3.9. The Basics of 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. The following sections explore the realm of wiring from a technical and a security perspective. Specifically, you'll learn about coaxial cable, UTP/STP, fiber optics, infrared, radio frequency, and microwave media.

3.9.1. 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 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

3.9.2. 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

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 STP cabling isn't as secure as coax because it can be easily tapped into, and it's used primarily for internal wiring. It's more difficult to splice into a twisted-pair cable, but three-way breakout boxes are easy to build or buy. The common networks that use UTP are 10Base-T, 100Base-T, and 1000Base-T. These networks use hubs for distribution, and hubs allow sniffers to be easily connected. Many modern networks include switches, and network monitoring doesn't work properly through a switch unless the switch is configured to allow it. Remember that each circuit through a switch is dedicated when switched and won't 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 a portable PC with a NIC for the network protocol.

3.9.3. 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 isn't common on the desktop.

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

Fiber, as a media, is relatively secure because it can't be tapped easily. 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 from there. The other common security issue associated with fiber optics is that fiber connections are usually bridged to wire connections. Figure 3.25 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 3.25. An inline fiber splitter

3.9.4. 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 connections 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.

IR is line of sight; it isn't secure and can be easily intercepted. 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.)

3.9.5. Radio Frequencies

Radio frequency (RF) communications have had an interesting love/hate relationship with data communication. Early data communications 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. The transmitters were very expensive, and large numbers of personnel were required 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. These signals can be easily intercepted. Anyone can connect a shortwave receiver to the sound card of a PC to intercept, receive, and record shortwave and higher-frequency transmissions. Figure 3.26 illustrates a shortwave transmission between two ground sites used for text transmission. This is an active pastime—tens of thousands of hobbyists worldwide are eavesdropping.

3.9.6. Microwave Systems

Microwaves use the RF spectrum, but they have some interesting characteristics and capabilities. The microwave frequency spectrum includes many types of communications; some involve huge amounts of data and information, and others involve small amounts. Common applications of microwave today include cellular phones, police and aircraft communications, fax, and broadband telecommunications 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 enormous amounts of data, communicate line of sight, and use broad power ranges. Figure 3.27 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 fast rate worldwide.

Figure 3.26. RF communications between two ground stations

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

A relative newcomer on the microwave 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. When implementing wireless networks, you would be wise to make sure 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.

Figure 3.27. Cellular network in a metropolitan area