A network administrator is responsible for using the correct type of cable and troubleshooting any cabling issues. In this video, you’ll learn about cable shielding, plenum-rated cable, serial cables, cross-over cables, and more.
In networking. You’ll use many different cables that are used for many different purposes, so we need to understand exactly the specifications associated with those connections. For example, the speed or bandwidth of a connection is the theoretical maximum data rate. It is 100% of the data that we would be able to put through that particular connection at any particular time.
On the networking side, we tend to measure this in bits per second. So if you look at an Ethernet cable, it might be a 100 megabit per second Ethernet cable or a gigabit per second Ethernet cable. You can think of the speed, or bandwidth, as the total size of the pipe that we would put data through.
We would describe the amount of data we’re putting through this pipe as the throughput. It’s the amount of data transferred in a particular time frame. And again, we commonly refer to this in bits per second.
If you ever look at file transfers occurring in an operating system, they tend to specify it in bytes per second. So if you’re troubleshooting a problem, make sure you understand whether the information provided to you is in bits per second or bytes per second. And with all of our Ethernet standards and other types of connections, we have a maximum distance that our cable might be able to go. For example, with 1000BASE-T, you can go 100 meters over category 5 or category 5e.
All of these distances will be based on the standard that you’re using and the type of cable that you’re using. And when we talk about copper Ethernet cabling, we’re often referring to either unshielded twisted pair, or shielded twisted pair. This top picture is an unshielded twisted pair cable. You can see there’s no shielding around these four different pairs of cables. But all four pair are twisted, which is why we refer to that as unshielded twisted pair.
On the bottom is a shielded cable. You can see the metal shield that’s going around the four pair. But again, we do have four pair of cable, and all four of those pairs are twisted. The shielded cable, also, has a grounding wire that you can use on one side of the connection.
If you look at the outside of the cable, you’ll see abbreviations that describe how this cable is constructed. For example, if you see the U, it would be unshielded twisted pair. S means that it is braided shielding. And F is referring to foil shielding.
We usually will write this as the overall cable, a slash, the individual pairs, and then twisted pair. So if the overall cable is braided shielding, you would have S, a slash– if the individual pairs are foil shielding, you’d have an F– and then TP. So if you happen to have braided shielding around the entire cable and foil around the pairs, then you refer to this cable as an S slash FTP.
If there’s foil around the cable and no shielding, very similar to this bottom picture, you would refer to this as F slash UTP. On this cable, you can see the writing on the cable. This is a category 7 cable and it is S slash FTP. That means there is a braided shielding along the outside and then foil shielding for each of the pairs of wires.
A lot of the cables that we use will go into the ceiling and then, finally, make their way to a wiring closet or data center. The type of cable we put into the ceiling will differ depending on what else might be in that ceiling area. For that reason, it’s important to know whether the ceiling has a plenum or does not have a plenum. It’s common to have a work area. There might be a false ceiling in that work area and above the false ceiling, you might have air ducts or plumbing pipes.
In this example, we have an air supply that is being brought in through ducts. And then we have an air return that is also being provided through ducts. In this example, your return air is through an air duct, and so it’s not shared with any other part of the infrastructure above that ceiling.
This means that if we have a fire in this building, our network cables that are in this non-circulating airspace above the false ceiling would not be mixing with any of the oxygen available in the forced air supply or the forced air return.
If there is a plenum, then there is a shared airspace for all these different components. You might have a forced air supply that’s coming out of vents. But notice, that the forced air return goes into a general area where you might have pipes, your network cables, and other infrastructure components. If there is a fire, you would have an oxygen source that would be in the same airspace as your network cables, and so there would be a special type of network cable designed for a plenum area.
The concern is that if the network cable catches on fire in a plenum area, then smoke and toxic fumes could be sent to other parts of the building. This means that if we’re running a network cable in this plenum area, we want to use this plenum-rated cable because it will have a minimum amount of smoke and toxic fumes to add to the overall airspace.
A traditional network cable has a jacket around the cable that’s usually made of PVC, or Polyvinyl Chloride. A fire-rated cable jacket, or a plenum-rated cable, has a Fluorinated Ethylene Polymer, FEP, or a low-smoke polyvinyl chloride, PVC. These are designed for the plenum. And if you get a plenum-rated cable, it will be one with FEP or the low-smoke PVC.
Unfortunately, you might find that the fire resistant materials in this plenum-rated cable make it not as flexible as a non-plenum-rated rated cable. So it’s important to plan for that limited bend radius when you’re designing where you’re going to put your cables.
We often see plenum-rated cable used in the plenum and, occasionally, in risers between floors. This limits the smoke that would be in the plenum on one floor. And it would limit the ability of the fire to be able to spread to other floors through your network cable.
If you look through the bag of any network administrator, they’re not only going to have Ethernet cables with them, they’re also going to have console cables with them. These console cables are usually serial cables. And there are many different connectors that you would use on these serial cables, some of the most common are DB-9 and DB-25 connections. The D is referring to this type of connector. It looks like the letter D. And the number that’s at the end refers to the number of pins that are available on that connector.
We, commonly, send RS-232 signals across these DB-9 or DB-25 connectors. It’s a very standardized serial type of connection, and it’s been around since 1969. In the past, we’ve used these RS-232 connections for modems, printer connections, mice, and almost anything else we were plugging into our computers. These days, if you see a DB-9 or a DB-25 connection on a switch or router, it’s commonly used as a management or configuration port.
With some older equipment, especially Cisco networking equipment, you may find that instead of using a serial connection, you’re using a rollover cable. You might refer to this as a Cisco console cable or a Yost cable.
This is a standard that allows us to use an RJ-45 connection to be able to manage the switch or router connections on a management port. This is often used in conjunction with a serial port connector that might be on a laptop or a desktop computer. On the switch or router, itself, is a console connection with an RJ-45 link. And if you see that, it’s very possible that you’re using a rollover cable.
In some situations, you may find it easier to plug into a router’s Ethernet connection instead of using a serial port or a management port. In those examples, you’re going to need a crossover cable to make the link between your device and the router interface. A crossover cable has a different pin-out than a straight through cable you would use on a normal Ethernet connection.
But if you don’t have a serial cable with you, this could come in handy as an alternative to plugging in to that router. This is another reason why network administrators might carry a straight through cable and a crossover cable or, at least, have an adapter that would allow them to convert a straight through cable into a crossover connection.
We’re putting an increasing number of PoE devices on our network. PoE is power over Ethernet, where the device gets its power source directly from the Ethernet cable. This means that a single cable can provide both the network connectivity and the power for one of these remote devices.
This means if you’re installing a voice over IP phone, a camera, a wireless access point, or some other type of device, you wouldn’t have to run an additional power source. You would, simply, plug in your PoE Ethernet connection.
This power on the Ethernet cable can come directly from the switch. If you have a PoE switch, it will put the power right on the cable. We refer to that as an endspan. But if you’re not using a PoE switch, you may need a separate piece of equipment called an injector that will add the power to the Ethernet connection. We often refer to these as midspans.
There are a number of different ways to put power onto an Ethernet cable. Mode A uses a common-mode data pair power, where the power is being put on the same wires as the data. There’s mode B, where if you have spare pairs in your cable, especially if you’re running 100 megabit Ethernet, you can put the power on the remaining pairs on that cable. And 4-pair is using power on all four of the data pairs, which is very common if you’re using gigabit Ethernet.
The original PoE specification was part of IEEE’s 802.3af. It was introduced in 2003, and it has now been integrated into the 802.3 standard. It provides 15.4 watts of DC power with a 350 milliamp max current.
An update to that standard is PoE+. This was introduced as the IEEE 802.3at in 2009. It has, also, been added to the 802.3 standard. And it has an increased number of wattage, 25.5 watts of DC power with a maximum current of 600 milliamps.
And PoE++ is the IEEE 802.3bt standard, which was introduced in 2018. It provides 51 watts of power over a type 3 connection, with a 600 milliamp max current and 71.3 watts over a type 4 connection with a 960 milliamp max current. This is the standard you would probably see if you were running power over Ethernet over a 10 gig Ethernet connection.