Question

Setting up an extended fabric over DWDM

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A SearchStorage.com reader recently asked:

I am attempting to set up an extended fabric over DWDM. I have two 32-port Brocade 3900 switches on either end, both running version 4.1.2 Fabric OS. We have two Nortel OPTera Metro 5200 (DWDM) cards on either end. Unfortunately, I have found out that these cards do not provide local buffering, therefore, I must set up an extended fabric via the switches.

I have turned on long distance mode on all switches in the fabric. I have made sure that each port connected to our DWDM cards, is the only port used on the ASIC (since buffers are shared across the ASIC). I have attempted to set the connected ports to the L2 long-distance level (command used: portcfglongdistance port# L2 1). With all the settings in place, I am still receiving CRC errors when running various spinfab/port tests.

I believe that my problem may be that I am not currently using Extended Long Wave (ELW) SFP modules (I am currently just using 2 GB SFP LC modules).

Before I purchase a few of these modules (and the appropriate 9 micron single-mode fiber optic cables), I thought I'd confirm if others agree with my assessment of the situation. If not, what else might I be missing?

Let?s start with a couple of questions to try a fill in the blank and an important one is how far apart the Nortel DWDM cards/devices are? Knowing the distance involved is important to have a handle on how many buffers will be needed on each end to support your ISL. For example at 2Gb/sec at 60km you will need about 60 buffers and at 100km you would need about 100 buffers. Once you know the distance verify that your switch supports this number of buffers at both ends. You should not need extended long wave or ultra long range optics for distance as that is one of the functions of the DWDM device. You should have however the appropriate SFPs to span the distance between the switch and the DWDM device. Now speaking of fiber optic cabling, do you know what you db loss is over the distance being covered? The db loss is effectively the amount the light signal degrades over distance. For example if the optic cable has several connections, splices, and traverses via multiple patch panel and other devices your db loss could increase. Your DWDM vendor should be able to measure your db loss for you. While we are on the subject of cabling, 9 micron SMF is what you want to be using however you should verify the wave length spacing (nm) of the cabling to meet your needs. Finally you may want to check all of your cable connectors to make sure that they are clean and tight connections exists as dirt and dust can cause problems at 2Gb that may not have been noticed at 1Gb. Hope this helps you isolate and resolve your ISL issues. You can learn more about fiber optic essentials and DWDM in chapter 5 ?Fiber Optic Essentials? in my book ?Resilient Storage Networks? (Elsevier).