Typical business environments and requirements change quickly. Companies restructure and reorganize at alarming rates. In some companies, the average employee changes work locations once every two years. During a two-year tenure, a friend changed offices at a particular company five times. Each time, his telephone, both networked computers, a VAX VT-100 terminal, and a networked printer had to be moved. The data and voice cabling system had to support these reconfigurations quickly and easily. Earlier cabling designs would not have easily supported this business environment.
Until the early 1990s, cabling systems were proprietary, vendor-specific, and lacking in flexibility. Some of the downsides of pre-1990 cabling systems included the following:
- Vendor-specific cabling locked the customer into a proprietary system.
- Upgrades or new systems often required a completely new cabling infrastructure.
- Moves and changes often necessitated major cabling plant reconfigurations. Some coaxial and twinax cabling systems required that entire areas (or the entire system) be brought down in order to make changes.
- Companies often had several cabling infrastructures that had to be maintained for their various applications.
- Troubleshooting proprietary systems was time consuming and difficult unless you were intimately familiar with a system.
Cabling has changed quite a bit over the years. Cabling installations have evolved from proprietary systems to flexible, open solutions that can be used by many vendors and applications. This change is the result of the adaptation of standards-based, structured cabling systems. The driving force behind this acceptance is due not only to customers but also to the cooperation between many telecommunications vendors and international standards organizations.
A properly designed structured cabling system is based around components or wiring units. An example of a wiring unit is a story of an office building, as shown in Figure 1. All the work locations on that floor are connected to a single wiring closet. All of the wiring units (stories of the office building) can be combined together using backbone cables as part of a larger system.
This point bears repeating: a structured cabling system is not designed around any specific application but rather is designed to be generic. This permits many applications to take advantage of the cabling system.
The components used to design a structured cabling system should be based on a widely accepted specification and should allow many applications (analog voice, digital voice, 10Base-T, 100Base-TX, 16Mbps Token Ring, RS-232, etc.) to use the cabling system. The components should also adhere to certain performance specifications so that the installer or customer will know exactly what types of applications will be supported.
A number of documents are related to data cabling. In the United States, the standard is ANSI/TIA-568-C, also known as the Commercial Building Telecommunications Cabling Standard. The ANSI/TIA-568-C standard is a specification adopted by ANSI (American National Standards Institute), but the ANSI portion of the document name is commonly left out. In Europe, the predominant standard is the ISO/IEC 11801 Ed. 2 standard, also known as the International Standard on Information Technology Generic Cabling for Customer Premises.
In the United States, a document is not officially a national standard until it is sanctioned by ANSI. In Canada, the CSA is the sanctioning body, and in Europe, it is the ISO. Until sanctioned by these organizations, a requirements document is merely a specification. However, many people use the words specification and standard interchangeably. (In Europe, the word norm also comes into play.) Just be aware that a "specification" can be created by anyone with a word processor, whereas a national standard carries the weight of governmental recognition as a comprehensive, fair, and objective document.
These two documents are quite similar, although their terminology is different, and the ISO/IEC 11801 Ed. 2 standard permits an additional type of UTP cabling. Throughout much of the rest of the world, countries and specification organizations have adopted one of these standards as their own.
Briefly introduces the ANSI/TIA-568-C and the ISO/IEC 11801 Ed. 2 standards, but it is not intended to be a comprehensive guide to either. Networking vendors and specifications committees are figuring out ways to transmit larger quantities of data, voice, and video over copper and fiber-optic cable. Therefore, the requirements and performance specifications for the standards are continually being updated. If you are responsible for large cabling-systems design and implementation, you should own a copy of the relevant documents.
Most of the TIA/EIA documents mentioned are available for purchase through Global Engineering Documents at (877) 413-5184 or on the Web at http://global.ihs.com. Global Engineering Documents sells printed versions of the ISO, TIA, EIA, and ETSI specifications, as well as others. The ITU recommendations are available for purchase from the ITU's website at www.itu.int/.
CSA International Standards documents are available from the CSA at www.csa.ca.