Optimized Link-State Routing Protocol

thoughtlessskytopNetworking and Communications

Oct 29, 2013 (3 years and 11 months ago)

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O
ptimized
L
ink
-
S
tate
R
outing Protocol

Authors:

P.
Jacquet
, etc.,

Qamar

Abbas
Tarar


Advanced Operating System


Spring 2012

by
Jeong

-

Ganghee

Agendas


Link
-
State Routing [LSR]


Optimized LSR [OLSR]


Protocol functioning


Conclusions

2

Advanced Operating System


Spring 2012

Link
-
State Routing (
eg
, OSPF)

Each node
periodically floods

status of its links

Each node
re
-
broadcast

link state

information received from its neighbor

Each node keeps track of link state


information received from other nodes

Each node uses above information


to determine next hope to each destination

3

Advanced Operating System


Spring 2012

24 re
-
transmissions to diffuse


a message up to 3 hops

Retransmission node

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

4

Advanced Operating System


Spring 2012

LSR & OLSR

In LSR

protocol a lot of control messages unnecessary duplicated.


In OLSR

Only MPR re
-
transmit control messages:

Reduce size of control message;

Minimize flooding;


Other adv. (the same for LSR):

Proactive

protocol (routes already known);

Does not depend upon any
central entity
;

Tolerates loss of control message;

Supports nodes mobility;

Good for dense network.

5

Advanced Operating System


Spring 2012

O
PTIMIZED
L
INK
-
S
TATE
R
OUTING

Advanced Operating System


Spring 2012

Optimized Link
-
State Routing (OLSR)

7

Advanced Operating System


Spring 2012

12

re
-
transmission to diffuse


a message up to 3 hops

24

re
-
transmission to diffuse


a message up to 3 hops

Retransmission node

Multipoint Relay [MPR]

8

Advanced Operating System


Spring 2012

MPR


MPR Selector


1
-
hop neighbors


2
-
hop neighbors

Multipoint Relay [MPR]

9

Advanced Operating System


Spring 2012

MPR


MPR Selector


1
-
hop neighbors


2
-
hop neighbors

Multipoint Relay [MPR]

10

Advanced Operating System


Spring 2012

MPR


MPR Selector


1
-
hop neighbors


2
-
hop neighbors

Multipoint Relay [MPR]

11

Advanced Operating System


Spring 2012

MPR

(set)


MPR Selector


1
-
hop neighbors


2
-
hop neighbors

Multipoint Relay [MPR]

12

Advanced Operating System


Spring 2012

MPR (set)


MPR Selector


1
-
hop neighbors


2
-
hop neighbors

Multipoint Relay [MPR]

13

Advanced Operating System


Spring 2012

MPR


MPR Selector


1
-
hop neighbors


2
-
hop neighbors

Multipoint Relay [MPR]

14

Advanced Operating System


Spring 2012

MPR


MPR Selector


1
-
hop neighbors


2
-
hop neighbors

Multipoint Relay [MPR]

15

Advanced Operating System


Spring 2012

MPR


MPR Selector


1
-
hop neighbors


2
-
hop neighbors

Multipoint Relay [MPR
]

16

Advanced Operating System


Spring 2012

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

N

Multipoint Relay [MPR
]

17

Advanced Operating System


Spring 2012

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

PROTOCOL FUNCTIONING

Advanced Operating System


Spring 2012

Neighbor sensing

19

Advanced Operating System


Spring 2012

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
-
hop


Based on Hello messages each node

selects its set of MPR’s

Example of neighbor table

Advanced Operating System


Spring 2012

20

B

A

C

F

G

D

E

Neighbor’s ID

Link
-
State

B

Bi
-
directional

G

Unidirectional

C

MPR





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.

One
-
hop neighbors

Two
-
hop neighbors

MPR selection

21

Advanced Operating System


Spring 2012

Each node select independently its own set of MPRs.


The MPR set is calculated in a manner
to contain a

subset
of 1
-
hop neighbors

which
covers all the 2
-
hop neighbors
.


In order to build the list of the 2
-
hop nodes

from a given
node, it suffices to
track the list of bi
-
directional link nodes
found in the HELLO messages

received by this node

(this 2
-
hop neighbor information is stored in the neighbor
table).



The MPR set re
-
calculated when:

A change in the neighborhood is detected when either a bi
-
directional link
with a neighbor is
failed
, or a new neighbor with a bi
-
directional link is
added
; or

A change in the 2
-
hop neighbor set with
bi
-
directional link

is detected.

MPR information declaration

22

Advanced Operating System


Spring 2012

A TC [Topology control] message is
Sent periodically

by each node
in the network
to declare its MPR Selector set
,

i.e., the message contains the list of neighbors who

have
selected

the sender node
as a MPR
.


TC messages will help each node
to build its topology table
.


The interval between the transmission of two TC messages depends
upon
whether the MPR Selector set is changed or not
,

since the last TC message transmitted.


When a change occurs in the MPR Selector set, the next TC
message may be
sent earlier that the scheduled time
, but after
some pre
-
specified minimum interval
, starting from the time the
last TC message was sent.

Topology Table

23

Advanced Operating System


Spring 2012

Destinations

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

Topology Table

24

Advanced Operating System


Spring 2012

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

&
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.

Routing table calculation

25

Advanced Operating System


Spring 2012

Each node maintains a routing table

to all know destinations in the network.

Based
-
on the information contained

in
the neighbor table

&
the topology table
.

Routing table:

Destination address

Next
-
hop address

Distance

Optimized Link
-
State Routing (OLSR)

26

Advanced Operating System


Spring 2012

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

END

Advanced Operating System


Spring 2012