types of internet connectivity

[the_prashn]

In what ways do ISPs connect to Internet.

I heard about OC3 and OC12 but not sure if they are the only ones and also what is the difference between them.

What are the technical questions to ask a Data Center salesman who says they are the best? Any online tutorial/article available?

Thanks very much!

[Variable]

ISP's are no different from anyone else needing bandwidth, they just buy bigger pipes from companies. These are called backbones.

Here is a breakdown of line speeds
http://www.cybercon.com/connection_wan.html

For a datacenter, you want to know if they have at least two different backbone providers. You could have an OC3 to one backbone provider and a fractional OC3 to another. Their backbone providers should be different companies, with different hardware and connectivity. If one company’s lines go down, you switch to your other provider. ISP's use BGP to monitor and switch connections to different backbones based on whatever criteria they have, one being a loss of signal.

How much speed they have is usually not relevant. The question is how much they use, versus how much they have. You will be rate limited anyway, so their max throughput is not really a way to measure anything. That is like asking your city how many cars they can handle on the main highway, as a way to measure if you should live in the city. What you should ask is how much traffic they have on their highway. But that analogy only gets you so far, because ISP's can always buy more bandwidth easily, while the city cannot build more highways easily. However, it gets the point across.

A datacenter should have redundant systems for power, AC, bandwidth, etc. Each individual system should be able to provide necessary service by them selves if one system fails.

[the_prashn]

Thanks much.

So should I ask an ISP that is trying to sell me some servers this way "How much traffic exists on your connection"? (If that is a right question, in what metrics should I get the response? Percentage?).

Also, when you say "Rate Limited" - does that mean that "if a client is connected at a lower speed, anyway the server network has to exchange the data at the same level"? (If so, do ISPs provide me a report on at what speends are clients accessing the server network)?

Thank you in advance!

[Variable]

I would ask them what their average daily load is. They know what that is. You can compare that to their total capacity. Bandwidth is measured in Mbps. If their average load is 60Mbps and they have a capacity of 155Mbps you can see that they have extra capacity for peaks.


Also, when you say "Rate Limited" - does that mean that "if a client is connected at a lower speed, anyway the server network has to exchange the data at the same level"? (If so, do ISPs provide me a report on at what speends are clients accessing the server network)?


No, when you set up servers your contract will specify a fixed amount of bandwidth per month and probably a rate-limited connection speed. So you will be given a monthly maximum and a real time maximum. Most people who put servers in datacenters do so because they are non technical and want someone else to handle that part of the business. Their view of what a "server" doing their important business tasks would require in the way of bandwidth is based on the speed they have on their home router. If they get 6 Mbps on their home cable modem their server in a datacenter would need to handle 600 or a 1000mbps per second. It is usually a baseless assumption, unless your youtube. Which you are not. So lets say you get a contract for 5 mbps rate limited with a monthly cap of 150GB. In order for the datacenter to handle your load they would need a whopping 5 Mbps of extra capacity to handle your servers. It is very likely that your servers average throuput will be a small fraction of that. I see it all the time.