Cabling, Wires, and Communications

Nothing happens in a network until data is moved from one place to another. Naturally, this requires some type of cable, wire, or transmission media. This section explores the realm of wiring from a technical and a security perspective. Specifically, you will learn about coaxial cable, UTP/STP, fiber optics, infrared, radio frequency, and microwave media.

Coax

Coaxial cable, or coax, is one of the oldest media used in networks. Coax is built around a center conductor or core that is used to carry data from point to point. The center conductor has an insulator wrapped around it, a shield over the insulator, and a nonconductive sheath around the shielding. This construction, depicted in Figure 3.18, allows the conducting core to be relatively free from outside interference. The shielding also prevents the conducting core from emanating signals externally from the cable.

Figure 3.18: Coaxial cable construction

Connections to a coax occur through a wide variety of connectors, often referred to as plumbing. These connectors allow 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, while broadband refers to multiple channels on the coax. Figure 3.20 illustrates this in detail. Baseband signaling would be 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. Each of these channels is selected by your TV set, which uses a tuner to select which channel you choose to watch.

Figure 3.20: Baseband versus broadband signaling

Coax is present in many older networks and tends to provide reliable service once it is installed. In a coax network, some type of device must terminate all of the ends of a coax. Figure 3.21 shows this termination process in more detail. If a terminator, NIC card, 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 tends to become brittle over time, and it can fail when handled. Coax is also expensive per foot when compared to UTP cable. These are the primary reasons that coax is falling from favor as a primary network media.

Figure 3.21: Network termination in a coax network

Coax has two primary vulnerabilities from a security perspective. The most common would be 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. Vampire taps are a type of connection that directly attaches to 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. Notice that the T-connector is a standard connector that can be used at any place there is a connector on the cable. Additionally, an inductive pickup or RF collar can be placed around a coaxial cable to capture any stray RF that does not get blocked by the shield of the coax.

Figure 3.22: A vampire tap and a T-connector on a coax

Unshielded Twisted Pair and Shielded Twisted Pair

Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP) are by far 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 more popular cabling in use. Figure 3.23 illustrates the difference between UTP and STP cable. Notice that the STP cable has a single shield around all of 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 and interference susceptibility in the cable.

Figure 3.23: UTP and STP cable construction

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 3.1.

Table 3.1: The Common UTP/STP Cable Specifications

Category	Speed	Usage
Category 1	Voice-grade cable	Used strictly for telephone and modems.
Category 2	4 Mbps speed	Used extensively in older mainframe systems.
Category 3	10 Mbps Ethernet	Used in 10Base-T networks.
Category 4	16 Mbps	Used extensively in Token Ring networks.
Category 5	1000 Mbps	Used in 10-, 100-, and 1000Base-T and similar networks. The most common wiring in newer networks.
Category 6	1000 Mbps	Used in high-speed network installations. Not yet common.
Category 7	1 Gbps	Used in very-high speed network installations. Not available—proposed standard.

The most common cable standards used at this time are Category 5 or CAT 5. CAT 3 is very 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 STP cabling is not as secure as coax, and it is used primarily for internal wiring. It is more difficult to splice into a twisted pair cable, but three-way breakout boxes are very easy to build or buy. The common networks that use UTP are 10Base-T and 100Base-T. These networks use hubs for distribution, and hubs allow sniffers to be easily connected. Many modern hubs also include the capability of switching, and network monitoring does not work properly through a switch. Remember that each circuit through a switch is dedicated when switched and will not be seen on the other ports. Figure 3.24 illustrates a hub in a 10Base-T network and a sniffer attached to the hub. The sniffer in this situation is merely a portable PC with a NIC card for the network protocol.

Figure 3.24: 10Base-T network with a sniffer attached at the hub

Fiber Optic

Fiber optic technology takes network bandwidth to new levels of performance. Telecommunications and data communication providers worldwide have laid fiber cables extensively. At one point, the industry claimed that fiber would surpass wire as the preferred method of making network connections. Fiber optics and its assembly continue to be very expensive when compared to wire, and this technology has still not largely made it to the desktop. Figure 3.25 shows several of the more common fiber connections. The construction of fiber cable is simplicity itself. The cable consists of a glass or plastic conductor, surrounded by a protective coating or by layers of coating.

Figure 3.25: Commonly used fiber connectors

Fiber, as a media, is relatively secure because it cannot be easily tapped. Fiber's greatest security weakness is at the connections to the fiber optic transceivers. Passive connections can be made at the connections, and signals can be tapped off from there. The other common security issue associated with fiber optics is that fiber connections are usually bridged to wire connections. Figure 3.26 shows how a fiber connection to a transceiver can be tapped. This type of splitter requires a signal regenerator for the split to function, and it can be easily detected.

Figure 3.26: An inline fiber splitter

Infrared

Infrared (IR) uses a type of radiation for communications. This infrared radiation allows a point-to-point connection to be made between two IR transceiver-equipped devices. IR is line of sight and is not secure, but the interception device must be either in position between the two connections or in an area where a reflection has occurred. IR can be bounced off windows and mirrors, as can other radiation. IR connections also tend to be slow and are used for limited amounts of data. Many newer laptop PCs, PDAs, and portable printers now come equipped with IR devices for wireless communications.

Radio Frequency

Radio frequency (RF) communication has had an interesting love/hate relationship with data communication. Early data communication systems, such as teletypes, used extensive networks of high-powered shortwave transmitters to send information and data. Most of the early news feeds were broadcast on shortwave frequencies and received around the world by news offices. These connections were also used for early facsimile transmission of weather maps and other graphically oriented images. These transmitters were very expensive, and they required large numbers of personnel to manage and maintain them. Telephone connections largely replaced this means of communications, but teleprinters are still in use today.

RF transmissions use antennas to send signals across the airwaves. They are very easily intercepted. Anyone could connect a shortwave receiver to the sound card of a PC to intercept and receive shortwave and higher frequency transmissions and record them. Figure 3.27 illustrates a short- wave transmission between two ground sites used for text transmission. This is a very active hobby with tens of thousands of hobbyists worldwide eavesdropping.

Figure 3.27: RF communications between two ground stations

Microwave

Microwaves use the RF spectrum, but they have some interesting characteristics and capabilities. The microwave frequency spectrum is the home of many interesting types of communications. Some of these communications involve huge amounts of data and information, and others involve very small amounts. Some of the more common applications of microwave today include cellular phones, police and aircraft communications, fax, and broadband telecommunication systems. The equipment to communicate on these frequencies is usually very small and power efficient.

Much of the telecommunications system we use today is built on microwave technology. Microwave has the ability to carry huge amounts of data, communicate line-of-sight, and use broad power ranges. Figure 3.28 illustrates a cell network in a metropolitan area. A typical cell network is capable of handling hundreds of calls simultaneously, and cell usage is growing at a very fast rate worldwide.

Figure 3.28: Cellular network in a metropolitan area

Communications on this cell network are easily intercepted by off-the- shelf equipment. Analog cellular communications can be easily understood, while digital cellular service requires additional equipment to decode transmissions. Many people use cell phones for data communications. Most people assume that cell connections are private when, in fact, they may not be.

A relative newcomer on the communications scene involves wireless networks. Some of the wireless networks allow pagers, PDAs, and internal or private networks. Wireless networks operate in the 2.5 to 5.0GHz spectrum. The frequency spectrum used in cellular and wireless networks is in the microwave band.

When implementing wireless networks, you would be wise to make sure that you implement or install communications security devices or encryption technology to prevent the unauthorized disclosure of information in your network. Many of the newer devices include encryption protocols similar to IPSec.