Computer Network | Cabling and Connectors

16 min readJul 26, 2021

The majority of networked systems link together using some type of cabling. Different types of networks over the years have used a number of different types of cables

All cables used in the networking industry can be categorized in two distinct groups: copper and fiber-optic. All styles of cables have distinct connector types that you need to know.

Copper Cabling and Connectors The most common form of cabling uses copper wire wrapped up in some kind of protective sheathing, thus the term copper cables. The two primary types of copper cabling used in the industry are coaxial and twisted pair. Both cable types sport a variety of connector types, none of which are actually copper connectors, but that’s the term used in the CompTIA Network+ objectives to lump them together.

Coaxial Cable

Coaxial cable contains a central conductor wire (usually copper) surrounded by an insulating material, which, in turn, is surrounded by a braided metal shield. The cable is referred to as coaxial (coax for short) because the center wire and the braided metal shield share a common axis or centerline

Coaxial cable shields data transmissions from electromagnetic interference (EMI). Many devices in the typical office environment generate magnetic fields, including lights, fans, copy machines, and refrigerators. When a metal wire encounters these magnetic fields, electrical current is generated

along the wire. This extra current — EMI — can shut down a network because it is easily misinterpreted as a signal by devices like NICs. To prevent EMI from affecting the network, the outer mesh layer of a coaxial cable shields the center wire (on which the data is transmitted) from interference

Early bus topology networks used coaxial cable to connect computers together. Back in the day, the most popular cable used special bayonet-style connectors called BNC connectors Even earlier bus networks used thick cable that required vampire connections — sometimes called vampire taps — that literally pierced the cable

You’ll find coaxial cable used today primarily to enable a cable modem to connect to an Internet service provider (ISP). Connecting a computer to the cable modem enables that computer to access the Internet. This cable is the same type used to connect televisions to cable boxes or to satellite receivers. These cables use an F-connector that screws on, making for a secure connection

Cable modems connect using either RG-6 or, rarely, RG-59. RG-59 was used primarily for cable television rather than networking. Its thinness and the introduction of digital cable motivated the move to the more robust RG-6, the predominant cabling used today

All coax cables have a Radio Grade (RG) rating. The U.S. military developed these ratings to provide a quick reference for the different types of coax. The only important measure of coax cabling is its Ohm rating, a relative measure of the resistance (or more precisely, characteristic impedance) on the cable. You may run across other coax cables that don’t have acceptable Ohm ratings, although they look just like network-rated coax. Fortunately, most coax cable types display their Ohm ratings on the cables themselves (Figure). Both RG-6 and RG-59 cables are rated at 75 Ohms.

Given the popularity of cable for television and Internet in homes today, you’ll run into situations where people need to take a single coaxial cable and split it. Coaxial handles this quite nicely with coaxial splitters like the one shown in Figure 3–19. You can also connect two coaxial cables together easily using a barrel connector when you need to add some distance to a connection

-RG specifies the thickness of the conductors, insulation and shielding

-Coaxial cable has two conductors, one center point, and a tubular conducting layer

-RG-59 has a 75ohm rating and uses a threaded F-type connector

Twisted Pair

The most common type of cabling used in networks consists of twisted pairs of cables, bundled together into a common jacket. Twisted-pair cabling for networks is composed of multiple pairs of wires twisted around each other at specific intervals. The twists reduce interference, called crosstalk: the more twists, the less crosstalk. Networks use two types of twisted-pair cabling: shielded twisted pair and unshielded twisted pair.

Shielded Twisted Pair

Shielded twisted pair (STP), as its name implies, consists of twisted pairs of wires surrounded by shielding to protect them from EMI. STP is pretty rare, primarily because there’s so little need for STP’s shielding. The shielding only really matters in locations with excessive electronic noise, such as a shop floor with lots of lights, electric motors, or other machinery that could cause problems for other cables. Figure shows the most common STP type: the venerable IBM Type 1 cable used in Token Ring network technology.

Unshielded Twisted Pair Unshielded twisted pair (UTP) is by far the most common type of network cabling used today. UTP consists of twisted pairs of wires surrounded by a plastic jacket (Figure). This jacket does not provide any protection from EMI, so when installing UTP cabling, you must be careful to avoid interference from fluorescent lights, motors, and so forth. UTP costs much less than STP but, in most cases, performs just as well.

-Modern twisted pair has 4 or more pairs of cable

-UTP cable is unshielded and subject to signal interference from environmental factors

-568A and 568B are wiring standards for how the wires are connected to a connector

Category (CAT) ratings

Not all UTP cables are the same! UTP cabling has a number of variations, such as the number of twists per foot. To help network installers get the right cable for the right network technology, the cabling industry has developed a variety of grades called category (CAT) ratings. CAT ratings are officially rated in megahertz (MHz), indicating the highest frequency the cable can handle.

-UTP cat ratings define the speed and cable length specifications

-Cat ratings have a different number of twists per inch

-Cat 6a and cat 7 are both rated for 10 Gbps speed and up to 100-meter cable length

Fiber-Optic Cabling and Connectors

Fiber-optic cable transmits light rather than electricity, making it attractive for both high-EMI areas and long-distance transmissions. Whereas a single copper cable cannot carry data more than a few hundred meters at best, a single piece of fiber-optic cabling will operate, depending on the implementation, for distances of up to tens of kilometers. A fiber-optic cable has four components: the glass fiber itself (the core); the cladding, which is the part that makes the light reflect down the fiber; buffer material to give strength, and the insulating jacket

Fiber cables are pretty tiny! Light can be sent down a fiber-optic cable as regular light or as laser light. The two types of light require totally different fiber-optic cables. Most network technologies that use fiber optics use LEDs (light emitting diodes) to send light signals. A fiber-optic cable that uses LEDs is known as multimode fiber (MMF). A fiber-optic cable that uses lasers is known as single-mode fiber (SMF). Using laser light and single-mode fiber-optic cables prevents a problem unique to multimode fiber optics called modal distortion (signals sent at the same time don’t arrive at the same time because the paths differ slightly in length) and enables a network to achieve phenomenally high transfer rates over incredibly long distances.

Fiber-optic cables come in a broad choice of connector types. There are over one hundred different connectors, but the four you need to know for the CompTIA Network+ exam are ST, SC, LC

Although all fiber connectors must be installed in pairs, the ST and SC connectors traditionally have unique ends. The LC connector is always duplex, meaning both the send and receive cables are attached. You can certainly find SC connectors or sleeves to make them duplex too, so don’t get too caught up with which can be which.

-Multimode cables carry LED signals

-Single mode cables carry Laser signals

-For the test, be able to recognize the different types of fiber connectors

Fire Ratings

The two most common fire ratings are PVC and plenum. Cable with a polyvinyl chloride (PVC) rating has no significant fire protection. If you burn a PVC cable, it creates lots of smoke and noxious fumes. Burning plenum-rated cable creates much less smoke and fumes, but plenum-rated cable — often referred to simply as “plenum” — costs about three to five times as much as PVC-rated cable. Most city ordinances require the use of plenum cable for network installations. The bottom line? Get plenum!

The space between the acoustical tile ceiling in an office building and the actual concrete ceiling above is called the plenum — hence the name for the proper fire rating of cabling to use in that space. A third type of fire rating, known as riser, designates the proper cabling to use for vertical runs between floors of a building. Riser-rated cable provides less protection than plenum cable, though, so most installations today use plenum for runs between floors.

-Plenum-rated cable is the most fire resistant

-Cable fire rating is normally clearly marked on the manufacturer’s box

Non-plenum is not considered fire/smoke resistant

Legacy Network Connections

Fiber-optic and UTP make up almost all network cabling, but a few other types of cabling appear on the CompTIA Network+ exam: the ancient serial and parallel cables from the earliest days of PCs. These cables were used for networking, but have not been in use for many years.

Classic Serial

Serial cabling predates both networking and the personal computer. RS-232, the recommended standard (RS) upon which all serial communication takes places on your PC, dates from 1969 and hasn’t substantially changed in around 40 years. When IBM invented the PC way back in 1980, serial connections were just about the only standard input/output technology available, so IBM included two serial ports on every PC. The most common serial port is a 9-pin, male D-subminiature (or DB-9) connector

Serial ports offered a poor option for networking, with very slow data rates — only about 56,000 bps — and only point-to-point connections. Serial ports were last used for connecting to networking devices, such as high-end switches.

Parallel

Parallel connections are as ancient as serial ports. Parallel can run up to around 2 Mbps, although when used for networking, they tend to be much slower. Parallel is also limited to point-to-point topology but uses a 25-pin female — rather than male — DB type connector commonly called a DB-25 (Figure 3–31). The IEEE 1284 committee sets the standards for parallel communication.