Help understand WAN connections. What really is going on in that cloud

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May 29th, 2008
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Hi i having trouble understanding the concept of a WAN connetion.

how do ISP's run a leased t-1 line all the way from CAlI to NC or such...

i just dont get that..

i knows the cable isnt 3000 miles long.

Does the ISP have mutilple locations in the U.S. and connect to them., (one in NC, one in TN all the way to california)

or actually how does this works.??

please someone shed the light

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cisco_lad2004 Thu, 05/29/2008 - 05:47
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what typically happens in WAN cloud is few ISPs peer together to extend the rechability.

within a given ISP, it is not any different from a campus (not strictly correct), you link up routers and core switches within limits and build up or stretch as far as geographically and financially possible. there are distance limitations, I believe for fiber we can get as far as 80-100Km on P2P fiber. Some ISPs use transmission equipment so it makes look that you have a line between NY and Paris and only 2 routers in between.



phswrestler125 Thu, 05/29/2008 - 08:05
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so different ISP are linked together.

So their core swtiches and routers are connected by Fiber huh??

this fiber can run up to 100km right?

do they run the fiber in the ground? or ar they up in the sky with the power lines?/


cisco_lad2004 Thu, 05/29/2008 - 09:17
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ISPs are connected together, its called peering.

Fiber runs between 80-100km between router to router, but can be extended to a lot more when transmission equipment is used.

Fiber is typically dug down.



blakeman Thu, 05/29/2008 - 11:49
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One thing to keep in mind is that ISP's don't use their own fiber (or copper) to connect over these great distances. They contract with an AT&T or Verizon to provide the telecommunications link. You can bet that it's fiber all the way, except for the demarcation on each end with the ISP. For a basic T-1, it'll be a RJ-45 copper cable for those last few feet. Bigger pipes will most likely require fiber to the CPE (Customer Premise Equipment), but that will depend on the equipment in use, and the ISP's logical location on the carriers facilities. I would think most "decent" ISP's sit on top of carrier SONET rings and can jump on the carrier's network, riding fiber all the way. Depending on their needs they may have multiple paths for redundancy. No ISP is going to dig their own fiber in the ground from California to North Carolina.

Hope this helps.

phswrestler125 Thu, 05/29/2008 - 14:28
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oh ok thanks for that info.

It really helped.

I also understand when you purchase a WAN connection from an ISP such, as a leased line t-1 , they are used for a logical point to point connection from lets say CA to NC.

and this is all connection by the companies router's serial t1 with an external CSU/DSU or a router's wic t1 rj48 port connected directly to the ISP wall jack that they isntalled in your corpations.

Now if i have this leased t1 line from CA to NC. it could only be used for communication between CA and NC and vise versa. Is that correct?

if that correct, then you could use a leased t1 line for internet could you, becuase you could be connecting to multiple web servers all across the world.

or could you have a lease t1 line that could connect to the internet? to allow constant t1 speeds to many other web servers, instead of just CA to NA ??


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