[EFM] RE: [EFM-P2MP] Point-to-Point plus Shared Media
John,
You raise an interesting and important challenge. However, if a system only
supports one view then I think one could make a case that the single copy
broadcast view is more important than the point-to-point view, at least for
the residential market. The reasoning is as follows: let us say that we are
able to do a 64 way split in a year or two. With a point-to-point service
(not emmulation) we would be limited to providing a maximum of 1000/64 = 16
Mb/s of broadcast capacity before we would run out of bandwidth. It would be
even less in practice as we would need to leave some capacity open for data
and administration. 16 Mb/s is not even enough to broadcast one HDTV channel
and no capacity for NVOD. If we ever get to a split of 128 the situation
gets worse.
Am I right in assuming that the worst inefficiency that would happen by
reflecting all upstream traffic on the downstream is 50%? This seems like a
much smaller penalty to make than the drastic limitation that would occur
with not permiting true broadcast.
Of course we could allocate a separate wavelength for video broadcast, but
that would be a severe restriction on how service could be deployed. Even
then, there are data broadcast services that would very rapidly eat into
downstream channel capacity.
John Limb
-----Original Message-----
From: owner-stds-802-3-efm-p2mp@majordomo.ieee.org
[mailto:owner-stds-802-3-efm-p2mp@majordomo.ieee.org]On Behalf Of John
Pickens
Sent: Tuesday, November 20, 2001 12:49 PM
To: Norman Finn; stds-802-3-efm@ieee.org; stds-802-3-efm-p2mp@ieee.org
Subject: Re: [EFM-P2MP] Point-to-Point plus Shared Media
Good clarification.
I would like to study one additional question related to this topic.
How can an operator offer the benefits (in the EPON link segment) of both
point to point AND point to multipoint to a single endpoint beyond the ONU
(e.g. personal computer concurrently a. viewing a 20Mbps HDTV video and b.
engaging in a 400Kbps point to point instant messenger video/audio session)
and also maintain the link efficiencies gained by point to point.
It is certainly possible to maintain separate networks to the end point -
separate MAC in ONU, separate 100BT port in the ONU, separate ethernet
LANs, and separate NICs in the personal computer (even better, separate
personal computers). What is less clear is how to converge the networks -
and configure the networks (PC, LAN, ONU, OLT) so that the "right" traffic
traverses the "right" path (instant messenger traverses point to point;
HDTV traverses shared media).
It is also possible to limit the options here and say that an ONU can be
either shared only or point to point only. And to say that if
single-copy-broadcast attribute of the media needs to be accessed, that it
is acceptable to operate in shared mode (up to 50% reduction in link
capacity if all ONUs require single-copy-broadcast).
I know there is a contingent within the working group that does not
consider it a requirement to access the single-copy-broadcast attribute of
the media, so probably we should poll this question at some point.
J