RE: [EFM] Video distribution
Kent,
I spent a lot of time at WorldCom in 1998 and 1999 understanding the
relationship that the characteristics of the transmission facility and
protocols have on the quality deliverability of different kinds of video
services. I found that while a video stream will burst to the available
bandwidth, as long as the bandwidth can deliver a "screen" within the
allowable time for it to be decoded and displayed, the bandwidth can be
restricted to close to that of the average of the video data stream
rate. This goes for streaming video as well as interactive video.
The issue with interactive video is not the bandwidth as much as it is with
the latency variance inherent with the transmission facility and
protocols. With low latency variance, streaming video and interactive
video becomes a consistent stream with fixed, predictable,
utilization. The more that there is a latency variance, the more that
higher bandwidth burst traffic has be supported in order to support the
"screen" rate. Traditionally, IP routers have not been very good at
controlling latency variance. This is where the higher bandwidth
requirements for video comes in.
Latency variance for non-blocking Ethernet switches, in non overload
conditions, is the bit time delta between the largest frames and the
smallest frames. Latency variance for Ethernet over SONET/SDH (X.86) is
125us because of the OAM overhead window.
At present, EPON appears to be headed for a latency variance in the
milliseconds. This might do for streaming video to residential
customers. I do not think that it will do for any type of high end
interactive video, regardless of the available bandwidth. If any kind of
bandwidth gain is applied to the EPON deployment, it will be no better than
what is in the copper facilities today.
Streaming video can be "buffered" to compensate for latency
variance. This, however, increases the cost of the video display equipment
because of the additional complexity in managing the "buffered"
stream. The least expensive would be a system that only needs to buffer a
single "screen" before each "refresh". I do not know if the current EPON
proposals will support that.
Thank you,
Roy Bynum
At 01:33 PM 9/9/2002 -0700, Mccammon, Kent G. wrote:
>John,
>I agree with your comments about higher efficiency when broadcasting video
>to all VDSL nodes. The PON capacity is a constraint for designing the
>system. VOD of course changes the numbers as that traffic would be node
>specific and customer specific depending on the type of VOD service. If the
>PON throughput looks to be insufficient considering all services needs;
>broadcast, VOD, telephony, and data services, an operator could plan for a
>smaller split ratio to the VDSL node. The differential path loss
>(attenuation range) specification of the optics should be made broad enough
>to handle PONs with low splits for VDSL, for example 1x4 while other
>operators deploy for large splits for FTTH such as 1x32 architectures. Thus,
>the operator could have architecture flexibility in the selection of the PON
>split ratio for the services planned.
>-Kent
>
>
> > -----Original Message-----
> > From: John Limb [mailto:limb@xxxxxxxxxxxx]
> > Sent: Monday, August 26, 2002 9:50 AM
> > To: 'Mccammon, Kent G.'; stds-802-3-efm@ieee.org
> > Subject: RE: [EFM] Video distribution
> >
> >
> > Kent,
> > I'm a little confused. Perhaps you could straighten me
> > out. If you are distributing digital video from the OLT to
> > ONUs (even if connected to a VDSL
> > DSLAM) I would not think that you would need to have an
> > unused slot remainder since the OLT scheduler could start one
> > packet as soon as the previous one finished. If you were
> > sending packets from the ONT to the OLT then I could see that
> > slot remainders could occur.
> > If you are serving several hundred subs then you would
> > probably want to do mostly broadcasting rather then VOD. You
> > would probably want to use variable rate video coding (rather
> > than constant rate) in order to get a little more efficiency
> > and some statistical averaging. Even so, I suspect that most
> > packets would be max size (as Hugh says).
> > If you assume an average rate of 3 Mb/s for a high
> > quality video stream (probably even a little high for some of
> > the newer VBR codecs) 200 streams would take about 600Mb/s
> > leaving (plenty?) of room for other data, again confirming Hugh.
> >
> > John
> >
> > -----Original Message-----
> > From: owner-stds-802-3-efm@majordomo.ieee.org
> > [mailto:owner-stds-802-3-efm@majordomo.ieee.org]On Behalf Of
> > Mccammon, Kent G.
> > Sent: Friday, August 23, 2002 6:22 PM
> > To: 'gkramer@xxxxxxxxxxx'; Thomas.Murphy@xxxxxxxxxxxx;
> > stds-802-3-efm@ieee.org
> > Subject: RE: [EFM] Minutes of P2MP Optics conference 22nd Aug 20002
> >
> >
> >
> > Glen,
> > Referring to your comment about frame size distribution from
> > actual traffic.
> >
> > > The size of unused slot remainder depends on frame size
> > distribution.
> > > This distribution for today's traffic is known and there
> > exist formula
> > > to calculate this unused remainder (for the case when assigned slot
> > > size has no correlation to the frame sizes).
> >
> > Does anyone in the group have a traffic sample from a network
> > transporting digital video streams to give frame size
> > distribution? For example, a traffic sample for digital video
> > over fiber to a VDSL ONU to serve several hundred VDSL lines
> > to a residential gateway. That scenario may be a good one to
> > look at for traffic on a residential GigaPON connected to
> > multiple VDSL ONU locations with data and switched digital
> > video content.
> >
> > -Kent
> >
> > > -----Original Message-----
> > > From: Glen Kramer [mailto:gkramer@xxxxxxxxxxx]
> > > Sent: Friday, August 23, 2002 9:44 AM
> > > To: Thomas.Murphy@infineon.com; stds-802-3-efm@ieee.org
> > > Subject: RE: [EFM] Minutes of P2MP Optics conference 22nd Aug 20002
> > >
> > >
> > >
> > > Tom,
> > >
> > > This is to address action item #2 from the minutes.
> > >
> > > 2. Efficiency model based on guard bands and traffic type - P2MP
> > > group?
> > >
> > >
> > > There are 3 types of overhead (or bandwidth loss):
> > >
> > > 1. Cycle overhead. This is overhead used by guard bands (including
> > > CDR). It is measured as a number of guard bands in one cycle. This
> > > number at least equal to the number of ONUs, but may be
> > even larger if
> > > we grant per LLID and there are multiple LLIDs per ONU.
> > >
> > > 2. Slot overhead. This overhead arises when granted slot does not
> > > take into account frame delineation in a buffer. Since
> > frames cannot
> > > be fragmented, a frame that doesn't fit in the remainder of a slot
> > > will be deferred to next slot (in next cycle), leaving current slot
> > > underutilized.
> > >
> > > The size of unused slot remainder depends on frame size
> > distribution.
> > > This distribution for today's traffic is known and there
> > exist formula
> > > to calculate this unused remainder (for the case when assigned slot
> > > size has no correlation to the frame sizes).
> > >
> > > Few protocol proposals consider how to eliminate unused
> > slot remainder
> > > completely, but it looks like it will require changes to the frame
> > > format. P2MP group is still debating about it.
> > >
> > > 3. Frame overhead. That includes IFG and headers. Nothing
> > we can do
> > > about it.
> > >
> > > Glen
> > >
> > > > -----Original Message-----
> > > > From: owner-stds-802-3-efm@majordomo.ieee.org
> > > [mailto:owner-stds-802-3-
> > > > efm@xxxxxxxxxxxxxxxxxx] On Behalf Of Thomas.Murphy@xxxxxxxxxxxx
> > > > Sent: Friday, August 23, 2002 1:57 AM
> > > > To: stds-802-3-efm@ieee.org
> > > > Subject: [EFM] Minutes of P2MP Optics conference 22nd Aug 20002
> > > >
> > > > Hello All,
> > > >
> > > > First off I apologise for sending this mail to the
> > > > EFM reflector, however, a number of issues arose which
> > > > are relevant for other groups.
> > > >
> > > > The next phone conference is planned for next Thursday
> > > > at the old time of 11:00 Eastern
> > > >
> > > > Regards
> > > >
> > > > Tom
> > > >
> > >
> > >
> >
> >
> >