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I have been doing some research on Datacenters and this is one of term that i have yet to wrap my mind around. I would appreciate if someone in the field could explain in simple terms what exactly does it mean.

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without any context, it could mean anything –  Javier Oct 5 '10 at 17:36
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up vote 6 down vote accepted

A cross-connect is any connection between facilities provided as separate units by the datacenter.

In other words, if you rent a cage, you can run cables betweeen your various racks and they are not really considered "cross connects".

But typically a user facility is a rack. Consider the uplink to a network provider. The line that runs from you to the telco's rack is a cross-connect. Any other between-rack cable run falls in this category. Even if the datacenter is bundling network access, it's still a cross-connect. (It's also typical to have a meet-me room that is the center of all the cross-connects, it's a patch-panel room or cage.)

This matters a lot to the datacenter because the crossconnect uses their overhead cable trays and typically comes with both a setup and a monthly charge.

Update: If itemized, the charge can be $100 - $300, and can depend on various things like the type and speed of the line.

I should also add that sometimes people will unfortunately use "cross-connect" in its literal english sense when referring to any kind of a network connection, even if it's in a datacenter context. I've seen fiber metro links between different buildings and uplink bandwidth contracts quoted as "cross-connects.

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Thanks for the great answer. Also is it typical for DCs to charge cross-connect fees and what would be guesstimate of typical cost for cross connect? –  user56192 Oct 5 '10 at 18:22
    
It's starting to be more common for crossconnects to be free. IO datacenters in Phoenix do that and from my research its kinda catching on. I'd never speak with a datacenter that charged monthly fees for cross connects. One time installation charges... sure. I once talked with a datacenter that, if my memory serves correctly, charged a $900 installation fee for each cross connect to a Catalyst that provided a connection to a no-name ISP. Not even a blended line. Fortunately, I was able to stifle my laughter until after I hung up. –  Wesley Oct 5 '10 at 18:28
    
We see $50/connect with no install fee. I have also seen free - but they are the type of data center to accidentally disconnect your cross-connect because their documentation wasn't up to date. –  Doug Luxem Oct 5 '10 at 19:38
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Cross Connects are simply a link from a carrier or ISP to customers suite or rack to provide services. Most DC's have more information on them on the web page. Cross connects had mainly been on copper (Cat5e/6 etc.) but recently a large amount are on OM3 50/125 fibre cables to carry the bandwidth.

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In the context of generic data center services, a cross connect typically refers to the patched connectivity between the data center's facilities and the line of demarcation into the building.

It would often be the patched connection between your servers and the Internet access or any additional network connectivity.

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So does it refer to connectivity to telco carriers? For example if we want to get bandwith from att or cogentco or just for redundancy purposes from both would it be cross connect ? Thanks for the explanation, i m kinda new to all these so just trying to wrap my mind around it. –  user56192 Oct 5 '10 at 17:54
    
It would be the interconnect between your equipment, the datacenter, and the ISP. Both ISPs would have a single cross connect. –  Warner Oct 5 '10 at 17:59
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