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

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

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

5. 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

6. 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

7. 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

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

9. 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

10. 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 ”

11. 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

12. 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

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

14. 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

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

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

17. 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

18. 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

19. Data packets, digests of missing packets, view RDG: Data Structures and Operations 1 3 0 2 Data StructuresOperations Identifier Group identifier View active passive remove Data buffer new old J OIN RECEIVE GR EQUEST RECEIVE GR EPLY G OSSIP RECEIVE G OSSIP L EAVE 5 4 5050 0505 1 501501 051051 1010 fanout F quiescence threshold τ q Pull Push

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

21. Self pruning Information: –Hello message (1-hop) –Piggyback adjacent node list in broadcast packets (2-hop) (2-hop) –Store adjacent node list in cache Forwarding node decision: –Node v j who receives the packet from v i checks whether the set N(v j )-N(v i )-{v i } is empty vivi vjvj

22. 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

23. LBM: Flooding based Geocasting Scheme I

24. LBM: Flooding based Geocasting Scheme II

25. 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

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

27. 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 each anycast 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 one sink

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

29. 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 Geocast Region A C E D F G B J K L

30. Common Issues Reliability Energy efficiency Qualify of service Security

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

32. 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

33. 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?

34. 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

35. 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

36. 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

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