DWDM interconnects

How common are DWDM interconnects between networks

Is DWDM considered a reliable/scalable/operable carrier
interconnection technology?

Is multi-vendor DWDM (whether internal to the network or for
carrier interconnection) practical or sensible, especially
for carrier/network interconnection? Many vendors proclaim
interoperability, but does that work in the real world?


Is DWDM considered a reliable/scalable/operable carrier
interconnection technology?

Is multi-vendor DWDM (whether internal to the network or for
carrier interconnection) practical or sensible, especially
for carrier/network interconnection? Many vendors proclaim
interoperability, but does that work in the real world?


I cannot speak to commonality, but I can offer a real world scenario:

We merged two light rails consisting of Ciena and the other Fujitsu,
both claimed to be standards compliant, but somehow inoperable after the
deal was signed. After much lab work (and many a lawyer's call), we
found that they both were in fact compliant; however, watch out for the
optional parameters. Where one may leave an optional bit blank, another
may use it... Or not understand the use of it. We ended up having to use
some intermediary gear to make the conversion, extra money, but it
narrowly saved a job or two.

Some wise man once said: That's the great thing standards, there are so
many to choose from.

Just do the homework yourself, and don't leave it up to the sales


DWDM comes in many flavors, and I doubt it makes much sense to hand another
carrier a fiber with a lot of different lambdas on it (if that is what you
were asking). There are way too many variables.

OTOH, if you were simply refering to buying the use of one "wave" (or
"lambda") that is a normal product for many companys. Unlike dark fiber,
they have lit the route and are just selling you a lambda off their big DWDM
system. They may choose to price it differently if you are running OC192 on
it than if you are running OC48, bit in any case the Sonet ADM gear is up to

Your connection is very apt to be a short range 1310 into them and their
DWDM gear then will convert it to an ITU grid color up in the 1550 range and
will coordinate signal levels, etc to eliminate crosstalk with adjacent
channels. All you can mess up is your traffic.

Lambda sales will become even more popular at major optical switching
centers as realtime open markets evolve.

Finisar is finally about to ship GBIC shaped pluggable optical devices in
ITU grid colors. They will have actually, I think, two speed ranges, one for
OC3 and OC12 and the other one for GIG-E and OC48. The exact application
depends on the card you plug this generic device into. First big batch
samples this month, and full production maybe April.

The SFP (Small Formfactor Pluggable) units won't be getting ITU grid colors
for over a year later.

Finisar has been armtwisted into protecting the largest router arrogance,
especially in the 80km GBIC product space. In the more plebian range down at
the 10 km 1310 units or the local MultiMode units you will find more price
competition and should pay respectively less than $200 and $100 even in
small quantities. Molex doesn't make 80km units but does make the rest, and
cisco as well as everyone else buys from both. Don't ever say whose
equipment you are go to use a GBIC with, because they then may not sell it
to you! The DOJ has to fit in here somewhere.

On a metro area scale, I bet someone might sell you a lambda on a passive
DWDM network to some building where your service didn't compete with
theirs, and where you were using the same power same brand pluggable "GBIC"
like devices and where there was no chance for your messing up their
adjacent channels with too hot a signal. These pluggable devices will open
up many options.

But the long haul intelligent DWDM systems are juggling way too many
variables and should be under one company's management. There is too much at
risk and too easy to screw up.

Of course two carriers can and will do whatever they want between
themselves. We were the first carrier to drag an RBOC into an
interoperability test with our cisco/cerent 15454s and their whatever. Cisco
had not been certified til then to interconnect to any RBOC and was very
eager. VZ, well, they did it because the letter from their legal dept said
to. They used the Fugitsu FLMs in various sizes to test against just one
Cerent using its wide range of cards. Now VZ is using Cerents themselves.

After the grief we went through to get simple RBOC OC3, OC12, and OC48
interconnections blessed, I would hate to try adding DWDM to the mix.

It was something that came up years ago on where would peering go if traffic levels kept the growth rate exponential.

Problem is that while the equipment vendors use "standard" channel frequencies. The implementation (ie protocols) is completely different. While both companies may have DWDM equipment they must hand off standard 1310nm.

While working on designs for Bellsouth Mix, we really wanted to extend DWDM directly to the customers. At the very least we hypothesized that with a colo we could see a benefit to DWDM cross-connects (ie intra-node, hair-pinning) however we quickly ran into the vendor issue.

If you approach the vendors, the incumbents have no desire to open up their technology since they feel they already "own" the customer base. New companies such as Sycamore or ONI have to find ways to reverse engineer without breaking the law or getting sued. They then run the risk of having this engineering break during an software upgrade to the incumbent's equipment.

Sycamore's fix product for example shot DWDM waves using the nortel upgrade port. So u could use sycamore's cheaper equipment to add capacity to your network. They shot at different wavelengths to the nortel gear and therefore caused no problems to the existing network. Nortel was not amused since they would have preferred to sell much for expensive waves.

So at the MIX even though we had DWDM throughout the network, we were handing off 1310 to customers. If they did buy similar gear we could have extended the DWDM directly to them. We also could allow for CNM (customer network management) which would allow the customer to control the waves they "owned" on our network.

It would seem logical at some point that carriers need to put pressure on their vendors to not only standardize on channels and frequencies but also on a common inter-vendor transport protocol. Treating each DWDM wave as a VPN (or VLAN) for peering btw specific peers makes sense for growth.


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.

If anyone has any info on seeing price drops over the last year please share the information.


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.


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.


Gee thanks Dave.. I now understand why we always get such sucky support
from vendors that care enough about us to not assign us to just any old
account rep, but give us a lead account rep..... :wink:

Valdis is being modest. His comment to me offlist shows he has true comedic talent :wink:

Lead? Never heard THAT one before. But I bet if you tell the salescritters
to pronounce it as in 'Leadership', you could charge extra for it. :wink:

The guarentee levels I always used with the DWDM switched network when we looked were: Platium, Gold, Silver and Lead.

Lead means what it sounds like. A best effort service. We were thinking for companies looking at providing offsite backup services, they would want they absolute cheapest pricing. At this level even if THEY did not have an outage occurring event, THEY were volunteering their capacity to protect Platinum or Gold. In other words, even if they were not affected by a fiber cut, we could bump them to protect a higher level service. In return they got ridiculously cheap pricing.

I guess another way to look at it was "we" would be allowing them to ride the "spare" capacity that was there for insurance. IN return they paid very little for it. What else would u call that service level but LEAD....

Lastly, the one issue then would be that you now have the environment for oversubscription of the switched network. We havent seen that at this layer yet. Very scary if not managed correctly.