1

Optimized Link State Routing Protocolfor Ad Hoc Networks

Jacquet, p IEEE INMIC Dec. 2001 park gi won 2004.06.18

2

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

3

IntroductionRouting Protocol

for MANET

Table-Driven/Proactive

Hybrid

Distance

Vector

Link-State

ZRP DSRAODVTORA

LANMARCEDAR

DSDV OLSRTBRPFFSRSTAR

MANET: Mobile Ad hoc Network (IETF working group)

On-Demand-driven/Reactive

Clusterbased/

Hierarchical

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

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

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

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

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

OLSR – Multipoint relays (cont.)Node 1 Hop Neighbors 2 Hop Neighbors MPR(s) B A,C,F,G D,E C

A

B

C

DE

F

G

Figure 2. Network example for MPR selection

10

OLSR – Multipoint relays (cont.)

MS(A) = {B,H,I}

A

G

F HE

ID C B

MS(C) = {B,D,E} MPR(B) = {A,C}

Figure 3. MPR 과 MPR Selector Set

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

Protocol functioning – Neighbor sensing (cont.)

Message type Vtime Message sizeOriginator Address

Time To Live Hop count Message Sequence NumberReserved

Htime Willingness

Link code Reserved Link message sizeNeighbor Interface AddressNeighbor interface Address

…Reserved Htime Willingness

Link code Reserved Link message sizeNeighbor interface addressNeighbor interface address

…

Table 1. Hello Message Format in OLSR

Link type Neighbor type

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

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

Protocol functioning – Neighbor sensing Example of neighbor table

One-hop neighbors

……

MPRC

UnidirectionalG

BidirectionalB

State of LinkNeighbor’s id

Two-hop neighbors

……

CDCE

Access thoughNeighbor’s id

Table 2. Example of neighbor table

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

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

Protocol functioning – MPR information declaration (cont.)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

Table 3. Topology table

19

Protocol functioning – MPR information declaration (cont.)

G

FE

D C B

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

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

Protocol functioning – MPR information declaration (cont.)

S

B

D

M

X YZ

P

A

Send TC message

Dest’ address Dest’ MPR

MPR Selector

sequence

X M 1

Y M 1

Z M 1

.. .. ..

S’ Topology table

TC’ originator

MPR selector

MPR selector

sequenceM X 2M Y 2M Z 2M R 2

TC message ( M send to S)

R

Figure 5. Topology table update

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

Protocol functioning – Routing table calculation (cont.)

Source

Destination

(last-hop, destination)

(last-hop, destination)

(last-hop, destination)

(last-hop, destination)

Figure 5. Building a route from topology table

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