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Showing posts with label Practice - Lab - Learning CCNA. Show all posts

Sunday, July 31, 2011

How the Application Layer Works

In the previous section we reviewed several aspects of the Transport Layer. We learned a great deal of information; covering sockets, ports, TCP, UDP, segments, and datagrams. Now we will take a look at the fourth and final layer of the TCP/IP stack: the Application Layer.

The Basics of Network Cable Testing

If 90% of all problems in a network are on the Physical Layer, then it isn’t any surprise that cable testing has become quite important in the industry. And although it may sound simple to test a pair of cables for faults, actually troubleshooting wire maps, crosstalk, propagation delay, or insertion loss can be more than headache-worthy. And thus, understanding how to troubleshoot these problems saves time, yet also supplies good information to prevent common mistakes in the future.

How to Avoid Crosstalk

You’ll come to find that the most common mistakes are usually the simplest to avoid. For instance, crosstalk is very commonly created when connectors are not installed properly at both ends of the cable. Crosstalk is the effect we get when electromagnetic energy from one cable leaves an imprint on adjacent cables. (You’ll often see this referred to as “noise.”)This usually isn’t a problem, however, since we twist wires inside Ethernet cable to cancel out this effect. So how, then, does crosstalk become such a problem?

You’ll notice that the Ethernet cable on the right has too much wire left over- we actually need to crimp the connector to the point where no internal wiring is visible. It’s important to note that while the wires do need to be separated to properly install a connector, they should only be separated as little as possible. Otherwise the lack of cancellation will create crosstalk- and possibly cause hard-to-track failures in a network.