Re: [dnssd] multicast over wireless links

[Robert Cragie <[e-mail]>]

But as Alf said earlier, there are other wireless technologies which are 
not well suited to IP multicast traffic. 802.15.4-based mesh networks 
are a very good example and there is certainly a use case for DNS-SD in 
these type of networks.

Robert

On 24/07/2014 7:23 PM, RJ Atkinson wrote:
> 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
>
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