1. Multicast in Mobile Ad-Hoc Networks Routing and Reliability

2. Outline of the Talk Characteristics of Ad-Hoc Networks Issues in Multicast Routing AODV Tree-based Multicast Routing MCEDAR Reliability Issues Our Work in Progress

3. Characteristics of Ad-Hoc Networks All mobile platforms(nodes) are capable of motion All the nodes have routing functionality. There is no need for centralized infrastructure for communication. Each node is equipped with wireless transmitters / receivers The node may be directly connected to a fixed network on a foreign subnet, or be connected via a wireless link, dial-up line, etc.

4. Salient features of MANETS Dynamic Topologies : Nodes move arbitrarily, and links can be uni as well as bidirectional. Bandwidth Constrained links : Significant lower capacity of wireless links. Congestion is the norm rather than the exception. Energy Constrained Operation : All the nodes rely on some exhaustible source for their energy. Limited Physical Security : More prone to spoofing, DoS attacks, eavesdropping, etc.

5. A Future Internetwork Ad Hoc Network Fixed Network Base Station Ad Hoc Network Switch Mobile Host Wired Link Wireless Link

6. An Ad Hoc Network : Our View A Graph with ‘n’ nodes A node can move in any direction with any speed Connectivity is defined on the basis of power considerations and land features, implies frequently changing connectivity, neighborhood of the nodes in the graph.

7. Issues in Multicast Routing Information stored : We want to store as less state as possible in the hosts. Messages Exchanged : Because the networks are bandwidth constrained, we would like as less exchange of state as possible between the nodes. Active Adaptability : We would like the nodes to adapt themselves to mobility, power considerations, environment, etc. Local Effect of Link Breakages

8. Multicast Routing Algorithms Some of them :  AODV (Ad Hoc On Demand Distance Vector) Routing  Tree – based Algorithms  MCEDAR (Multicast Core-Extraction Distributed Ad Hoc Routing)

9. AODV Initially developed as a reactive, unicast routing protocol. Elegantly adapts to a Multicast routing protocol. Based on building a Multicast Routing Tree on demand. The current version assumes bidirectional links.

10. AODV : Unicast Route Discovery Source broadcasts route request. (RREQ) Node can reply to RREQ :  If it is destination  It has a fresh route to destination Nodes create reverse route entry Record Source IP address/Broadcast ID to prevent multiple processing Source Destination Route Propagation

11. AODV : Forward Path Setup Destination or Intermediate Node with route to destination unicasts RREP back to source. Nodes along path create forward route to destination Source begins sending data when it receives the first RREP. Source Destination

12. AODV : Local Connectivity Management Nodes must periodically hear from their active neighbors to know that they are still within range Every time it hears the broadcast, it updates the lifetime If it does not broadcast within hello_interval, it broadcasts a hello packet. Failure to hear from neighbor within (1 + allowed_hello_loss)*hello_lifetime indicates loss of link.

13. AODV : Multicast Overview Utilizes same RREQ/RREP message cycle Shared tree composed of group members and connecting nodes is formed Dynamic Group Membership Group Leader : Maintains and distributes group sequence number Is not a central point of failure. Multicast Group Members are also routers of the Multicast Tree.

14. AODV : Multicast Routing Tables Multicast Group IP Address Multicast Group Leader IP Address Multicast Group Sequence Number Hop Count to Multicast Leader Next Hops Lifetime

15. AODV : Multicast Route Discovery Source node sends RREQ Sets ‘J’ flag if joining If no reply recd try rebroadcast RREQ rreq_retries additional times If still no reply, then become the group leader Nodes receiving RREQ set up reverse route entries. Multicast Group Members Multicast Tree Members Non-Members Multicast Group Leader Source

16. AODV : Route Reply Generation Only members of multicast tree can respond to join request Any node with route to multicast tree can reply to non-join request RREP generated and unicast back to the source RREP has address of group member and distance from closest tree member Nodes forwarding RREP update RT and MRT entries. Multicast Group Members Multicast Tree Members Non-Members Multicast Group Leader Source

17. AODV : Route Activation Source waits rte_disc_tmo Notes route with largest seq# and smallest hopcnt to nearest tree member After rte_disc_tmo, unicast MACT (Multicast Activation) to selected next hop. Node receiving MACT enables MRT entry for source Unicasts own MACT if not member of tree. Multicast Group Members Multicast Tree Members Non-Members Multicast Group Leader Source Multicast Tree

18. AODV : Leaving the Group Node may revoke its member status at any time Unicast MACT with ‘P’(prune) flag set to next hop If node is a leaf and not a group member, prunes self

19. AODV : Link Breakages Node downstream of the break initiates repair Broadcast RREQ with Multicast Group hop count field and small TTL Accept RREPs as before

20. AODV : Reconnecting Partitioned Trees New partition detected by differing Group Leader Information Any member whose Group Leader has lower IP address initiates repair Unicasts RREQ with ‘R’(Repair) flag set to the other Group Leader The other Group Leader does not give permission to any other node to initiate repair unless this fails.

21. Group Hello Messages First member of group becomes the Group Leader Maintains, disseminates the Group Sequence Number Broadcasts Group Hello every group_hello_interval seconds Multicast Group IP address Multicast Group leader IP address Current Group Sequence Number Hopcount Used by multicast tree members to update current distance to Group Leader

22. AODV : Simulation Used Glomosim Each node chooses destination, speed Carrier Sensing performed before every transmission Simulated length of time : 300 seconds Data Rate : 1 Mbit/sec Data packet size : 64 bytes Transmission Radius : 10 m

23. AODV : Performance 50m x 50m Multicast slightly reduced Goodput Ratio 85m x 85m Multicast has high rate of group merges and partitions.

24. Multicast Routing Algorithms Some of them :  AODV (Ad Hoc On Demand Distance Vector) Routing  Tree – based Routing Algorithms  MCEDAR (Multicast Core-Extraction Distributed Ad Hoc Routing)

25. Per-Source Multicast A Proactive Protocol Extension of DVMRP for fixed networks DVMRP : Each sender selectively “floods” multicast packets to all nodes within a specified range They use reverse shortest path forwarding scheme Periodically non-member leaf nodes and nodes without any downstream members send prune messages They become alive again after a timeout.

26. Per Source Multicast Problems of DVMRP in Ad-Hoc Networks : Leaf Node Detection Flooding for Grafting/Pruning Reverse Path Forwarding does not work due to mobility. Scalability ??? Very poor!!!

27. Shared Tree Multicast Another Proactive Protocol Based on the concept of a rendezvous point (RP) Sender Messages send multicast packets to the RP. Join requests are also sent to the RP Multicast packets are forwarded to receiver members along the multicast forwarding tree, either in the unicast mode or multicast mode.

28. Multicast Routing Algorithms Some of them :  AODV (Ad Hoc On Demand Distance Vector) Routing  Tree – based Routing Algorithms  MCEDAR (Multicast Core-Extraction Distributed Ad Hoc Routing)

29. Ad-hoc routing using CEDAR Core: subset of nodes in network involved in route computation and management, with tunnels between them. Core Broadcast: an efficient broadcast mechanism among core nodes using O(V) messages Increase/Decrease waves: the state propagation mechanism in CEDAR Route Computation: approximation to shortest widest path.

30. CEDAR components in MCEDAR Core –Only core nodes become part of the multicast mesh Core Broadcast –for joining the multicast mesh –for data forwarding on the mesh Ad-hoc networkCore Graph Multicast Mesh (subgraph of Core) M M M

31. MCEDAR Characteristics Robustness of a mesh Efficiency of a tree based forwarding protocol. Involves only a subset of nodes (core nodes) in multicast route management Independent of the underlying unicast routing protocol.

32. MCEDAR - Two aspects Route Management –the multicast infrastructure –joins –leaves Data forwarding

33. MCEDAR : The Multicast Infrastructure A mesh of core nodes A non-core node requests its dominator (a core node in its one hop neighborhood) to become a member on its behalf. Senders and receivers are not distinguished Has a robustness factor of R

34. MCEDAR : Joining a Group Joining core nodes send Join Request using Core broadcast Members with a lesser JoinID reply with Join-ACK On the reverse (Join-ACK) path, each node accepts upto R acks. –Upto R paths to the mesh. Each member has a JoinID and non members have a joinID of -INF Members (including intermediate core nodes), keep track of parents and children

35. MCEDAR : Joins (contd.) Mesh is essentially a DAG where the JoinIDs increase as we go down the DAG On accepting a Join-ACK JoinID <- MAX(JoinID, ID in ACK + 1) MAX allows a node to distinguish between set of ancestors and descendants

36. Illustration (R=2) New member Join -INF ACK 5 ACK 6ACK 4 ACK 3 4 5 6 1 2 3 3 4 Core node Multicast member Multicast mesh link

37. MCEDAR : Leaving a Group A node can leave if –A member becomes a non-core node, OR –It has no members attached to it AND it does not have any children Send a leave message to each of its parents Set JoinID to -INF

38. MCEDAR : Data Forwarding Forward data on all mesh links except on the link from which it came from Core broadcast mechanism used for data forwarding on the multicast mesh –Use overheard RTS/CTS packets to optimize data forwarding

39. MCEDAR : Link Failures/Partitions A member does a new join only if it loses connection with all parents Only members of lesser JoinID respond –avoids joining back with the descendants –if no response for time T partition then a partition is assumed.

40. Conclusions MCEDAR –Provides robustness of a mesh based mechanism. –Provides efficiency of a tree based forwarding protocol. –Involves only few nodes in multicast route management. No results available yet, so cannot predict performance.

41. Multicast Routing : Our Views The Tree based Algorithms are : Too costly w.r.t. messages exchanged Shared Tree depends on the correct functioning of a single node Both these algorithms are not at all scalable Hence neither algorithm is useful.

42. Multicast Routing : Our Views AODV has : Less overhead because it is a reactive protocol Not as good as it can be, because again most of the traffic is directed towards the Multicast Group Leader Another improvement could be to incorporate a mesh-like routing infrastructure The results of AODV do not give any result on scalability.

43. Multicast Routing : Our Views MCEDAR, we believe : Is good in that it has distributed computation. But again, your performance depends on the performance of your core nodes, is that acceptable?? Shouldn’t power awareness be a feature of routing protocols too?? Is it necessary to have some central control for good performance??

44. Reliability Different Aspects QoS guarantees Eventual Delivery Consistency Properties All group members deliver all the messages with a high probability

45. Reliability : Previous Work Pagani et al. in 1997 Reliable Multicast : Validity and Agreement : at least once delivery Integrity : Message m is delivered only if m has been multicast by a group member Termination : Integrity, validity and termination are guaranteed for m within a finite time

46. Reliability : Pagani et al These guarantees hold only as long as there is : Eventual Subsidence : For each m, eventually no more messages are generated regarding m Liveness : Each mobile is connected for at least a given time to its clusterhead Clusterhead Stability : A node chosen as the clusterhead remains as one for at least a given duration.

47. Reliability : Pagani et al Drawbacks : No performance results were given Is dependent on the underlying multicast protocol Based on ack-mechanism, so scalability is an issue, since much more failures The conditions are difficult to maintain in the mobile environment Can we really provide strong guarantees ??

48. Reliability : Previous work Viswanath et al, 1999 Reliability Robustness and efficiency specifically for high speed ad hoc networks No preset speed constraints No direction constraints Environment has high mobility and frequent outages

49. Reliability : Viswanath et al Adaptive Flooding as their technique Routes stored as states become stale soon So resort to techniques where minimum state stored in the routers Simulation Environment : 50 nodes places in a 1000m x 1000m field Each node sends 25 packets/sec Packet Loss : ratio of unique packets not sent to packets sent Overhead : Number of duplicate packets received

50. Reliability : Viswanath et al

52. Reliability : Our views Flooding is valid only for very high speed AHNs Pagani’s work requires too many restrictions to hold Can we have probabilistic guarantees of delivery ??

53. Reliability : Our Work in Progress We are designing a gossip protocol on top of AODV Our protocol does not add any significant overhead to AODV, in messages and even the algorithm. How will this effect performance and reliability??? Simulations going on!!

54. Future Work Develop Power Aware Algorithms.. Have a theoretical model for our environment, and prove its properties How do these algorithms perform in reality?? In what environment will these mobiles operate?? Are the current algorithms suited for it??

55. Questions ??