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RE: PMD Objectives

A few comments and a question.

Using the GbE link model approach, the distance capability of the link is
reduced by connection loss only if one exceeds the power budget allocated to
connections. We allotted 1.5 dB for connection loss in MMF links in GbE, and
MMF proposals for 10GbE follow this same approach. This amount of power is
sufficient to support a minimum of 2 worst case connections (0.75
dB/connection max). Therefore the power budgets contain sufficient power to
support at least two interconnections or one cross-connection without
incurring a distance penalty. These interconnections could, for example,
exist at patch panels, one at either end of a "backbone" cable, that serve
as a connection point to equipment cables (i.e. those patch cords that plug
into equipment on one end and the patch panel on the other end). A
cross-connection, which uses a patch cord to join the ends of two cables,
could exist, for example, between two equipment cables. 

The "Backbone + Equipment Cable" represents a link configuration that has
the following topology:

Equip ----Equip Cable---x---Backbone cable---x---Equip Cable---Equip

Where x = a connection (in this case an interconnection at a patch panel)

This topology is useful in larger COs to support links between bays of
equipment, which may be on different floors or across large rooms. And, as
you pointed out, it is certainly useful for commercial building backbone
links, especially as "risers" within buildings. 

In your delineation of the need for 30 vs 50 m, are you saying that 30 m is
more appropriate for new data rooms built exclusively for 10GbE and that 50
m is needed for overbuilds of existing data rooms? Or do I have that
backwards? If I have it backwards, please explain the rationale. If I do not
have it backwards, then I think I understand.

Paul Kolesar

	From:  Roy Bynum [SMTP:rabynum@xxxxxxxxxxxxxx]
	Sent:  Thursday, August 10, 2000 9:58 AM
	To:  Chris Diminico; stds-802-3-hssg@xxxxxxxx
	Subject:  Re: PMD Objectives


	You had sent this table to me asking for my input before you sent it
to the 
	reflector in general.  I have not had time to do that before you
sent it 
	out.  I have some very specific issues with your table.  In the
	place, as I have stated to you before, I do not believe that there
will be 
	a lot of patch panels in use except for extended distance and
	applications.  In situations where patch panels are used, the
	distance is greater because of the attenuation of the connectors in
	patch panels.

	What are you referring to as far as "Backbone + Equipment Cable"?
	than a few building "riser" and campus applications, I see little
use for 
	the 300m distance objective.  WAN PHY (WIS) interconnections will
either be 
	at the < 50m distance or at the 10km distance, depending on whether
it will 
	be used with DWDM and/or Optical Switching.

	I would expand the distance of all of your 30m applications to 50m.
	distinction should be between overbuilding existing data rooms with
	which is very near term and the building of data rooms exclusively
	10GbE which is more long term.

	Thank you,
	Roy Bynum

	At 02:15 PM 8/9/00 -0400, Chris Diminico wrote:
	>As I pointed out in e-mail to Jonathan, for completeness, we need
to simply
	>state all of the relevant application spaces and associated
distances in
	>order to address the applicability of the current set of distance
	>further the PMD discussion.
	>The table attached is my attempt at characterizing the cabling
	>10 Gb/s application space. The customer  premise cabling lengths
	>(by survey and reference). I am collecting information on the
	>lengths associated with
	>the central office and the data center. The lengths provided for
the data
	>center and central office are reasonable target values which may be
	>based on further study. Any help would be
	>  Chris Di Minico
	>Cable Design Technologies (CDT) Corporation
	>Director of Network Systems Technology
	>Phone: 800-422-9961 ext:333
	>e-mail: cd@xxxxxxxxxxxxxx