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### OLSRv2High Level Overview

Topology DisseminationTask 1:MPR selection algorithm: example (cont)MPR Selection Objective: each nodes determines a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message

Task 1:MPR selection algorithm: example (cont)MPR Selection Objective: each nodes determines a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message

Task 1:MPR selection algorithm: example (cont)MPR Selection Objective: each nodes determines a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message

Task 1:MPR selection algorithm: example (cont)MPR Selection Objective: each nodes determines a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message

Topology Dissemination

Carlos Rodrigo Aponte

Overview of OLSR

- OLSR is a link-state proactive routing protocol with four basic parts:
- Neighbor Discovery
- A node estimates its local topology.
- By local topology, we mean 1- and 2-hop topology
- Selector of Topology Information to Disseminate
- Not all links are needed to form shortest paths
- Advertising a subset of all links reduces total overhead
- Topology Dissemination
- Once the link information to be advertised is determined, it must be disseminated over the network
- Route Calculation
- Once the link advertisements are received, paths can be computed.

Overview of OLSR

- OLSR is a link-state proactive routing protocol with four basic parts:
- Neighbor Discovery
- A node estimates its local topology.
- By local topology, we mean 1- and 2-hop topology
- Selector of Topology Information to Disseminate
- Not all links are needed to form shortest paths
- Advertising a subset of all links reduces total overhead
- Topology Dissemination
- Once the link information to be advertised is determined, it must be disseminated over the network
- Route Calculation
- Once the link advertisements are received, paths can be computed.

Neighborhood Discovery

- In OLSR, Hello messages are used to estimate the local topology
- Two tasks
- Estimation the one-hop neighbors
- One-hop neighbors are those with bidirectional links
- Local dissemination of the one-hop topology to estimate the two-hop topology

Task 1: Estimating one-hop neighbors

9

1

19

10

18

1

2

11

8

S

3

17

From the point of view of nodes S and 1

Initially, neither of the nodes know about the topology

12

7

4

5

6

16

13

14

15

Task 1: Estimating one-hop neighbors (cont)

9

1

19

10

18

1

2

11

8

S

3

17

Node S broadcasts a HELLO message.

12

7

4

5

6

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13

14

15

Task 1: Estimating one-hop neighbors (cont)

9

1

19

10

18

1

2

11

8

S

3

17

- Node 1 receives the HELLO message and learns:
- It can hear S
- Thus a unidirectional link is discovered by 1

12

7

4

5

6

16

13

14

15

Task 1: Estimating one-hop neighbors (cont)

9

1

19

10

18

1

2

11

8

S

3

17

Node 8 broadcasts a HELLO message.

12

7

4

Source: 8

Dest: Broadcast

Info: 8 has heard S

5

6

16

13

14

15

Task 1: Estimating one-hop neighbors (cont)

9

1

1

19

10

18

1

2

11

- Node S receives the HELLO message, and learns:
- It was heard by 8
- It can hear 8
- Thus node S discovers a bidirectional link to 8
- Node 1 receives the HELLO message and learns:
- It can hear 8
- Thus a unidirectional link is discovered by 1

8

S

3

17

12

7

4

Source: 8

Dest: Broadcast

Info: 8 has heard S

5

6

16

13

14

15

Task 1: Estimating one-hop neighbors (cont)

9

1

1

19

10

18

1

2

11

8

S

3

17

Node 1 broadcasts a HELLO message.

Source: 1

Dest: Broadcast

Info: 1 has heard S and 8

12

7

4

5

6

16

13

14

15

Task 1: Estimating one-hop neighbors (cont)

9

1

1

19

10

1

18

1

2

- Node S receives the HELLO message, and learns:
- It was heard by 1
- It can hear 1
- Thus node S discovers a bidirectional link to 1
- Node 8 receives the HELLO message and learns:
- It was heard by 1
- It can hear 1
- Thus node 8 discovers a bidirectional link to 1

11

8

S

3

17

Source: 1

Dest: Broadcast

Info: 1 has heard S and 8

12

7

4

5

6

16

13

14

15

Task 1: Estimating one-hop neighbors (cont)

9

1

1

19

10

1

18

1

2

11

8

Source: 18

Dest: Broadcast

Info: 18 has heard 1 and 8

S

3

17

Node 18 broadcasts a HELLO message.

12

7

4

5

6

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13

14

15

Task 1: Estimating one-hop neighbors (cont)

9

1

1

19

10

1

18

1

2

- Node 1 receives the HELLO message, and learns:
- It was heard by 18
- It can hear 18
- Thus node 1 discovers a bidirectional link to 18
- Node 8 receives the HELLO message and learns:
- It was heard by 18
- It can hear 18
- Thus node 8 discovers a bidirectional link to 18

11

8

Source: 18

Dest: Broadcast

Info: 18 has heard 1 and 8

S

3

17

12

7

4

5

6

16

13

14

15

Task 1: Estimating one-hop neighbors (cont)

9

1

1

19

10

1

18

1

2

11

8

S

3

17

After a while, nodes 1 and S discover their entire 1-hop topology

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6

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14

15

Task 2: Estimating 2-hop Topology

9

1

1

19

10

1

1

18

1

2

11

8

S

3

17

Node 1 broadcasts a HELLO message, including information about its neighbors.

Source: 1

Dest: Broadcast

Info: Neighbors: S,8,18,19

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Task 2: Estimating 2-hop Topology (cont)

9

1

1

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10

1

1

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1

2

11

8

S

3

17

- Node S receives the HELLO message, and learns:
- All 1-hop neighbors of node 1
- Part of its 2-hop topology

Source: 1

Dest: Broadcast

Info: Neighbors: S,8,18,19

12

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6

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Task 2: Estimating 2-hop Topology (cont)

9

1

1

19

10

1

1

18

1

2

11

8

S

3

17

Source: S

Dest: Broadcast

Info: Neighbors: 1,2,3,4,5,6,7,8

Node S broadcasts a HELLO message, including information about its neighbors.

12

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5

6

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13

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Task 2: Estimating 2-hop Topology (cont)

9

1

1

1

1

19

10

1

1

18

1

2

11

8

S

3

17

Source: S

Dest: Broadcast

Info: Neighbors: 1,2,3,4,5,6,7,8

- Node 1 receives the HELLO message, and learns:
- All 1-hop neighbors of node S
- Part of its 2-hop topology

12

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6

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13

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15

Task 2: Estimating 2-hop Topology (cont)

9

19

10

18

1

2

11

8

S

3

17

Eventually, nodes 1 and S will discover their entire 2-hop neighborhood

12

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4

5

6

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13

14

15

Detecting bidirectional links

9

19

10

18

1

2

11

8

S

3

17

In order to consider a link “symmetric”, a node has to receive U HELLOs from the neighbor.

In OLSR, U=1.

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4

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6

16

13

14

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Detecting bidirectional links

9

Node 1 received HELLO message from S

#RCVD_HELLO=1

#RCVD_HELLO<U

=>unheardNode

19

10

18

Source: S

Dest: Broadcast

Info:

1

2

11

8

S

3

17

In order to consider a link “symmetric”, a node has to receive U HELLOs from the neighbor.

In OLSR, U=1.

12

7

4

5

6

16

13

14

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Detecting bidirectional links

9

19

10

Node S received HELLO message from 1

#RCVD_HELLO=1

#RCVD_HELLO<U

=>unheardNode

18

1

2

Source: 1

Dest: Broadcast

Info:

11

8

S

3

17

In order to consider a link “symmetric”, a node has to receive U HELLOs from the neighbor.

In OLSR, U=1.

12

7

4

5

6

16

13

14

15

Detecting bidirectional links

9

Node 1 received HELLO message from S

#RCVD_HELLO=2

#RCVD_HELLO<U

=>unheardNode

19

10

18

Source: S

Dest: Broadcast

Info:

1

2

11

8

S

3

17

In order to consider a link “symmetric”, a node has to receive U HELLOs from the neighbor.

In OLSR, U=1.

12

7

4

5

6

16

13

14

15

Detecting bidirectional links

9

19

10

Node S received HELLO message from 1

#RCVD_HELLO=2

#RCVD_HELLO<U

=>unheardNode

18

1

2

Source: 1

Dest: Broadcast

Info:

11

8

S

3

17

In order to consider a link “symmetric”, a node has to receive U HELLOs from the neighbor.

In OLSR, U=1.

12

7

4

5

6

16

13

14

15

Detecting bidirectional links

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3

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U-1

Node 1 received HELLO message from S

#RCVD_HELLO=

#RCVD_HELLO<U

=>unheardNode

19

10

6

U-1

3

5

7

4

Node S received HELLO message from 1

#RCVD_HELLO=

#RCVD_HELLO<U

=>unheardNode

U-1

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3

6

7

4

U-1

3

5

6

4

7

18

Source: S

Dest: Broadcast

Info:

1

2

Source: 1

Dest: Broadcast

Info:

11

8

S

3

17

In order to consider a link “symmetric”, a node has to receive U HELLOs from the neighbor.

In OLSR, U=1.

12

7

4

5

6

16

13

14

15

Detecting bidirectional links

9

U

Node 1 received HELLO message from S

#RCVD_HELLO=

#RCVD_HELLO=U

=>AsymmetricLink

19

10

U

18

Source: S

Dest: Broadcast

Info:

1

2

11

8

S

3

17

In order to consider a link “symmetric”, a node has to receive U HELLOs from the neighbor.

In OLSR, U=1.

12

7

4

5

6

16

13

14

15

Detecting bidirectional links

9

19

10

U

Node S received HELLO message from 1

#RCVD_HELLO=

#RCVD_HELLO=U

=>SymmetricLink

U

18

1

2

Source: 1

Dest: Broadcast

Info: AsymmetricLink with S

11

8

S

3

17

In order to consider a link “symmetric”, a node has to receive U HELLOs from the neighbor.

In OLSR, U=1.

12

7

4

5

6

16

13

14

15

Detecting bidirectional links

9

U+1

Node 1 received HELLO message from S

#RCVD_HELLO=

#RCVD_HELLO>U

=>SymmetricLink

19

10

U+1

18

Source: S

Dest: Broadcast

Info: SymmetricLink with 1

1

2

11

8

S

3

17

In order to consider a link “symmetric”, a node has to receive U HELLOs from the neighbor.

In OLSR, U=1.

12

7

4

5

6

16

13

14

15

Detecting bidirectional links

9

19

10

U

Node 1 received HELLO message from S

#RCVD_HELLO=

#RCVD_HELLO=U

=>SymmetricLink

U

18

1

2

11

8

S

3

17

In order to consider a link “lost”, a node has to lose D HELLOs from the neighbor.

In OLSR, D=3.

12

7

4

5

6

16

13

14

15

Detecting bidirectional links

9

19

10

1

0

1

2

4

3

…

D-1

D

5

Node 1 detected lost HELLO messages from S

#LOST_HELLO=

#LOST_HELLO<D

=>SymmetricLink

Node 1 detected lost HELLO messages

from S

#LOST_HELLO=

#LOST_HELLO=D

=>LostLink

2

1

4

3

…

0

D-1

D

5

18

Source: S

Dest: Broadcast

Info: SymmetricLink with 1

2

11

8

S

3

17

In order to consider a link “lost”, a node has to lose D HELLOs from the neighbor.

In OLSR, D=3.

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Event Counting (Generalization of RFC)

When link is up

When link is down

Parameters: U, D

1

Transmission Probability

0.5

U

0

0

10

20

30

40

50

60

70

80

Hellos

D

4

3

Number of Sequential Success/Failures

2

<----- DOWN ----->

<----- UP ----->

Ck

1

0

0

10

20

30

40

50

60

70

80

Hello

arrival

Hellos

OLSR v1: U=1 D=3. Generalized by UMD

Exponential Moving Average w/ Hysteresis (RFC)

When link is up

Qk+1 = Qk + (1- ) 1{Received Hello k}

Qk >TDown link is down

When link is down

Qk+1 = Qk + (1- ) 1{Received Hello k}

Qk >TUp link is up

Parameters: , Tup, Tdown

Cumulative Sum (CumSum) Link Detection

When link is up

Sk+1 = max(0, Sk +1{Missed Hello} - PDown)

Sk > T link is down

When link is down

Sk+1 = max(0, Sk - 1{Missed Hello} + PUp)

Sk >T link is up

Parameters: Pup, Pdown, T

PerrUp

PerrDown

T

Hello

received

Overview of OLSR

- OLSR is a link-state proactive routing protocol with four basic parts:
- Neighbor Discovery
- A node estimates its local topology.
- By local topology, we mean 1- and 2-hop topology
- Selector of Topology Information to Disseminate
- Not all links are needed to form shortest paths
- Advertising a subset of all links reduces total overhead
- Topology Dissemination
- Once the link information to be advertised is determined, it must be disseminated over the network
- Route Calculation
- Once the link advertisements are received, paths can be computed.

OLSR merges selector of Topology Information to Disseminate with Topology Dissemination. But in CBR, these are two different components

Topology Dissemination

- In order to limit control traffic, only a subset of nodes (Multi-Point Relays: MPRs) forwards control packets
- Two tasks
- Determine the set of MPRs
- MPR Selection Objective: determine a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message
- Flood TC messages over the reduced graph

Topology Dissemination

- In order to limit control traffic, only a subset of nodes (Multi-Point Relays: MPRs) forwards control packets
- Two tasks
- Determine the set of MPRs
- MPR Selection Objective: determine a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message
- Flood TC messages over the reduced graph

Why use MPRs?

In traditional flooding, each node relays the messages.

This approach typically results in each node receiving the message many times (i.e, it wastes bandwidth/ creates excess overhead)

Why use MPRs?

In traditional flooding, each node relays the messages.

This approach typically results in each node receiving the message many times (i.e, it wastes bandwidth/ creates excess overhead)

By carefully selecting which nodes forward messages, the overhead can be reduced.

This is the objective of MPR-based flooding

(note there are many other ways to accomplish this goal )

Topology Dissemination

- In order to limit control traffic, only a subset of nodes (Multi-Point Relays: MPRs) forwards control packets
- Two tasks
- Determine the set of MPRs
- MPR Selection Objective: determine a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message
- Flood TC messages over the reduced graph

- Two tasks
- Determine the set of MPRs
- Flood TC messages over the reduced graph

Task 1:MPR selection algorithm : example

MPR Selection Objective: each nodes determines a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message

1. Determine all 2-hop neighbors which are only reachable through just one 1-hop neighbor

From the perspective of node S

9

19

10

2. Select those 1-hop neighbors as MPRs

1

2

18

3. Determine C = reachable 2-hop nodes through the current set of MPRs.

11

8

4. Let U = 2-hop neighbors which are not reachable through the MPRs.

S

3

12

17

7

5. If U= , then done

Else

Add the 1-hop node that has the highest number of neighbors in U to the set of MPRs

Go to step 3

4

5

6

16

13

14

15

Task 1:MPR selection algorithm: example (cont)

MPR Selection Objective: each nodes determines a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message

1. Determine all 2-hop neighbors which are only reachable through just one 1-hop neighbor

From the perspective of node S

9

19

10

2. Select those 1-hop neighbors as MPRs

1

2

18

3. Determine C = reachable 2-hop nodes through the current set of MPRs.

11

8

S

3

4. Let U = 2-hop neighbors which are not reachable through the MPRs.

12

7

4

5

17

6

5. If U= , then done

Else

Add the 1-hop node that has the highest number of neighbors in U to the set of MPRs

Go to step 3

16

13

14

15

Task 1:MPR selection algorithm: example (cont)

MPR Selection Objective: each nodes determines a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message

1. Determine all 2-hop neighbors which are only reachable through just one 1-hop neighbor

From the perspective of node S

9

19

10

2. Select those 1-hop neighbors as MPRs

1

2

18

3. Determine C = reachable 2-hop nodes through the current set of MPRs.

11

8

S

3

4. Let U = 2-hop neighbors which are not reachable through the MPRs.

12

7

4

5

17

6

5. If U= , then done

Else

Add the 1-hop node that has the highest number of neighbors in U to the set of MPRs

Go to step 3

16

13

14

15

Task 1:MPR selection algorithm: example (cont)MPR Selection Objective: each nodes determines a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message

1. Determine all 2-hop neighbors which are only reachable through just one 1-hop neighbor

From the perspective of node S

9

19

10

2. Select those 1-hop neighbors as MPRs

1

2

18

3. Determine C = reachable 2-hop nodes through the current set of MPRs.

11

8

S

3

4. Let U = 2-hop neighbors which are not reachable through the MPRs.

12

7

4

5

17

6

5. If U= , then done

Else

Add the 1-hop node that has the highest number of neighbors in U to the set of MPRs

Go to step 3

16

13

14

15

Task 1:MPR selection algorithm: example (cont)MPR Selection Objective: each nodes determines a minimal set of neighbors such that if each neighbor relays the message then each node in the two-hop neighborhood receives the message

1. Determine all 2-hop neighbors which are only reachable through just one 1-hop neighbor

From the perspective of node S

9

19

10

2. Select those 1-hop neighbors as MPRs

1

2

18

3. Determine C = reachable 2-hop nodes through the current set of MPRs.

11

8

S

3

4. Let U = 2-hop neighbors which are not reachable through the MPRs.

12

7

4

5

17

6

5. If U= , then done

Else

Add the 1-hop node that has the highest number of neighbors in U to the set of MPRs

Go to step 3

16

13

14

15

1. Determine all 2-hop neighbors which are only reachable through just one 1-hop neighbor

From the perspective of node S

9

19

10

2. Select those 1-hop neighbors as MPRs

1

2

18

3. Determine C = reachable 2-hop nodes through the current set of MPRs.

11

8

S

3

4. Let U = 2-hop neighbors which are not reachable through the MPRs.

12

7

4

5

17

6

5. If U= , then done

Else

Add the 1-hop node that has the highest number of neighbors in U to the set of MPRs

Go to step 3

16

13

14

15

1. Determine all 2-hop neighbors which are only reachable through just one 1-hop neighbor

From the perspective of node S

9

19

10

2. Select those 1-hop neighbors as MPRs

1

2

18

3. Determine C = reachable 2-hop nodes through the current set of MPRs.

11

8

S

3

4. Let U = 2-hop neighbors which are not reachable through the MPRs.

12

7

4

5

17

6

5. If U= , then done

Else

Add the 1-hop node that has the highest number of neighbors in U to the set of MPRs

Go to step 3

16

13

14

15

1. Determine all 2-hop neighbors which are only reachable through just one 1-hop neighbor

From the perspective of node S

9

19

10

2. Select those 1-hop neighbors as MPRs

1

2

18

3. Determine C = reachable 2-hop nodes through the current set of MPRs.

11

8

S

3

4. Let U = 2-hop neighbors which are not reachable through the MPRs.

12

7

4

5

17

6

5. If U= , then done

Else

Add the 1-hop node that has the highest number of neighbors in U to the set of MPRs

Go to step 3

16

13

14

15

1. Determine all 2-hop neighbors which are only reachable through just one 1-hop neighbor

From the perspective of node S

9

19

10

2. Select those 1-hop neighbors as MPRs

1

2

18

3. Determine C = reachable 2-hop nodes through the current set of MPRs.

11

8

S

3

4. Let U = 2-hop neighbors which are not reachable through the MPRs.

12

7

4

5

17

6

5. If U= , then done

Else

Add the 1-hop node that has the highest number of neighbors in U to the set of MPRs

Go to step 3

16

13

14

15

Local Topology Information is Required to Make Routes

MPRs advertise links to MPR selectors

Original Graph

9

9

19

10

19

10

1

2

18

1

2

18

11

8

11

8

0

3

0

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15

1 is a MPR for 0

Legend:

If only MPRMPR Selectors are used, then 7 could not reach 16 in one hop.

0

1

Overview of OLSR

- OLSR is a link-state proactive routing protocol with four basic parts:
- Neighbor Discovery
- A node estimates its local topology.
- By local topology, we mean 1- and 2-hop topology
- Selector of Topology Information to Disseminate
- Not all links are needed to form shortest paths
- Advertising a subset of all links reduces total overhead
- Topology Dissemination
- Once the link information to be advertised is determined, it must be disseminated over the network
- Route Calculation
- Once the link advertisements are received, paths can be computed.

OLSR merges selector of Topology Information to Disseminate with Topology Dissemination. But in CBR, these are two different components

Are Paths Composed of Advertised Links the Shortest Paths?Yes, they are.

Length >N

N-1

C1

N-2

D

B1

S

C2

B2

- Suppose that
- D is N hops from S
- But, S is not aware of a N-hop path to D.
- However, S is aware of N-1-hops paths to some of D’s neighbors, C1, C2, …
- This means that there are neighbors of C’s, denoted by B1, B2, … that are N-2 hops from the C1, C2, …
- Since S can’t reach D in N hops, but can reach C1, C2, … in N-1 hops, the links from C1, C2, … to D are not advertised
- Thus, C1, C2, … are not MPRs of D
- This is cannot happen, one of the Ci must be a MPR for D.
- Otherwise, how will the two-hop neighbors (B1, B2, … ) be covered?
- Therefore, if there are shortest paths to all nodes N-2 and N-1 hops away, then there are shortest paths to nodes N hops away.
- Clearly, there are shortest paths to nodes 1 hop away and to nodes 2 hops away (the set of MPRs guarantee this). So there are shortest paths to nodes 3 hops away, and therefore, there are shortest paths to node 4 hops away, ….

- Two tasks
- Determine the set of MPRs
- Flood TC messages over the reduced graph

Task 2: Topology Dissemination

Topology dissemination = deciding which nodes relay the topology information

RFC and INRIAs approach

E

S

D

F

C

B

A

G

H

Task 2: Topology Dissemination

Topology dissemination = deciding which nodes relay the topology information

RFC and INRIAs approach

E

S

D

F

C

Node S Broadcasts a TC Message

B

A

G

H

Task 2: Topology Dissemination

Topology dissemination = deciding which nodes relay the topology information

RFC and INRIAs approach

E

S

D

F

Only nodes that have not previously received the message will update the Information Base

C

B

A

G

H

Task 2: Topology Dissemination

Topology dissemination = deciding which nodes relay the topology information

RFC and INRIAs approach

E

S

D

Only nodes that have not previously received the message and that have the transmitter as an MPR Selector, will forward the message

F

C

B

A

G

H

Nodes that have S as an MPR Selector

Task 2: Topology Dissemination

Topology dissemination = deciding which nodes relay the topology information

OLSR-D and Qualnets approach

E

S

D

F

C

Node S Broadcasts a TC Message

B

A

G

H

Task 2: Topology Dissemination

Topology dissemination = deciding which nodes relay the topology information

OLSR-D and Qualnets approach

E

S

D

F

Only nodes that have not previously processed the message will update the information base

C

B

A

G

H

Task 2: Topology Dissemination

Topology dissemination = deciding which nodes relay the topology information

OLSR-D and Qualnets approach

E

S

D

F

Only nodes that have not already forwarded the messageand that have the transmitter as an MPR Selector, will forward the message

C

B

A

G

H

Nodes that have S as an MPR Selector

Comparison of Flooding Techniques

- MPRs
- 4 is the only MPR for 0 (0 had degree 5, but only one MPR!)
- 6 and 9 are MPRs for 4
- 1 is the MPR for 3 (2 is an MPR for 5)

8

7

6

9

4

3

5

1

0

2

RFC/INRIA Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1

0

2

RFC/INRIA Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 have received the TC message

1

0

2

RFC/INRIA Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 have received the TC message

4 is a MPR for 0

1

0

2

RFC/INRIA Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 have received the TC message

4 is a MPR for 0

6, 7, 8, and 9 have received the TC message

1

0

2

RFC/INRIA Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 have received the TC message

4 is a MPR for 0

6, 7, 8, and 9 have received the TC message

6 and 9 are MPRs for 4

1

0

2

RFC/INRIA Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 have received the TC message

4 is a MPR for 0

6, 7, 8, and 9 have received the TC message

6 and 9 are MPRs for 4

All nodes have received the TC message

1

0

2

RFC/INRIA Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 have received the TC message

4 is a MPR for 0

6, 7, 8, and 9 have received the TC message

6 and 9 are MPRs for 4

All nodes have received the TC message

Note, while 3 is a MPR for 6, it has already received the TC message, and does not forward it

1

0

2

OLSRd/Qualnet Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1

0

2

OLSRd/Qualnet Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 received TC message from 0

1

0

2

OLSRd/Qualnet Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 received TC message from 0

4 is the MPR or 0

1

0

2

OLSRd/Qualnet Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 received TC message from 0

4 is the MPR or 0

6, 7, 8, and 9 received the TC message from 6

1

0

2

OLSRd/Qualnet Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 received TC message from 0

4 is the MPR or 0

6, 7, 8, and 9 received the TC message from 6

6 and 9 are MPRs of 4

1

0

2

OLSRd/Qualnet Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 received TC message from 0

4 is the MPR or 0

6, 7, 8, and 9 received the TC message from 6

6 and 9 are MPRs of 4

All nodes have received the TC message

1

0

2

OLSRd/Qualnet Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 received TC message from 0

4 is the MPR or 0

6, 7, 8, and 9 received the TC message from 6

6 and 9 are MPRs of 4

All nodes have received the TC message

3 is a MPR for 6 (5 is a MPR for 9)

1

0

2

OLSRd/Qualnet Method

Originator of TC message

Received TC message

Relayed TC message

8

7

6

9

4

3

5

0 is the originator

1, 2, 3, 4, and 5 received TC message from 0

4 is the MPR or 0

6, 7, 8, and 9 received the TC message from 6

6 and 9 are MPRs of 4

All nodes have received the TC message

3 is a MPR for 6 (5 is a MPR for 9)

1 is a MPR for 3 (2 is a MPR for 5)

1

0

2

What is the difference between MPR-based flooding and full flooding?!

Hazy-Sighted Topology Dissemination

- Note: hazy sighted dissemination does not work. But the idea is as follows
- Idea: Topology information from far away links is not important for making local forwarding decisions
- When forwarding a packet, one only needs to move the packet in the right direction. This does not require detailed topology information

Idea (which turns out to be incorrect)

The potential next hop is a next hop for any destination in this region

More up-to-date information is required to reach destinations that are close than to reach destinations that are far.

Conclusion, topology information should not be flooded over the entire region.

This seems like such a good idea that many military systems are using this approach

pkt

This node must travel further in order to exit the “next-hop region”

potential next-hop

This node does not need to travel very far in order to exit the “next-hop region”

Hazy-Sighted Topology Dissemination

- Set TTL for the number of hops that a topology control (TC) message will travel.
- Adjust the TTL for each TC message so that the TTL 2k every 2k periods
- TTL 1 every period
- TTL 2 every 2 periods (i.e., periods 2, 4, 6, …)
- TTL 4 every 4 periods (i.e., period 4, 8, 12, 16, …)
- TTL 8 every 8 periods (i.e., period 8, 16, 24, 32, …)
- TTL 16 every 16 periods (i.e., period 16, 32, …)
- The time between TC messages from a distance k is 2ceil(log2(k))
- Topology information 7 hops away will be received every

2ceil(log2(7)) = 2ceil(2.8) = 23 = 8 periods

- This approach could potentially reduce the overhead, especially for large topologies
- Note that each TC message is forwarded by most nodes.
- For large networks, topology dissemination can consume much of the available bandwidth

This node must travel further in order to exit the “next-hop region”

potential next-hop

This node does not need to travel very far in order to exit the “next-hop region”

Problems with Hazy-Sighted- The basic idea has the critical flaw in that the path to a destination does not only depend on the location of the destination, but also depends on the other nodes in the network.
- Thus, a path can be impacted not only by the destination moving, but by nodes between the source and destination moving
- I guess this is obvious
- A correct model considers all links

Performance of Hazy-Sighted Dissemination

Change in topology that causes neighbor to stop being a next-hop

Duration that the originator is unaware of the topology change and forwards the pkt to a node that is no longer a suitable next hop.

T(kL ) = average duration

The fraction of the number line covered by the PS region is approximately the rate of topology changes the average duration, T

(another approximation is exp(-rate*T) )

Performance of Hazy-Sighted Dissemination

- Let be the rate that a link breaks (or form).
- Let NL(kL ,kD) be the number of links kL away given the destination is kD hops away
- Why does the number of links kL away depend on kD?
- Suppose that a destination is very far away, like 100 hops. Then, NL(90,100)>1 (otherwise, the dest can’t be 100 hops away).
- So, given a destination is kD hops away, the rate that any link breaks kL hops away is NL(kL, kD).
- Here we assume that is independent of kL and kD
- Let F(kL,kD) be the probility of PS when the break is at kL and the destinations is kD hops away
- NL(kL,kD)F(kL,kD) is the rate of PS events from links kL away, given that the destination is kD away
- Summing over all values of kL
- Expected value over all distances to destinations

Path Stretch Calculation

In the hazy-sighted case, T(kL) = Ths2ceil(log2(kL))

In regular case, T(kL) = To

By adjusting THS and To we can make the path stretch the same for both cases

so

Overhead Ratio

Conclusion: In order to keep path stretch the same as with regular flooding, hazy-sighted results in higher overhead.

One must focus on the intermediate nodes, not just the destination.

Overview of OLSR

- OLSR is a link-state proactive routing protocol with four basic parts:
- Neighbor Discovery
- A node estimates its local topology.
- By local topology, we mean 1- and 2-hop topology
- Selector of Topology Information to Disseminate
- Not all links are needed to form shortest paths
- Advertising a subset of all links reduces total overhead
- Topology Dissemination
- Once the link information to be advertised is determined, it must be disseminated over the network
- Route Calculation
- Once the link advertisements are received, paths can be computed.

Update Topology Set

Check all “advertised addresses” that came in the message.

These addresses are from the nodes that selected the “originator node” as an MPR.

Update Topology Set (cont)

Check all Topology Tuples in the Information Bases and verify if it exists an entry with the information just received.

Update Topology Set (cont)

If no information is stored in the Data Bases, create a new tuple.

Existing or new tuple has to update its sequence number and holding time.

Removing Topology Tuples

- To remove a Topology Tuple on of two things must occur:
- The timer (tuple holding time) has to expire.
- A TC message has to explicitly remove a tuple. (i.e. notify that a link is broken)

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