[mythtv] "New" Feature: RTSP streaming for myth backend

Mattias Holmlund mattias.holmlund at gmail.com
Tue Feb 21 18:56:36 UTC 2006

On 2/21/06, Devan Lippman <devan.lippman at gmail.com> wrote:
> Also on a seemingly unrelated note is there someone out there that can
> answer an IGMP question?  Seems like in the case of networking
> equipment everything needs to support IGMP, linux is an easy one but
> what about the home networking structure.  Will home switches know how
> to pass these messages or should I start looking into other solutions?

IGMP and IP multicast is transmitted as Ethernet mutlicast (i.e. with
the multicast bit set in the destination MAC address). A simple
Ethernet switch will treat multicast packets as broadcast, i.e. it
will transmit the packet out on all its ports except the port that it
received the packet on. So yes, IGMP will work just fine on "home
switches", however the traffic will be transmitted on all ports and
not just the ports that actually needs the traffic. If there is more
than one receiver and not a lot of other traffic on the network, then
you will still save bandwidth by using multicast instead of unicast.

For a more efficient solution, you need an Ethernet switch that
supports IGMP Snooping. This means that the switch looks at the IGMP
messages and decides which ports really need the multicast packets.
IGMP Snooping is normally only available in managed switches.

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