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RE: [EFM] Necessity of DBA mechanisms ...

Well, I think it is highly likely that the EPON requirements will change the
PHY silicon.

There is a spare 100M (even with 'cheap' optics), so why not use this for
circuits with a TDM mechanism, and leave the 1GE as it's original,
traditional, full duplex, stat. muxed mode. Most of the fiber can handle
2.5G, so muxing up to 1.11M would be simple enough.

I have the opinion that at least one EPON contributor has technology that
works like this (not I), and they just haven't presented it yet. The PHY
level muxing technology that I could contribute is designed for p2p, but
could be adapted for p2mp I'm sure.


-----Original Message-----
[]On Behalf Of Harry
Sent: 16 July 2001 17:49
To: 'Menard, Francois'; Ajay Gummalla
Subject: RE: [EFM] Necessity of DBA mechanisms ...


I agree that P2P topologies may not present the DBA challenge.

However, wasting 20% on a Gigabit link represents 200 Mbps - compared to 2
Mbps on HFC. Hence the need to use intelligent b/w allocation on ePON

VoIP will require the use of various compression algorithms, not just G.711.
Hence, the ePON link will need to support isochronous traffic with arbitrary
periods. This requires dynamic b/w allocation, not a rigid TDM scheme. The
same applies to IP video with its periodic variable size grant needs.

B/w overhead associated with dynamic requests can be further reduced if a
traffic flow parameters are described a priori. An example is an isochronous
traffic flow which requires
grants of fixed size at periodic intervals - without explicit requests sent
by ONUs.

In addition, the request/grant scheme offers direct feedback of ONU state,
including such critical measurements as queue occupancy.

In general, I have a feeling that those of us familiar with DOCSIS tend to
favor the dynamic request/grant protocol approach, while those that are not,
favor reinventing the wheel.


-----Original Message-----
From: Menard, Francois [mailto:f.menard@xxxxxxxxxxxxxx]
Sent: Monday, July 16, 2001 7:24 AM
To: Ajay Gummalla
Subject: RE: [EFM] Necessity of DBA mechanisms ...
Importance: High

Ajay wrote: > It seems to me that there is a consensus in this group that
dynamic adaptation is required though there are differences on how
exactly and on what time scale the adaptation is done.


In EFM, there are 3 issues, and DBA may only apply to only one of the three:

Issue #1) For P2P EFM, DBA is clearly not an issue.
Issue #2) For P2P EPON, DBA is clearly not an issue
Issue #3) For P2MP EPON, DBA may be an issue,

For those of us not seeking that IEEE wastes time delaying issues 1 and 2 in
order to develop products surrounding issue #3, saying that there is
consensus in this group that DBA is required is not accurate.  Saving 20% of
bandwidth at Gigabit speeds is not as crucial as saving 20% of bandwidth
over bandwidth-limited HFC systems.  The complexity and costs associated
with shielding DBA head-end grants with security mechanisms protecting them,
do not represent, in my view, an effort that is worth the costs of more
expensive CPE and head-end equipment for EFM.

My personal agenda with EFM is being distracted by those seeking DSL EFM and
those seeking the development of P2MP EPON.  I do not claim however that one
of my specific issues represent "consensus in this group".  One of the merit
of dealing with all EFM issues as a whole right now is that we can discern
what constitutes consensus from what does not.  We agree that minimal
modifications to the MAC for O&M to indicate link failures and signal levels
are a good idea.  We also agree that single-strand tranceivers are worth
standardizing.  While we have discussed this, little discussions surround
how 802.1s/w/x will integrate to EFM.  We need to look at this from a
systemic point of view.  While mine surrounds FTTx P2P EFM, others may have
different priorities for different markets.  I am willing to consider that
issue #1 is being delayed, but not at the expense of seeing claims of
consensus being reached on issues which I think have nothing to do with
ensuring the development of cost-effective FTTx P2P EFM products.

> If a Voice packet arrives behind a large data packets, mechanisms to
voice packet ahead of the data packet will be useful.

A G.711 packet arriving behind a 1500 bytes data at one megabit per second
is clealy not the same than a G.711 packet arriving behind a 1500 bytes
packet at one gigabit per second.