1. 1 Optimized Link State Routing Protocol for Ad Hoc Networks Jacquet, p IEEE INMIC Dec. 2001 park gi won 2004.06.18

2. 2 contents  Introduction  Reactive versus Proactive routing approach  OLSR (Optimized Link State Routing) Protocol  Protocol functioning  Conclusions

3. 3 Introduction Routing Protocol for MANET Table-Driven/ Proactive Hybrid Distance Vector Link- State ZRPDSR AODV TORA LANMAR CEDAR DSDVOLSR TBRPF FSR STAR MANET: Mobile Ad hoc Network (IETF working group) On-Demand- driven/Reactive Clusterbased/ Hierarchical

4. 4 Reactive versus Proactive routing approach  Proactive Routing Protocols  Periodec exchange of control messages  + immediately provide the required routes when needed  - Larger signalling traffic and power consumption.  Reactive Routing Protocols  Attempts to discover routes only on-demand by flooding  + Smaller signalling traffic and power consumption.  - A long delay for application when no route to the destination available

5. 5 OLSR - Overview  OLSR  Inherits Stability of Link-state protocol  Selective Flooding  only MPR retransmit control messages:  Minimize flooding  Suitable for large and dense networks

6. 6 OLSR – Multipoint relays (MPRs)  MPRs = Set of selected neighbor nodes  Minimize the flooding of broadcast packets  Each node selects its MPRs among its on hop neighbors  The set covers all the nodes that are two hops away  MPR Selector = a node which has selected node as MPR  The information required to calculate the multipoint relays :  The set of one-hop neighbors and the two-hop neighbors  Set of MPRs is able to transmit to all two-hop neighbors  Link between node and it’s MPR is bidirectional.

7. 7 OLSR – Multipoint relays (cont.)  To obtain the information about one-hop neighbors :  Use HELLO message (received by all one-hop neighbors)  To obtain the information about two-hop neighbors :  Each node attaches the list of its own neighbors  Once a node has its one and two-hop neighbor sets :  Can select a MPRs which covers all its two-hop neighbors

8. 8 OLSR – Multipoint relays (cont.) Figure 1. Diffusion of a broadcast message using multipoint relays 4 retransmission to diffuse a message up to 2 hops MPR(Retransmission node)

9. 9 OLSR – Multipoint relays (cont.) Node 1 Hop Neighbors 2 Hop Neighbors MPR(s) B A,C,F,G D,E C A B C D E F G Figure 2. Network example for MPR selection

10. 10 OLSR – Multipoint relays (cont.) MS(A) = {B,H,I} A G F H E ID CB MS(C) = {B,D,E}MPR(B) = {A,C} Figure 3. MPR 과 MPR Selector Set

11. 11 Protocol functioning – Neighbor sensing  Each node periodically broadcasts its HELLO messages:  Containing the information about its neighbors and their link status  Hello messages are received by all one-hop neighbors  HELLO message contains:  List of addresses of the neighbors to which there exists a valid bi-directional link  List of addresses of the neighbors which are heard by node( a HELLO has been received )  But link is not yet validated as bi-directional

12. 12 Protocol functioning – Neighbor sensing (cont.) Message typeVtimeMessage size Originator Address Time To LiveHop countMessage Sequence Number ReservedHtime Willingness Link codeReservedLink message size Neighbor Interface Address Neighbor interface Address … ReservedHtime Willingness Link codeReservedLink message size Neighbor interface address … Table 1. Hello Message Format in OLSR Link typeNeighbor type

13. 13 Protocol functioning – Neighbor sensing (cont.)  HELLO messages :  Serves Link sensing  Permit each node to learn the knowledge of its neighbors up to two-hops (neighbor detection)  On the basis of this information, each node performs the selection of its multipoint relays (MPR selection signaling)  Indicate selected multipoint relays  On the reception of HELLO message:  Each node constructs its MPR Selector table

14. 14 Protocol functioning – Neighbor sensing ( cont.)  In the neighbor table:  Each node records the information about its on hop neighbor and a list of two hop neighbors  Entry in the neighbor table has an holding time  Upon expiry of holding time, removed  Contains a sequence number value which specifies the most recent MPR set  Every time updates its MPR set, this sequence number is incremented

15. 15 Protocol functioning – Neighbor sensing  Example of neighbor table One-hop neighbors …… MPRC UnidirectionalG BidirectionalB State of LinkNeighbor’s id Two-hop neighbors …… C D CE Access thoughNeighbor ’ s id Table 2. Example of neighbor table

16. 16 Protocol functioning – Multipoint relay selection  Each node selects own set of multipoint relays  Multipoint relays are declared in the transmitted HELLO messages  Multipoint relay set is re-calculated when:  A change in the neighborhood( neighbor is failed or add new neighbor )  A change in the two-hop neighbor set  Each node also construct its MPR Selector table with information obtained from the HELLO message  A node updates its MPR Selector set with information in the received HELLO messages

17. 17 Protocol functioning – MPR information declaration  TC – Topology control message:  In order to build intra-forwarding database  Only MPR nodes forward periodically to declare its MPR Selector set  Message might not be sent if there are no updates  Contains:  MPR Selector  Sequence number  Each node maintains a Topology Table based on TC messages  Routing Tables are calculated based on Topology tables

18. 18 Protocol functioning – MPR information declaration (cont.) Destination addressDestination’s MPRMPR Selector sequence number Holding time MPR Selector in the received TC message Last-hop node to the destination. Originator of TC message Table 3. Topology table

19. 19 Protocol functioning – MPR information declaration (cont.) G F E D CB MS(C) = {B,D,E}MPR(B) = {A,C} Figure 4. TC message and Topology table Send TC message {B,D,E} build the topology table

20. 20 Protocol functioning – MPR information declaration (cont.)  Upon receipt of TC message:  If there exist some entry to the same destination with higher Sequence Number, the TC message is ignored  If there exist some entry to the same destination with lower Sequence Number, the topology entry is removed and the new one is recorded  If the entry is the same as in TC message, the holding time of this entry is refreshed  If there are no corresponding entry – the new entry is recorded

21. 21 Protocol functioning – MPR information declaration (cont.) S B D M X Y Z P A Send TC message Dest’ address Dest’ MPR MPR Selector sequence XM1 YM1 ZM1.. S’ Topology table TC’ originator MPR selector MPR selector sequence MX2 MY2 MZ2 MR2 TC message ( M send to S) R Figure 5. Topology table update

22. 22 Protocol functioning – Routing table calculation  Each node maintains a routing table to all known destinations in the network  After each node TC message receives, store connected pairs of form ( last-hop, node)  Routing table is based on the information contained in the neighbor table and the topology table  Routing table:  Destination address  Next Hop address  Distance  Routing Table is recalculated after every change in neighbor table or in topology table

23. 23 Protocol functioning – Routing table calculation (cont.) Source Destination (last-hop, destination) Figure 5. Building a route from topology table

24. 24 conclusion  OLSR protocol is proactive or table driven in nature  Advantages  Route immediately available  Minimize flooding by using MPR  OLSR protocol is suitable for large and dense networks