[mythtv-users] simultaneous viewing

Jean-Yves Avenard jyavenard at gmail.com
Fri Apr 13 01:14:50 UTC 2012


On 12 April 2012 22:09, Mark Lord <mythtv at rtr.ca> wrote:
> Sure it does.  A typical home network these days uses ethernet switches,
> rather than hubs.  The switches are smart, they memorize MAC addresses
> and then send traffic only where it needs to go, keeping other ports
> free for their own traffic.

That's not at all how a home (dumb) switch work for multicast traffic.
Only a L2/L3 managed switch with IGMP snooping would act like what you
describe.

Multicast is muticast, it is sent to all members of the network.

>
> Multicast defeats that, sending all (multicast) traffic to all ports
> all of the time.  Much, much heavier network load.

It isn't heavier load, it's designed to carry that load to start with.

The issue however with multicast is when you have a bridged wireless
network. Multicast rate by default on a 802.11g network is at 1Mbit/s
only. Sending multicast will saturate the wireless network which would
end up saturating the whole network.

That's when you need a switch supporting IGMP snooping, so the data is
only sent to the devices requesting it.


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