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1. MACA-BI(MACA By Invitation)A Wireless MAC Protocol for High Speed ad hoc Networking 컴퓨터 및 정보통신공학과 200730038 김 연주

2. 목차 • 논문 소개 • Introduction • MACA-BI Illustrated • Collisions in MACA-BI • Predicting Traffic • MACA-BI Performance • Conclusion

3. 논문 소개

4. 논문 소개 • Introduction to MACA-BI • Show that MACA-BI outperforms other multiple access protocol in high speed

5. Introduction

6. Introduction (1/3) • MACA • Solves the hidden terminal problem • Outperforms CSMA in a Wireless multi-hop network • MACA with Carrier Sensing (FAMA-NTR) • Can perform almost as well as CSMA in a single-hop wireless network • FAMA-PJ, CARMA • Achieve better performance at high load • MACAW • Five-way handshake • Overhead cause low channel utilization! • TX-RX turn-around time, preamble bits, control bits, checksum bits

7. Introduction (2/3) • In order to better appraise the turn-around overhead, every transmission should be delayed by TX to RX turn-around time to give a chance to the previous transmitter to switch to receive mode. • The relative impact of turn-around time becomes more critical at high channel speed and low propagation delays. • So turn-around time is important role in future high speed, indoor wireless LANs and, more generally, multihop ad hoc networks!!

8. Introduction (3/3) • MACA-BI (MACA By Invitation) • Reduces the turn-around time • Two handshake • Waits for an “Invitation” by the intended receiver in the form of an RTR (Ready to Receive) control packet

9. MACA-BI Illustrated

10. RTS CTS DATA A B A B A B C C C Blocked MACA-BI Illustrated (1/2) • Three basic cycles of the MACA protocol • “driven by the transmitter” • The three-way handshake

11. RTR DATA A B A B C C Blocked MACA-BI Illustrated (2/2) • Two basic cycles of the MACA-BI protocol • The two-way handshake • Node B does not have exact knowledge of packet arrival times at Node A • The each data packet carries the information • Backlog in transmitter: # of packet and their lengths, the average rate and future backlog • Node A replies with the transmission of the requested number of packet and with new backlog information

12. Collisions in MACA-BI

13. Analysis of collision states (1/3) • Examination • 6 node hidden terminal configuration • Identify possible collisions • Node A and B issue RTRs at about the same time to different neighbors • Only three possible combinations • Two type of RTR collision • Direct collision • Between nodes within hearing distance (due to carrier sense failure) • Indirect collision • Between nodes hidden from each other and transmitting to a common neighbor

14. Analysis of collision states (2/3)

15. Analysis of collision states (3/3) • If node receives the RTR packet, • Knows the duration of the impending data packet data packet transmissions by its two-hop neighbors • Is able to decide if its transmission can disturb its neighbors reception

16. Data collision free property (1/2) • No collision among data packet in MACA-BI • Direct collision among data packet • A transmits data packet to B, then C cannot transmits data packet to B • Only if C did not hear the RTR from B to A, C can transmit a data packet to D • B transmitted RTR to A while C was transmitting-> impossible! • B transmitted RTR to A while C was receiving a RTR from D -> impossible!

17. Data collision free property (2/2) • Hidden terminal problem은 여전히 control packet을 방해 • RTR과 Data packet간에 충돌 가능 • Carrier Sensing 실패로 Control Packet간에 충돌 가능 • MACA-BI는 이러한 충돌 가능성이 존재하지만, MACA는 이러한 충돌을 줄이려고 하지 않는다.

18. Comparing MACA & MACA-BI protocol states (1/4) • Assume • The channel is symmetric as in all other MACA protocols • Control packet can be corrupted by noise • Direction collision • Indirection collision

19. Comparing MACA & MACA-BI protocol states (2/4) • Direction Collision

20. Comparing MACA & MACA-BI protocol states (3/4) • Indirection Collision

21. Comparing MACA & MACA-BI protocol states (4/4) • If the protocols work properly, they are data collision free • Cannot speculate a priori on the probability of each configuration, but can qualitatively say that introducing the third pass in the handshake (as MACA dose) does not reduce the dangerous situations • 프로토콜은 channel noise나 fading등으로 control packet 방해를 받아 실패 할 수 있는데 MACA가 MACA-BI보다 훨씬 취약!

22. Predicting Traffic

24. MACA-BI performance

25. MACA-BI performance (1/8) • MACA-BI multi-hop network는 시뮬레이션을 통해 조사 • 시뮬레이션 • Four nodes • 네트워크의 기본적인 기능, data link, MAC layer는 구현 • Routing은 Bellman-Ford scheme • 모든 node는 size 50의 buffer를 공유 • Data link layer는 선택적인 반복을 가진 size 8의 sliding window • separate window는 각 pair node가 사용 • Flow control은 sliding window mechanism을 통해 공급 • Separate MAC protocol 시뮬레이션 모듈은 개발

26. MACA-BI performance (2/8) • 시뮬레이션 (계속) • Neighbor with highest buffer occupancy is invited to transmit • Channels are error free • Packet transmission can collide due to the hidden terminal problem and the non negligible propagation delay • 방해받은 packet들은 sliding window mechanism에 의해 재 전송 -> packet loss는 오직 네트워크 레벨에서만 발생 • FAMA-NTR은 매 handshake마다 하나의 data packet을 전송 • Floor 충돌이 반복되는 것을 막기 위해 Poisson process를 가진 floor로 node들은 reschedule • Datagram traffic을 시뮬레이션하기 위해 Poisson process를 가진 모든 노드들에서 External packet들 발생

27. MACA-BI performance (3/8) • 첫 번째 시뮬레이션 • Null propagation time의 1Mbps의 링크 • Control packet 4 bytes • Data packet 1000bits • Floor generation interval 2.5ms

28. MACA-BI performance (4/8)

29. MACA-BI performance (5/8) • 두 번째 시뮬레이션 • 유한한 propagation time • 전송 범위 3미터의 near-filed signal strength • Four node • 10Mbps channel speed • Average floor generation interval 0.3ms • Data packet size 53 bites • Control packet size 4 bytes

30. MACA-BI performance (6/8)

31. MACA-BI performance (7/8)

32. MACA-BI performance (8/8)

33. Conclusion

34. Conclusion • Eliminate RTS packet • Reducing the overhead for each packet transmission • Simplifying the implementation • More robust to hidden terminal collision, direct collision and noise corruption • Not very sensitive to the TX-RX turn-around time • In simulation, shows its superiority

35. Q&A