The document describes the Optimized Link State Routing (OLSR) protocol, a proactive routing protocol for mobile ad hoc networks. OLSR is an optimization of a pure link-state protocol where only selected nodes (multipoint relays) flood link-state information periodically. Each node selects multipoint relays that can reach all of its two-hop neighbors. Only multipoint relays retransmit broadcast messages to reduce flooding. Nodes learn network topology through periodic hello messages and topology control messages from multipoint relays to build routing tables.

1. Optimized Link State Routing
Protocol for Ad Hoc Networks
“Mobile ad-hoc networks”
OLSR Protocol 1

2. Proactive Protocols
 Proactive: maintain routing information
independently of need for
communication
 Update messages send throughout
the network periodically or when
network topology changes.
 Low latency, suitable for real-time
traffic
 Bandwidth might get wasted due to
periodic updates
 Larger signalling traffic and power
OLSR Protocol 2

3. Optimized Link State Routing
OLSR
OLSR Protocol 3
 OLSR
 Developed by IETF
 Table driven
 Inherits Stability of
Link-state protocol
 Selective Flooding
 Periodic Link State
• Information generated only by Multipoint
relay (MPR)
 MPRs employed for optimization

4. Optimized Link State Routing OLSR
OLSR Protocol 4
 Two types of messages:
1- Hello message to all neighbors, contains the nodes
address and a list of all its one hop neighbors
 The hello message gives each node a
complete two-hop topology
2- Topology Control TC messages
 Only sent out by MPR nodes and contains the
list of the senders MPR selector
 Allows each node to learn the partial network
topology and they can build a route to any node
 MPR Selection
 In OLSR a node selects as its MPR set the set
of nodes that can reach all its two-hop
neighbors.

5. Link State Routing (eg, OSPF)
OLSR Protocol 5
 Each node periodically floods status of its links
 Each node re-broadcasts link state
information received from its neighbour
 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 retransmissions to diffuse
a message up to 3 hops
Retransmission node

6. Optimized Link State Routing
OLSR
OLSR Protocol 6
Two-hop node
One-hop node
MPR node
originating node
1
2
3
5
4
MPR(1)={2,3,4,5}

7. Optimized Link state routing (OLSR)
OLSR Protocol 7
24 retransmissions to diffuse
a message up to 3 hops
Retransmission node
11 retransmission to diffuse a
message up to 3 hops
Retransmission node

8. OLSR vs. LSR
OLSR Protocol 8
 In LSR
 a lot of control messages unnecessary duplicated
 In OLSR
 only MPR retransmit control messages:
 Reduce size of control message;
 Minimize flooding
 Other advantages (the same as for LSR):
 As stable as LSR protocol;
 Proactive protocol(routes already known);
 Does not depend upon any central entity;
 Tolerates loss of control messages;
 Supports nodes mobility.
 Good for dense network

9. Neighbor sensing
OLSR Protocol 9
 Each node periodically broadcasts Hello message:
 List of neighbors with bi-directional link
 List of other known neighbors.
 Hello messages permit each node
to learn topology up to 2 hops
 Based on Hello messages each
node selects its set of MPR’s
A
E
C
H
F
I
D
B
J
G

10. Multipoint Relays (MPR)
OLSR Protocol 10
 Reduce re-transmission
in the same region
 Each node select a set
of MPR Selectors
 MPR Selectors of node
N - MPR(N)
- one-hop neighbors of N
A
E
C
H
F
I
D
B
J
G
K
reference node
1-hop neighbors
Multi Point Relays
2-hop neighbors
 MPR set of Node N
 Set of MPR’s is able to
transmit to all two-hop neighbors
 Link between node and it’s MPR is
bidirectional.

11. OLSR Protocol 11
Multi Point Relay Selection
 Only Multi Point
Relays (MPRs)
retransmit
broadcast
packets from the
MPR selector
A
E
C
H
F
I
D
B
J
G
K
reference node
1-hop neighbors
Multi Point Relays
2-hop neighbors

12. OLSR Protocol 12
Topology Info Dissemination
 EVERY node
MPR-broadcasts
its links between
itself and
neighbors that
selected this
node as MPR
A
E
C
H
F
I
D
B
J
G
K
reference node
1-hop neighbors
Multi Point Relays
2-hop neighbors

13. OLSR Protocol 13
Topology Info Dissemination
 EVERY node
MPR-broadcasts
its links between
itself and
neighbors that
selected this
node as MPR
A
E
C
H
F
I
D
B
J
G
K
reference node
1-hop neighbors
Multi Point Relays
2-hop neighbors

14. OLSR Protocol 14
 TC – Topology control message:
 Sent periodically. Message might not be sent if there are no
updates and sent earlier if there are updates
 Contains:
 MPR Selector Table
 Sequence number
 Each node maintains a Topology Table based on TC messages
 Routing Tables are calculated based on Topology tables
Topology Table

15. OLSR Protocol 15
Topology Table
Destination
address
Destination’s
MPR
MPR Selector
sequence
number
Holding time
MPR Selector in
the received TC
message
Last-hop node to the
destination.
Originator of TC
message

16. OLSR Protocol 16
Topology Table (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

17. OLSR Protocol 17
Path Computation
 Each node maintains a routing
table to all known destinations
in the network
 Iterative shortest path algorithm
using information from neighbor
table and topology table.
 Routing table:
 Destination address
 Next Hop address
 Distance
 Routing Table is recalculated
after every change in
neighborhood table or in
topological table
A
E
C
H
F
I
D
B
J
G
K

18. OLSR Protocol 18
Route Break
 compute new
MPR set
 broadcast TC
message
 compute new
path
A
E
C
H
F
I
D
B
J
G
K
Link
Break

19. Experimental Results
OLSR Protocol 19
Algorithm Transmissi
on
Range
Performace Cost
Error
Rate
Average difference Over-
head
MPR
Count
Standard
OLSR
300 M 28% 46% 12 65
200 M 41% 51% 24 68
100 M 12% 45% 5 42
OLSR_R1 300 M 14% 22% 12 65
200 M 21% 26% 24 68
100 M 8% 44% 5 42
OLSR_R2 300 M 0% 0% 18 70
200 M 0% 0% 33 72
100 M 0% 0% 5.7 45
OLSR_R3 300 M 0% 0% 26 71
200 M 0% 0% 38 73
100 M 0% 0% 5.7 44
Pure Link
State
Algorithm
300 M 0% 0% 1245 100
200 M 0% 0% 979 100
100 M 0% 0% 28 100

20. Readings
OLSR Protocol 20
 G. Pei, M. Gerla, and X. Hong, " LANMAR: Landmark Routing for
Large Scale Wireless Ad Hoc Networks with Group Mobility," In
Proceedings of IEEE/ACM MobiHOC 2000, Boston, MA, Aug.
2000.
 R. Ogier, F. Templin, M. Lewis, " Topology Dissemination Based on
Reverse-Path Forwarding (TBRPF) ," IETF Internet Draft , July 28
2003.
 Thomas Clausen, Philippe Jacquet, " Optimized Link State Routing
Protocol (OLSR) ," IETF Internet Draft , July 3 2003.
 X. Hong, K. Xu, and M. Gerla, " Scalable Routing Protocols for
Mobile Ad Hoc Networks " IEEE Network Magazine, July-Aug,
2002, pp. 11-21
 Thomas Kunz,Ying Ge, Louise Lamont, “ Quality of Service Routing
in Ad-Hoc Networks Using OLSR” Carleton University, CRC,2002
 M Benzaid, P Minet and K AAgha, “Integrating fast mobility in the
OLSR routing protocol” INRIA, LRI, France,September 2002.