[opendtv] Re: Global standard

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
  • Date: Sun, 29 Apr 2012 17:28:23 -0500

Mike Tsinberg wrote:

> What is efficiency gain when you switch from ATSC to IPv6 transport
> with HTML5? I assume these are open standards.

Depending what "efficiency" means, none. Actually, you lose *spectral* 
efficiency because you're carrying greater overhead. Although you would gain if 
you went to a more efficient compression algorithm than MPEG-2 compression 
(H.262).

People forget that the only reason you have IPv4 or IPv6 overhead at Layer 3 is 
to enable packet routing through a digital network. But if the packets are 
meant to be BROADCAST, through any medium, and especially through a medium that 
is constrained in bandwidth, such that packet routing is not an issue, then 
there's no strict technical reason to carry that layer 3 overhead. In 
broadcast, "routing" degenerates into a very simple rule: send packets to all 
receivers. The receivers do the filtering of whatever they don't want to 
consume. The network can be dumb.

At layer 2, ATSC and all the others use MPEG-2 TS, which is quite adequate. 
There's more capability in MPEG-2 TS than there is in Ethernet framing, for 
example. Such as packet synchronization. So, no apologies there.

The advantage of encapsulating broadcast TV in IP overhead is to allow use of 
client software that's already used for Internet streaming. The same sort of 
features could be provided if the software used the MPEG-2 TS framing 
effectively, but since it's already been developed at layer 3 for Internet 
streaming, might as well not reinvent that wheel. That's the advantage of using 
IP overhead. So for example, you can more easily move the ATSC broadcast 
packets into a home network, and have them available to PCs or tablets in the 
home. But this IP encapsulation could also be performed by a home server, 
potentially software resident in the cable or ISP modem. So it's not like IP 
encapsulation during broadcast is the only way to go.

And for that matter, if you compare the spectral efficiency of even the most 
modern LTE, compared with ATSC 1.0, LTE would lose. Reason being, it is meant 
to be two-way wireless protocol. That costs you. In order for LTE to approach 
ATSC 1.0 in spectral efficiency, you need to have the towers no further apart 
than something like 2 Km (1 1/4 mi). Image that for a broadcast TV 
infrastructure! (Okay, so you share that with a wireless broadband carrier, and 
then you have this identity crisis for local broadcasters!)

Bert

 
 
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