The Fiber Optic Association

  The Fiber Optic Association, Inc.
the non-profit professional society of fiber optics

Reference Guide To Fiber Optics


Topic: Premises Cabling Table of Contents: The FOA Reference Guide To Fiber Optics

A History of Cabling for Communications
The history of telecommunications spans slightly more than 150 years, starting with the development of the telegraph in the early 19th century. Telegraphy gave man the means to transmit a series of impulses that represented letters, called Morse Code for Samuel F. B. Morse, who is credited with the invention of telegraphy. When these letters were received and decoded, they provided a way to convey messages over long distances.
 
Naturally, the next step was to consider whether sound might also somehow be electrically transmitted. Alexander Graham Bell applied for his patent for an "electrical speaking telephone" in 1876, beating Elisha Gray by only a few hours. In reality, many people contributed to telephone improvements including Thomas Alva Edison, Lars Ericsson and  David Edward Hughes whose invention of the microphone became universally used in telephones.
 
It is amazing how quickly the use of the telephone spread. The first switchboard, an experiment, was installed in Boston in 1877. Just four years later, there were 54,000 telephones in the United States! The first connections from Boston to New York begain in 1884. Wireless communications developed from the work of Nikola Tesla and Guglielmo Marconi. In the first decade of the 20th century, Dr. Lee deForest's invention of the vacuum tube amplifier enabled long distance communications.
 
Technology allowed the expansion of telecommunications. With the advent of the space program in the 1960s, communications satellites expanded the worldwide telecommunications network faster than could be done by laying transoceanic cables. By the 1970s, integrated circuit technogy and the microprocessor began to influence telecommunications and computers. Experiments began in digital voice transmission and fiber optics. Computer networks like Ethernet and the predecessor of the Internet were developed.
 
The 1980s brought wide scale use of digital telecom, computer networks and fiber optics, but was also the era of the breakup of the Bell system. Users who once depended on AT&T for telecom standards and IBM or other computer companies for the "rules" they depended on were left stranded.
 
Manufacturers assumed responsibility for standards development to ensure interoperability of their products - under the auspices of the IEEE for computer networking electronics and EIA/TIA for cabling in the US and ISO and IEC worldwide. Thus was born the industry standards that we all depend on for today's communications networks.

The 1990s to today are the era of computer LANs and the Internet. Although not every proposed usage of cabling has been successful, today every PC is connected to a LAN or the Internet or both. Telephone systems are using VoIP (Voice over Internet Protocol) over the Internet as well as traditional telecom protocols, with wireless connection being used in many cases instead of wiring. Internet access over cell phones has added even more expansion to the market. Perhaps the biggest change of the current era is the final expansion of fiber optic networks direct to the subscriber, either homes or business (FTTx), using passive optical network (PON) technology.

But all telecommunications and the Internet depend on cabling, even wireless. Typically it's all on a worldwide fiber optic backbone connected into private networks that utilize a combination of copper, fiber and wireless connections.

What is Premises Cabling?
By premises cabling, we mean the cabling used inside buildings (and in restricted geographic areas like campuses or among business facilities) that follows industry standards. Mostly we are refering to structured cabling systems defined by TIA-568 or ISO/IEC 11801  and related standards that are used for LANs, telephone systems and even other systems adapted to structured cabling like CCTV, security or building management. Other systems that depend on cabling such as security and building control are migrating to structured cabing for its widespread availability and predictability.
 
Other Uses For Standardized Premises Cabling
TIA-568 originally considered the use of structured cabling to be corporate LANs, primarily Ethernet but some legacy IBM Token Ring. However the large-scale adoption of UTP cabling standards has gained the attention of many other applications. UTP is now used for CCTV cameras, security systems, building management systems, etc. Some of these systems have been redesigned for UTP cable while others require adapters, such as BALUNs which convert coax to balanced UTP transmission. One can also get adapters that allow multiple equipment to use separate pairs of the UTP cable, for example for a POTS phone line and a Fast Ethernet connection. Most of these applications will also use fiber optics where the length or bandwidth exceeds the limitations of UTP copper cable.

What Are Cabling Standards?
 
Widespread useage of any technology depends on the existence of acceptable standards for components and systems. These standards are written as minimum specifications for components and systems that will  ensure interoperability of equipment from various manufacturers. The most important "standard" and the only one that is legally mandatory is the National Electrical Code developed by the National Fire Protection Assn. that covers all aspects of electrical and fire safety. Article 800 of the NEC covers communication circuits, such as telephone systems and outside wiring for fire and burglar alarm systems and Article 770 covers fiber optics. Also, all VDV wiring must comply with building and electrical codes applicable in your state or city.
 
But during the 1980s, technology changed rapidly. Phone signals became digital, fiber proliferated, PCs became connected over LANs and new cables and cabling architecture were needed. The goal was to make buildings "smart," able to allow computer and phone conversations over a standardized wiring system. By the early 90s, a scheme of "structured cabling" was standardized by technical committee of a trade association, the merged Electronic Industries Association and Telecommunications Industry Association (hereafter referred to as EIA/TIA) in the USA and ISO/IEC worldwide.
 
This cabling standard, developed by what was then called the EIA/TIA TR 41.8 committee - now renamed TR 42 - is referred to by the number of the primary standard, EIA/TIA 568, although there are actually a number of standards, technical advisories, etc. that cover all aspects of structured cabling. When most people simply say "568" when they mean the entire output of the TR 42 committee (see below.)

The model for premises cabling standards was AT&T’s design guidelines for communications cabling developed originally  from a 1982 survey of 79 businesses located in New York, California, Florida and Arkansas involving over 10,000 cable runs. At the time, cabling was used mainly for telephones to wiring closets and PBXes (Private Branch Exchanges or local phone switches), but it established a baseline for cable length requirements for commercial customers that was used in creating TIA-568. The AT&T survey determined that 99.9% of all stations were less than 300 feet (about 100 meters) from the wiring closet, so that became the goal of the 568 standard. Much of the terminology from the telephone industry also carried over into the development of structured cabling standards, although some of that terminology is being replaced by less telephone-specific terminology.

Today's premises cabling standards define cabling systems, using both copper and fiber optic cables, that can support premises networks called LANs for "local area networks" from 10 megabits per second to 10 gigabits per second over 100 meter distances. Other premises systems such as building management, HVAC, security systems including CCTV that previously used coax cabling, etc. now are designed around structured cabling standards.

Cabling standards are not developed for end users or installers, but for component and equipment manufacturers who need to develop products that offer interoperability andthe mutliple sources of supply demanded by users. The manufacturers develop products around the standards specifications and are responsible for telling installers and end users how to use these components. The designers, installers and users of networks can rely on the instructions of the manufacturers on how to utilize these "standard products" correctly.

The essence of standards for structured cabling is they provide a minimum performance level for components and cabling systems that manufacturers use to develop products for the marketplace. The competition in the cabling marketplace requires companies to make cables that are better than those standards in order to differentiate their products from competitors. So using those standards, manufacturers make cables that will be compatible with other cables meeting the same standards but offer advantages in performance, installation or cost.
 
Many people think this standard is a mandatory, even legal, document like the NEC. In fact, "568" is a voluntary interoperability standard for communications cabling, developed by a number of manufacturers of cabling components and networking equipment, so that they might make equipment that could use any 568-compliant cabling system and be upgraded in the future as long as it was designed for the same cable plant. What 568 is, in fact, is a common sense approach to cabling that defines component and cabling system specifications and offers interoperability, upgradability and low cost due to the numerous manufacturers offering compatible products. 
 
Note: TIA-568 is a US standard. Worldwide, ISO/IEC writes the standards and a summary of their standards is below.
The Basics of "568"
 
The TIA "568" structured cabling standard calls for connecting the desktop (work area) to a telecom closet (the "horizontal" run) with up to 100 meters of cable (including 90 m of permanently installed cable (permanent link) and no more than 10 m total of patchcords), which is usually unshielded twisted pair - UTP - with 4 pairs of wires - called Cat 3, Cat 5, Cat5e, Cat 6 or Cat 6A. The "Cat" or "category" designation refers to a performance level or grade for UTP cabling, which we will explain in the Cables section. Most copper installations today use Cat 5e or Cat 6 exclusively, as they aren't that much more expensive than Cat 3 and can support phones or any LAN on any outlet. Screened twisted pair (foil shielded over the 4 pairs) and shielded twisted pair (STP) are also acceptable and in fact widely used outside the USA.
 
 
The backbone cabling can be either UTP or fiber optics. In larger networks, fiber is most often used for its longer distance capability and higher bandwidth. 568 specifies two multimode fibers, 62.5/125 - the most common MM fiber until recently, and 50/125 - a higher bandwidth fiber rated for use with lasers for gigabit networks that is rapidly overtaking 62.5/125 in popularity. Singlemode fiber is also specified for longer backbone links, as in a campus, for high speed networks.
 
Fiber optics is also a horizontal option in 568, but not often used because of the higher cost except where high bitrate networks or future upgrades are expected. However, a properly designed centralized fiber network that connects the desktop directly to the computer room with no intermediate electronics does not need a telecom closet and saves the cost of conditioned power, data ground, AC and the floor space, which may offset the additional cost of the fiber electronics.
 
Virtually every corporate network now includes wireless, which is, of course, not wireless since access points are connected into the network with copper or fiber cabling. Issues for wireless include proper siting of the wireless access points (antennas, also abbreviated as APs), providing adequate bandwidth to the access points and ensuring network security since wireless signals are easily intercepted.
The telecom closet, or telecom room (TR) as it is now called, houses the hubs for the computers in the work areas. These hubs are interconnected on "backbone" wiring which is mostly fiber optics, as it usually carries higher speed signals over longer distances and provides isolation from ground loops, another problem with copper cabling in LANs. The main cross-connect (MXC) or equipment room contains the network and telco hardware. For the telephones, their lower bandwidth requirements allow longer runs, so they are usually simply connected to backbone cables in the telecom closet with a punchdown and run straight to the MXC.
 
TIA 568 standards have also included IBM Type 1 cable, a shielded two pair cable, since it is still used in some networks. However, it does not include coax cable, like RG-58 used in some Ethernet LANs and RG-6 used in CATV and CCTV, except in the residential standard.

A general restriction for structured cabling is the permissible distances for cable runs. The table below lists cable distances for various types of permitted cabling. The restrictions on fiber links in the horizontal are arbitrary to be equal to copper cabling and may be exceeded for many network uses as long as the equipment provider allows such use. Fiber lengths in the backbone may be restricted by the bandwidth of multimode fiber when used with high speed networks, so the choice of fiber type may determine the actual length possible.

Cable TypeDistance (Meters)Distance (Feet)
UTP copper (data)100330
UTP copper (voice-POTS)8002625
DSL/ADSL500016404
MM fiber (horizontal)100330
MM fiber (centralized)3001000
MM fiber (backbone)20006560
SM fiber (backbone)30009840

TIA-568-C revision proposes to change the nomenclature of structured cabling systems. Here is an explanation of the proposal, as of 12/2008.
 
Beyond "568"
568 is only part of the structured cabling standards. It's a multi-part standard itself and there are several more standards cover other areas of cabling:
EIA/TIA 568: The main standard document for structured cabling, usually referred to as simply "568." It is now on the "C" revision, published in 2009. Always check with manufacturers for the latest revisions.
EIA/TIA 569: Covers pathways and spaces. Defines the "telecom closet" or telecom room as it is now called.
EIA/TIA 570: Residential cabling.
EIA/TIA 606: Cabling system administration (documentation)
EIA/TIA 607: Grounding and bonding
 
 
International Standards
 
The international equivalent of EIA/TIA 568 is ISO/IEC 11801. The standards are written similarly to what has been done by TR 42. Here are their relevant standards:
ISO/IEC 11801 - Cabling for customer premises - structured cabling similar to TIA 568
ISO/IEC 14763-1 - Administration, documentation -
similar to TIA 606
ISO/IEC 14763-2 - Planning and Installation - similar to TIA 569
ISO/IEC 14763-3 - Testing optical fibre cabling - included in TIA 568
IEC 61935-1 - Testing copper cabling - included in TIA 568


Electrical Codes For Cabling
The most important "standards" and the only ones that are legally mandatory are  the local building and electrical codes, such as the US National Electrical Code (NEC.) The NEC is developed by the National Fire Protection Assn. and covers all aspects of electrical and fire safety. Article 800 of the NEC covers communication circuits, such as telephone systems and outside wiring for fire and burglar alarm systems and Article 770 covers fiber optics. All premises cabling must comply with building and electrical codes applicable in your area. Below is a listing of current NEC articles covering premises cabling.

NEC Articles Covering Cabling
Chapter Article Topic
6 640 Sound Systems
7 725 Remote-Control, Signaling and Power-Limited Circuits
7 760 Fire Alarm Signaling Systems
7 770 Optical Fiber Cables and Raceways
7 780 "Smart House" Wiring
8 800 Telecommunications Circuits (Telephone and LAN)
8 810 Radio and TV Equipment
8 820 CATV Systems
8 830 Network-Powered Broadband Systems


Learning More About Standards and Codes
There are a number of ways of finding out more about cabling standards. You can buy a complete copy of the EIA/TIA or ISO/IEC standards which can be very expensive and wade through page after page of standards language. You can also get catalogs and/or visit the websites of a number of cabling manufacturers who have extremely complete explanations of the standards which have been created for their installers and end users. The second method is the recommended one.
Understanding codes requires not only learning what codes cover but what codes are applicable in the local area and who inspects installations. Furthermore, codes change regularly, usually every 2-5 years, and installers are required to keep up to date on the codes. Understand what is required in the areas you do installations and know when the codes are updated.


The "Cables" of "Cabling"
 
The choice of  cable in network cabling (or communication medium as it is sometimes called) is rather important because of the extremely high frequencies of the signals. Sending a 60-cycle utility power through a wire rarely presents a difficulty; but sending a 1 or 10 billion bits per second signal can be a lot more difficult. For this reason, the method of sending signals and the materials they are sent through can be important.
 
 
Network Cabling Types
 
A number of cabling options have been developed over the history of communications and are still in use for networking connections.
 
Unshielded Twisted pair (UTP) - UTP cable is the primary cable used for networks, as specified in the EIA/TIA 568 standard. UTP was developed from the original phone wires but refined to enhance its bandwidth capability. This cable type has been widely used because it is inexpensive and simple to install. The limited bandwidth of early UTP (which translates into slower transmissions) has pushed development of new cable performance grades (the "categories" of 568) but has created a more expensive product and more complicated installation process.
 
Screened Twisted pair (ScTP) - Same as UTP with an overall shield around the 4 pairs. While not currently specified for any networks or covered in the EIA/TIA 568 standard (but not prohibited), it is used in many networks in Europe where EMI is a greater concern. It tends to be more expensive, harder to terminate and requires special shielded plugs and jacks.
 
Shielded Twisted Pair (STP) - Like UTP but with a shield around every pair. Widely used in IBM systems (IBM Type 1 cable) and included in early versions of 568.
 
Coaxial Cables - The original Ethernet cable was coax and coax is still used in video (CCTV, CATV) systems. This is familiar and easy to install, has good bandwidth and lower attenuation but more expensive and bulky. Not included in 568, but in 570 for residential video use. Coax is also used in residential applications for LANs using a transmission scheme called MoCA that works like a cable modem. Read more on coax
 
Optical Fiber - Optional for most networks, top performance, excellent bandwidth, very long life span, excellent security but slightlly higher installed cost than twisted pair cables, more expensive electronics interface to them. Fiber can be cost efffective with optimal architecture. See FIber in Premises Cabling and the FOA Online Fiber Optic Reference Guide Table of Contents .
 
Other transmission options:
Wireless - no data transmission cables are required to connect any individual terminal, but wireless requires cabling to every antenna (called an Access Point.) Within the range of the radio signals, a terminal can be moved anywhere. Usually wireless is more expensive but can be used in locations where is would be difficult to install cables. In the modern network, wireless is a requirement because so many users want "mobility" - so they are not "tethered" to a desktop. More on wireless
 
Infrared Transmission - Also transmits data without wires or fibers using infrared (IR) light but each transmitter requires cabling. By sending pulses of infrared light in the same patterns as electronic pulses sent over cables, it is possible to send data from one place to another. Networks based on IR transmission have been developed for use in office and for line-of-sight transmissions between buildings. It is generally limited in range and can be interrupted by blocking or weather.
 
Powerline or Phone Line Transmission - Networks using available power line cabling have been under development for many years, but  with mixed results due the unpredictability of wiring performance and interference from power line noise.
 
We will focus only on the most popular types of cabling, UTP, coax and fiber optics, as well as cabling for wireless.



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Table of Contents: The FOA Reference Guide To Fiber Optics



 


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