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How can ISPs on one continent connect to ISPs on another continent? From a physical layer standpoint? Say one ISP is located in Asia and another one in Europe how would they connect their fiber optic cable to exchange traffic? Also how would they connect physically through IXP (Internet Exchange Points) http://en.wikipedia.org/wiki/List_of_Internet_exchange_points_by_size Do they have to drag their fiber optics cable all the way to these locations?

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up vote 15 down vote accepted

There are a number of things ISP's do:

  • drag bundles of fibers across continents. Since this is very costly, only a smallnumber of very large companies do this and many ISP's rent fiberpairs from these companies
  • rent capacity (a wavelength, VLAN, MPLS circuit, etc) between to an IXP from a company who owns (or rents) fibers. Since capacity on fibers is shared, this usually is less costly
  • buy IP transit from a transit provider. These transit providers typically have their own global connectivity. Transit providers can offer ISP's routes to the entire internet, so an ISP does not have to be present on every IXP to connect to every other ISP on the planet.

The last option is most common. There is only a limited number of transit providers who don't buy transit from another ISP, they're usually called Tier 1. Most ISP's combine IXP connectivity and IP transit for their global connectivity.

Edit: Here's a real world example: I used NLNOG Ring's ring-trace to create a graph of how networks around the world reach Facebook's network. ring-trace to www.facebook.com.

As you can see from this example, a lot of networks reach Facebook via DE-CIX (the IXP in Frankfurt, Germany, one of the largest in the world), but there are also a large number of networks which use Telia (AS1299) and NTT (AS2914) to reach Facebook. Telia and NTT are tier 1 transit providers.

Edit 2: Since the image is downscaled it's hard to read. here is a fullsize version.

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Say Facebook, or Google or any big player on the Internet, Would they have to buy IP transit to route their traffic across the internet from their Data Centers? Or are these companies Tier1, Tier2 or Tier3 networks? –  chris Feb 8 at 12:22
    
Considering these companies have ASNs(autonomous sytem numbers) meaning they have backbone/core networks that can sustain their own connection without the need of an ISP? –  chris Feb 8 at 12:24
    
Having an ASN doesn't say anything about the size of the network. I have my own ASN (57771) and I am directly connected only to a few other ISPs. In the end every ISP will do what is best or cheapest for them in each specific situation, even Facebook and Google. If it is cheaper to run their own fibers to a certain location then they will do that. If it is cheaper to buy transit ... etc ... –  Sander Steffann Feb 8 at 12:34
    
"buy IP transit from a transit provider. These transit providers typically have their own global connectivity. Transit providers can offer ISP's routes to the entire internet, so an ISP does not have to be present on every IXP to connect to every other ISP on the planet." So how would they go about connecting a Tier3 network to a Tier 1 network what technology would they use? Is it physical connectivity or virtual communication? –  chris Feb 8 at 12:35
    
A smaller ISP can connect directly to a tier 1 using fiber (or copper), or it can rent capacity (like a wavelength or MPLS circuit) to reach that tier 1. –  Teun Vink Feb 8 at 12:40
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