• Choose a category
• All
• Classic-Fiction

Connections to a coax occur through a wide variety of connectors, often referred to as plumbing. These connectors provide a modular design that allows for easy expansion. The three primary connections used in this case are the T-connector, the inline connector, and the terminating connector (also known as a terminating resistor or terminator). Figure 3.19 shows some of these common connectors in a coaxial cable-based network.

FIGURE 3.19 Common BNC connectors

Coax supports both baseband and broadband signaling. Baseband signaling means that a single channel is carried through the coax, and broadband refers to multiple channels on the coax. Figure 3.20 illustrates this difference. Baseband signaling is similar in concept to a speaker wire. The speaker wire in your stereo connects one channel from the amplifier to the speaker. Broadband is similar to the cable TV connection in your home. The cable from the cable company carries hundreds of channels. Your TV set uses a tuner to select the channel you choose to watch.

In a coax network, some type of device must terminate all the coax ends. Figure 3.21 shows this termination process in more detail. Coax is present in many older networks and tends to provide reliable service once it’s installed. However, if a terminator, NIC, T-connector, or inline connector malfunctions or becomes disconnected, the entire segment of wire in that network will malfunction, and network services will cease operation. Coax also tends to become brittle over time, and it can fail when handled. In addition, coax is expensive per foot when compared to UTP cable. These are the primary reasons that coax is falling from favor as a primary network media.

Coax has two primary vulnerabilities from a security perspective. The most common is the addition of a T-connector attached to a network sniffer. This sniffer would have unrestricted access to the signaling on the cable. The second and less common method involves a connection called a vampire tap. A vampire tap is a type of connection that hooks directly into a coax by piercing the outer sheath and attaching a small wire to the center conductor or core. This type of attachment allows a tap to occur almost anywhere in the network. Taps can be hard to find because they can be anywhere in the cable. Figure 3.22 shows the two common methods of tapping a coax cable. The T-connector is a standard connector that can be used any place there is a connector on the cable. An inductive pickup or RF collar can be placed around a coaxial cable to capture any stray RF that isn’t blocked by the coax’s shield.

FIGURE 3.20 Broadband versus baseband signaling

FIGURE 3.21 Network termination in a coax network

Unshielded Twisted Pair and Shielded Twisted Pair

Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP) are the most prevalent media installed today. UTP cabling and STP cabling are similar in function, with the exception that STP wraps a shield, like a coax, over the wires. STP is popular, but UTP is by far the most popular cabling in use.

FIGURE 3.22 A vampire tap and a T-connector on a coax

Figure 3.23 illustrates the difference between UTP and STP cable. Notice that the STP cable has a single shield around all the pairs. Some versions of STP also have shields around each pair of wires. This is much less common in computer networks, but it reduces electrical interference susceptibility in the cable.

This discussion will revolve around UTP, but STP operates the same way. UTP cabling comes in seven grades or categories, which are listed in Table 3.2.

FIGURE 3.23 STP and UTP cable construction

TABLE 3.2 The Common UTP/STP Cable Specifications

The most common cable standard used at this time is Category 5 (CAT 5). CAT 3 is common in older twisted-pair networks. The limit of a cable segment length of twisted pair for use with Ethernet is 100 meters; beyond this length, the attenuation of the cables may cause reliability problems.

UTP and