quality of service issues in multi-service wireless internet links

Quality of Service Issuesin Multi-Service

Wireless Internet Links

George Xylomenos and George C. PolyzosGeorge Xylomenos and George C. Polyzos

Department of InformaticsAthens 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

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Outline

Motivation Wireless systems and Internet applications TCP throughput degradation UDP and real-time application issues Proposed approaches

Flexible Link Layer Internet Protocol (FLLIP) Multi-protocol, adaptive, QoS/DS aware solution Goals, architecture, implementation Implicit and explicit service selection

Conclusion

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Modern Wireless Systems

Opportunities and issues Digital wireless systems

Cellular, PCS, 3G Wireless LANs LEO/MEO Satellites, LMDS

Mobility Internet protocols: designed for networks that were

Wired: low error rate TCP: loss congestion

Fixed: no mobility, no handoffs Physical layer solutions

Inflexible: one size fits all

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Internet Applications and Protocols

Conventional data exchange applications Usually TCP based Error intolerance Delay tolerance Jitter intolerance (TCP)

Interactive and real-time applications Often UDP based (plus RTP) Often multipoint (IP Multicast) Some error tolerance Delay intolerance

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Proposed Approaches

Indirect TCP violation of semantics (not end-to-end anymore)

Snoop TCP works well only in the direction towards the mobile

Modifications to TCP Compatibility: usually both ends need to be updated End-to-end retransmissions for a local problem Not multi-protocol: useless for non TCP applications

Conventional link-layer schemes Inflexible: one service only Irrelevant for some protocols/applications

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Simulation Experiments

One and two wireless link scenarios Exponential intervals between errors

0.8-5.9% frame loss rates (1 Kbyte frames) TCP: 100 Mbyte file transfer UDP: Voice activated CBR video (1 Mbps) Each test repeated 30 times

PHY

LL

IP

TCP/UDP

Wireless Host A

PHY

LL

IP

Base Station A

10Mbps1ms

PHY

LL

IP

PHY

LL

IP

TCP/UDP

Wireless Host BBase Station B

2Mbps3ms

2Mbps3ms

TCP/UDP

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TCP Performance: Throughput

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UDP Performance: Delay

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Flexible Link Layer Internet Protocol (FLLIP)

Address the problem at its source Local solution to a local problem

Compatible with Internet protocols & architecture IP and higher layers unchanged

Aware of QoS requirements Implicitly or explicitly

Per stream or class QoS differentiation Fully or mostly reliable

Dynamic adaptation to stream/class mix Variable bandwidth allocation

Dynamic adaptation to channel conditions

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FLLIP Architecture

Multiple link layer modules Packet classifier

Protocol, TCP/UDP ports IP ToS, DS field

Per class load measurements Incoming bandwidth allocations

Service class specific processing Isolation between services

Frame scheduler (SCFQ) Enforces incoming bandwidth allocations

Frame SchedulerMAC

Packet Classifier

Service BService A

Protocol Port DS

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SCFQ Frame Scheduler

TimeStamper

Sorted Heap

SCFQ Frame Scheduler

Rate Table Virtual Tim

e

Enforces incoming allocations Protects services Encourages efficiency

Self-clocked fair queueing (SCFQ) Efficient, simple, fair One queue per class Heap sort

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TCP Performance: Throughput with FLLIP

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UDP Performance: Delay with FLLIP

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Service Selection

Implicit QoS specification Assigns applications to services Protocol and TCP/UDP port fields No changes to Internet protocols and applications Immediate applicability

Explicit QoS specification Assigns traffic classes to services QoS provision

Integrated Services, RSVP QoS differentiation

Differentiated Services More flexible

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Heuristic Packet Classifier

Implicit QoS specification

TOS

Hashing Function

Lookup Table

Packet Classifier

Protocol

Service Measurements

Source Port (TCP/UDP) Destination Port (TCP/UDP)

IPv4 Packet Mask

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Differentiated Services Packet Classifier

Explicit QoS specification Dynamic service selection

Traffic Class

Hashing Function

Lookup Table

Packet Classifier

IPv6 Packet Mask

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Service Measurement and Mobility Feedback

Service selection Standard metrics Refinement

Adaptive applications

Mobility

Adaptive Mobility Aware Transport Transport Layer

Network Layer

Standard Measurements and Signals

Hardware/Firmware Physical Layer

Adaptive Mobility Aware Application Application Layer

Application Metrics

Protocol Metrics

Link Layer

Service Metrics

Link Specific Metrics

CBQ RSVP

Vertical Handoffs

Horizontal Handoffs

Mobility Hint Signals

Link Specific Signals

Mobile IP

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Conclusions

TCP performance severely impacted by wireless losses TCP is not the only concern

Real-time multimedia over UDP New applications and protocols

Link layer enhancements Fast local recovery Customized to underlying link

Wireless links: natural choice to introduce QoS support Differentiated servicesbecause Bandwidth is scarce and expensive Link performance is variable and unpredictable