By the mid-1980s, growing pains from expansion in the field of networking were felt, especially by those companies that had instituted many different network technologies. It became increasingly difficult for networks that used different specifications and implementations to communicate with each other. An organization, called the International Organization for Standardization (ISO), researched various networks and created a network model, called the OSI Reference Model. (Note: Do not confuse the name of the model [OSI] with the name of the organization [ISO].) It was designed to help vendors create networks that would work compatibly and interoperably. By creating the OSI model, the ISO provided vendors with a set of standards.

Standards are sets of rules or procedures that are either widely used, or officially specified, and that serve as the gauge or model of excellence. The OSI model standards ensured compatibility and interoperability between the various types of network technologies that were produced by the many companies around the world. The early standards that were developed for networking media were largely proprietary. They were developed for use by various companies. Eventually, many more organizations and government bodies joined the movement to regulate and specify the types of cable that could be used for specific purposes or functions. Until recently, there has been a somewhat confusing mix of standards governing networking media. Standards have ranged from fire and building codes to detailed electrical specifications. Others have focused on tests to ensure safety and performance.

As you begin designing and building networks, make certain that you comply with all applicable fire codes, building codes, and safety standards. You should also follow any established performance standards in order to ensure optimal network operation and, because of the wide variety of options available today in networking media, to ensure compatibility and interoperability. Your work in this curriculum will focus on the standards for networking media that have been developed and issued by the following groups:

• IEEE - Institute of Electrical and Electronics Engineers
• UL - Underwriters Laboratories
• EIA - Electronic Industries Alliance
• TIA - Telecommunications Industry Association

The latter two organizations, jointly, issue a list of standards that you will frequently see listed as the TIA/EIA standards. In addition to these groups and organizations, local, state, county, and national government agencies issue specifications and requirements that can impact the type of cabling that can be used in a local area network.

The IEEE has outlined cabling requirements in its 802.3 and 802.5 specifications for Ethernet and Token Ring systems, and the standards for FDDI. Underwriters Laboratories issues cabling specifications that are primarily concerned with safety standards, however, they also rate twisted-pair networking media for performance. The Underwriters Laboratories established an identification program that lists markings for shielded and unshielded twisted-pair networking media in order to simplify the job of ensuring that materials used in LAN installations meet specifications

Of all of the organizations mentioned here, the TIA/EIA has had the greatest impact on networking media standards. Specifically, TIA/EIA-568-A and TIA/EIA-569-A, have been, and continue to be, the most widely used standards for technical performance of networking media.

The TIA/EIA standards specify the minimum  requirements for multi-product and multi-vendor environments. They allow for the planning and installation of LAN systems without dictating the use of specific equipment, thus giving LAN designers the freedom to create options for improvement and expansion.

The TIA/EIA standards address six elements of the LAN cabling process.  These are:

• horizontal cabling
• telecommunications closets
• backbone cabling
• equipment rooms
• work areas
• entrance facilities

This lesson will focus on TIA/EIA-568-A standards for horizontal cabling, which defines horizontal cabling as cabling that runs from a telecommunications outlet to a horizontal cross-connect. It includes the networking medium that runs along a horizontal pathway, the telecommunications outlet or connector, the mechanical terminations in the wiring closet, and the patch cords or jumpers in the wiring closet. In short, horizontal cabling includes the networking media that is used in the area that extends from the wiring closet to a workstation.

TIA/EIA-568-A contains specifications governing cable performance. It calls for running two cables, one for voice and one for data, to each outlet. Of the two cables, the one for voice must be four-pair UTP. The TIA/EIA-568-A standard specifies five categories in the specifications. These are category 1 (CAT 1), category 2 (CAT 2), category 3 (CAT 3), category 4 (CAT 4), and category 5  (CAT 5) cabling. Of these, only CAT 3, CAT 4, and CAT 5 are recognized for use in LANs. Of these three categories, CAT 5 is the one most frequently recommended and implemented in installations today.

The networking media that are recognized for these categories are the ones you have studied:

• shielded twisted-pair
• unshielded twisted-pair
• fiber-optic cable
• coaxial cable

For shielded twisted-pair cable, the TIA/EIA-568-A standard calls for two pair 150 ohm cable. For unshielded-twisted pair, the standard calls for four pair 100 ohm cable. For fiber-optic, the standard calls for two fibers of 62.5/125  multi-mode cable. Although 50 ohm coaxial cable is a recognized type of networking media in TIA/EIA-568-A, it is not recommended for new installations. Moreover, this type of coaxial cable is expected to be removed from the list of recognized networking media the next time this standard is revised.

For the horizontal cabling component, TIA/EIA-568A requires a minimum of two telecommunications outlets or connectors at each work area. This telecommunications outlet/connector is supported by two cables. The first is a four-pair 100 ohm CAT 3 or higher UTP cable along with its appropriate connector. The second can be any one of the following:

• four-pair 100 ohm unshielded twisted-pair cable and its appropriate connector
• 150 ohm shielded twisted-pair cable and its appropriate connector 
• coaxial cable and its appropriate connector
• two-fiber 62.5/125 µ optical fiber cable and its appropriate connector

According to TIA/EIA-568-A, the maximum distance for cable runs in horizontal cabling is 90 meters (m). This is true for all types of CAT 5 UTP recognized networking media. The standard also specifies that patch cords or cross-connect jumpers located at the horizontal cross-connect cannot exceed 6 m in length. TIA/EIA-568-A also allows 3 m for patch cords that are used to connect equipment at the work area. The total length of the patch cords and cross-connect jumpers used in the horizontal cabling cannot exceed 10 m. A final specification for horizontal cabling contained in TIA/EIA-568-A requires that all grounding and bonding must conform to TIA/EIA-607 as well as to any other applicable codes.

The latest industry standards being developed are for Cat 5e, Cat 6, and Cat 7 cabling, all of which offer improvements over Cat 5

Cables must eventually be terminated in order to provide connectivity. This process involves much transition and innovation as far as computer networking is concerned. This presents a tremendous challenge for students, who must learn a wide variety of networking medium standards, properties, and terminations.

Explore the following Web sites to examine the variety of cable and termination products that are available.