1. Milano, 4-5 Ottobre 2004 IS-MANET The Virtual Routing Protocol for Ad Hoc Networks ISTI – CNR S. Chessa

2. Wireless Ad Hoc Networks Autonomous system of mobile hosts connected by wireless links The nodes are autonomous and independent Battery powered Mobile Cooperate in a peer-to-peer fashion No fixed network infrastructure Pure distributed system No centralized coordinators Nodes communicate by exchanging packets via radio waves

3. Features: Rapidly deployable Easily configured Robustness Potential drawbacks Distributed control Neighbor knowledge Mobility is a challenge Wireless Ad Hoc Networks Applications : communication in remote or hostile environments management of emergencies disaster recovery ad hoc commercial installations sensor networks

4. Wireless Ad Hoc Networks Wireless communications: Transmission range of the nodes is limited Obstacles may prevent direct communication between a pair of nodes Point-to-point Network Communication between non-adjacent nodes requires cooperation of other nodes

5. Wireless Ad Hoc Networks

6. Proactive Routing Solution derived from wired networks (Proactive approach) Table driven Link state Drawbacks: Updates overhead, especially in presence of high mobility Large routing tables Low scalability

7. On Demand (Reactive) protocols No information about routes is maintained proactively routes established only when needed (on- demand routing) Route discovery process generally based on flooding: A route request message (RREQ) is sent (flooded) to discover a path to the destination Upon receiving the RREQ the destination sends a route reply message (RREP) back to the source

8. Virtual Routing Protocol (VRP) The Virtual Routing Protocol (VRP): Designed to reduce the overhead of route discovery based on flooding Does not assume any geographical information of the nodes. Hybrid routing algorithm Exhibits features of both reactive and proactive protocols Can be tuned to behave as a reactive or as a proactive Three different priorities for messages

9. Virtual Routing Protocol (VRP) Units are arranged in a Logical Structure : No relation with the physical position of the units Units must proactively maintain routes to the units to which they are connected in the logical structure Examples: Ring of Rings Hypercube CCC 3d-Torus Node u which proactively maintains a route to unit v is a scout for v Node v is a peer of u Three protocols: Route acquisition (Route Discovery) Route maintenance Scouts Update

10. Virtual Routing Protocol (VRP) A example of Logical Structure: The Ring of Rings (RoR)

11. Virtual Routing Protocol (VRP) Route Acquisition (Route Discovery) Based mainly on unicast messages High priority Virtual path setup Path on the logical structure from the source to the destination Route setup Translation of the virtual path into a real physical route Route Maintenance Used when a previously established route gets broken during communication Scouts Update Based on flooding Low priority Can be completely Reactive or partially proactive

12. VRP – Route Acquisition Virtual path setup The source computes a virtual path between itself and the destination The virtual path is computed on the logical structure The virtual path is computed recursively The virtual path is a sequence of scouts

13. VRP – Route Acquisition Route setup - Virtual path translation Virtual path: RTRANS route from source to destination: u3u3 u0u0 u1u1 u2u2 v u0u0 u3u3 u1u1 u2u2

14. VRP – Route Acquisition Route setup - Virtual path translation Destination cuts the loops of the collected route and return to the source a loop-free route u3u3 u0u0 u1u1 u2u2 v v z u0u0 u3u3  u3u3 u0u0 u1u1 u2u2 v z z

15. VRP – Route Acquisition Route setup - Virtual path translation Shortcut to the destination u3u3 u0u0 u1u1 u2u2 v z Transmission range

16. VRP – Route Acquisition u3u3 u0u0 u1u1 u2u2 v z u4u4 u5u5 Route setup - Virtual path translation RTRANS detour z u0u0 u4u4 u1u1 u5u5 u3u3

17. VRP – Route Acquisition Route setup (cont.) Route Request Used if a certain number of virtual path translations failed Based on flooding Similar to the route request of the other reactive routing protocols

18. u3u3 VRP – Route Acquisition Broken Route Detour Broken link message to the last scout z u0u0 u4u4 u1u1 u5u5 Route Acquisition When translating a virtual path Upstream unit detects the broken link Upstream unit computes a detour to deliver the RTRANS to its destination (If possible) Upstream unit warns the last scout through which the RTRANS has passed that the route archived in this unit is broken When the last scout receives the warnning it invokes the scout update phase of the protocol

19. VRP – Route Maintenance Data communication Upstream unit discovers the broken link Upstream unit send a route error message to the source Source establishes a new route to the destination if desired u0u0 u3u3

20. VRP – Scouts Update Invoked when: A scout receives a broken link message During the route acquisition phase the scout does not have a valid physical route to the next scout Completely Reactive Scout updates the route just to the broken unit Partily Proactive Scout updates the route to all of its peered unit Use multiple destinations flooding

21. VRP – Scouts Update Multiple Destinations flooding Message has a special character in the destination field to identify that it is for multiple destinations It is forwarded even by its destinations Each unit forward the message just once Destinations of a multiple destination flooding are always all peered units of the source When a unit receives a multiple destination flooding: If it has already received this message: It drops the message Else It looks in the logical structure if it is a destination of the flooding If it is a destination it sends a reply to the source of the flooding It rebroadcast the message

22. VRP – Scouts Update If each unit has k peered units, each multiple destination flooding generates k replies The use of multiple destination flooding allows the scout to maintain their routes more up-to-date The use of multiple destination flooding reduces the number of floodings perfomed for scouts update (demonstrated through simulation) Multiple destination floodings increases the number of flooding replies (unicast messages) and reduces the number of flooding in the network

23. VRP – Simulation Simulation Model Simplified MAC layer CSMA – Listen the medium before try to transmit RTS/CTS – When a unit is transmitting, its neighbors and the neighbors of the destination remain quiet Exponential Delay – If transmission is not possible because the medium is not empty Roughest Approximation: the simulator does not consider collisions Neighbors information – the MAC layer provides to the routing protocols information about the neighbors of the units Out Buffer of 300 messages with LRU Three routing protocols were implemented: VRP DSR (draft version 9) ZRP with unicast and ZRP with multicast (draft version 4)

24. VRP – Simulation Units: 75 Network field: 1000m x 1000m Transmission Range: 250m Ring of Rings: 3 rings 25 units per ring 5 scouts Units’ velocity: 0m/s to 20 m/s Units’ pause time: 0s to 600s Simultaneous CBR connections: 10 to 50 Messages per second per CBR source: 2 Duration of each CBR connection: 15s or 120s

25. VRP – Simulation VRP versus DSR: Delivery ratio as a function of the units' speed for 20 simultaneous CBR connections.

26. VRP – Simulation VRP versus DSR: Delivery ratio as a function of the units' speed for 40 simultaneous CBR connections.

27. VRP – Simulation VRP versus DSR: Delay to build a route as a function of the units‘ speed for 20 simultaneous CBR connections.

28. VRP – Simulation VRP versus DSR: Routing load as a function of the units' speed with 20 simultaneous CBR connections. VRP without proactive scout setup

29. VRP – Simulation VRP versus DSR: Routing load as a function of the units' speed with 40 simultaneous CBR connections. VRP without proactive scout setup

30. VRP – Simulation VRP versus DSR: Average size of the units' routing table.

31. VRP – Simulation VRP versus ZRP: Delivery ratio as a function of the units' speed 20 simultaneous CBR connections of at most 15 seconds duration.

32. VRP – Simulation VRP(up) versus ZRP(right): Delay to build a route as a function of the units' speed

33. VRP – Simulation VRP versus ZRP: Routing load as a function of the units' speed 20 simultaneous CBR connections.

34. VRP – Conclusions Delivery ratio: Light traffic conditions: VRP always above 95% DSR about 70% ZRP about 82% Heavy traffic conditions: VRP never below 75% DSR about 50% ZRP around 80% Route Acquisition Delay: VRP has a delay significantly higher than DSR and ZRP Unit’s Routing Tables: DSR and ZRP: O(N) (N  number of units in the system) VRP: O(k) (k  number of scouts per unit – connectivity of the logical structure)

35. VRP – Improvements Scout Update over Received Messages Shortcuts in Virtual Path Translation Avoiding High Priority Flooding Proactive Zone Avoid route acquisition by immediately sending data during virtual path translation