OLSR - Optimized Link State Routing Protocol
Proactive protocol.
Efficient link state packet forwarding mechanism.
Multipoint relaying.
Reduced size of the control packets.
Only a subset of the links in the link state updates.
Packet forwarding is performed only by multipoint relays.
Reduced number of links used for forwarding the link state packets.
Multipoint relays.
MPR in OLSR
Link state forwarding
Nodes C and E are multipoint relays of node A.
Multipoint relays of A are its neighbors such that each two-hop neighbor of A is a one-hop neighbor of one multipoint relay of A.
Nodes exchange neighbor lists to know their 2-hop neighbors and choose the multipoint relays.
Nodes C and E forward information received from A.
Nodes E and K are multipoint relays for node H.
Node K forwards information received from H.
Example
MPR
Members of MPR sets and MPR selectors change over time – efficient selection mechanisms.
Sets
Set of nodes that are multipoint relays.
Each node selects an MPRset to process and forward every link state packet originated by it.
Other nodes process the link state packets but do not forward them.
Selectors
Set of neighbors that have selected a node as a multipoint relay.
Node forwards packets received from node's MPR selectors.
Selection
Impact on performance.
A node calculates routes to all destinations through the members of the MPR set.
Decide on the membership of nodes in the MPR set.
A node sends Hello messages.
List of neighbors with which the node has bidirectional links.
List of neighbors whose transmissions were received in the recent past (do not know if there is bi-directionality).
A node receiving Hello messages.
Update two-hop topology tables.
Selection of multipoint relays.
Select as MPR every node in the node’s two-hop neighborhood has a bidirectional link with the node.
Select as MPR, the nodes covering ”isolated” nodes, i.e. for which there is a neighbor which has another node as a single parent.
Select as MPR the node which covers the maximal number of nodes.
Neighbor relationships
Each device emits a periodic “Hello”.
Advertise itself to its neighbors.
Determine who else is there.
Select some systems to act as MultiPoint Relays.
MultiPoint Relays
Passes Topology Information.
Acts as a router between hosts.
Minimizes information retransmission.
Forms a routing backbone.
Structure of an OLSR Network
MPRs form the routing backbone.
Other nodes act as “hosts”.
As devices move.
Topological relationships change.
Routes change.
Backbone shape and composition changes.
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