Protocol and TCP/UDP port fields u No changes to Internet protocols and applications u Immediate applicability l Explicit QoS specification u Assigns traffic classes to services u QoS provision n Integrated Services, RSVP u QoS differentiation n Differentiated Services u More flexible

15. polyzos@aueb.gr15 Heuristic Packet Classifier l Implicit QoS specification

16. polyzos@aueb.gr16 Differentiated Services Packet Classifier l Explicit QoS specification l Dynamic service selection

17. polyzos@aueb.gr17 Service Measurement and Mobility Feedback l Service selection u Standard metrics u Refinement l Adaptive applications u Mobility

18. polyzos@aueb.gr18 Conclusions l TCP performance severely impacted by wireless losses l TCP is not the only concern u Real-time multimedia over UDP u New applications and protocols l Link layer enhancements u Fast local recovery u Customized to underlying link l Wireless links: natural choice to introduce u QoS support u Differentiated services because u Bandwidth is scarce and expensive u Link performance is variable and unpredictable