1. Wrap-up Myungchul Kim mckim@cs.kaist.ac.kr

2. Ch 5. MAC in WMNs Myungchul Kim mckim@cs.kaist.ac.kr

3. IEEE 802.11 DCF protocol Conventional wireless MAC protocols

4. IEEE 802.11e MAC protocol –Define the channel access functions and the traffic specification (TSPEC) management –Channel access function : hybrid coordination function (HCF) A contention-based protocol called enhanced distributed channel access (EDCA) A polling mechanism called HCF controlled channel access (HCCA): central control Conventional wireless MAC protocols

5. IEEE 802.11e MAC protocol –EDCA: enhance the original DCF by providing prioritized medium access based on different traffic classes, access categories (ACs) –TXOP: a bounded time interval in which a node is allowed to transmit a series of frames. Conventional wireless MAC protocols

6. IEEE 802.11e MAC protocol Conventional wireless MAC protocols

7. IEEE 802.11e MAC protocol Conventional wireless MAC protocols

8. Common channel framework (optional) –Simultaneous transmissions on multiple channels –Request-to-switch (RTX) and clear-to-switch (CTX) Advanced MAC features proposed by the 802.11 TDs group

9. Ch 6. Security in WMNs Myungchul Kim mckim@cs.kaist.ac.kr

10. –Generic security services Security technology overview

11. Performance of VoIP in a 802.11 Wireless Mesh Networks by D. Niculescu, S. Ganguly, K. Kim and R. Izmailov Infocom 2006 Myungchul Kim mckim@cs.kaist.ac.kr

12. 12 Fig 1 With 2Mbps link speed, 8 calls in single hop to one call after 5 hops due to the following: –Decrease in the UDP throughput because of self interference –Packet loss over multiple hops –High protocol overhead for small VoIP packets

13. 13 Aggregation –802.11 networks incur a high overhead to transfer one packet –For a 20 byte VoIP payload (43.6 microsec at 11 Mbps) RTP/UDP/IP 12+8+20 = 40 bytes MAC header + ACK = 38 bytes MAC/PHY procedure overhead = 754 microsec –DIFS(50microsec), SIFS(10microsec) –Preamble + PLCP(192microsec) for data and ACK –Contention (approx 310microsec) 800 microsec at 11 Mbps -> 1250 packets per sec -> G.729a: 12 calls (2Mbps -> 8 calls) Throughput: T(x) = 8x / (754 + (78 + x) 8/B)) where x is the payload size in bytes and B is the raw bandwidth of the channel

14. 14 –Reducing the overhead Aggregation (Fig 12) -> increase packet delay Header compression –Fig 12

15. Toward an Improvement of H.264 Video Transmission over IEEE 802.11e through a Cross-Layer Architecture by A. Ksentini, M. Naimi, and A. Gueroui IEEE Communications Mag. Jan. 2006 Myungchul Kim mckim@cs.kaist.ac.kr

16. 16 The proposed cross-layer architecture Table 1. 802.11 MAC parameters

17. 17 The proposed cross-layer architecture Figure 1

18. 18 Simulation and results Result analysis –Fig 2 IDR loss rate

19. 19 Simulation and results Result analysis –Fig 4 Partition B loss rate

20. 20 Simulation and results Result analysis –Fig 5 Partition C loss rate

21. 21 Simulation and results Result analysis (final decoded frame #76) –Dropped frames: DCF(87), EDCA(41) out of 250 frames –Fig 8 a) DCF, b) EDCA, c) QoS architecture

22. Link Layer Assisted Mobility Support Using SIP for Real-time Multimedia Communications October 1, 2004 Wooseong Kim, Myungchul Kim, Kyounghee Lee Information and Communications Univ. {wskim, mckim, leekhe}@icu.ac.kr Chansu Yu Cleveland State Univ. c.yu91@csuohio.edu Ben Lee Oregon State Univ. benl@eecs.oregonstate.edu

23. Mobiwac 04 23 Problem Definition  Handoff delay of SIP mid-call mobility [12] –Handoff Delay =  Tn (n=0 to 5) –Link layer handoff delay (T0) –Movement Detection (T1) –DHCP transaction (T2) –Configuration time (T3) –re-INVITE (T4) –RTT/2 (T5) –DHCP [2]: T2 > 1 sec, –DRCP [8]: T2 = 100 ~ 180 ms [7,10] –Total handoff delay of SIP mid-call mobility is not adoptable to real-time applications

24. Mobiwac 04 24 Proposed scheme: PAR-SIP (cont’d)  Handoff delay of PAR-SIP mid- call mobility PAR-SIP handoff delay =  Tn ( n=0,1,3,5) < SIP handoff delay DHCP transaction time(T2) and SIP re-INVITE procedure time (T4) are removed Movement detection time (T1) is diminished T0,T3 and T5 is same as SIP terminal mobility

25. Mobiwac 04 25 Experiments (cont’d)  Handoff Delay of Conventional SIP Mobility –SIP_Handoff_Delay =  Tn ( n=0 to 5) = 50 ms +5 ms + 1.35 sec + 10 ms + 10 ms + RTT/2  1.4 s. –Both nodes can not receive packets for 1.5 seconds. Rx delay of a MN is a little longer than that of a CN due to re-INVITE delay

26. Mobiwac 04 26 Experiments (cont’d)  Handoff Delay of PAR-SIP Mobility –PAR-SIP_Handoff_Delay =  Tn ( n=0,1,3,5) = T0+T1+T3+T5 = 50 ms +1 ms + 7 ms + RTT/2  60ms. –A MN transmission rate is a little shorter than a CN because a CN keeps bi-casting for a MN during handoff

27. Mobiwac 04 27 Experiments (cont’d)  Average transmission rate variation during handoff PAR-SIP Mobility shows better transmission rate due to handoff than existing SIP mobility while receiving 2500 packets. PAR-SIP only drops by 2 kbps during handoff

28. Mobiwac 04 28 Experiments (cont’d)  Packet loss Low latency handoff and bi-casting can reduce the number of lost packets Packet loss of PAR-SIP mobility using all kinds of codecs shows about 1% of total packets comparing to 5% in conventional SIP mobility (handoff :4 times/sec)

29. The Symbiosis of Cognitive Radio and WMNs from “Guide to WMNs” by Sudip Misra and et al, 2009 Myungchul Kim mckim@cs.kaist.ac.kr

30. Spectrum usage –new spectrum increasingly scarce –Spectrum is vastly under-used: 5.2% usage Change –“command and control” approach to spectrum regulation Background

31. Static core topology –For CR, the fixed network changes the problem of collecting awareness of the network’s surroundings Spectrum information collection –The WMN presents a distributed infrastructure to collect spectrum data at a large number of locations –CR devices act as sensors to gauge interference levels Traffic awareness –Fairly easy to obtain from the gateway Directions for future research

32. Data distribution and decision making –Within the mesh itself Spectrum monitoring and policing –Primary spectrum rights should be protected –The WMN may be able to collaborate to detect users and determine the location of illegal transmissions Directions for future research

33. Construction and Evaluation of a WMN Testbed from “Guide to WMNs” by Sudip Misra and et al, 2009 Myungchul Kim mckim@cs.kaist.ac.kr

34. OLSR –Link-state routing protocol –MPR Methodology Performance evaluation

35. Measurement discussion Performance evaluation

36. Measurement discussion Performance evaluation

37. Existing testbeds Related work