Group Communications in Mobile Ad hoc Networks

1. Group Communications in Mobile Ad hoc Networks Jian Li http://networks.cs.ucdavis.edu/~lijian/slides/ecs257/

2. References • P. Mohapatra, C. Gui, and J. Li. Group Communications in Mobile Ad hoc Networks. IEEE Computer Magazine, Feb. 2004, pp. 52-59.

3. Agenda • Introduction • Group Comm. Models • Multicasting • Broadcasting • Geocasting & Anycasting • Common Issues • Reliability • Energy efficiency • QoS • Security • Concluding Remarks

4. Manet • No infrastructure, ad hoc deployment • Nodes are free to move around • Wireless media • Multihop routing • Various potential applications • Group Communication is a critical building block

5. Group Comm. In Manet • Differ from wireline networks • Wireless medium has varying characteristics • Signal strength and propagation fluctuation w.r.t time and place • Node mobility is unpredictable • Changing topology • Limited resources • Bandwidth, battery, CPU, memory, etc

6. Multicasting: Exploiting Characteristics of Manet • Variable topology • Mesh-based protocols • Soft-state & state aggregation • Stateless multicast • Knowledge of location • Location aided multicast • Randomness • Gossip-based multicast

7. Mesh-based Protocols • Core-Assisted Mesh Protocol (CAMP) • On-demand Multicast Routing Protocol (ODMRP)

8. CAMP: Features • Assume the underlying unicast routing protocol can provide correct distance to known destination within a finite time • Ensure reverse shortest paths from receivers to sources are part of a group’s mesh • Anchor • Neighbor nodes which are required to re-broadcast any non-duplicate data packets they receive

9. CAMP: Operation • Consult a neighbor table • Confirm membership via a CAMP-UPDATE • Otherwise, JOIN-REQUEST packet is sent • JOIN-ACK received • Receiver nodes periodically reviews packet cache to determine whether it is receiving data packets from those neighbors are on the reverse shortest path • Nodes periodically choose their “anchors”

10. ODMRP: Features • A Mesh-Based & On-Demand protocol • Forwarding group concept • A group of nodes participating in multicast packet forwarding • Robustness to host mobility • Scalability to large number of nodes • Provide path redundancy • Join table, Member table

11. ODMRP – Protocol Overview • Join table • The table broadcasted by each multicast receiver and forwarding node to establish / update group memberships and routes • Member table • The table maintained by multicast receivers containing information of multicast sources for each multicast group it is associated with • Suffers from excessive control packet transmission overhead • Control Packets • JOIN-REQ, JOIN-TABLE

12. s | i s r j i n k m

13. State Maintenance • Unconstrained state • Both member and non-member • Constrained state • Through abstraction via application-layer multicasting • By aggregation via hierarchical multicasting • Zero state • No state information is maintained

14. Location Aided Multicasting • ODMRP • can utilize location and mobility information to estimate route lifetime • Position Based Multicasting (PBM) • Greedy forwarding • Perimeter forwarding

15. Gossip-based Multicasting • Anonymous Gossip (AG) • Route Driven Gossip (RDG)

16. Anonymous Gossip • Enhancement technique atop any tree- or mesh-based protocol • A member node does not know any other member nodes • Two phases • Data packets are multicast to the group • Anonymous gossip in the background: attempt to recover lost data packets from other group members

17. Route Driven Gossip (RDG) • Rely on an underlying unicasting protocol for guidance • CSMA/CA MAC (e.g., IEEE 802.11) provides reliable, sequenced single-hop unicast by RTS/CTS–Data/Ack handshake sequence

18. RDG: Data Structures and Operations Data Structures Operations 4 5 0 1 5 0 5 JOIN Identifier RECEIVEGREQUEST Group identifier • Data buffer • new • old RECEIVEGREPLY 0 5 1 0 5 GOSSIP 0 3 RECEIVEGOSSIP • View • active • passive • remove LEAVE quiescence threshold τq fanoutF 2 1 0 1 1 Push Pull Data packets, digests of missing packets, view

19. Broadcasting • Important building block for on demand route discovery • Categorizations • Simple flooding • Probability based broadcasting • Area-based broadcasting • Neighbor knowledge based broadcasting

20. Self pruning • Information: • Hello message (1-hop) • Piggyback adjacent node list in broadcast packets (2-hop) • Store adjacent node list in cache • Forwarding node decision: • Node vj who receives the packet from vi checks whether the set N(vj)-N(vi)-{vi} is empty vj vi

21. Geocasting • Group membership is defined by geographical coordinates • Suitable for delivering messages to every node in a specific area • Examples • Flooding based geocasting • Route based geocasting

22. LBM: Flooding based Geocasting • Scheme I

23. LBM: Flooding based Geocasting • Scheme II

24. Route Based Geocasting: GeoTORA • Based on TORA • Temporally Ordered Routing Algorithm • Destination-oriented directed acyclic graphs (DAGs) • Uses “Link-Reversal” techniques to maintain DAGs • GeoTORA • Modify TORA to do anycasting • Modify further to do geocasting

25. B B C C A D A D G G F F E E B B C C A D A D G G F F E E TORA – Link Reversal • When a node has no downstream links, it reverses the direction of one or more links

26. Anycasting with Modified TORA • In GeoTORA, the TORA protocol is modified to be able to perform anycast • Anycast - deliver to any one node in the anycast group • Protocol • Maintain a DAG for eachanycast group • Make each member of the anycast group a sink • No logical direction for links between sinks • Following the directed links results in packets being delivered to any onesink

27. Anycasting Example Anycast group = {A, B, C, D}, DAG structure for the anycast group K K K L L L C D C D C D A B A B A B G J J J G G F F F E E E

28. K Geocast Region L C D A B G J F E Geocasting using Modified Anycasting • Small variation on the previous anycasting • All nodes within a specified geocasting region are made sinks • Maintain a single DAG for a given geocast group • Source first performs an anycast to the geocast group members • When a group member receives a packet, it floods it within the geocast region

29. Common Issues • Reliability • Energy efficiency • Qualify of service • Security

30. Reliability • Clustering structure + acknowledgement along reversal path • Probabilistic reliability • RDG approach • Reliable MAC support • BMW protocol

31. Energy Efficiency: Routing • Wireless transmissions are major energy consumers • Protocols attempt to reduce forwarding set of nodes • Broadcast Incremental Power (BIP) protocol • Add new node one at a time • Increment transmission power to add one new node

32. Energy Efficiency: MAC • Reception and idle-listening also major energy consumers • Power aware MAC • Example: PAMAS MAC • Separate signaling channel • Turn off nodes when appropriate • Overhear RTS/CTS to determine when to sleep, for how long, • What to do if destination node is asleep?

33. Energy Efficiency: Wakeup Mechanisms • On-demand wakeup • Use a wakeup tone • Scheduled wakeup • Require synchronization among nodes • Asynchronous wakeup • Guaranteed overlap active time over a certain duration

34. Quality of Service • A set of measurable service attributes • Bandwidth, delay, loss rate • Power consumption, service coverage • QoS support are desirable in various applications • Resource limitation and variability add to the need of QoS support • QoS aware group comm. Remains an open problem

35. Security • Broadcast medium is more prone to active and passive attacks • Dynamic nature of Manet adds to the challenges • Lack of trusted centralized infrastructure • Ad hoc link • Group comm. models are different • Light weight requirement • Also an open problem

36. Concluding Remarks • Group Communication is essential for ad hoc networks • More efforts are needed • MAC • Transport • QoS • Security