[Mp4-tech] [opendtv] Re: HDTV and SDTV Decoders for MPEG-2 andMPEG-4 AVC

[Craig Birkmaier]

At 2:30 PM +0530 2/16/05, Prashant Desai wrote:
>Craig
>
>  thanks for your detailed reply ........i got your point...... what i am not
>able to understand wrt to the STB is
>see in case of cable based iTV deployments  they require  multiple tuners
>[ say 2 tuners ] so that the user can do both  ......i mean user can watch
>TV and simultaneously  record the TV programe for PVR ......... correct ?

Yes, this is correct. In order to provide a bit stream for decoding, 
a demodulator is required to convert the "analog" transmission back 
into a bit stream that the decoder can work with.
In the case of an IPTV system using TCP/IP packets, the Ethernet 
connection provides the equivalent of the demods. In order to 
demodulate two streams that are being delivered via different 
frequency bands you need two tuners. But with the packet based system 
you need only properly identify the packets that belong to each of 
the streams that are being sent to the STB. The only limitation of 
the IP packet approach is bandwidth - i.e. how many streams can be 
delivered simultaneously to any home or devices within that home.
>
>but since in case of IPTV  there isnt any concept of tuners since it's
>purely on IP multicast so in such case what is required on the STB which is
>IP equivelent of STB tuners .....so the user can do both the things at the
>same time that is user can watch the TV and also record the programe at the
>same time

I partially answered this above.
In order to drive the entire system, it is necessary to download some 
form of Electronic Program Guide to the STB. The customer can then 
choose the streams that they want to watch in real-time or to cache 
in a PVR. And there may be other IP packet services being delivered 
alongside any streams that the home requests, such as e-mail or HTTP 
(web) content.
Assuming there is sufficient bandwidth, the problem is just that of 
routing the correct packets to the STB. We can assume that the viewer 
will have the ability to choose from any existing multicast, or 
perhaps , a unicast for a VOD event. Once you know what needs to be 
routed to the STB, the issue becomes one of timing and 
synchronization. That is, you must have adequate buffering in the STB 
to deal with any latency in the network and you must multiplex the 
streams in a manner that assures that these buffers do not underflow, 
causing an interruption of service.
Regards
Craig