[NUT-devel] Broadcast sufficiency - my assumptions/reasoning/design for it

[Måns Rullgård]

Rich Felker <dalias at aerifal.cx> writes:

> On Wed, Feb 06, 2008 at 06:27:47PM +0100, Michael Niedermayer wrote:
>> On Wed, Feb 06, 2008 at 12:08:37PM -0500, Rich Felker wrote:
>> > OK since there seems to be a disagreement (to put it lightly :) as to
>> > what the current NUT framework can do for synchronizing timing between
>> > a transmitter and receiver, I'd like to lay down the hypotheses and
>> > reasoning I'm working from. Maybe others disagree on the basic
>> > assumptions or haven't though of them. So, here it goes:
>> > 
>> > Transmitter side:
>> > 
>> > Key assumption is that frames are actually transmitted according to
>> > dts. In a VBR transmission with immensely excessive bandwidth, or a
>> > pure CBR (e.g. uncompressed, single-stream) transmission, this can be
>> > done almost exactly. In CBR with buffer restraints, obviously it will
>> > not be exact. 
>> 
>> > It is sufficient that the mean difference between dts
>> > and actual transmission time be constant over intervals of time whose
>> > length is on the order of the maximal length of time in which
>> > transmitter and receiver clocks can be expected to remain within an
>> > acceptable error relative to one another.
>> 
>> This is too vague to argue about it.
>
> It's trivially true for any live broadcast or broadcast with a fixed
> channel bitrate.

Nobody uses fixed channel bitrate.  A multiplex has a fixed bitrate
dictated by the modulation.  This fixed bitrate is then shared by
10-15 independent channels.  It is even common to over-allocate the
bitrate somewhat, since it is highly unlikely that all channels will
need peak rates at the same time.

-- 
Måns Rullgård
mans at mansr.com