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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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