Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

RE: 1310 nm vs. 1550 nm links greater than 40 km

Meeting our longest distance objective requires at least 40 km distance
capability. This objective could be achieved without amplification,
dispersion compensation, or regeneration. These additional techniques appear
to be required to support link lengths beyond 40 km. But achieving distances
beyond 40km, while possibly useful, is beyond the requirement. Therefore
802.3ae is not REQUIRED to address the specifications for any of these link
extension elements or to provide PMD functionality that ensures
compatibility with these elements. While 802.3ae is not required to do so,
it is also not prohibited from doing so, if that is the will of the task
force. But we must recognize the additional work load this may represent and
the resultant tightening of the 40 km PMD specification that could result. 

Link extension techniques like optical amplification and dispersion
compensation do not necessarily tighten or change the requirements on the 40
km optics if 1550 nm nominal wavelength is selected. But, embracing these
techniques in the standard means addressing the concept of engineered links,
which is a new area for 802.3, and could involve much work. If we choose
1310 nm nominal wavelength, then the most commonly deployed optical
amplification devices would not work, so additional power budget is required
to exceed 40 km. But on the plus side, dispersion compensation would not be
needed for 1310 nm systems, so we avoid dealing with engineered links. The
task force must reconcile these choices as we make PMD selections. At this
point it seems that the 1550 nm route is in the lead, but the wavelength
choice trade-offs have not received vigorous debate at the standards
meetings, only to a small degree on the reflector. 

My suggestion for those who wish to employ regeneration would be to rely on
transport thru SONET/SDH compliant systems rather than impose ever more
stringent requirements on the 802.3ae 40 km PMD. Otherwise we risk imposing
SONET/SDH cost structures on Ethernet. 

Paul Kolesar
Lucent Technologies

	From:  Savara, Raj [SMTP:RSavara@xxxxxxxxxxxxxxxxxxx]
	Sent:  Wednesday, May 31, 2000 5:56 PM
	To:  'Bruce Tolley'; vipul.bhatt@xxxxxxxxxxx;
	Subject:  RE: 1310 nm vs. 1550 nm links greater than 40 km 

	As a PMD supplier, I agree with your statements.  The SONET
infrastructure is in place and for 40km and greater distances, the 1550nm
solution is the only way to go. 

	 I am interested in seeing any jitter data to support multable
regeneration without SONET compliant transmit jitter for the long reach
applications.  The VSR applications may not need the jitter as stringently
specified if no regeneration is to be done.  I would like to see some feed
back on this from the group.


	Raj Savara 
	Network Elements Inc. 

	-----Original Message----- 
	From: Bruce Tolley [ mailto:btolley@xxxxxxxxx
<mailto:btolley@xxxxxxxxx> ] 
	Sent: Wednesday, May 31, 2000 2:06 PM 
	To: vipul.bhatt@xxxxxxxxxxx; stds-802-3-hssg@xxxxxxxx 
	Subject: Re: 1310 nm vs. 1550 nm links greater than 40 km 


	We have an objective as a task force to support a distance of at
least 40 
	km over SM fiber. 

	On the basis of discussions with multiple customers especially
	providers over the last year, I have determined that the market
	exists to support distances of 50 to 70 km on SM fiber. 

	Therefore, I support the PMD that can go much further than 40 km and
	to existing infrastructure: 1550 nm serial. 


	Bruce Tolley 
	Enterprise Line of Business 
	Cisco Systems 

	At 12:11 PM 5/31/00 -0700, Vipul Bhatt wrote: 

	>I would like to respond to a couple of comments made on this 
	>reflector about the possibility of using 1310 nm wavelength for 40 
	>km Serial links. I think we should stay with 1550 nm. 
	>Following a presentation I gave at the 10GEA Santa Clara meeting, 
	>and also during Serial SIG discussions, the feedback I have
	>from many members is that for Metro Area Networks, it is desirable 
	>to be able to extend the link distance beyond the stated 40 km
	>Metro Area links capable of supporting distances beyond 40 kms will

	>be a significant potential application of 10G Ethernet. This does 
	>not mean that we need to include optical amplifiers or dispersion 
	>compensation blocks in the standard, only that our link should be 
	>compatible with them. Compatibility with long distance 
	>infrastructure tilts the balance in favor of 1550 nm. Limiting the 
	>operation of this link to 40 kms will be like clipping the wings of

	>10G Ethernet. 
	>If you ask the question - "Do we want a link that is the lowest
	>solution for 40 kms, or do we want a link that is more expensive
	>capable of plugging into the long distance infrastructure?" - my 
	>recommendation is to choose the latter.