[opendtv] Re: opendtv Digest V3 #110
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 10 May 2006 11:10:54 -0400
James Fancher wrote:
> Lost in the fog of guaranteed bandwidth. Until storage
> developers can deliver storage with dual 10 GigE
> interfaces that provide guaranteed bandwidth, video
> developers are going to continue to use the protocols
> that provide the latency and bandwidth that their
> users require. Firewire may be old but it delivers
> deterministic latency and isochronous data. Infiniband
> is the only protocol today that can over a single
> connection deliver 4K playback. This year at NAB AJA
> had a demo in their booth of 2K playback using dual 4
> Gbit FC. In order to do 4K playback it takes 6 channels
> of 4 Gbit FC. Using UDP you can achieve rates that
> approach the lower end of the 4K playback curve. FC
> uses 8/10 coding to insure data at the other end. Until
> the TOE's in 10 GigE products offer similar FEC UDP is
> not a practical way to send data for playback. In the
> end all of this adds latency and when I have editors
> complaining about "slow" systems with one millisecond
> increase in delay this is not what you want to add to
> the mix.
These same topics have been argued back and forth for at least as long
as packet switching has been around. On the latency and jitter fronts,
the thinking of the best effort packet switching camp has always been
that this scheme is so much simpler that it's worth throwing more
bandwidth at the problem, to resolve any guaranteed bandwidth issues.
That's one reason why the promised cleverness of ATM over SONET never
really materialized. Rather than attempt to make efficient use of
limited bandwidth, with fancy traffic management schemes, just increase
the network capacity. It seems to be the way things are going.
The line coding used for faster-than-10 Mb/s Ethernets is also 8B/10B,
4B/5B, 64B/66B, and who knows what others are on the way. 10Gb/s
Ethernet offers several options. Matter of fact, it can also be carried
over SONET OC-192 (10GBASE-R).
Bert
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