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On Packet Concatenation with QoS Support for Wireless LANs

May 17, 2005. On Packet Concatenation with QoS Support for Wireless LANs. Dzmitry Kliazovich and Fabrizio Granelli University of Trento, Italy [klezovic,granelli]@dit.unitn.it. Presentation Outline. Performance in Wireless LANs Efficiency (IEEE 802.11 a, b and g) Wireless Ovehead

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On Packet Concatenation with QoS Support for Wireless LANs

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  1. May 17, 2005 On Packet Concatenation with QoS Support for Wireless LANs Dzmitry Kliazovich and Fabrizio Granelli University of Trento, Italy [klezovic,granelli]@dit.unitn.it

  2. Presentation Outline • Performance in Wireless LANs • Efficiency (IEEE 802.11 a, b and g) • Wireless Ovehead • Available Concatenation Solutions • IP-level Concatenation (PAC-IP) • Position, Implementation • QoS Support • Operation Scenarios • Conclusions

  3. Performance in Wireless LANs • IEEE 802.11 is the dominant standard in the WLAN environment, providing wireless access to tlc services • Actual performance is far from nominal bitrate • Theoretical maximum throughput [Ref.] The Norwegian academic and research data network,http://www.uninett.no/wlan/throughput.html

  4. Performance in Wireless LANs • Main reason – wireless per packet Overhead Physical Layer (Basic Rate) Link Layer (Data Rate) Data Payload Wireless Overhead

  5. Performance in Wireless LANs • More than 50% of Intenet packets < 100 bytes • Client-server applications (Application layer) • Dominant TCP with 40-bytes ACKs (Transport layer) • Wireless overhead dramatically degrades perfromance • Solution: Group small data units to increase packet size for performance improvement! 802.11a 802.11g 802.11b

  6. Related Solutions • Nagle algorithm (Transport layer) • Collect more data from application instead of immediate output of small TCP packet • Currently, requirement for TCP implementations [RFC 896] • Useful for applications with continuous user input such as Telnet • Performs poor • For real-time applications (X-terminal) • With Delayed-ACK option enabled in TCP

  7. Related Solutions • Packet Frame Grouping (PFG)(Link layer) • Group link layer frames • Contend for medium access not per every frame but per group • Advantages • Latency is not increased • Not limited for packets destined to a particular host • Minor modifications to MAC protocol

  8. PAC-IP Concatenation • PAC-IP • Concatenate IP packets into a single link layer payload • Share wireless overhead by entire group of packets Sender Receiver Network Link Payload Physical Payload

  9. PAC-IP Possilbe Impementation

  10. Quality of Service • QoS support module(Optional) • Differentiate traffic classes according to their delay requirements • Limit concatenation time on per traffic class basis • Temporary enlarge concatenation time if medium is busy (Channel Estimator)

  11. Evaluation Results • Testbed • Modified Orinoco Silver card’s driver • Iperf traffic generator • Simulation • Ns-2 network simulator Concatenation OFF Concatenation ON • No need to change Link or Transport layers • Good performance for small (< 750 bytes) packets

  12. PAC-IP Operation Scenarios • Infrastructure and Ad hoc multi-hop • Traffic sources • Traffic aggregation routers (Access Point) Infrastructure Ad hoc

  13. PAC-IP Pros and Cons • Advantages • Single wireless overhead (link and physical layers) per group of IP packets • Performance improvement through better link utilization for small packets • Drawbacks • Increased packet delivery delay • Limited to packets destined to a particular host • Increased complexity of wireless stations

  14. Conclusion • PAC-IP produce packet concatenation (opposite to fragmentation) on IP level • Results show improved performance for small packets • PAC-IP is an all-IP network solution. However it should be used in networks with large link and/or physical overhead

  15. Thank you!

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