Until now we’ve talked a lot about the Ethernet Protocol, but we have not necessarily explored the media types which are defined by the ethernet standards. There are multiple modes of communication as well as media types relating to Ethernet that we will cover in this chapter.
All of which are topics on the CCNA exam.
Modes of Communication
First let’s discuss some modes of communication.
There are two modes of communication:
- The first one is Half-duplex where one person sends at a time or one person receives at a time.
- Full-duplex where we can be sending and receiving information at the same time.
There are many different physical layer connections which are defined by the ethernet standards one that you may not be as familiar with is something called coaxial cabling. We use coaxial cabling for connectivity between devices we would use thick net through the ceiling and thin net to come down from the ceiling to the actual devices. We would have to use BNC type connectors and attenuators in certain circumstances. You obviously still see service providers using coaxial cable today. One of the newer and more prevalent media types is twisted pair cables. Twisted pair cables contain multiple wires for which the devices use to communicate over. There are multiple types of twisted pair cabling and the cabling can either be shielded or unshielded depending upon the type of cabling that you’re using. Common applications are cat 3 for 10-megabit, cat 5 for a 100 megabit and cat 6 and cat 7 as the new standards have continued to develop. Twisted pair cables are commonly used because they are less expensive medium, readily available and easy to use. There are limitations to category 5 unshielded twisted-pair cable. The maximum transmission distance is 100 meters or around 300 feet and it uses a connection type called RJ45.
For this reason, there are other media types available called fiber. Fiber often has greater maximum distances but is more expensive to work with.
There are two types of fiber:
- Multimode fiber which is not necessarily better than single mode fiber but is less expensive than single mode fiber and does not carry the signal as far of a distance
- The other type of fiber is single mode fiber which can extend great distances, but it needs specific expertise to work with and is more expensive to implement.
You also need to be aware that there are several cabling standards that define the pinout of the wires in an RJ45 cable. Most commonly today we see the T568B but there are others as well.
There is also a standard for creating something called a crossover cable in certain instances we need to swap wires 1 and 2 with 3 and to create connectivity between certain types of devices.
For instance, if I was connecting PC to another PC, I would use a crossover cable, the same thing goes with a router to a router or a switch to a switch.
Crossover cables aren’t needed as much as they were in the past because switches now have the capability to do something called M Dix Auto or to be able to switch the signals on the cables by themselves without having a special cable.
Another important cable is a rollover cable and we use a rollover cable to connect to a router or switches console port in most cases. This is a special cable that normally comes with your Cisco device when you purchase it and is something that every engineer will most likely become very familiar with.