Ad Hoc Wireless Networks: Protocols and Applications Capri Wireless School Sept 13-17, 2004

1. Ad Hoc Wireless Networks: Protocols and ApplicationsCapri Wireless SchoolSept 13-17, 2004 Mario Gerla Computer Science Dept UCLA

2. Ad Hoc Networks - Outline • What is an Ad Hoc Network • Ad hoc network projects at UCLA • The ONR Minuteman project • The NSF WHYNET project • The MAC protocol • Scalable routing • On demand routing • Proactive routing • Bringing ad hoc networks to market • The vehicular grid • The future of ad hoc networking

3. The three wireless network “waves” • Wave #1: cellular telephony (late 80’s) • Still, biggest profit maker • Wave #2 : wireless Internet access (mid 90s) • Most Internet access on US campuses is via WiFi • Hot spots are rapidly proliferating in the US; Europe and Asia to follow soon • 2.5 G and 3G trying to keep up; competitive edge? • Wave #3: ad hoc wireless nets (now) • Set up in an area with NO infrastructure; to respond to a specific, time limited need

4. The 3rd Wave: Infrastructure vs Ad Hoc Infrastructure Network (cellular or Hot spot) Ad Hoc, Multihop wireless Network

5. General Ad Hoc Network Characteristics • Instantly deployable, re-configurable (no fixed infrastructure) • Created to satisfy a “temporary” need • Node portability (eg sensors), mobility • Limited battery power • Multi-hopping ( to save power, overcome obstacles, enhance spatial spectrum reuse, etc.)

6. Ad Hoc Network Applications Military • Automated battlefield • Special operations • Homeland defense Civilian • Disaster Recovery (flood, fire, earthquakes etc) • Law enforcement (crowd control) • Search and rescue in remote areas • Environment monitoring (sensors) • Space/planet exploration (Issue: ad hoc nets vs sensor nets)

7. Ad Hoc Network Applications (cont) Commercial • Sport events, festivals, conventions • Patient monitoring • Ad hoc collaborative computing (Bluetooth) • Sensors on cars (car navigation safety) • Car to car communications • Networked video games at amusement parks, etc Commercial Killer Application? ….stay tuned!

8. The Battlefield • Soon after ARPANET birth, DoD was quick to understand the value of ad hoc networks for the battlefield • In 1971 (two years after ARPANET) DARPA starts the Packet Radio project • Since 1971, several DARPA, Army and Navy programs supported ad hoc net research and helped enhance this technology • So far, government has been the main funding source: battlefield is the “killer” application.

9. DARPA Packet Radio Project (1971-1985) • Goals: • extend P/S to mobile environment • provide network access to mobile terminals • quick (re) deployment • Fully distributed design philosophy: • self initialization • dynamic reconfiguration • asynchronous MAC protocol (CSMA) • dynamic routing • automated network management • “compact”, portable radio design

11. Ad Hoc Networks - Outline • What is an Ad Hoc Network • Ad hoc network projects at UCLA • The ONR Minuteman project • The NSF WHYNET project • The MAC protocol • Scalable routing • On demand routing • Proactive routing • Scalable, fair TCP • Bringing ad hoc networks to market • The vehicular grid • The future of ad hoc networking

12. The AINS (Autonomous Intelligent Networked Systems) Program at UCLA • 5 year research program (Dec 2000 – Dec 2005) sponsored by ONR • 7 Faculty Participants: 3 in CS Dept, 4 in EE Dept • Goal: design a robust, self-configurable, scalable network architecture for intelligent, autonomous mobile agents

13. SURVEILLANCE MISSION AIR-TO-AIR MISSION STRIKE MISSION RESUPPLY MISSION FRIENDLY GROUND CONTROL (MOBILE) SATELLITE COMMS SURVEILLANCE MISSION UAV-UAV NETWORK COMM/TASKING COMM/TASKING Unmanned UAV-UGV NETWORK Control Platform COMM/TASKING Manned Control Platform Network of Autonomous Agents

14. Urban warfare scenario: Swarm communications Autonomous Perching

15. Central AINS theme: networking FLIR

16. The AINS Project Field Demo at UCLAMay 2004 • Goals • Demonstrate the integration and interworking of various protocols: • Routing • Multicast • Sensors • Adaptive video • Approach • Aerial nodes: Blimps with laptops • Mobile ground nodes: men/robots carrying laptops • Routing protocol: ODMRP • Scenario: cooperative surveillance of a large area

17. Blimp driven by robot

18. Detailed Demo scenario: 1.Mobile robots with cameras do routine patrolling Mobile robots Command Post

19. 2. Command post (CP) detects an irregular activity far away

20. 3.CP sends out a mobile robot for a closer investigation; it becomes disconnected due to the short radio range

21. 4.Another robot moves in to re-connect

22. 5.Another suspect activity detected

23. 6.Second robot moves out to investigate, breaking the network

24. Bring in the Blimp to reconnect

25. View From the Blimp

27. WHYNET - Network Testbed at UCLA • Wireless Hybrid Networked Testbed • Sponsored by NSF (2003 to 2007) • A “consortium” of seven Universities (UCLA, USC, UCB, UCD, UCR, UCSD, U-Delaware) • Main Goal: develop test environments/tools: • Radios (MIMO, OFDM, UWB, sensor radios, etc) • MAC protocols (directional antennae) • Sensor (low energy protocols) • Network protocols (QoS, Scalability, interconnection) • Security • Approach: share results/code/platforms • Center piece: hybrid emulation environment

28. Hybrid Emulation testbed Simulated large-scale network Access Nodes & Hybrid Simulation Server Cluster Small-scale Real Testbed • Internet

29. Sample WHYNET projects • Radio testbed for MIMO and smart antenna technology • A lab for UWB studies/experiemnts • A MANET Security benchmark • A vehicular ad hoc network testbed • Interconnection of MANETs across the Internet

30. Ad Hoc Networks - Outline • What is an Ad Hoc Network • Ad hoc network projects at UCLA • The ONR Minuteman project • The NSF WHYNET project • The MAC protocol • Scalable routing • On demand routing • Proactive routing • Scalable, fair TCP • Bringing ad hoc networks to market • The vehicular grid • The future of ad hoc networking

31. Wireless Nets – the MAC layer • MAC Protocols Overview • IEEE 802.11 • Bluetooth • Zigbee

32. Multiple Access Control (MAC) Protocols • MAC protocol: coordinates transmissions to minimize/avoid collisions • (a) Channel Partitioning : TDMA, FDMA, CDMA (cellular systems) • (b) Random Access : CSMA (802.11, Zig Bee) • (c) “Polling” : Bluetooth • Goal: efficient, fair, simple, decentralized

33. Random Access protocols • A node transmits at random (ie, no a priory coordination among nodes) at full channel data rate R. • If two or more nodes “collide”, they retransmit at random times • The random access MAC protocol specifies how to detect collisions and how to recover from them (via delayed retransmissions, for example) • Examples of random access MAC protocols: (a) SLOTTED ALOHA (b) CSMA and CSMA/CD

34. Slotted Aloha • Time is divided into equal size slots (= full packet size) • a newly arriving station transmits a the beginning of the next slot • if collision occurs the source retransmits the packet at each slot with probability P, until successful. • Success (S), Collision (C), Empty (E) slots

35. CSMA (Carrier Sense Multiple Access) • CSMA: listen before transmit. If channel is sensed busy, defer transmission • Persistent CSMA: retry immediately when channel becomes idle (this may cause instability) • Non persistent CSMA: retry after random interval • Upon collision, reattempt tx after random timeout

36. CSMA collisions

37. Wireless LAN Configurations Peer-to-peer Networking Ad-hoc Networking BS With or without control (base) station

38. IEEE 802.11 Wireless LAN • IEEE 802.11 standards define MAC protocol; unlicensed frequency spectrum bands: 900Mhz, 2.4Ghz, 5.7Ghz • Like a bridged LAN (flat MAC address)

39. IEEE 802.11 MAC Protocol CSMA Version of the Protocol: sense channel idle for DISF sec (Distributed Inter Frame Space) transmit frame (no Collision Detection) receiver returns ACK after SIFS(Short Inter Frame Space) if channel sensed busy => binary backoff NAV: Network Allocation Vector (min time of deferral)

40. Hidden Terminal effect • CSMA inefficient in presence of hidden terminals • Hidden terminals: A and B cannot hear each other because of obstacles or signal attenuation; so, their packets collide at B • Solution? CSMA + RTS/CTS

41. Collision Avoidance with RTS/CTS • RTSfreezes stations near the transmitter • CTS “freezes” stations within range of receiver (but possibly hidden from transmitter); this prevents collisions by hidden station during data transfer • RTSand CTS are very short: collisions are thus very unlikely • Note: IEEE 802.11 allows both CSMA, CSMA+RTS/CTS

42. 802.11 - CSMA basic access method contention window (randomized back-offmechanism) DIFS DIFS • station ready to send starts sensing the medium (Carrier Sense based on CCA, Clear Channel Assessment) • if the medium is free for the duration of an Inter-Frame Space (DIFS), the station can start sending after CWmin • if the medium is busy, the station has to wait for a free DIFS, then the station must additionally wait a random back-off time (collision avoidance, multiple of slot-time) • if another station occupies the medium during the back-off time of the station, the back-off timer stops (fairness) medium busy next frame t direct access if medium is free  DIFS + CWmin slot time

43. 802.11 - CSMA (cont) • Sending unicast packets • station has to wait for DIFS (and CWmin) before sending data • receivers acknowledge at once (after waiting for SIFS) if the packet was received correctly (CRC) • automatic retransmission of data packets in case of transmission errors DIFS data sender SIFS ACK receiver DIFS data other stations t waiting time contention

44. 802.11 - CSMA with RTS/CTS • Sending unicast packets • station can send RTS with reservation parameter after waiting for DIFS (reservation declares amount of time the data packet needs the medium) • acknowledgement via CTS after SIFS by receiver (if ready to receive) • sender can now send data at once, acknowledgement via ACK • other stations store medium reservations distributed via RTS and CTS DIFS RTS data sender SIFS SIFS SIFS CTS ACK receiver DIFS NAV (RTS) data other stations NAV (CTS) t defer access contention

45. MAC-PCF (Point Coordination Function)like polling t0 t1 SuperFrame medium busy PIFS SIFS SIFS D1 D2 point coordinator SIFS SIFS U1 U2 wireless stations stations‘ NAV NAV

46. MAC-PCF (cont) t2 t3 t4 PIFS SIFS D3 D4 CFend point coordinator SIFS U4 wireless stations stations‘ NAV NAV contention free period t contention period

47. Higher Speeds? • IEEE 802.11a • compatible MAC, but now 5.7 GHz ISM band • OFDM (orthogonal freq division multiplexing) • transmission rates up to 50 Mbit/s • close cooperation with BRAN (ETSI Broadband Radio Access Network) • IEEE 802.11 g: up to 50Mbps, in the 2.5 range • IEEE 802.11 n: up to 100 Mbps, using OFDM and MIMO technologies

48. Better QoS guarantees? • QoS guarantees desirable for real time traffic • IEEE 802.11 e is the answer • EDCF mode (Enhanced DCF): • Traffic class dependent CWmin and DIFS • Frame bursting: RTS-CTS-DATA-ACK-DATA-ACK-DATA-ACK….. • HCF mode (Hybrid Coordination Function): • Similar to the PCF of 802.11b • Alternation of CP (contention periods) and CFP (cont free periods) • During the contention period EDCF mode is enacted, except that the AP can issue a QoS poll to specific stations (using PIFS) • High priority stations can tell the AP about their needs (to get the Poll) • Clearly, the Best Effort traffic is second citizen in this case! • Another challenge is the coexistence of 802.11b and e

49. Bluetooth : a polling/TDMA scheme • February 1998: The Bluetooth SIG is formed • (Ericsson, IBM, Intel, Nokia, Toshiba)

50. What does Bluetooth do for you? Synchronization • Automatic synchronization of calendars, address books, business cards • Push button synchronization • Proximity operation