[mythtv-users] Way out idea on watching same thing inmultiplerooms

Tortise tortise at paradise.net.nz
Wed Jan 6 23:43:12 UTC 2010


----- Original Message ----- 
From: "Gareth Glaccum" <gareth.glaccum at btopenworld.com>
To: "Discussion about mythtv" <mythtv-users at mythtv.org>
Sent: Thursday, January 07, 2010 11:07 AM
Subject: Re: [mythtv-users] Way out idea on watching same thing inmultiplerooms


>----- Original Message ----- 
>From: David Brodbeck
>>On Jan 5, 2010, at 5:29 AM, Gareth Glaccum wrote:
>>Yup, I agree with that in principle. What about if they only have a 100mb/s switch or hub though?
>>Don't get me wrong, I think unicast is the way forward at the moment.
>>However, I think that whatever is put in place, should be done with the idea that sometime in the future, multicast could be 
>>implemented /safely/ and an 'upgrade' to multicast should be >>coded in easily.
>That's reasonable...however, how far in the future are we talking?  100 mb/s is on its way out.  In fact, cutting-edge sites are 
>already starting to install 10 Gb, which means in another few >years it'll probably start turning up in consumer gear.


>I started implementing 10G networks into client sites over 4 years ago.
The problem with the multicast suggestion is not that the bandwidth is not
there, it is the fact that most switches by default are not configured to
correctly handle multicast packets (ignoring hubs which cannot perform
multicast).
>The problem is, that as standard, most switches do not decode/ perform
multicast snooping. This means that they do not listen for multicast joins
and leaves, and instead broadcast multicast communications to all ports.
This is a major waste of bandwidth.

_______________________________________________

Interesting.  Awhile ago I wondered about using a hub for its inherent broadcast nature (every port gets everything) and putting all 
mythboxes on an old 100M Hub (branched off a switch) however looking into that I realised the way FE connect with BE's is currently 
done seems to be by pulling AV from various ports on the BE, which are not fixed.  Which mean't it was not going to be simple(!), 
and that a hub was not going to help, which got me onto multicast.

With the DVD / mythtv / VLC multicast trial I did I recall all the port lights flashed, which surprised me however is consistent 
with what you are saying.  (CNET Gigaport Switch in my case)  I'll run it again and check the various port lights to be sure.

Seems ironic that you are implying that with multicast traffic many switches behave as hubs anyway! 



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