DWDM interconnects

Tue Jan 7 04:57:29 UTC 2003

Ive had an interesting offline thread.

Someone was asking how come carriers would need to stock so many 
lasers.  If they have an 8 wave network he could not see why they 
would have to have a spare for each wave length in each region.  I 
explained that without tunable lasers this was necessary.  Usually 
the customer includes it in their contract with the vendor.  The 
vendor stocks each card in a region such that they could have it 
onsite within 24hrs.  The vendor then can have 1 space covering all 
customers in the region.

I was asked why could the carrier not just reroute the lost wave onto 
another one.  Generally that was the question.

1st, yes with sonet, the carrier might have a traffic protected in a 
ring fashion.  I would say this is a waste.  Many customers may also 
have protection at a higher layer.

2nd, DWDM does not imply switching capability.  So that you could not 
have traffic from one way just "move" over to another.  DWDM 
transport gear just creates the waves and shots them down the line. 
Now, most next-gen gear coming out does have switching capabilities, 
OR the switch companies are including DWDM into the same box.  That 
means yes, if u have DWDM fed (or combined) into a switch at most big 
points, you could remap the traffic onto a spare wave.

The only problem is, this protects ONLY a failure of a card or 
particular laser.  Truth is it's far more  likely we would see a 
fiber cut.  In which case ALL those waves would have to be moved to 
spare capacity.

At this point it's pretty clear that unless you have 1 to 1 spare 
capacity someone is going to have to see an outage.  Prioritizing 
kicks in at this point.  Different service levels (ie Platinum, Gold, 
Lead) kick in.  Most lead customers would likely not be protected at 
this point. But these may be simple backup links for those customers.

I got flamed last time, but I will just say: Good, Fast, Cheap... pick any 2.

I would love to see a Bill Norton type white paper on DWDM peering. 
What it would take etc.  I know DWDM may not be up Bill's ally but I 
really thing we need to start hypothesizing about where we see this 
scaling.

David

At 21:17 -0700 1/6/03, brett watson wrote:
>>  -----Original Message-----
>>  From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu] On
>>  Behalf Of David Diaz
>>  Sent: Monday, January 06, 2003 5:24 PM
>>  To: nanog at merit.edu
>>  Subject: Re: DWDM interconnects
>>
>>  Actually I forgot to mention.  Since we have different frequencies
>>  for the lasers, you and your peer would have to agree ahead of time
>>  and stock that particular frequency or "color."  IT's a major
>>  stocking nightmare especially for spares.  The real explosion may
>>  occur as tunable lasers drop in price that can allow 8 or more
>>  different frequencies.
>
>there are nifty boxes out (have been for 8 months or so) that do
>wavelength conversion.  so the box-operator in the middle handles the
>wavelength map, and users on each end can all use the same lasers
>(colors).  they were expensive at the time I looked but I would think
>prices would have come down.
>
>but yes, cheap tunables would be great.
>
>-b
>

-- 

David Diaz
dave at smoton.net [Email]
pagedave at smoton.net [Pager]
www.smoton.net [Peering Site under development]
Smotons (Smart Photons) trump dumb photons