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IV. CABLING AND NETWORKS
The standards which will be discussed in this chapter deal with the safe installation of electrical components and the data cabling used in connecting remote peripherals to a host computer or clients to a server. Most of the data cabling in libraries today was installed more than five years ago. It consists of unshielded twisted pair (UTP) cabling similar to the cabling used by telcos. In most cases, each terminal is wired directly to the computer or to a terminal server which connects several terminals to a computer. Terminals remote from the central site are normally connected to a mux (multiplexor) which communicates with a similar mux in the computer room.
With the increasing use of PCs on desktops and the desire to provide PC users with access to a variety of information sources, simple cabling schemes are being replaced with LANs (local area networks) within buildings and MANs (metropolitan area networks) among sites. LANs and MANs typically are made of components from different suppliers; therefore, standards are increasingly important to assure compatibility. Because of changing needs, especially the need for ever greater bandwidths, standards in this area are changing quite rapidly.
The specific standards discussed are:
UL National Electrical Code
TIA/EIA-568A 95 Commercial Building Telecommunications Cabling
IEEE 802 Telecommunications & Information Exchange between
Systems-LANs & MANs
IEEE 802.3 Telecommunications & Information Exchange between
ISO 8802.3 Telecommunications & Information Exchange between
IEEE 802.4 Token Bus Standard
IEEE 802.5 Telecommunications & Information Exchange among
ISO 8802.5 Telecommunications & Information Exchange between
Systems (Token Ring)
ITU FDDI Fiber Distributed Data Interface
ANSI T1-617-618 Frame Relay
ITU ATM Asynchronous Transfer Mode
IEEE 1003.1 Portable Operating System Interface
ISO 9945 Information Technology-Portable Operating
System Interface (POSIX)
ANSI ASC X3. Standards for Programming Languages
IEEE 1224 X.400-based Electronic Messaging
UL. National Electrical Code
The National Electrical Code of Underwriters Laboratories spells out electrical shock and fire hazard requirements for electrical products. A manufacturer may merely follow the code in its manufacturing practices or it may go further and submit its products to Underwriters Laboratories for testing. If the testing determines that the submitted product complies with all applicable requirements of the National Electrical Code, the product may be labeled as "UL certified."
A library should specify that all electrical components used in the system shall comply with the National Electrical Code and shall be UL certified.
TIA/EIA-568A 95. Commercial Building Telecommunications Cabling Standard
The purpose of the TIA/EIA-568A standard is threefold: (1) to establish a generic telecommunications cabling standard that will support a multi-vendor environment; (2) enable the planning and installation of a structured cabling system for buildings; and (3) establish performance and technical criteria for various cabling systems configurations.
The standard specifies minimum requirements for telecommunications cabling within a building. It also recommended topology and distances, media parameters which determine performance, connector and pin assignments to ensure interconnectivity, and it specifies the useful life of telecommunications cabling systems as being in excess of ten years.
There are three tiers of cabling in a typical building: backbone, horizontal, and work area. The backbone cabling is that which comes into a building and to the computer room, goes from the computer room to the various floors, and--in large buildings--goes from a telecommunications closet to telecommunications closets in sectors of a floor. The horizontal cabling is that which goes from a computer room or telecommunications closets to the work area wallplate or network connection. The work area cabling consists of all components between the horizontal wiring wallplate or network connection and the user's workstation.
A telecommunications closet is a room or cabinet that holds the hardware needed to connect the building's horizontal wiring to the backbone wiring. Examples of such hardware are hubs, bridges, patch panels, jumper panels, switches, etc. The EIA/TIA 568A addresses all of these components.
The "topology" of a cabling system is the underlying structure which determines how the telecommunications closets, main cross-connects, and intermediate cross-connects will be linked. There are three major topologies: bus, star, and ring. The bus topology consists of one continuous cable with connections made along its length; the star topology consists of several cables radiating out from a central site. The ring topology consists of a series of connections made to form a close loop. The EIA/TIA 568A standard recommends the star topology for backbone and horizontal cabling, but also provides standards for using the bus topology for the backbone. It advises against using either star or ring topology for the horizontal cabling.
The standard accommodates any of several choices for cabling: UTP (unshielded twisted pair), STP (shielded twisted pair), coaxial cable, and fiber optic. The standard recommends using only STP IBM type 1A cable, Category 5 UTP cable, 50-ohm coax cable, or 62.5-micron fiber cable. The standard details how each type of cable is to be constructed and how each is to be installed.
STP IBM type 1A cabling is two-pair 150-ohm cabling with shielding. The cable supports data transfer rates of up to 16 Mbps (megabits per second) unless it is designated as "extended STP," which is a cabling suitable for data transfer up to 100 Mbps. STP is normally used only when IBM Token Ring is chosen as the topology. There is a type 2A-STP cable which consists of the same two pairs of shielded twisted-pair strands, plus an extra four pairs of unshielded twisted-pair wire for phone use.
UTP is four-pair 100-ohm unshielded twisted-pair cable. It consists of 24 thermoplastic insulated conductors which are configured into four individually twisted pairs. There are three categories or levels in current use:
Category 3 -- cables/connecting hardware with transmission parameters characterized up to 16 Mbps. Its use is now limited to voice communication.
Category 4 -- cables/connecting hardware with transmission parameters characterized up to 20 Mbps. It is suitable for either voice or data.
Category 5 -- cables/connecting hardware with transmission parameters characterized up to 100 Mbps.
While the standard provides specifications for each, libraries should limit themselves to the use of Category 5 UTP cabling. On average, it costs only $.02 more per foot than Category 3 or 4, but it can accommodate much higher data transfer rates. As libraries begin to move full-text, images, and multimedia from the computer room to desktop PCs, data transfer rates of 100 Mbps will be required, therefore outstripping the capacities of Category 3 and Category 4 UTP cabling.
Category 5 UTP comprises four copper pairs, twisted together and protected by a thin polyvinyl chloride (PVC) jacket. It is suitable for use throughout a facility, although that pulled through a plenum (the space between a ceiling and the floor above) must be "plenum rated," meaning that the construction resists fire and produces less smoke when it burns.
The ISO's International Electrotechnical Committee (ISO IEC) is working on a standard for Category 5 UTP. There are two proposals before the group: one defines performance specifications for 300 Mbps and the other for 600 Mbps. The copper wire may be the same, but the standard would call for different hardware and software.
Coaxial cable consists of a solid-conductor center wire that is surrounded by a dielectric, or nonconducting, material. Surrounding the dielectric is a foil shield and wire braid, and surrounding that is the jacket. Coax is both more expensive and more difficult to install than UTP; therefore, its use is limited to long distances, harsh environments, or when video is to be transmitted. There are PVC versions for general use and plenum-rated versions for use where required. Coaxial cable can support data transfer rates up to 100 Mbps. There is a special 50-ohm coaxial cable called "ThinNet," which has been developed specifically for Ethernet, but it is limited to 10 Mbps data transfer. While widely used in the past, it is less popular now because UTP now offers 100 Mbps data transfer.
The 62.5-micron fiber optic cable consists of a glass fiber that transmits signals by light pulses. The glass fiber is surrounded by a jacket. Insulative material surrounds the jacketed fiber, and another jacket surrounds and protects the entire assembly. There are PVC and plenum versions. The standard provides for 100 Mbps bandwidth using fiber optic.
A special type of fiber optic cable is called FDDI fiber optic. This cable features two 62.5-125-micron fibers enclosed in a common jacket. It is used when an optical fiber ring is to be installed.
The main drawback to fiber optic is its cost, typically 40 percent more installed than Category 5 UTP, although the price of the cabling is coming down and the difference in installation labor between it and Category 5 UTP is diminishing. More significant than the cost of fiber optic cable and its installation is the higher cost of the telecommunications hardware: as much as 70 percent higher for fiber optic than for Category 5 UTP. Nevertheless, it is a good choice for backbone cabling in large buildings or on multi-building campuses. While the current standard only provides for data transfer rates up to 100 Mbps, there is reason to believe that a 600 Mbps standard will become available by 1998. Fiber optic is also a good …