A Link Layer Scheme for Reliable Multicast in Wireless Networks

1. A Link Layer Scheme for Reliable Multicast in Wireless Networks Thesis defense of: Aarthi Natarajan Advising Committee: Dr. Sandeep Gupta Dr. Partha Dasgupta Dr. Andrea Richa

2. Outline • Motivation • Challenges • Related Work: IEEE 802.11 Multicast, LBP, DBTMA • System Model • Protocols: RDNP and M-RDNP • Simulation Environment • Performance Results: Wireless LANs, Ad hoc networks • Conclusions and Future Work Mobile Computing and Networking Group Arizona State University

3. Group Applications Search and Rescue Operation Chat Application • More Applications … • Military Operations • Emergency operations • Whiteboard Applications NEED “RELIABLE” COMMUNICATION Mobile Computing and Networking Group Arizona State University

4. Why Wireless ? Motivation Wireless Network : devices with wireless adapters communicating with each other using EM waves • Ease and Speed of deployment. • Wired network may not be possible. Wireless Network Architectures Centralized or LAN Distributed or Ad hoc Wired network Base Station 1.Collection of autonomous hosts 2. No Infrastructure 3. All hop wireless 1. All devices connect to base station 2. Infrastructure based 3. End hop wireless Mobile Computing and Networking Group Arizona State University

5. Problem Statement Motivation • To build a reliable link-layer protocol for multicast in single channel multi-access wireless networks • Reliability can be achieved at • End-to-end: across several hop. • Link level: across a single hop. • Why reliable multicast at the link layer[IG00]? • Allows local error recovery. • Improves throughput. • Conserves energy. • Reduces end-to-end delay. link level reliability Destination Source End to end reliability Mobile Computing and Networking Group Arizona State University

6. Link Level Multicasting • Repeated unicast transmissions • Redundant data, Wastes energy, Increases delay, Reduces throughput • Reliable Broadcast at the multicast address and filter at the receivers Design Issues: • Medium Access: • Wired Networks use CSMA/CD • Wireless Networks signal strength fades with distance • self interference, hidden terminals exposed terminals, capture effect • Error Recovery • Controlling the flow of feedback information Sender 5 transmissions Sender 1 transmissions Mobile Computing and Networking Group Arizona State University

7. Hidden Terminals Nodes not within the senders range but within the receiver range Causes collisions at the receivers Collision detection cannot be used Location dependant carrier sensing: Even if the receiver may experience collisions, the sender may not. Self Interference: transmit signal flows into receive path Capture Effect Picks up stronger signal as long as the ratio of the stronger to weaker signal exceeds the capture threshold. Signal from Node B Capture Threshold (SNRT) > Signal from Node G Medium Access Issues Challenges Node B Node O Node G HIDDEN TERMINAL Can still pick up packet from Node B Node O Node B Node G Mobile Computing and Networking Group Arizona State University

8. Error Recovery and Feedback Control • Local Error Recovery • High channel BER • Channel bit error rate can be as high as 1 in 104 or higher. • Almost 40% or more of the packets are in error when payload is 512b. • Retransmission based [TKP97] • ACK based : absence of ACK • NACK based : presence of NACK • Explicit retransmission requests : reception of retransmit request packet • FEC based • Controlling the flow of feedback from multiple receivers Battery Anemic • Size and weight limitation restrict the lifetime of the device battery. • Energy conservation techniques Mobile Computing and Networking Group Arizona State University

9. Single channel multi-access networks Single transceiver Infrastructure-based as well as ad hoc Packet loss : Bit errors and Collisions Group membership maintained by the higher layer protocols Two Ray Ground Propagation Model Signal has to greater than the reception threshold to receive the packet correctly The medium is perceived as busy as long as the signal is greater than the noise threshold. System Model and Assumptions Preliminaries Mobile Computing and Networking Group Arizona State University

10. Some Related Work… Related Work • Solutions to Hidden Terminals • RTS-CTS based : Single Channel • Unicast: IEEE 802.11Unicast • Multicast: LBP, PBP, DBP • Busy Tone based : Two channels • Unicast: DBTMA [DJ98] • Multicast: IEEE 802.11MX [Sha02] • IEEE 802.11 Multicast Mobile Computing and Networking Group Arizona State University

11. DIFS SIFS SIFS SIFS X X X X RTS CTS X X DATA X ACK IEEE 802.11 Unicast [Com99] Related Work • RTS-CTS • ACK based error recovery • Physical + virtual carrier sensing • DIFS, SIFS inter-frame space for prioritization of DATA Sender H Hidden Terminal Receiver H RTS DATA Sender H CTS ACK Receiver H Update NAV from CTS Update NAV from RTS Others Mobile Computing and Networking Group Arizona State University

12. RTS-CTS for Multicast Related Work • Several receivers : feedback collision • Try to eliminate the collision of feedback • LBP[KK01] – leader node sends the feedback information • DBP[KK01] – all nodes send out feedback after a certain random delay. • PBP[KK01] – every node sends out feedback with certain probability “p”. • BSMA[TG00b], BMW[TG00a], BMMM, LAMM [Shal02] • RTS-CTS does not solve all hidden terminal problems[XGB02] RTS H CTS Collision Mobile Computing and Networking Group Arizona State University

13. DIFS IEEE 802.11 Multicast [Com99] Related Work • Not Reliable • Hidden terminal problems • No local error recovery DATA Sender Consume data Group Neighbors Ignore data Others Mobile Computing and Networking Group Arizona State University

14. Our Protocol • Salient Features • Protocol RDNP • Deals only with local error recovery • No CTS packet. • Uses a NACK or collision of NACKs to prompt retransmissions. • NACKs do not contain any relevant information. • Does not suppress hidden terminals • Protocol M-RDNP • Mitigate the effect of hidden terminals • Reliable neighbors do not suffer from hidden terminals as long as sender is transmitting • Forces routing layer to build routes only using reliable neighbors Mobile Computing and Networking Group Arizona State University

15. DIFS SIFS SIFS Protocol RDNP Protocol • Good for wireless LANs when there are no hidden terminals • base station is the only node that can transmit multicast data. • Not so good for ad hoc networks because of hidden terminals. RTS DATA Sender NACK Group Neighbors Without packet Update NAV from RTS Others & Group Neighbors With packet Mobile Computing and Networking Group Arizona State University

16. CSI CS RX RL Reliable and Interference Region Protocol Reception range: Radius within which the signal is greater than the reception threshold Noise Range: Radius within which the signal is greater than the noise threshold Hey! I cannot transmit. I am within A’s noise range Hey! I can transmit. I am not within A’s noise range Reliable Neighbors: All neighbors within the collision free zone. Unreliable Neighbors: All neighbors not in the reliable range Node A Node B1 Node B2 Node C1 Node C2 Booo Hooo! I experience collisions Yippee! I still receive A’s signal Thanks to capture effect. Mobile Computing and Networking Group Arizona State University

17. Minimum Reliable Radius Protocol Minimum RL ≈ 170m when CS = 550m • Assumption: No two nodes “start” transmitting simultaneously. • Two simultaneous transmissions must be separated from each other by a distance of CS • Around a sender the maximum number of nodes which can be transmitting simultaneously is 6 Node E Node F CS dER dFR CS Node R dAR dDR d Node D Φ RL CS Node A Node S dCR dBR Node C Node B Mobile Computing and Networking Group Arizona State University

18. Protocol M-RDNP Protocol • Force all routes to be formed using only reliable neighbors. • Thus transmissions use only reliable hops in which there are no hidden terminal problems. • Might use more number of hops to transmit to the same node Mobile Computing and Networking Group Arizona State University

19. An example Protocol RL ≈ 170m Routes using IEEE 802.11 and RDNP at the MAC layer Routes using M-RDNP at the MAC layer 1 1 2 2 3 3 Number of hops = 4 Number of hops = 6 Mobile Computing and Networking Group Arizona State University

20. Simulation Environment Results • Network Simulator [Net02] • Performance Metrics • Average Packet Drop Ratio per Node = • Average Energy Consumed per Node per packet = • Wireless LANs: • IEEE 802.11, LBP, DBP, PBP, RDNP • Ad hoc networks • Routing Layer: SPST [GBS00], SPST [Sri03] better than M-AODV, ODMRP, MST • IEEE 802.11, RDNP, M-RDNP • All simulation points averaged over 45 runs • Accuracy 5% confidence interval 99% [Jai91] Number of packets dropped per node Number of packets sent Energy consumed per node Number of packets recv Mobile Computing and Networking Group Arizona State University

21. 2 2 2 4 3 1 1 4 1 With Unicast traffic AVG DROP RATIO NUMBER OF NODES Simulation Results – Wireless LANs Results Stationary nodes Mobile nodes AVG DROP RATIO AVG DROP RATIO BER (X 10e5) BER (X 10e5) Stationary nodes with explicit retransmission requests END-TO-END DELAY BER (X 10e5) Mobile Computing and Networking Group Arizona State University

22. 2 2 3 3 2 2 1 1 1 1 Simulation - Stationary Ad Hoc networks Results Nodes = 10, Avg. neighbor density ≈4,3 Nodes = 20, Avg. neighbor density ≈6,4 AVG DROP RATIO AVG DROP RATIO BER (X 10e5) BER (X 10e5) Nodes = 30, Avg. neighbor density ≈8,5 Nodes = 40, Avg. neighbor density ≈10,6 AVG DROP RATIO AVG DROP RATIO 3 3 BER (X 10e5) BER (X 10e5) Mobile Computing and Networking Group Arizona State University

23. 3 2 2 1 1 3 Simulation – MANETs Results Nodes = 30, Low BER Nodes = 10, Low BER AVG DROP RATIO AVG DROP RATIO Speed (m/s) Speed (m/s) Nodes = 10, High BER Nodes = 30, High BER AVG DROP RATIO AVG DROP RATIO Speed (m/s) Speed (m/s) Mobile Computing and Networking Group Arizona State University

24. Simulation – MANETS (Very High Speed ≈ 100miles/hr) Results Nodes = 10, Speed = 80 miles/hr Nodes = 30, Speed = 80 miles/hr AVG DROP RATIO AVG DROP RATIO BER BER Nodes = 10, Speed = 150 miles/hr Nodes = 30, Speed = 150 miles/hr AVG DROP RATIO AVG DROP RATIO BER BER Mobile Computing and Networking Group Arizona State University

25. Summarizing Reliability • Stationary Ad hoc networks • M-RDNP - “Good” for low neighbor density. • M-RDNP and RDNP – Statistically indifferent for high neighbor density, “better” than IEEE 802.11. • Mobile Ad hoc Networks Low/Moderate Speeds • M-RDNP – “Good” for low neighbor density. • IEEE 802.11 - “Good” for low BER and high neighbor density. • RDNP – “Good” for high BER and high neighbor density. • Mobile Ad hoc Networks Very High Speeds • All three statistically indifferent. Mobile Computing and Networking Group Arizona State University

26. Energy Results • The energy consumed for a retransmission is much higher than the energy consumed for a transmission. • For stationary ad hoc networks, • As the BER increases the energy consumed per packet is much higher for RDNP and M-RDNP owing to the increase in the number of retransmissions. • RDNP consumes more energy than M-RDNP because of high drop ratio hidden terminals. • For mobile ad hoc networks • As the mobility increases, the energy consumed also increases. • For low BER the energy consumed by RDNP and IEEE 802.11 is almost the same, because no energy is lost in retransmissions. • M-RDNP consumes the least energy for low BER because is does not lose packets due to hidden terminals. • For higher BER RDNP and M-RDNP consumes more energy because of retransmissions Mobile Computing and Networking Group Arizona State University

27. Conclusions • RDNP and M-RDNP was proposed as a NACK based reliable multicast extension to IEEE 802.11 • Reliable multicast is extremely desirable when channel BER is high. • Frequent changes in route caused by SPST, “not good” for the MAC layer. • Energy cost associated with retransmission very high. • For very high speed networks MAC layer is insignificant. Future Work • Addition of energy saving strategies • Adapt the MAC layer based on the network characteristics • Estimate the link metric for SPST based on the conclusions Mobile Computing and Networking Group Arizona State University

28. Thank You! Questions ? Mobile Computing and Networking Group Arizona State University

29. References [Com 99] ANSI/IEEE Standard 802.11 Wireless LAN medium control (MAC) and physical layer (PHY) specifications, In 1999 Edition. [DJ98] J. Deng, Z. J. Haas, “Dual Busy Tone Multiple Access (DBTMA): A New Medium Access Control for Packet Radio Networks”, In IEEE ICUPC’98, Italy, 1998. [KK01] J. Kuri, S. Kasera, “Reliable Multicast in Multi-access Wireless LANs”, Wireless Networks, 7(4):359-369, July 2001. [Net02] Network Simulator – ns-2, Available via http://www.isi.edu/nsnam/ns/, [Accessed on Aug 02] [Sha02] Vikram Shankar, “A Medium Access Control Protocol with reliable multicast support for wireless networks”, Master’s Thesis, Arizona State University, Tempe, AZ 85287, December 2002 [SG03] Ganesh Sridharan and Sandeep K.S.Gupta, “Performance comparison study of self stabilizing routing protocols for mobile ad hoc networks”, In preparation [GBS00] Sandeep K.S. Gupta, A. Bouadallah and P.K. Srimani, “Self Stabilizing Protocols for Shortest Path Tree for multi-cast routing in mobile networks”, In proceedings of LCNS:1900, Euro-Par’00 Parallel Proceedings, pages 600-604, 2000. [TKP97] Fouad A. Tobagi and Leonard Kleinrock, “Comparison of Sender-Initiated and Receiver-Initiated Multicast Protocols”, In IEEE Journal on Selected Areas in Communication, April 1997. [SHAL02] Min-Te Sun, Lifei Huang, Anish Arora and Ten-Hwang Lai, “Reliable MAC Layer Multicast in IEEE 802.11 wireless networks”, In Proceedings of International Conference on Parallel Processing, ICPP ’02, pages 527-536, August 2002. [XGB02] K.Xu, M.Gerla and S.Bae, “How effective is the IEEE 802.11 RTS/CTS handshake in ad hoc networks”, In Proceedings of IEEE Globecom 2002. [TG00a] Kent Tang and Mario Gerla. “MAC Layer Broadcast Support in 802.11 Wireless Networks”, In Proceedings of 21st Century Military Communication Conference, MILCOM’00, pages 544-548, 2000 [TG00b] Kent Tang and Mario Gerla. “Random Access MAC for Efficient Broadcast Support in Ad Hoc Networks”, In IEEE Wireless Communications and Networking Conference, WCNC 2000, pages 454-459, 2000 [TG01] Kent Tang and Mario Gerla. “MAC Reliable Broadcast Ad hoc Networks”, In Communications for Network Centric Operations: Creating the Information force. IEEE Military Communication Conference, MILCOM’01, pages 1008-1013, 2001 Mobile Computing and Networking Group Arizona State University

30. Capture Effect Picks up stronger signal as long as the ratio of the stronger to weaker signal exceeds the capture threshold. Oops! I would like to transmit but cannot !!! Signal from Node B Capture Threshold > Signal from Node G Medium Access Issues • Exposed Terminals • Nodes within the senders range but not within the receivers range • Reduces throughput Can still pick up packet from Node B Node O Node O Node P Node B Node B Node G Node G EXPOSED TERMINAL Mobile Computing and Networking Group Arizona State University

31. Why RTS-CTS does not work ??? RX dAB Node A Node B Node C1 Node C2 Mobile Computing and Networking Group Arizona State University

32. DIFS SIFS SIFS SIFS RTS ACK DATA CTS Group neighbor Sender Non group neighbor Group Leader Leader Based Protocol Related Work RTS DATA Sender CTS ACK Leader NCTS NACK Group neighbors Update NAV from CTS Update NAV from RTS • Problems: • Leader Mobility reduces throughput • “Capture Effect” may hide NCTS and NAK from distant nodes • Incoming nodes may not have heard RTS/CTS exchange and may cause collision • Sender has to know the multicast group members a priori Mobile Computing and Networking Group Arizona State University

33. Busy Tone Solution to Hidden Terminals Related Work Cannot transmit because I sense a receiver busy tone tone RTS Node O Node B Node G Node P • Problems: • Extra hardware, more energy Mobile Computing and Networking Group Arizona State University

34. CSI CS RX RL Node A Area around a Transmitter Protocol • Collision Free Zone: The area around a transmitter in which receiver do not suffer from hidden terminals when the transmitter is transmitting data. • Collision Zone: The area around the transmitter within which receivers are within the range of the sender but might suffer from hidden terminals. • Interference Free Zone: The area around a transmitter within which no node transmits because of physical carrier sensing. • Interference Zone: The area around a transmitter within which nodes can cause hidden terminal problems for receivers in the collision zone. Reliable Neighbors: All neighbors within the collision free zone. Unreliable Neighbors: All neighbors not in the reliable range Mobile Computing and Networking Group Arizona State University

35. Calculate RL and CSI For CSI - dAB dBC Node A Node B Node C For RL - Mobile Computing and Networking Group Arizona State University

36. An example Protocol RL ≈ 170m Routes using IEEE 802.11 and RDNP at the MAC layer Routes using M-RDNP at the MAC layer Number of hops = 4 Number of hops = 6 Mobile Computing and Networking Group Arizona State University

37. SPST Self Stabilizing Routing Protocol Related Work • Every node periodically sends out beacon messages • Using values in the beacon messages SPST builds routes to the root of the multicast group. Mobile Computing and Networking Group Arizona State University

38. Confidence Interval • Each sample mean is an estimate of the population mean • With k samples we have k estimates • Problem: get one from k. • Best is get probabilistic bounds • Two bounds c1 and c2 such that there is a high probability, 1-α, that the population means is in interval (c1,c2) Probability(c1≤μ≤c2) = 1-α (c1,c2) confidence interval α significance level(≈0) 100(1- α) confidence level (≈100) 1- α confidence coefficient(≈1) Mobile Computing and Networking Group Arizona State University

39. Energy - Stationary Ad Hoc networks Results Nodes = 20, Avg. neighbor density ≈6,4 Nodes = 10, Avg. neighbor density ≈4,3 AVG Energy consumed per packet AVG Energy consumed per packet BER (X 10e5) BER (X 10e5) Nodes = 30, Avg. neighbor density ≈8,5 Nodes = 40, Avg. neighbor density ≈10,6 AVG Energy consumed per packet AVG Energy consumed per packet BER (X 10e5) BER (X 10e5) Mobile Computing and Networking Group Arizona State University

40. Energy – MANETs (Walking Speeds) Results Nodes = 30, Low BER Nodes = 10, Low BER AVG Energy consumed per packet AVG Energy consumed per packet Speed (m/s) Speed (m/s) Nodes = 10, High BER Nodes = 30, High BER AVG Energy consumed per packet AVG Energy consumed per packet Speed (m/s) Speed (m/s) Mobile Computing and Networking Group Arizona State University

41. Energy – MANETS (Vehicular Speeds) Results Nodes = 10, Low BER Nodes = 30, Low BER AVG Energy consumed per packet AVG Energy consumed per packet Speed (m/s) Speed (m/s) Nodes = 10, High BER Nodes = 30, High BER AVG Energy consumed per packet AVG Energy consumed per packet Speed (m/s) Speed (m/s) Mobile Computing and Networking Group Arizona State University

42. Reliability – MANETS (Very High Speed ≈ 100miles/hr) Results Nodes = 10, Low BER Nodes = 30, Low BER AVG DROP RATIO AVG DROP RATIO Speed (m/s) Speed (m/s) Nodes = 10, High BER Nodes = 30, High BER AVG DROP RATIO AVG DROP RATIO Speed (m/s) Speed (m/s) Mobile Computing and Networking Group Arizona State University