O ptimized L ink- S tate R outing Protocol

1. Optimized Link-State Routing Protocol Authors:P. Jacquet, etc., Qamar Abbas Tarar by Jeong - Ganghee Advanced Operating System – Spring 2012

2. Advanced Operating System – Spring 2012 • Link-State Routing [LSR] • Optimized LSR [OLSR] • Protocol functioning • Conclusions Agendas

3. Advanced Operating System – Spring 2012 • Each node periodically floods status of its links • Each node re-broadcast link stateinformation received from its neighbor • Each node keeps track of link state information received from other nodes • Each node uses above information to determine next hope to each destination 24 re-transmissions to diffuse a message up to 3 hops Retransmission node Link-State Routing (eg, OSPF)

4. Advanced Operating System – Spring 2012 • OLSR • Developed by IETF • Table-driven • Inherits Stability ofLink-State protocol • Selective Flooding • Periodic Link-StateInformation generated only by MPR • MPRs employed for optimization Overview

5. Advanced Operating System – Spring 2012 • In LSR • protocol a lot of control messages unnecessary duplicated. • In OLSR • Only MPR re-transmit control messages: • Reduce size of control message; • Minimize flooding; • Other adv. (the same for LSR): • Proactive protocol (routes already known); • Does not depend upon any central entity; • Tolerates loss of control message; • Supports nodes mobility; • Good for dense network. LSR & OLSR

6. Advanced Operating System – Spring 2012 Optimized Link-State Routing

7. Advanced Operating System – Spring 2012 12 re-transmission to diffuse a message up to 3 hops 24 re-transmission to diffuse a message up to 3 hops Retransmission node Optimized Link-State Routing (OLSR)

8. Advanced Operating System – Spring 2012 • Reduce re-transmissionin the same region • Each node select a set of MPR Selectors • MPR set of nodeN– MPR(N) • One-hop neighbors of N N Multipoint Relay [MPR]

9. Advanced Operating System – Spring 2012 • Reduce re-transmissionin the same region • Each node select a set of MPR Selectors • MPR set of node N– MPR(N) • One-hop neighbors of N • Set of MPR’s is able totransmit to all two-hop neighbors • Link between node and it’s MPR is bidirectional Multipoint Relay [MPR]

10. Advanced Operating System – Spring 2012 Protocol Functioning

11. Advanced Operating System – Spring 2012 • Each node periodically broadcasts Hello message: • List of neighbors with bi-directional link • List of other known neighbors. • Hello messages permit each nodeto learn topology up to 2-hop • Based on Hello messages each nodeselects its set of MPR’s Neighbor sensing

12. Advanced Operating System – Spring 2012 • Also every entry in the tablehas a timestamp, after whichthe entry in not valid. One-hop neighbors D E A F C Two-hop neighbors B G Example of neighbor table

13. Advanced Operating System – Spring 2012 • Each node select independently its own set of MPRs. • The MPR set is calculated in a manner to contain asubset of 1-hop neighbors which covers all the 2-hop neighbors. • In order to build the list of the 2-hop nodes from a given node, it suffices to track the list of bi-directional link nodes found in the HELLO messages received by this node (this 2-hop neighbor information is stored in the neighbor table). • The MPR set re-calculated when: • A change in the neighborhood is detected when either a bi-directional link with a neighbor is failed, or a new neighbor with a bi-directional link is added; or • A change in the 2-hop neighbor set with bi-directional link is detected. MPR selection

14. Advanced Operating System – Spring 2012 • A TC [Topology control] message is Sent periodically by each node in the network to declare its MPR Selector set,i.e., the message contains the list of neighbors whohave selected the sender node as a MPR. • TC messages will help each node to build its topology table. • Nobody has selected node as a MPR, may not generate any TC message. • The interval between the transmission of two TC messages depends upon whether the MPR Selector set is changed or not,since the last TC message transmitted. • All subsequent TC messages are sent with the normal default interval for sending TC messages, until the MPR Selector set is changed again. MPR information declaration

15. Advanced Operating System – Spring 2012 Last-hop node to the destination Originator of TC message MPR Selector in the received TC message Topology Table

16. Advanced Operating System – Spring 2012 • Upon receipt of TC message: • If there exist some entry to the same destinationwith 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 & 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. Topology Table

17. Advanced Operating System – Spring 2012 • Each node maintains a routing tableto all know destinations in the network. • Based-on the information containedin the neighbor table & the topology table. • Routing table: • Destination address • Next-hop address • Distance Routing table calculation

18. Advanced Operating System – Spring 2012 • The nodes which receive a TC message parse and store some of the connected pairs of form [last-hop, node] where “nodes” are the addresses found in the TC message list. • The routing table is built from this database by tracking the connected pairs in a descending order. • To find a path from a given origin to a remote node R,one has to find a connected pair (X, R), thena connected pair (Y, X), and so forth until one finds a node Y in the neighbor set of the origin. Routing table calculation

19. Advanced Operating System – Spring 2012 Y, X S, Z Z, Y X, Dest. Routing table calculation

20. Advanced Operating System – Spring 2012 • Advantages • Route immediately available • Reactivity to topological changes can be adjusted by setting the time interval for HELLO messages • Minimize flooding by using MPR • Can be integrated into existing system as it requires no change to IP format Optimized Link-State Routing (OLSR)