Routing
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Routing. Flooding, Link-State. EE122 Section 4. First off, where are we?. Application. Transport. Mostly still here. Network. Datalink. Physical. Flooding. B. A. C. D. A  G. E. G. F. Does every node receive A’s packet? Does every node receive exactly one copy of A’s packet?

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Routing

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Routing

Flooding, Link-State

EE122 Section 4


First off, where are we?

Application

Transport

Mostly still here

Network

Datalink

Physical


Flooding

B

A

C

D

A  G

E

G

F

Does every node receive A’s packet?

Does every node receive exactly one copy of A’s packet?

(i.e. is there exactly one way to reach every node?)

NOT a Spanning Tree


Flooding

B

A

C

D

A  G

E

G

F

Does every node receive A’s packet?

Does every node receive exactly one copy of A’s packet?

(i.e. is there exactly one way to reach every node?)

Spanning Tree


Spanning Tree Rooted at G

B

A

C

D

E

G

F

Every node can reach G by following the arrows


Spanning Tree Rooted at E

B

A

C

D

E

G

F

Every node can reach E by following the arrows


Spanning Tree

  • Loop-free, dead-end-free topology

  • Easiest way to reach destination is Flooding

B

A

C

D

E

G

F

  • Wasteful  Motivation for Learning Switch


Learning Switch

  • Q1a) Node A wants to reach Node G

    • All nodes now know which

    • port to reach Node A on

    • Packet takes the path A – E – F – G

  • Q1b) Node F wants to reach Node A

    • Node F knows Node A is

    • on its left port

    • Node E knows Node A is

    • on its upper port

    • Packet takes the path F– E – A

B

A

C

D

E

G

F

NO NEED TO FLOOD!


Learning Switch

  • Q1c) Node B wants to reach Node F

    • Flood or no?

    • When do we stop?

    • Nodes ACEF receive the packet

    • Packet takes the path B-A-E-F

B

A

C

D

E

G

F


Learning Switch

Q1d)

1

1

1

1

3

1

Node A

Node B

Node C

Node D


Learning Switch

Q1d)

1

1

1

1

1

2

Node E

Node F

Node G


Link-State Routing

A

B

C

D


Link-State Routing

Q2a)

A

(1, A)

(5, A)

(1, A)

(3, B)

(9, B)

1

5

(1, A)

(3, B)

(7, C)

B

2

C

Node A

8

4

(1, B)

(2, B)

(8, B)

D

(2, B)

(8, B)

(1, B)

(1, B)

(2, B)

(6, C)

Node B


Link-State Routing

Q2a)

A

(5, C)

(2, C)

(4, C)

(3, B)

(2, C)

(4, C)

1

5

(3, B)

(2, C)

(4, C)

B

2

C

Node C

8

4

(8, D)

(4, D)

D

(6, C)

(4, D)

(9, C)

(7, B)

(6, C)

(4, D)

Node D


Link-State Routing

  • Q2b) Node A sends to D

    • Shortest path: ABCD

    • Cost: 7

  • What if the nodes don’t have the same map?

  • A

    1

    5

    B

    2

    C

    8

    4

    D


    Link-State Routing

    • Q2c) Cost of link BC = 20, B sends to C

      • B thinks shortest path is BAC

      • A thinks shortest path is ABC

      • B  A  B  A…

      • Cost: ∞

    A

    1

    5

    B

    C

    20

    8

    4

    D


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