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AW: [EFM] RE: Wavelength allocation

Hi Gerry,

Thanks for the feedback.
I have interleaved some responses in the text.


-----Ursprüngliche Nachricht-----
Von: gerry.pesavento@xxxxxxxxxxxx [mailto:gerry.pesavento@xxxxxxxxxxxx]
Gesendet am: Donnerstag, 26. Juli 2001 00:55
Betreff: RE: [EFM] RE: Wavelength allocation

Hi Tom,

Thanks for the good comments. I have a question about your last sentence:

> A minimum aim of the group could be to make provision
> for such an overlayed analogue video delivery system.

I'd like to know what you mean by "provision" here.  Do you mean (a) just
leave the window open for indeterminate usage out of our scope or (b)
engineer it into the spec?  I prefer (a), because writing a specific
provision for analog video overlay (b) offers these dangers:

T.M. I may not be necessary to go into the detail
of "do it this and that way". One could envisage
intelligent allocation of a window and wavelength guardband so that based
on isolation requirements for analogue video (or other digital services) 
that filter manufacturers can produce the goods. This is following the G983.wdm
approach where they say 'these are the windows' and with other
issues they just make recommendations.

(1) it requires extra margin in the optical power budget

T.M. Not sure I understand this point. Analogue video will have of course
a higher power requirement. However, this is likely to be a provider issue?
If digital services were provided, the power budget difference
across the window is minimal and the 'digital' values would not change.

(2) it eliminates 1550nm as a PMD option

T.M. Yes and no, but is this really an issue?.  The possibility of a one channel 
downstream solution will still exist, at 1490 or 1550nm.
The technical issues of DFBs at 1490 and 1550nm are the same.  If cost issues exist
its just because of the current higher availability of 1550nm pieces. An 'old' ONU BiDi
will not differentiate between incoming digital data at 1490 or 1550nm.

(3) it would logically apply to both P2P and P2MP PMDs? 

T.M. Yes, but I think that the business case is not so interesting for the
P2P case becasue the OLT costs are not split
between 16/32 end users. Perhaps in a business environment.

(4) increased isolation is required for analog video, which comes in very
"hot" following an EDFA.  Analog video requires 40 dB isolation. 

T.M. Yes, but this is a manageable issue .

(5) Blocking filters may be required for subscriber nodes that may not use
an overlay wavelength.

T.M. True, but we envisage a relatively small cost increase between 2 port
and 3 port devices. A nice approach would be to install 3 port optical devices for
a user who only wants 2 port services and use the 2nd WDM filter as a blocking filter.
When the customer sees all the cool services his neighbours have and wants an upgrade,
hey, half the equipment is already there!

(6) APC (angled connectors) would become a requirement to deal with an
analog channel sensitive to reflections. 

T.M. These are already in use in the 2 and 3 port components. I am sure
that this problem can be minimised at the other sections of the link.

(7) This discussion will turn to upstream return traffic from cable modems,
which can add further complications (4th wavelength, synchronization, etc).

T.M. Not necessarily. If we are talking about normal TV services delivery,
than we are just duplicating the electrical signal that already comes out of the wall.
Hence, we don't have a problem of stranded investments.
For cases of VoD etc, there is already an upstream channel in place
which could take care of this.
(8) it is perhaps another sidetrack away from pure Ethernet P2P and P2MP

The point I am making is that an analog video "provision" written in a
specification for WDM overlays comes with additional system cost, complexity
and restrictions, not just component cost.  But this depends on what you
mean by provision - what is your thought?   

T.M. Yes it will cost a little more and yes it will bring more
work but the business case for full video services to the home
is so darn attractive that I thing its worth the effort.
The way I see it is, for FTTH to work we need to provide
a full range of services, at least better than the current situation and
then start with the extras! Without a wavelength overlay (i.e. streaming video) 
when we start talking about CATV, DBS and VoD (not to mention HDTV), those bits are eaten
up very quickly, leaving very little pure Ethernet for the user.

Gerry Pesavento
Alloptic, Inc. 

-----Original Message-----
From: Thomas.Murphy@xxxxxxxxxxxx [mailto:Thomas.Murphy@xxxxxxxxxxxx]
Sent: Wednesday, July 25, 2001 9:37 AM
Subject: Re: [EFM] RE: Wavelength allocation


I agree that wavelength allocation can become a pretty 
complex discussion when we start to get into wavelength grids definitions
etc etc.
However, I don't think we have to go this far to have some
of the benefits of an additional channel downstream. For example, integrated
ONU optics
components (and almost a standard) are available for separating two incoming
where one channel could carry analogue video.
The expected increase to ONU optics costs are not so high and
costs at the OLT are shared amongst all users. 

A minimum aim of the group could be to make provision
for such an overlayed analogue video delivery system.


Tom Murphy