[dnssd] multicast over wireless links

[RJ Atkinson <[e-mail]>]

Ted,

  When IP multicasting originated, wired Ethernet was a shared
medium using CSMA/CD.  A single IP/Ethernet frame would reach
all nodes on that IP subnet.  I still remember vampire taps 
and the big yellow Coax cable in my office from back then.

  In the 1990s, switched Ethernet became commonplace and 
(as deployed) the wire to the desktop was not a shared
medium, but instead was a solo link back to the Ethernet
switch.  This meant that the IP/Ethernet frame did not 
automatically get seen by all nodes on that Ethernet 
(bridged) link.  The IETF didn't drop IP multicasting, 
or discourage use of IP multicasting.  Instead, Ethernet 
switch vendors made various optimisations inside their 
Ethernet switch products (e.g. IGMP snooping) to make 
IP multicasting work well over wired switched Ethernet.  
IETF folks were involved in helping the Ethernet vendors 
understand some implementation options for those optimisations 
in those Ethernet products.

  The situation today with 802.11 is entirely analogous
to that previous situation with wired Ethernet moving
from shared CSMA/CD to switched dedicated links, and the
IETF community should have the same response -- don't drop 
the use of IP multicasting, don't discourage use of 
IP multicasting -- instead engage with others so that a 
link-specific optimisation can be put into use only for 
-- and only within -- those link-specific vendor devices 
(e.g., wireless access point, 802.11 radio, or whatever 
term one prefers).

Yours,

Ran