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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

Routing

Flooding, Link-State

EE122 Section 4


First off where are we
First off, where are we?

Application

Transport

Mostly still here

Network

Datalink

Physical


Flooding
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
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
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 switch1
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 switch2
Learning Switch

Q1d)

1

1

1

1

3

1

Node A

Node B

Node C

Node D


Learning switch3
Learning Switch

Q1d)

1

1

1

1

1

2

Node E

Node F

Node G



Link state routing1
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 routing2
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 routing3
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 routing4
    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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