I am working with some colleges in another geographical location on connecting two satellite locations to a co-location facility. We are going to be moving all our server infrastructure to the co-location facility. They are talking about putting a "transport connection" in from my location is FL to the co-lo in PA. They described the "transport connection" as essentially a really long ethernet cable to connect the sites. My question is what is this technology that is being implemented and how does it work

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    – Ron Maupin
    Aug 8, 2017 at 15:46

1 Answer 1


They have described the technology ("a really long Ethernet cable") pretty accurately. Typically transport in this case is referring to "lit services" by a provider. The technologies used will vary widely depending on a number of factors, including the provider, the geographic area, etc. but the most common instances I've seen are the following:

1) The provider gives you an Ethernet handoff/presentation (typically fiber, but sometimes copper) and then they will carry your signal across their backbone by turning it into a *WDM (not necessarily the technology used, but it's probably the most common) signal on their network, and then they'll spit it back out to you as another Ethernet handoff at the other site.

2) If the two locations are geographically close enough, the provider may not bother with using *WDM and carry it across their metro Ethernet backbone either as a VLAN or pseudowire service such as a VLL - this is frequently used for peering if an exchange or entity is in one colocation and the entity wanting to peer is not in that same colocation facility, but they are in another one that's very geographically close.

Contrast this with "unlit" services (usually offered by a provider that has a lot of fiber in the ground already) where the responsibility to light the "wave", as we call them in the industry, falls on you and you alone - these are commonly used in conjunction with WDM deployments because you get more for your money out of the dark fiber.

Regarding the technology and how it works, CWDM and DWDM are just ways to multiplex multiple signals (called 'channels' or wavelengths) over a single fiber pair. You get more channels per pair out of DWDM vs. CWDM, but CWDM is always cheaper to build and deploy. WDM technologies are strictly layer 1 and are protocol agnostic, so it's entirely possible to carry Ethernet and SONET traffic on the same WDM metro ring.

  • 2
    This tends to be done with MPLS these days. Years ago, it'd would've been done with frame-relay or ATM PVCs, to create a "virtual wire" path through the provider's network.
    – Ricky
    Dec 13, 2013 at 21:09

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