Qamar A Tarar OLSR Protocol 1
Optimized Link State Routing Protocol for Ad Hoc Networks
Qamar Abbas Tarar
“Mobile ad-hoc networks based on wireless LAN”
Qamar A Tarar OLSR Protocol 2
Problems in MANETs
Scalability
QoS
Security
Interoperation with the Internet
Limited Battery Life
Node Mobility
Unreliable radio channel Hidden terminal problem
Route maintenace
Unpredictable link properties
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Unicast-Routing Protocol for MANET (Topology-based)
Table-Driven/Proactive
Hybrid On-Demand-driven/Reactive
Clusterbased/Hierarchical
Distance-Vector
Link-State
ZRP DSRAODVTORA
LANMARCEDAR
DSDV OLSRTBRPFFSRSTAR
MANET: Mobile Ad hoc Network
(IETF working group)
Classification of Routing Protocols for MANETS
CBRP
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Proactive vs Reactive Routing Protocols
Proactive Routing Protocols (DSDV, OLSR)
+ Routes to all reachable nodes in the network available.
+ Minimal initial delay for application.
- Larger signalling traffic and power consumption.
Reactive Routing Protocols (DSR, CBR etc)
+ Smaller signalling traffic and power consumption.
- A long delay for application when no route to the destination available
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Structure
OLSR Overview
Multipoint relays
Neighbor sensing
MPR selection
MPR information declaration
Routing table calculation
Extensions in OLSR
Conclusions
Qamar A Tarar OLSR Protocol 6
Overview
OLSR Developed by IETF Table driven Inherits Stability of
Link-state protocol Selective Flooding Periodic Link State
Information generated only by MPR MPRs employed for optimization
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Link State Routing (eg, OSPF)
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
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OLSR Overview In LSR
protocol 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
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Optimized Link state routing (OLSR)
24 retransmissions to diffuse a message up to 3 hops
Retransmission node
11 retransmission to diffuse a message up to 3 hops
Retransmission node
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Description of OLSR
MPR (Multipoint relays)
MPR selector
Symmetric 1-hop
neighbours
Symmetric strict 2-hop
neighbours D
S
B
M
X YZ
P
A
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Neighbor sensing
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
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Example of neighbor table
One-hop neighbors
Neighbor’s id State of Link
B Bidirectional
G Unidirectional
C MPR
… …
Two-hop neighbors
Neighbor’s id Access though
E C
D C
… …
Also every entry in the table has a timestamp, after which the entry in not valid
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Multipoint Relays (MPR)
N
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
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Multipoint Relays (MPR)
N
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
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.
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Every node keeps a table of routes to all known destination through its MPR nodes
Every node periodically broadcasts list of its MPR Selectors (instead of the whole list of neighbors).
Upon receipt of MPR information each node recalculates and updates routes to each known destination
Multipoint Relays (MPR)
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MRP selection in OLSR
Node 1 Hop Neighbors 2 Hop Neighbors MPR(s)
B A,C,F,G D,E C
Available BW
OLSR: node B will select C as its MPR So all the other nodes know that they can reach B via C
30
10050110
25
60
10
40
5 10
D->B route is D-C-B, whose bottleneck BW is 3
3
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MRP selection in OLSR
Node 1 Hop Neighbors 2 Hop Neighbors MPR(s)
B A,C,F,G D,E C
Available BW
OLSR: node B will select C as its MPR So all the other nodes know that they can reach B via C
30
10050110
25
60
10
40
5 10
D->B route is D-C-B, whose bottleneck BW is 3
3
Optimal route (i.e., path with maximum bottleneck bandwidth: D-F-B (bottleneck bandwidth of 10)
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Multi-Point Relays/routers
Passes Topology Information
Acts as router between hosts
Minimizes information retransmission
Forms a routing backbone
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Structure of an OLSR Network
MPRs form routing backboneOther nodes act as “hosts”
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Structure of an OLSR Network
MPRs form routing backboneOther nodes act as “hosts”
As devices move
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Structure of an OLSR Network
MPRs form routing backboneOther nodes act as “hosts”
As devices moveTopological relationships changeRoutes changeBackbone shape and composition changes
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MPR information declaration
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
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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
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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
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Routing Table
Each node maintains a routing table to all known destinations in the network Routing table is calculated from Topological Table, taking the connected pairs Routing table:
Destination address Next Hop address Distance
Routing Table is recalculated after every change in neighborhood table or in topological table
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Extensions in OLSR
Qos OLSR
Fast OLSR
Towards IPv6 OLSR
Power saver mode
Change in the contents of TC packet
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QoS Routing: Difficulties in QoS routing
Due to mobility Availability and manageability of Link state metrics Link quality changes quickly and continuously
Computational cost and protocol overhead affect
the performance of the QoS routing protocol
Protocol performance evaluation is complex
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Proactive QoS Routing
Advantages suitable for the unpredictable nature of Ad-Hoc networks suitable for the requirement of quick reaction to QoS demands makes call admission control possible avoids the waste of network resources
Disadvantages introduces additional protocol overhead trade-off between the QoS performance and traditional protocol
performance
But.. Little work has been done to analyse the impact of the additional
overhead on pro-active QoS routing
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QoS Versions of OLSR
30
10050110
25
60
10
40
510
OLSR protocol does not guarantee
to find the best bandwidth route
3 heuristics are proposed to enhance
OLSR in bandwidth aspect
The heuristics select good bandwidth
neighbour as MPR
3
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QoS Versions of OLSR OLSR_R1: similar to OLSR (i.e., choose 1-hop neighbours that cover max. number of 2-hop neighbours), tie-breaker now max BW
Node 1 Hop Neighbors 2 Hop Neighbors MPR(s) B A,C,F,G D,E C
OLSR_R2: select the best BW neighbors as MPRs until all the 2-hop neighbors are covered.
Node 1 Hop Neighbors 2 Hop Neighbors MPR(s) B A,C,F,G D,E F
OLSR_R3: selects the MPRs in a way such that all the 2-hop neighbors have the max. bottleneck BW path through the MPRs to the current node.
Node 1 Hop Neighbors 2 Hop Neighbors MPR(s) B A,C,F,G D,E A,F
30
10050110
25
60
10
40
5103
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Evaluation of QoS OLSR
Simulation: generate networks, run OLSR algorithms, compare results against paths calculated by Link-State algorithm (i.e. complete knowledge, all-pair shortest path)
Network area: 1000 M 1000 M
Number of nodes: 100
Transmission range: 100 M, 200 M, 300 M
Bandwidth: assigned randomly
Results are averaged over 100 randomly generated networks
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Performance Metrics
Error rate: percentage of routes with non-optimal bandwidth
Average difference: for routes with non-optimal bandwidth, how far off the optimal bandwidth are we
Overhead: the average number of control messages transmitted per node
MPR count: average number of MPRs in the network
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Experimental ResultsAlgorithm 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
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Fast OLSR
Due to Proactive nature,routes available
when needed
However In dense network, due to fast node Mobility, links valid only for short time period.
Hence to minize packet loss,
broken links between node and its
neighbors must be quickly detected.
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Neighbor Discovery in Fast OLSR
3-procedures:
Switch to Fast-Moving/Default mode:
In Fast mode,send Fast-Hellos and vice versa.
A Fast-Hello is smaller than a Hello
Establishing fast Links:
A node in Fast-Moving mode sends Fast-Hello
messages at high frequency.
Refresh Fast links & Detect new broken links:
by sending periodic Fast-Hellos
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Towards IPv6 OLSR
OLSR operate well with both IPv4 and IPv6
To operate with IPv6, the only required change is to replace the IPv4 addresses with IPv6 address.
The minimum packet and message sizes should be adjusted accordingly, considering the greater size of
IPv6 addresses.
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Power saver mode
A node can indicate if it agrees to keep the packets of its neighbors
Any node, who wants to go in sleep mode, will select ONLY that neighbor as MPR who can keep its packets
TC packet will diffuse this info, and all data packets will be routed through that “power saver” node
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Change in the contents of TC packet
Instead of advertising its set of MPRs, a node
will list its neighbors who has selected him as
an MPR
Many nodes (loosely connected, or at the boundaries) will not be selected MPR any node. So they will not send any TC (25% less overhead)
Less frequent changes in this set
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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
Disadvantages
Bigger overhead
Need more power
Not all allgoritms pubically documented
Needs more operational experience to debug
Conclusions
Qamar A Tarar OLSR Protocol 40
Readings 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 A Agha, “Integrating fast mobility in the
OLSR routing protocol” INRIA, LRI, France,September 2002.
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Q & A