[mythtv-users] IP TV support on the agenda?

Brian J. Murrell brian at interlinx.bc.ca
Wed Jul 20 11:54:26 EDT 2005

On Wed, 2005-07-20 at 08:40 -0700, Joe Votour wrote:
> (At this point, we're kind of off-topic.)

Yeah.  But but so is >50% of the traffic on this list.  :-)

> My guess then is that you haven't tried to stream tons
> of multicast data through switches then (either
> high-end or low-end).


> Where I work, we have.  And we have found many of
> those switches to be broken, only supporting a few
> IGMP groups (no higher than 16 as I recall), or just
> not able to keep up with a full 38Mbps MPEG-2 stream. 

Then network carriers are either going to have to demand a working
product from their vendors, or switch vendors.  That some equipment does
not work with a technology does make the technology bad.  It makes good
vendors shine.

> There's apparently a few DSLAMs (for DSL) that can't
> keep up with anything close to that kind of traffic
> either.

If anything, multicast should be easier on a DSLAM than unicast x n
streams will be.  Given that a DSLAM is essentially a
multiplexor/aggregator or whatever else you want to call it:

                         |    D    |----- DSL customer 1 -----
                         |    S    |----- DSL customer 2 -----
   ---- network pipe ----|    L    |----- DSL customer 3 -----
                         |    A    |----- DSL customer 4 -----
                         |    M    |----- DSL customer n -----

Having a single stream of data on that "network pipe" which is
"replicated" in the DSLAM itself has got to be easier to handle than
having that same stream sent n number of times down the "network pipe".

This is essentially the beauty of multicast of course.  If there is
*any* device out there that should handle multicast correctly it should
be a DSLAM.  That, after-all is the last mile, where the pipe is
dedicated and no longer shared amongst users -- until we start to see
true routers at customer premises, but that's probably going to be a
niche market.  In probably most cases there is "one customer" at the end
of a DSL pipe.

> I agree that multicast is the way to go for broadcast
> TV.  But if the underlying equipment can't deliver the
> traffic, then there will be problems.

Indeed.  And demand will take care of that.

> Then again, we've also had our share of problems with
> GigaBit switches not being able to deliver a GigaBit
> of data.  But that's another story.


Customer: Can your switch actually handle a gigabit of traffic?
Vendor: A gigabit of traffic?  Sure.  Wait.  Do you mean like you mean
all in one second?  Let me get back to you on that.



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