Tuesday, June 28, 2011

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:
  • Two-fiber (duplex) 62.5/125-micron (aka OM1 per ISO 11801)
  • 50/125-micron multimode fiber-optic cable
Within the 50/125-micron multimode fiber-optic classification, there are two options:
  • A standard 50-micron fiber (aka OM2 per ISO 11801)
  • 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.

Saturday, June 25, 2011

Basic Requirements for Backbone Cabling

Backbone cabling includes:
  • Cabling between equipment rooms and building entrance facilities
  • In a campus environment, cabling between buildings' entrance facilities
  • 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. (A hierarchical star topology is one in which all cables lead from their termination points back to a central location.) 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. Figure 1 shows multiple levels of equipment rooms and telecommunications rooms.
    Figure 1: Star topology of equipment room and telecommunication rooms connected via backbone cabling
  • 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.

Wednesday, June 22, 2011

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. Refer to Figure 2.7 later in the chapter to see backbone cabling that connects an equipment room with telecommunications rooms. 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.
KEY TERM: cross-connect 
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).

Sunday, June 19, 2011

Subsystems of a Structured Cabling System

The ANSI/TIA-568-C.1 standard breaks structured cabling into six areas:
  • Horizontal cabling
  • Backbone cabling
  • Work area
  • Telecommunications rooms and enclosures
  • Equipment rooms
  • Entrance facility (building entrance)
This chapter provides an overview of the ANSI/TIA-568-C standard and is not meant as a substitute for the official document. Cabling professionals should purchase a full copy; you can do so at the Global Engineering Documents website (www.global.ihs.com).

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
Figure 1 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.
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:
Figure 1: Horizontal cabling in a star topology from the telecommunications room
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.
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.

Thursday, June 16, 2011

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 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
In this chapter, we'll discuss the standard as a whole, without focusing too much on specific sections.
This chapter provides an overview of the ANSI/TIA-568-C standard and is not meant as a substitute for the official document. Cabling professionals should purchase a full copy; you can do so at the Global Engineering Documents website (www.global.ihs.com).
Welcome to the Nomenclature Twilight Zone. 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.

Monday, June 13, 2011

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.

Friday, June 10, 2011

Insulated Cable Engineers Association (ICEA) | Standards and Specification Organizations

The ICEA is a nonprofit professional organization sponsored by leading cable manufacturers in the United States. It was established in 1925 with the goal of producing cable specifications for telecommunication, electrical power, and control cables. The organization draws from the technical expertise of the representative engineer members to create documents that reflect the most current cable-design, material-content, and performance criteria. The group is organized in four sections: Power Cable, Control & Instrumentation Cable, Portable Cable, and Communications Cable.
The ICEA has an important role in relation to the ANSI/TIA/EIA standards for network cabling infrastructure. ICEA cable specifications for both indoor and outdoor cables, copper and fiber optic, are referenced by the TIA documents to specify the design, construction, and physical performance requirements for cables.
ICEA specifications are issued as national standards. In the Communications section, ANSI requirements for participation by an appropriate cross section of industry representatives in a document's development is accomplished through TWCSTAC (pronounced twix-tak), the Telecommunications Wire and Cable Standards Technical Advisory Committee. The TWCSTAC consists of ICEA members, along with other manufacturers, material suppliers, and end users. The ICEA maintains a website at www.icea.net.

Wednesday, June 8, 2011

Telecommunications Industry Association (TIA) | Standards and Specification Organizations

The Telecommunications Industry Association (TIA) is a trade organization that consists of a membership of over 1,100 telecommunications and electronics companies that provide services, materials, and products throughout the world. The TIA membership manufactures and distributes virtually all the telecommunication products used in the world today. TIA's mission is to represent its membership on issues relating to standards, public policy, and market development. The 1988 merger of the United States Telecommunications Suppliers Association (USTSA) and the EIA's Information and Telecommunications Technologies Group formed the TIA.
The TIA (along with the EIA) was instrumental in the development of the ANSI/TIA/EIA-568 Commercial Building Telecommunications Cabling Standard. TIA can be found on the Web at www.tiaonline.org.

Sunday, June 5, 2011

American National Standards Institute (ANSI) | Standards and Specification Organizations

Five engineering societies and three U.S. government agencies founded the American National Standards Institute (ANSI) in 1918 as a private, nonprofit membership organization sustained by its membership. ANSI's mission is to encourage voluntary compliance with standards and methods. ANSI's membership includes almost 1,400 private companies and government organizations in the United States as well as international members.
ANSI does not develop the American National Standards (ANS) documents, but it facilitates their development by establishing a consensus between the members interested in developing a particular standard.
To gain ANSI approval, a document must be developed by a representative cross section of interested industry participants. The cross section must include both manufacturers and end users. In addition, a rigorous balloting and revision process must be adhered to so that a single powerful member does not drive proprietary requirements through and establish a particular market advantage.
Through membership in various international organizations such as the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC), ANSI promotes standards developed in the United States. ANSI was a founding member of the ISO and is one of the five permanent members of the ISO governing council and one of four permanent members on the ISO's Technical Management Board.
ANSI standards include a wide range of information-technology specifications, such as SCSI interface specifications, programming language specifications, and specifications for character sets. ANSI helped to coordinate the efforts of the Electronic Industries Alliance (EIA) and the Telecommunications Industry Association (TIA) to develop ANSI/TIA/EIA-568, the cabling specification in the United States. ANSI/TIA-568-C is discussed in more detail later in this chapter. You can find information on it and links to purchase the documents on ANSI's website at www.ansi.org.

Wednesday, June 1, 2011

Standards and Specification Organizations | Cabling

If you pick up any document or catalog on data cabling, you will see acronyms and abbreviations for the names of specification organizations. If you want to know more about a particular specification, you should be familiar with the organization that publishes that particular document. These U.S.-based and international organizations publish hardware, software, and physical-infrastructure specifications to ensure interoperability between electrical, communications, and other technology systems. Your customers and coworkers may laugh at the elation you express when you get even simple networked devices to work, but you are not alone. In fact, the simple act of getting two stations communicating with one another on a 10Base-T network, for example, is a monumental achievement considering the number of components and vendors involved. Just think: Computers from two different vendors may use Ethernet adapters that also may be from different manufacturers. These Ethernet adapters may also be connected by cable and connectors provided by another manufacturer, which in turn may be connected to a hub built by still another manufacturer. Even the software that the two computers are running may come from different companies. Dozens of other components must work together.
That anything is interoperable at all is amazing. Thankfully, a number of organizations around the world are devoted to the development of specifications that encourage interoperability. These are often nonprofit organizations, and the people who devote much of their time to the development of these specifications are usually volunteers. These specifications include not only cabling specifications and performance and installation practices but also the development of networking equipment like Ethernet cards. As long as the manufacturer follows the appropriate specifications, their devices should be interoperable with other networking devices.
The number of organizations that provide specifications is still more amazing. It might be simpler if a single international organization were responsible for all standards. However, if that were the case, probably nothing would ever get accomplished—hence the number of specifications organizations. The following sections describe a number of these organizations, but the list is by no means exhaustive.