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Multicasting. Jean Walrand EECS. Outline. Definitions Broadcast, Multicast, Anycast Examples ARP, ICMP, Group Flooding Routing Multicast Tree of shortest paths; shortest tree Multicast Backbone Overlay Join Groups Soft State Reliable Multicast Nacks, Aggregation

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Multicasting

Multicasting

Jean WalrandEECS


Outline
Outline

  • Definitions

    • Broadcast, Multicast, Anycast

  • Examples

    • ARP, ICMP, Group

  • Flooding

  • Routing Multicast

    • Tree of shortest paths; shortest tree

  • Multicast Backbone

    • Overlay

    • Join Groups

    • Soft State

  • Reliable Multicast

    • Nacks, Aggregation

  • Multilayer Multicast


Definitions
Definitions

  • Broadcast

    • One to all

  • Multicast

    • One to all members of a group

  • Anycast

    • One to any member of a group


Examples
Examples

  • ARP:

    • Broadcast to LAN (Note: VLANs)

    • 11…11 = “broadcast” address on Ethernet

  • ICMP:

    • Routers broadcast their link states in OSPF

  • Group:

    • Multicast of seminar to “subscribers”

    • Class-D IP addresses = group addresses


Flooding

A

A

[1; A]

[1; A]

[1]

[1]

B

B

C

C

{1}

{1}

[1]

[1]

[1; A, B]

[1; A, C]

Flooding

  • Send on all other ports:

    • Remember seen packets, or

    • Mark route on packets

[1]

[1]

{1}


Routing multicast

1

1

D1

2

2

1

2

S

2

D2

1

1

Routing Multicast

  • Simplest: Tree of shortest paths

    • Example


Routing multicast continued

1

1

D1

2

2

1

2

S

2

D2

1

1

Routing Multicast (continued)

  • Optimal: Shortest tree

    • Example


Routing multicast continued1

1

1

1

1

D1

D1

2

2

2

2

1

1

2

2

S

S

2

2

D2

D2

1

1

1

1

Routing Multicast (continued)

  • Comparison:

Tree of shortest paths

Sum of lengths = 9

Shortest tree

Sum of lengths = 8


Routing multicast continued2

1

1

D1

2

2

1

2

S

2

D2

1

1

Routing Multicast (continued)

  • RPB: Reverse Path Broadcast

    Router R sends packet received from A if A is on the shortest path from R to S.

Link AR

A

R


Routing multicast continued3

1

1

D1

Link RP

2

R

2

P

1

2

S

2

D2

1

1

Routing Multicast (continued)

  • RPM: Reverse Path Multicast

    RPB + Prune back if no member of Mcast group

G

Prune

Prune

Prune

Not G


Routing multicast continued4

1

1

D1

2

2

Prune

1

2

S

2

D2

1

1

Routing Multicast (continued)

  • PIM-Dense Mode

    RPR + Prune + Graft (+ periodic RPR + Prune)

G

Prune

Graft

Graft

Graft

Join G


Routing multicast continued5
Routing Multicast (continued)

  • PIM-Sparse Mode

    Periodic Join/Prune Messages from DR to RP

    Assumption: Relatively few group members


Reliable multicast continued

1

1

1

1

1

1

1

Reliable Multicast (continued)

  • ACKs do not scale

  • NACKs may implode

  • => NACK aggregation


Reliable multicast continued1

2

2

2

2

Reliable Multicast (continued)

  • ACKs do not scale

  • NACKs may implode

  • => NACK aggregation


Reliable multicast continued2

3

3

[Remember for T seconds]

NACK2

3

3

3

3

3

Reliable Multicast (continued)

  • ACKs do not scale

  • NACKs may implode

  • => NACK aggregation


Reliable multicast continued3

[n]

NACK n

Reliable Multicast (continued)

  • Other idea: Designated Receivers

Source

DR

DR


Multilayer multicast

Source

Layer 1

Layer 2

Multilayer Multicast

  • Different channel bandwidths

  • => Multiple Layers

Random “join” experiments


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