Structured Cabling Specifications and Standards

January 19, 2012
By Colin Yao

In the past, companies often had several cabling infrastructures because no single cabling system would support all of a company’s applications. Nowadays, a standardized cabling system is important not only for consumers but also for vendors and cabling installers. Vendors must clearly understand how to design and build products that will operate on a universal cabling system. Cable installers need to understand what products can be used, proper installation techniques and practices, and how to test installed systems.

In this tutorial, we will cover some of the important topics related to cabling standards.

  1. Identify the key elements of the ANSI/TIA-568-C Commercial Building Telecommunications Cabling Standard
  2. Identify other ANSI/TIA standards required to properly design the pathways and spaces and grounding of a cabling system
  3. Identify key elements of the ISO/IEC 11801 Generic Cabling for Customer Premises Standard

>> Structured Cabling and Standardization

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. The data and voice cabling system had to support these reconfigurations quickly and easily.

Until the early 1990s, cabling systems were proprietary, vendor-specific, and lacking in flexibility. Cabling has changed a lot 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 the following figure. 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.

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Note: 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.

  1. 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.
  2. 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.

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.

 

>> ANSI/TIA-568-C Cabling Standard

In the mid-1980s, consumers, contractors, vendors, and manufacturers became concerned about the lack of specifications relating to telecommunications cabling. Before then, all communications cabling was proprietary and often suited only to a single-purpose use. The Computer Communications Industry Association (CCIA) asked the EIA to develop a specification that would encourage structured, standardized cabling.

Under the guidance of the TIA TR-41 committee and associated subcommittees, the TIA and EIA in 1991 published the first version of the Commercial Building Telecommunications Cabling Standard, better known as ANSI/TIA/EIA-568 or sometimes simply as TIA/EIA-568.

> 1. ANSI/TIA-568-C Purpose and Scope

The ANSI/TIA/EIA-568 standard was developed and has evolved into its current form for several reasons:

  • To establish a cabling specification that would support more than a single vendor application
  • To provide direction of the design of telecommunications equipment and cabling products that are intended to serve commercial organizations
  • To specify a cabling system generic enough to support both voice and data
  • To establish technical and performance guidelines and provide guidelines for the planning and installation of structured cabling systems

The ANSI/TIA-568-C standard addresses the following:

  • Subsystems of structured cabling
  • Minimum requirements for telecommunications cabling
  • Installation methods and practices
  • Connector and pin assignments
  • The life span of a telecommunications cabling system (which should exceed 10 years)
  • Media types and performance specifications for horizontal and backbone cabling
  • Connecting hardware performance specifications
  • Recommended topology and distances
  • The definitions of cabling elements (horizontal cable, cross-connects, telecommunication outlets, etc.)

The current configuration of ANSI/TIA-568-C subdivides the standard as follows:

  • ANSI/TIA-568-C.0: Generic Telecommunications Cabling for Customer Premises
  • ANSI/TIA-568-C.1: Commercial Building Telecommunications Cabling Standard
  • ANSI/TIA-568-C.2: Balanced Twisted-Pair Telecommunications Cabling and Components Standard
  • ANSI/TIA-568-C.3: Optical Fiber Cabling Components Standard

Note:

The ANSI/TIA-568-C standard contains two wiring patterns for use with UTP jacks and plugs. They indicate the order in which the wire conductors should be connected to the pins in modular jacks and plugs and are known as T568A and T568B. Do not confuse these with the documents ANSI/TIA/EIA-568-B and the previous version, ANSI/TIA/EIA-568-A. The wiring schemes are both covered in ANSI/TIA/EIA-568.

 

> 2. Subsystems of a Structured Cabling System

The ANSI/TIA-568-C.1 standard breaks structured cabling into six areas:

  1. Horizontal cabling
  2. Backbone cabling
  3. Work area
  4. Telecommunications rooms and enclosures
  5. Equipment rooms
  6. Entrance facility (building entrance)

1) Horizontal Cabling

Horizontal cabling, as specified by ANSI/TIA-568-C.1, is the cabling that extends from horizontal cross-connect, intermediate cross-connect, or main cross-connect to the work area and terminates in telecommunications outlets (information outlets or wall plates). Horizontal cabling includes the following:

  • Cable from the patch panel to the work area
  • Telecommunications outlets
  • Cable terminations
  • Cross-connections (where permitted)
  • A maximum of one transition point
  • Cross-connects in telecommunications rooms or enclosures

The following figure shows a typical horizontal-cabling infrastructure spanning out in a star topology from a telecommunications room. The horizontal cabling is typically connected into patch panels and switches/hubs in telecommunications rooms or enclosures. A telecommunications room is sometimes referred to as a telecommunications closet or wiring closet. A telecommunications enclosure is essentially a small assembly in the work area that contains the features found in a telecommunications room.

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(A) Transition point

ANSI/TIA-568-C allows for one transition point in horizontal cabling.

The transition point is where one type of cable connects to another, such as where round cable connects to under-carpet cable. A transition point can also be a point where cabling is distributed out to modular furniture. Two types of transition points are recognized:

  1. MUTOA – This acronym stands for multiuser telecommunications outlet assembly, which is an outlet that consolidates telecommunications jacks for many users into one area. Think of it as a patch panel located out in the office area instead of in a telecommunications room.
  2. CP – CP stands for consolidation point, which is an intermediate interconnection scheme that allows horizontal cables that are part of the building pathways to extend to telecommunication outlets in open-office pathways such as those in modular furniture. The ISO/IEC 11801 refers to the CP as a transition point (TP).

If you plan to use modular furniture or movable partitions, check with the vendor of the furniture or partitions to see if it provides data-cabling pathways within its furniture. Then ask what type of interface it may provide or require for your existing cabling system. You will have to plan for connectivity to the furniture in your wiring scheme.

Application-specific components (baluns, repeaters) should not be installed as part of the horizontal-cabling system (inside the walls). These should be installed in the telecommunication rooms or work areas.

(B) Recognized Media

ANSI/TIA-568-C recognizes two types of media (cables) that can be used as horizontal cabling. More than one media type may be run to a single work-area telecommunications outlet; for example, a UTP cable can be used for voice, and a fiber-optic cable can be used for data. The maximum distance for horizontal cable from the telecommunications room to the telecommunications outlet is 90 meters (295’) regardless of the cable media used. Horizontal cables recognized by the ANSI/TIA-568-C standard are limited to the following:

  1. Four-pair, 100 ohm, unshielded or shielded twisted-pair cabling: Category 5e, Category 6 or Category 6A (ANSI/TIA-568-C.2)
  2. Two-fiber 62.5/125-micron or 50/125-micron optical fiber (or higher fiber count) multimode cabling (ANSI/TIA-568-C.3)
  3. Two-fiber (or higher fiber count) optical fiber single-mode cabling (ANSI/TIA-568-C.3)

(C) Telecommunications Outlets

ANSI/TIA-568-C.1 specifies that each work area shall have a minimum of two information-outlet ports. Typically, one is used for voice and another for data.

The following figure shows a possible telecommunications outlet configuration. The outlets go by a number of names, including equipment outlets, information outlets, wall jacks, and wall plates. However, an information outlet is officially considered to be one jack on a telecommunications outlet; the telecommunications outlet is considered to be part of the horizontal-cabling system.

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The information outlets wired for UTP should follow one of two conventions for wire-pair assignments or wiring patterns: T568A or T568B. They are nearly identical, except that pairs 2 and 3 are interchanged. Neither of the two is the correct choice, as long as the same convention is used at each end of a permanent link. It is best, of course, to always use the same convention throughout the cabling system. T568B used to be much more common in commercial installations, but T568A is now the recommended configuration. (T568A is the required configuration for residential installations, in accordance with ANSI/TIA-570-B.) The T568A configuration is partially compatible with an older wiring scheme called USOC, which was commonly used for voice systems.

Be consistent at both ends of the horizontal cable. When you purchase patch panels and jacks, you may be required to specify which pattern you are using, as the equipment may be color-coded to make installation of the wire pairs easier. However, most manufacturers now include options that allow either configuration to be punched down on the patch panel or jack.

The following figure shows the T568A and T568B pin-out assignments. The wire/pin assignments in this figure are designated by wire color. The standard wire colors are shown in the following table.

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Although your application may not require all the pins in the information outlet, you should make sure that all wires are terminated to the appropriate pins if for no other reason than to ensure interoperability with future applications on the same media. The table below shows some common applications and the pins that they use, and clearly illustrates why all pairs should be terminated in order to make the structured-wiring installation application generic.

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A good structured-wiring system will include documentation printed Tip and placed on each of the telecommunications outlets.

(D) Pair Numbers and Color Coding

The conductors in a UTP cable are twisted in pairs and color coded so that each pair of wires can be easily identified and quickly terminated to the appropriate pin on the connecting hardware (patch panels or telecommunication outlets). With four-pair UTP cables, each pair of wire is coded with two colors, the tip color and the ring color.

In a four-pair cable, the tip color of every pair is white. To keep the tip conductors associated with the correct ring conductors, often the tip conductor has bands in the color of the ring conductor. Such positive identification (PI) color coding is not necessary in some cases, such as with Category 5 and higher cables, because the intervals between twists in the pair are very close together, making separation unlikely.

You identify the conductors by their color codes, such as white-blue and blue. With premises (indoor) cables, it is common to read the tip color first (including its PI color), then the ring color. The table below lists the pair numbers, color codes, and pin assignments for T568A and T568B.

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2) Backbone Cabling

The next subsystem of structured cabling is called backbone cabling. (Backbone cabling is also sometimes called vertical cabling, cross-connect cabling, riser cabling, or intercloset cabling.)

Backbone cabling is necessary to connect entrance facilities, equipment rooms, and telecommunications rooms and enclosures. Backbone cabling consists of not only the cables that connect the telecommunications rooms, equipment rooms, and building entrances but also the cross-connect cables, mechanical terminations, or patch cords used for backbone-to-backbone cross-connection.

cross-connect – A cross-connect is a facility or location within the cabling system that permits the termination of cable elements and their intereconnection or cross-connection by jumpers, termination blocks, and/or cables to another cabling element (another cable or patch panel).

(A) Basic Requirements for Backbone Cabling

Backbone cabling includes:

  1. Cabling between equipment rooms and building entrance facilities
  2. In a campus environment, cabling between buildings’ entrance facilities
  3. Vertical connections between floors

ANSI/TIA-568-C.1 specifies additional design requirements for backbone cabling, some of which carry certain stipulations, as follows:

  • Grounding should meet the requirements as defined in J-STD-607-A, the Commercial Building Grounding and Bonding Requirements for Telecommunications.
  • The pathways and spaces to support backbone cabling shall be designed and installed in accordance with the requirements of TIA-569-B. Care must be taken when running backbone cables to avoid sources of EMI or radio frequency interference.
  • No more than two hierarchical levels of cross-connects are allowed, and the topology of backbone cable will be a hierarchical star topology. Each horizontal cross-connect should be connected directly to a main cross-connect or to an intermediate cross-connect that then connects to a main cross-connect. No more than one cross-connect can exist between a main cross-connect and a horizontal cross-connect.
  • Centralized optical fiber cabling is designed as an alternative to the optical cross-connection located in the telecommunications room or telecommunications enclosure when deploying recognized optical fiber to the work area from a centralized cross-connect.
  • The length of the cord used to connect telecommunications equipment directly to the main or intermediate cross-connect should not exceed 30 meters (98’).
  • Unlike horizontal cabling, backbone cabling lengths are dependent on the application and on the specific media chosen. (See ANSI/TIA-568-C.0 Annex D.) For optical fiber, this can be as high as 10,000 meters depending on the application! However, distances of ≤ 550 meters are more likely inside a building. This distance is for uninterrupted lengths of cable between the main cross-connect and intermediate or horizontal cross-connect.
  • Bridge taps or splices are not allowed.
  • Cables with more than four pairs may be used as long as they meet additional performance requirements such as for power-sum crosstalk. These requirements are specified in the standard. Currently, only Category 5e cables are allowed to have more than four pairs.

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(B) Recognized Backbone Media

ANSI/TIA-568-C recognizes several types of media (cable) for backbone cabling. These media types can be used in combination as required by the installation. The application and the area being served will determine the quantity and number of pairs required. The maximum distances permitted depend on the application standard and are available in ANSI/TIA-568-C.0 Annex D. In general, the higher the speed, the shorter the distance. Also, optical fiber maximums can range from 220 to 10,000 meters depending on the media and application, whereas UTP is limited to 100 meters.

The distances for recognized media are dependent on the application and are shown in ANSI/TIA-568-C.0 Annex D. (Note: distances are the total cable length allowed between the main cross-connect and the horizontal cross-connect, allowing for one intermediate cross-connect.)

Note: Coaxial cabling is not recognized by the ANSI/TIA-568-C version of the standard.

 

3) Work Area

The work area is where the horizontal cable terminates at the wall outlet, also called the telecommunications outlet. In the work area, the users and telecommunications equipment connect to the structured-cabling infrastructure. The work area begins at the telecommunications area and includes components such as the following:

  • Patch cables, modular cords, fiber jumpers, and adapter cables
  • Adapters such as baluns and other devices that modify the signal or impedance of the cable (these devices must be external to the information outlet)
  • Station equipment such as computers, telephones, fax machines, data terminals, and modems

The work area wiring should be simple and easy to manipulate. In today’s business environments, it is frequently necessary to move, add, or remove equipment. Consequently, the cabling system needs to be easily adaptable to these changes.

 

4) Telecommunications Rooms and Telecommunications Enclosures

The telecommunications rooms (along with equipment rooms, often referred to as wiring closets) and telecommunications enclosures are the location within a building where cabling components such as cross-connects and patch panels are located. These rooms or enclosures are where the horizontal structured cabling originates.

Horizontal cabling is terminated in patch panels or termination blocks and then uses horizontal pathways to reach work areas. The telecommunications room or enclosure may also contain networking equipment such as LAN hubs, switches, routers, and repeaters. Backbone-cabling equipment rooms terminate in the telecommunications room or enclosure. The figure above illustrates the relationship of a telecommunications room to the backbone cabling and equipment rooms.

A telecommunications enclosure is intended to serve a smaller floor area than a telecommunications room.

TIA’s Fiber Optics LAN Section (www.fols.org) has compared the cost differences between network cabling systems using either telecommunications rooms or telecommunications enclosures on each floor of a commercial building and has found as much as 30 percent savings when using multiple telecommunications enclosures.

TIA-569-B discusses telecommunications room design and specifications. TIA-569-B recommends that telecommunications rooms be stacked vertically between one floor and another. ANSI/TIA-568-C further dictates the following specifications relating to telecommunications rooms:

  • Care must be taken to avoid cable stress, tight bends, staples, cable wrapped too tightly, and excessive tension. You can avoid these pitfalls with good cable-management techniques.
  • Use only connecting hardware that is in compliance with the specifications you want to achieve.
  • Horizontal cabling should terminate directly not to an application-specific device but rather to a telecommunications outlet. Patch cables or equipment cords should be used to connect the device to the cabling. For example, horizontal cabling should never come directly out of the wall and plug in to a phone or network adapter.

 

5) Entrance Facility

The entrance facility (building entrance) as defined by ANSI/TIA-568-C.1 specifies the point in the building where cabling interfaces with the outside world. All external cabling (campus backbone, inter-building, antennae pathways, and telecommunications provider) should enter the building and terminate in a single point.

Telecommunications carriers are usually required to terminate within 50’ of a building entrance. The physical requirements of the interface equipment are defined in TIA-569-B, the Commercial Building Standard for Telecommunications Pathways and Spaces. The specification covers telecommunications room design and cable pathways.

TIA-569-B recommends a dedicated entrance facility for buildings with more than 20,000 usable square feet. If the building has more than 70,000 usable square feet, TIA-569-B requires a dedicated, locked room with plywood termination fields on two walls. The TIA-569-B standard also specifies recommendations for the amount of plywood termination fields, based on the building’s square footage.

Demarcation Point – The demarcation point (also called the demarc, pronounced dee-mark) is the point within a facility, property, or campus where a circuit provided by an outside vendor, such as the phone company, terminates. Past this point, the customer provides the equipment and cabling. Maintenance and operation of equipment past the demarc is the customer’s responsibility.

The entrance facility may share space with the equipment room, if necessary or possible. Telephone companies often refer to the entrance facility as the demarcation point. Some entrance facilities also house telephone or PBX (private branch exchange) equipment. The following figure shows an example of an entrance facility.

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6) Equipment Room

The next subsystem of structured cabling defined by ANSI/TIA-568-C.1 is the equipment room, which is a centralized space specified to house more sophisticated equipment than the entrance facility or the telecommunications rooms. Often, telephone equipment or data networking equipment such as routers, switches, and hubs are located there. Computer equipment may possibly be stored there. Backbone cabling is specified to terminate in the equipment room.

In smaller organizations, it is desirable to have the equipment room located in the same area as the computer room, which houses network servers and possibly phone equipment. The following figure shows the equipment room. For information on the proper design of an equipment room, refer to TIA-569-B.

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> 3. Media and Connecting Hardware Performance

ANSI/TIA-568-C specifies performance requirements for twisted-pair cabling and fiber-optic cabling. Further, specifications are laid out for length of cable and conductor types for horizontal, backbone, and patch cables.

1) 100 Ohm Unshielded Twisted-Pair Cabling

ANSI/TIA-568-C.2 recognizes four categories of UTP cable to be used with structured cabling systems. These UTP cables are specified to have a characteristic impedance of 100 ohms, plus or minus 15 percent, from 1MHz up to the maximum bandwidth supported by the cable. They are commonly referred to by their category number and are rated based on the maximum frequency bandwidth. The categories are found in the following table.

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Ensuring a Specific Level of Cabling Performance

UTP cabling systems cannot be considered Category 3–, 5e–, 6–, or 6A–compliant (and consequently certified) unless all components of the cabling system satisfy the specific performance requirements of the particular category.

The components include the following:

  • All backbone and horizontal cabling
  • Telecommunications outlets
  • Patch panels
  • Cross-connect wires and cross-connect blocks

All patch panel terminations, wall-plate terminations, crimping, and cross-connect punch-downs also must follow the specific recommendations for the respective category. In other words, a network link will perform only as well as the lowest category-compliant component in the link.

Connecting Hardware: Performance Loss

Part of the ANSI/TIA-568-C.2 standard is intended to ensure that connecting hardware (crossconnects, patch panels, patch cables, telecommunications outlets, and connectors) does not have an adverse effect on attenuation and NEXT. To this end, the standard specifies requirements for connecting hardware to ensure compatibility with cables.

Patch Cables and Cross-Connect Jumpers

ANSI/TIA-568-C.1 also specifies requirements that apply to cables used for patch cables and cross-connect jumpers. The requirements include recommendations for maximum-distance limitations for patch cables and cross-connects, as shown here:

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The total maximum distance of the channel should not exceed the maximum distance recommended for the application being used. For example, the channel distance for 100Base-TX Ethernet should not exceed 100 meters.

Note: Patch cables should use stranded conductors rather than solid conductors Tip so that the cable is more flexible. Solid conductor cables are easily damaged if they are bent too tightly or too often.

Patch cables usually have a slightly higher attenuation than horizontal cables because they are stranded rather than solid conductors. Though stranded conductors increase patch cable flexibility, they also increase attenuation.

Detailed requirements for copper cabling and connectivity components are found in ANSI/TIA 568-C.2. Fiber-optic cabling and connectivity components are contained in ANSI/TIA 568-C.3. We highly recommend that you familiarize yourself with cabling requirements if you need to specify performance to a cabling contractor. You should only have to reference the standard for purposes of the Request for Quotation, but your knowledge will help in your discussions with the contractor.

2) Fiber Optic Cabling

The ANSI/TIA-568-C standard permits both single-mode and multimode fiber-optic cables.

Two connectors were formerly widely used with fiber-optic cabling systems: the ST and SC connectors. Many installations have employed the ST connector type, but the standard now recognizes only the 568SC-type connector. This was changed so that the fiber-optic specifications in ANSI/TIA-568-C.3 could agree with the ISO 11801 standard used in Europe.

The ANSI/TIA-568-C.3 standard also recognizes small-form-factor connectors such as the MT-RJ and LC connectors as well as array connectors such as MPO connectors.

What Are Fiber Modes

Fiber-optic cable is referred to as either single-mode or multimode fiber. The term mode refers to the number of independent subcomponents of light that propagate through distinct areas of the fiber-optic cable core. Single-mode fiber-optic cable uses only a single mode of light to propagate through the fiber cable, whereas multimode fiber allows multiple modes of light to propagate.

Multimode Optical Fiber Cable

Multimode optical fiber is most often used as backbone cable inside a building and for horizontal cable. Multimode cable permits multiple modes of light to propagate through the cable and thus lowers cable distances and has a lower available bandwidth. Devices that use multimode fiber-optic cable typically use light-emitting diodes (LEDs) to generate the light that travels through the cable; however, higher-bandwidth network devices such as Gigabit Ethernet are now using lasers with multimode fiber-optic cable. ANSI/TIA-568-C.3 recognizes two types of multimode optical fiber cable:

  1. Two-fiber (duplex) 62.5/125-micron (aka OM1 per ISO 11801)
  2. 50/125-micron multimode fiber-optic cable

Within the 50/125-micron multimode fiber-optic classification, there are two options:

  1. A standard 50-micron fiber (aka OM2 per ISO 11801)
  2. A higher bandwidth option known as 850nm laser-optimized 50/125-micron (aka OM3)

ANSI/TIA-568-C.3 recommends the use of 850nm laser-optimized 50/125-micron (OM3) since it has much higher bandwidth and supports all Gigabit Ethernet applications to the longest distances.

The same connectors and transmission electronics are used on both 62.5/125-micron and 50/125-micron multimode fiber-optic cable. Since multimode fiber has a large core diameter, the connectors and transmitters do not need the same level of precision required with single-mode connectors and transmitters. As a result, they are less expensive than single-mode parts.

Single-Mode Optical-Fiber Cable

Single-mode optical-fiber cable is commonly used as backbone cabling outside the building and is also usually the cable type for long-distance phone systems. Light travels through single mode fiber-optic cable using only a single mode, meaning it travels straight down the fiber and does not “bounce” off the cable walls. Because only a single mode of light travels through the cable, single-mode fiber-optic cable supports higher bandwidth and longer distances than multimode fiber-optic cable.

Devices that use single-mode fiber-optic cable typically use lasers to generate the light that travels through the cable. Since the core size of single-mode cable is much smaller than multimode fiber, the connecting hardware and especially the lasers are much more expensive than those used for multimode fiber. As a result, single-mode based systems (cable plus electronics) are more costly than multimode systems.

ANSI/TIA-568-C.3 recognizes OSI and OS2 single-mode optical fiber cables.

Optical Fiber and Telecommunications Rooms

The ANSI/TIA-568-C standard specifies that certain features of telecommunications must be adhered to in order for the installation to be specifications-compliant:

  • The telecommunications outlet(s) must have the ability to terminate a minimum of two fibers into 568SC couplings.
  • To prevent damage to the fiber, the telecommunications outlet(s) must provide a means of securing fiber and maintaining a minimum bend radius of 30 millimeters.
  • The telecommunications outlet(s) must be able to store at least one meter of two-fiber (duplex) cable.
  • The telecommunications outlet(s) supporting fiber cable must be a surface-mount box that attaches on top of a standard 4” × 4” electrical box.