Network Cabling Main and Optional Types of Backbone Cable
Cable Type Main Optional UTP 100-ohm, multi-pair UTP cable, to be used for voice-grade communications only STP 150-ohm STP cable, such as that defined in the IBM Cable System (ICS) 100-ohm STP cable Coaxial 50-ohm thick coaxial cable, such as the cable used in thick Ethernet networks 75-ohm (broadband) coaxial cable, such as CATV cable Optical fiber 62.5/125-micron (step- or graded-index) multi-mode optical fiber Single-mode optical fiber Coaxial Cable
Coaxial cable, often called coax, is used for data transmissions. This cable's remarkably stable electrical properties at frequencies below 1 GHz (gigahertz) makes the cable popular for cable television (CATV) transmissions and for creating local-area networks (LANs). Telephone company switching offices also use coaxial cable to route long-distance calls. The figure "Context and properties of coaxial cable" summarizes the features of this type of cable.Coaxial Properties
- Stable and predictable electrical properties
- At least one shield around conductor wire
- Subject to electromagnetic interference
- Variable impedance levels
- Thin and thick varieties
- Broadband and baseband varieties
- Thin coaxial uses BNC/TNC connectors; thick coaxial uses N-series connectors
- Twinaxial runs two cables within a single jacket
- Triaxial and quadrax have extra shielding for special uses
Coaxial Uses
- Ethernet networks
- ARCnet networks
- Cable TV lines
- Video cable
- IBM mainframe and midrange-based networks (twinaxial)
- Telephone switching offices
Coaxial Cable Components
A coaxial cable consists of the following layers (moving outward from the center):
- Carrier wire
- Insulation
- Foil shield
- Braid shield
- Jacket
Coaxial Cable Performance
he main features that affect the performance of coaxial cable are its composition, width, and impedance. The carrier wire's composition determines how good a conductor the cable will be. Copper is among the best materials for this purpose. The IEEE specifies stranded copper carrier wire with tin coating for thin coaxial and solid copper carrier wire for thick coaxial. Cable width helps determine the electrical demands that can be made on the cable. In general, thick coaxial can support a much higher level of electrical activity than thin coaxial. Impedance helps determine the cable's electrical properties and also limits the contexts in which the cable can be used. For example, Ethernet and ARCnet architectures can both use thin coaxial cable, but they have different impedances; therefore, Ethernet and ARCnet cables are not compatible. In networks the impedances range from 50 ohms (for and Ethernet architecture) to 93 ohms (for an ARCnet architecture).Coaxial Cable Connectors
A segment of coaxial cable has an end connector at each end. The cable is attached through these end connectors to a T-connector, a barrel connector, another end connector, or to a terminator. Through these connectors, another cable or a hardware device is attached to the coaxial cable. In addition to their function, connectors differ in their attachment mechanism and components. For example, BNC connectors join two components by plugging them together and then turning the components to click the connection into place. Different size coaxial cable requires a different-sized connector. For coaxial cable, the following types of connectors are available:
- A BNC (bayonet nut connector) is used for thin coaxial cable.
- The N-series connectors are used for thick coaxial cable.
- A TNC (threaded nut connector) may be used in the same situations as a BNC, provided that the other connector is also using TNC.
Connectors for coaxial cable should be plated with silver, not tin. This improves the contact and the durability of the connector.
Coaxial Cable Designations
Coaxial cable types:
- RG-6
- RG-8
- RG-11
- RG-58
- RG-59
- RG-62
Advantages of Coaxial Cable
Coaxial cable has the following advantages over other types of cable that might be used for a network. The advantages are general and may not apply in a particular situation. Note also that advantages change or disappear over time, as technology advances and products improve.
- Broadband coaxial can be used to transmit voice, data, and even video.
- The cable is relatively easy to install
- Coaxial cable is reasonably priced compared with other cable types.
Disadvantages of Coaxial Cable Coaxial cable has the following disadvantages when used for a network:
- It is easily damaged and sometimes difficult to work with, especially in the case of thick coaxial.
- Coaxial is more difficult to work with than twisted-pair cable.
- This type of cable cannot be used with token-ring network architectures.
- Thick coaxial can be expensive to install, especially if it needs to be pulled through existing cable conduits.
- Connectors can be expensive.
- Baseband coaxial cannot carry integrated voice, data and video signals
Copyright © 1998.