All things related to multicast

[Bill Nickless <>]

It seems to me that there are five levels of efficiency for a multilateral 
multicast exchange point, listed in order of (my) preference:

EFFECTIVELY SHARED MEDIA
========================
Any participant gets all multicast traffic at the exchange point, whether 
or not they want to get multicast traffic.  An example of this is an 
exchange point built on FDDI or a multicast-ignorant Ethernet switch.

(*,*,*) SWITCHING
=================
Any participant who has PIM-SM configured gets all the multicast traffic at 
the exchange point.  An example of this is the use of an IGMPv2 snooping 
Ethernet switch.  I believe the NASA AMES MIX is at this efficiency level 
based on Hugh LaMaster's earlier note in this thread.

(*,G,*) SWITCHING
=================
Participants only get multicast traffic for groups they are interested in 
receiving.  Examples of this include RGMP (Cisco world) and the current 
implementation of Foundry PIM-SM snooping.

(S,G,*) SWITCHING
=================
Participants only get multicast traffic for specific sources in specific 
groups they are interested in receiving.  The Foundry PIM-SM snooping 
feature may be extended to this level.

(S,G,RPF) SWITCHING
===================
Participants get multicast traffic for specific sources in specific groups 
from a single RPF peer (eliminating the possibility of packet duplication 
if more than one participant is sourcing traffic to the exchange 
point).  Three sub-cases:

  - Point-to-point bilateral PIM-SM peerings (using MPLS, ATM VCs,
    VLANs, etc) meet this goal, but each participant must do their
    own outbound packet replication.

  - The Toerless Eckert VLAN-per-participant scheme is an example
    of how to implement this at the lesser cost of a single VLAN per
    participant, while letting the exchange point do the packet
    replication.  The cost is configuration complexity and sparse
    use of exchange IP address space.

  - Having each participant peer with an exchange-point router over
    a private VLAN also meets this goal but at the cost of delegating
    the choice of RPF for any given source to the exchange point
    managers.

Is this a reasonable taxonomy?

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Bill Nickless    http://www.mcs.anl.gov/people/nickless      +1 630 252 7390
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