Date post: | 20-Jan-2018 |
Category: |
Documents |
Upload: | brianne-wilcox |
View: | 215 times |
Download: | 0 times |
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