general question about metro-e ring/dark fiber

[west33637]

Hello all. I am new to optical networking and I have a question in regards to a comment that was made to me during an interview. My potential client had expressed the desire to move away from the AT&T metro-ethernet ring that their metro area office locations are currently on to dark fiber. I cannot give specifics because I dont have the specifics. What I do know is that their network contains several site locations all in a metro area, and they are all supposed to be joined to this 'metro-ethernet ring'. Apparently, they want to move from this solution to dark fiber. and again I apologize, I dont have specifics.

My questions is what exactly is a metro-ethernet ring? What is the redundancy provided by this solution at the physical layer? Is this not just an ISPs fiber network that run across the city and provides hand-offs to customer locations. Hows is 'purchasing' dark fiber a more beneficial option. Whats the difference? Is 'purchasing' dark fiber really not just leasing unlit fiber strands from the ISP or whoever is leasing it to you. Is there a difference in monthly payments? If you 'purchase'  or 'lease' your own dark fiber, will you be responsible for lighting it up? Will you be responsible for DWDM? What is DWDM in the simplest of terms and how is it different from being joined to the metro-ethernet ring? I have searched the web over and over and never get a clear answer.

Thanks, I really appreciate anyone who can shed light on this technology for me. I know that I should buy a book, but I do not have the time right at this moment and just need a quick overview.

[Tom Randstrom · Accepted solution]

My questions is what exactly is a metro-ethernet ring?

Unfortunately, there is not one answer.  Read the following fairly brief entry on Wikipedia for that Metro Ethernet can be.

http://en.wikipedia.org/wiki/Metro_ethernet

What is the  redundancy provided by this solution at the physical layer?

It can use a number of protocols, STP, RSTP, MPLS, optical switching, SONET, much of this outlined in Wiki....

Is this not  just an ISPs fiber network that run across the city and provides  hand-offs to customer locations. Hows is 'purchasing' dark fiber a more  beneficial option.

Leasing, purchasing or building dark fiber can be cheaper than buying circuits from a service provider, but it will heavily depend on the amount of bandwidth the customer is using and the locations of their facilities.  Once you have the fiber, it is yours to do as you may.

Whats the difference? Is 'purchasing' dark fiber  really not just leasing unlit fiber strands from the ISP or whoever is  leasing it to you.

Usually, people lease fiber for a long period of time.  Lots of companies, i.e. Darkstrand, Level3, Spread Networks, etc., offer fiber leasing options. 

Is there a difference in monthly payments? If you  'purchase'  or 'lease' your own dark fiber, will you be responsible for  lighting it up?

It is hard to purchase dark fiber because there are maintenance aspects to a fiber network and most customers don't want to own an entire fiber cable with many fibers.  The bulk of the cost of a fiber plant is in the labor to install the fiber; so typically, the fiber cables are installed with many fiber (432 or more).  

Will you be responsible for DWDM?

If the customer is deploying DWDM, then they will be responsible for the equipment. There are probably third-party companies you can hire to manage your network.

What is DWDM in the  simplest of terms

Think of DWDM as a way to slice a single fiber into many fibers so that multiple circuits can be carried over it. 

Instead of having 20 strands of fiber to carry a 10 - 10GE signals (2 fibers per 10GE circuit), you may use DWDM using 2 fibers, each fiber with 10 wavelengths to do the same job.

and how is it different from being joined to the  metro-ethernet ring?

Metro Ethernet can run over many types of networking equipment and media.  Optical fiber is usually the medium used in the core to support large bandwidths and distances between facilities. The fiber could be connected directly to the switches or routers.  DWDM can be used to allow scale to the network and the ability to aggregate many signals (Ethernet, Fiber Channel, SONET, etc.) across a common fiber infrastructure.   

DARK FIBER COMMUNITY

http://dark-fiber.tmcnet.com/

Hope this helps... might be more confusing...

Tom

[rayframe1 · Accepted solution]

In regards to a metro-e ring and dark fiber, the big difference is that the company you buy from sets up the metro-e network and with dark fiber you set it up and run it yourself. It seems the person interviewing you thinks he can save money and/or get better service if they buy dark fiber and do it themselves. It might not be so simple.

When the company purchased the metro-e they got a bunch of services. How that service is actually provided, by what equipment, with what redundancy, etc. etc. is up to the provider to figure out. I work for a metro-e and dark fiber provider and for metro-e we look at where our fiber is, where we have to lease fiber, where we need new fiber. Then look at the equipment, can we use the equipment we have available, then we make an offer and see if it's accepted. Sometimes users get new equipment but usually added in the core to existing equipment, it all depends on what is where and how its put together and all that affects the cost. With dark fiber customers put their own equipment on the line and run it themselves, but may still need cross-connects and a patchwork. With regards to costs you never know, depends if there's lots of fiber already built or not.

You can try to ask the provider exactly what is set up, on what equipment etc but the carriers don't have to and may not want to let you know. In terms of getting the darlk fiber you cant always get what you want. If it's really fiber all the way to every location, maybe AT&T own all the fiber or lease some or all of it. Maybe another carrier who AT&T leases from would love to sell direct to you, maybe not. More likely with dark fiber theres a few carriers to deal with and you have to patch the netwrok together. If AT&T built the last mile of fiber you might be stuck with them either way.

The person in the interview thinks they can put thier own equipment on the fiber, and run it themselves. I'm not sure if they would save much, dark fiber is expensive. It only makes sense it they have people who know what they are doing. Setting up an optical network is not for beginners it can be very complicated. The ring part probably means its redundant, that would imply you need mutliple diverse fibers to replicate what that have. It sounds like the person doing the interview is asking you if you can set up a metro-e network. If you are not sure what's in a metro-e network, you probably are not ready to set one up. Optical uses a different knowledge base than copper.

Ray

[west33637]

Thanks Ray. This was particularly insightful. If you dont mind, I may be contacting you in the future with questions as I get the feeling I may be in deep waters with this dark fiber idea that my prospective management is completely sold on.

[west33637]

Thanks so much for your response. It was helpful.