[Udpcast] multi computer cast problem

Paweł Ufnalewski // BSS archon at pjwstk.edu.pl
Thu Sep 25 11:56:41 CEST 2008

None of this works for me. I think it's something wrong with ACKs from

Alain Knaff pisze:
> Paweł Ufnalewski // BSS wrote:
>> Problem is that, when I'm doing it one-by-one (I mean server-1 client) I
>> get full speed - ~70MB/s, but when I'm trying to to this with >= 2
>> computers transfer drops to >0,5Mb/s. Why?
> This is most likely a switch issue. Many switches limit (throttle)
> multicast traffic, as they consider it "not important". Fortunately,
> this can be configured on most switches.
But why when there's one client it goes full speed and when there are >=
2 it drops to 0.29? It's problem with unicast not the mulitcast.
> Another thing to watch out for is the lonely network printer (or other
> ancient device) that can't take data at more than one Mb/s. If you
> broadcast or multicast, most switches send out the data to all ports,
> and adapt the speed to the slowest device connected. Try to find out if
> that is the case by only connecting a bunch of "known-good" PC's to a
> switch (no uplink, no unknown devices).
Tried that - only 1gb nics connected to 100Mb/s backbone.
> Some high-end switches do actually understand the IGMP messages by which
> receivers inform that they are interested in the transmission. However,
> these devices are rare, and even if they do support IGMP snooping, it is
> often switched off by default.
It's on.
> Another thing you can try is switch off flow control. Some switches even
> allow to do this on a per port basis.
> Regards,
> Alain

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