Leased Lines and Metro Ethernet – CompTIA Network+ N10-006 – 1.4

| March 29, 2015 | 0 Comments


If you need to communicate outside of your building or campus, you’ll probably lease a line from a third-party telecommunications provider. In this video, you’ll learn about T1/E1, T3/E3, OC-3/OC-12, and metro Ethernet leased lines.

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If you’re in a business and you’re connecting multiple sites together or you need to connect your organization to the internet, you’re probably leasing a line from a third party to be able to provide this connectivity. And in this video, we’ll look at many different ways for providing some of this leased line connections.

A type of leased line that’s been around for a very long time is the T1 and the E1. T1 stands for T-Carrier Level 1. It uses time-domain multiplexing to send traffic from one site to the other. And you commonly see T1s in North America, Japan, and South Korea. A T1 has 24 channels. And each channel can transmit 64 kilobits per second. And you put all of that together, and you have a total amount of bandwidth on a T1 of 1.544 megabits per second as a total line rate.

If you’re elsewhere in the world, for instance in Europe, you have the E1. E1s have 32 channels, again 64 kilobits per second, giving you a total of 2.048 megabits as a total line rate over an E1. The upgrade to the T1 and the E1 are the T3 and E3. A T3 stands for T-Carrier Level 3. It’s usually brought into your facility over coax. So you still have a copper connection for these. And there’s usually BNC connectors on the coax that’s provided by the leasing carrier.

If you ever hear someone referring to a DS3 connection, that’s really referring to the data that’s riding on a T3, but we tend to use those terms interchangeably. A T3 combines 28 separate T1 circuits into this single T3 link, giving you a total bandwidth of 44.736 megabits per second. An E3 is combining 16 E1 circuits into this single piece of coax. And that gives you a total bandwidth of 34.368 megabits per second.

Here’s a summary of the T1, E1, T3, E3 networks. You can see a T1 has 24 channels at 64 kilobits per second each, giving us about 1.5 megabits per second of bandwidth. An E1 is 32 channels, again 64 kilobits each. And if we do the math, it’s about two megabits of total bandwidth.

A T3 is 28 T1 circuits. And if we know there are 24 channels in a circuit, that is 672 T1 channels for 44.736 megabits per second. And an E3 is 16 E1 circuits or 512 E1 channels, giving us 34.368 megabits per second of bandwidth.

In an earlier video, we talked about SONET and SDH-based networks. And you’ll still see these used for leased lines from a telecommunications provider. As a reminder, the STS-3 or OC-3 links would give you a bandwidth of 155.52 megabits per second. And an STS-12 or an OC-12 connection provides you with 622.08 megabits per second of bandwidth.

An increasingly popular leased line is one called Metro Ethernet. This is ethernet that you would connect in a regional area or a city area and be able to simply have ethernet at both ends of the connection. We would normally use a T1, or E1, or some other type of WAN. So this is not something that you commonly see, but you can obviously see the advantages. All of your equipment already has ethernet on it, so why not simply plug-in and not use any additional equipment just to connect sites together.

Although it’s certainly possible for a telecommunications provider to give you pure ethernet from one site to the other, it’s more likely that there’s some other kind of networking technology in the middle. There’s probably ethernet over SDH. They may be doing MPLS in the middle of this network, or it might be DWDM, and they’re simply providing you with ethernet on either side.

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Category: CompTIA Network+ N10-006

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