Cabling is the umbilical cord that connects voice/data/video networks in a building.
Each day, millions of workers and consumers avidly listen to the raucous cry of their computer calling across a stretch of cable to its mate - the Internet. Some form of cabling generally serves as the plumbing that holds the pieces of the Internet together and supports a myriad of services vital to animating this digital age.
And, whether the services are delivered by satellite, CATV coaxial cable, fiber-optic or copper-based telephone cables, microwave or infrared signaling, these services must be connected to an internal network and its related devices within a building. The usual term for such an internal network is the premises distribution system (PDS). The various types of cabling used by a premises distribution system are seen in the Sidebar, page 36.
Research indicates that the growth in premise networks is set to continue well into the next decade. Frost and Sullivan, a high-technology market research company, predicts that the total market, including media and hardware, will nearly double from $3.71 billion in 1998 to $7.01 billion in 2004. Specifically, the company predicts cabling sales to grow about 64% from $1.49 billion in 1998 to $2.44 in 2004, with hardware making up the difference.
In addition, a dynamic and emerging segment - residential cabling - is contributing to the overall growth of the premises cabling market. Research indicates that by the end of next year, the United States. will have 55 million work-at-home households. That number is up from 34.7 million homes in 1997.
With the growing presence of the Internet, the expansion of PCs into the home and increasing use of entertainment centers, residential network wiring needs are growing. According to Cahners In-Stat Group, a high-tech market research firm, response to these changing needs will create a residential structured wring market that will exceed $1.4 billion by 2004.
STRUCTURED WIRING SOLUTIONS A structured wiring solution allows the integration of voice data and video services into a central, manageable distribution center, or hub. High-grade cable, such as Category 5 twisted pair copper or RG-6 coaxial cable, carries services from the distribution center throughout the home. Modular wall plates or receptacles are the final component. These plates allow for multi-serve access from a single location.
Additional cabling can support add-on features such as a voice-prompted alarm system or an infrared remote-control system network.
Today, electrical contractors in the voice, data and video (V/D/V) business must respond to their customers who want to install top-flight communications networks and services. Often, a client will ask for your company's recommendations on cabling for broadband (that's the buzzword today!) applications in an office.
A good supplier relationship can contribute greatly to a contractor's knowledge of cabling. Think of the "supplier" as anyone in your company's supply chain, including distributor, manufacturer's representative, manufacturer and/or others, who has technical expertise and offers useful service.
This partnering activity can consist of anything from informal teaming with a supplier to better serve a customer on a project, to a long-term business relationship built on a written agreement, such as a franchise. Another approach in the market is to become a "certified installer" for a complete cabling system, which includes the cabling, connectors and other hardware.
The datacom market is entirely different from the power distribution market. For example, in the power distribution market you can consider a 500MCM stranded power cable from one maker as compatible to that from another manufacturer. But in the datacom market, for example, unshielded twisted-pair (UTP) cabling from one manufacturer may not offer the same performance as a similar product from another cable maker. Also, two or more cabling products suitable for a specific application can have vastly different installation requirements and hardware needs.
The number and variety of cable options is vast and confusing, and the wrong selection could adversely affect the efficiency of a network. How can you hack through the jungle of cabling products and specifications?
UNDERSTANDING BROADBAND Let's start by understanding the meaning of the word broadband, which is the information-carrying capability of a transmission medium. Consider it as being opposed to, or better than, a baseband network.
A baseband network provides a single channel for communications across the physical medium (cable) so that only one device can transmit at one time. A device on a baseband network, such as Ethernet, uses all of the available bandwidth for transmission. Another useful analogy is a telephone line where only one person can talk at a time.
A broadband network allows the physical cable to be virtually divided into several different channels, each with its own unique carrier frequency, using a technique called frequency division modulation. Thus, multiple conversions can take place at the same time. Cable TV, using a coaxial cable, is a useful example of a broadband network, which supports a number of individual channels, each of which can be selected by a subscriber.
An Ethernet network, mentioned above, started out as a baseband transmission technology (10BaseT - a 10MHz network running over unshielded twisted pair cabling). The 10 stands for signaling speed, 10MHz, and Base means baseband. However, Ethernet now also runs on a broadband cable.
As previously indicated, high-performance networks also are defined by transmission speed. Data rates have nearly doubled each year over the past decade. In 1995, typical data rates to the desktop were 10 Mbps, with 100Mbps in the backbone. Five years later, these rates have jumped to 100Mbps to the desktop and 1,000 Mbps - 1 Gbps - in the backbone. These numbers will leap anther order of magnitude by 2005.
A wide array of twisted-pair copper conductor and fiber optic cables can support the broadband networks currently being discussed. And with the continuing emphasis on new service, such as video conferencing, office workers want these services at their computer terminals. All of the cable makers offer products for the horizontal cable run, which starts in the telecommunications closet and ends at the faceplate in the work area. Consider this 300-ft (or 90-meter) horizontal segment of the network, to be a hotly contested market because it usually makes up the greatest quantity of LAN cabling in a building.
If the choice for horizontal cabling is copper, sophisticated digital signal processing allows current Category 5 copper cabling to support speeds up to 1Gbps. But let's look at some details.
You can select Category 5 UTP copper cable, but it is now surpassed by type Category 5e (the e stands for enhanced) since it offers improved performance. Category 5e became an industry standard last fall. For even higher performance, consider an "above-Category 5e" performance type of UTP cable. These UTP type cables are called Category 6 and Category 7 cabling, which uses a thicker shielded twisted-pair construction.
Draft versions of a Category 6 standard are circulating in the telecommunications industry, and manufacturers are producing and marketing cabling products based on these [preliminary] specifications. You can consider Category 6 products as falling into a "pre-standard" classification.
Many contractors in the voice/data market are building up a base of experience in Category 5 copper cable installations but are not yet comfortable on advising their customers regarding the higher performance copper cabling. If a customer is in a leased building or a facility that will not be occupied for a long period of time, an investment in something other than Cat 5e is not recommended. But for those who have a longer horizon, who will be at the same facility for more than five years, Category 6 or fiber is a good recommendation.
LOOKING CAREFULLY AT FIBER-OPTIC CABLE Once confined to backbones, optical fiber is now common in the riser and horizontal, as fiber-to-the-desk designs no longer are considered unusual. With a variety of fiber types to select from, which type is best for specific segments of the network?
Optical fiber is available in two types, single-mode and multi-mode. Both types have the same outer diameter, 125 æm, about the thickness of a human hair. Multi-mode fiber, however, has a much larger core, the light-carrying region of the fiber - either 50 æm or 62.5 æm - as compared with 7 to 10 æm for single-mode fiber.
Information is carried through single-mode fiber on just one mode, or ray of light. However, a multimode fiber's larger core size, allows hundreds of modes, or light rays, to pass along at the same time. Strangely, single-mode fiber offers much higher bandwidth and lower signal attenuation than multimode fiber. This is because a single mode fiber eliminates the problem of modal dispersion, which is the spreading of light pulses as modes travel paths of different length within a fiber's core. The modes arrive at a receiver at different times, discrete pulses merge, causing what is called bit errors.
Single- mode fiber is generally used for long distance links, because it carries signals great lengths before requiring amplification. For campus backbone links, a hybrid single-mode/multi-mode fiber cable can be used. The single-mode strands can remain unused, awaiting a future application.
Preferred for most premise applications, multimode fiber uses inexpensive light-emitting diodes (LEDs) and more recently, vertical cavity surface emitting lasers (VCSELs), as light sources.
To work with the VCSELs, multimode fiber is now made in a 50-æm-core size as well as the more familiar 62.5-æm-core size. The 50-æm fiber is becoming increasingly important in premises cabling because it offers higher bandwidth at the 858-nm wavelength. Specifically, the 50-æm fiber triples the bandwidth at the shorter wavelength: 500 MHz/km vs. 16 MHz/km. This is important because the inexpensive laser transmitter and the 50-æm fiber offer important economic advantages.
Furthermore, the VCSEL technology that gave us low-cost lasers at 850 nm is now yielding 1,300 nm lasers, compatible with single-mode fiber. Single-mode fiber, which telephone companies and CATV operators use to cover long distances, offers practically unlimited bandwidth. The combination of 1,300 nm VCSELs and single-mode fiber may obsolete multi-mode fiber some time in the future.
Single-mode fiber, which is the choice for sending light pulses for miles along an outdoor route, as mentioned above, is available in various constructions to resist harsh environments. Specifically, these cables can stand up to: moisture, rodents, crush loads, chemicals, high-voltage, abrasion and ionizing radiation. In addition, five different moisture-resistant materials are used in outdoor cables: gel-filled, gel-filled and grease-filled, gel-filled with water-swellable tapes, and water-swellable tapes without gel or grease. Choosing between a gel-filled cable and one without gel may depend on the time needed to remove the gel material and clean the fiber strands at terminations.
For a fiber-optic cable run between nearby buildings on a campus, consider the types of cable that are available. Indoor-type fiber-optic cable may be spliced or patched to outdoor type cable that enters the building from the outside. In addition to satisfying the NEC requirements on insulation flammability, an indoor-type fiber-optic cable has requirements regarding the bend radius, the operating temperature range and the installation load. The experience level of the installers can influence the installation load: novice installers may need an increased installation load rating to avoid damaging the fibers.
Alternatively, an indoor/outdoor cable may be used for the fiber cable run between buildings and also as the riser cable within the building. Indoor/outdoor type FO cable has a double jacket construction, polyethylene (PE) for outside plant protection, and beneath that jacket, a polyvinyl chloride (PVC) jacket. Because the National Electrical Code requires a flame retardant cable jacket for an indoor environment, the outer jacket of the indoor/outdoor cable is removed when it enters the building.
An outdoor plant fiber-optic cable usually has a loose-tube construction, but in some cases, a tight buffer, loose-tube cable is preferred.
FIBER-OPTIC CONNECTORS The choice of a connector to use with an optical fiber cable is another major concern. The three main types of fiber-optic connectors used are: the straight-tip (ST), the subscriber connector (SC) and the small form factor (SFF) type. Available in five different designs, the SFF connectors are as small as a modular eight-pin connector used on Category 5 copper cable. Finally, the LC connector, with a ceramic ferrule and plastic shell, resembles the SC type but is half the size.
Compared to copper, fiber optics seems to offer the advantage of a one-time install, at least in regard to the cabling. However, the cost of the active electronic components for fiber is much higher than similar equipment used in copper networks. According to one manufacturer, for the same performance in an end-to-end installation, you'll end up paying more for fiber than copper.
The Anixter Levels program offers a solution for anyone specifying or purchasing copper cabling. The Levels program is based on a stringent purchasing specification that required the company's suppliers to qualify their high performance unshielded twisted-pair products. Recently updated, the program helps to fill in the holes in existing standards and provides needed information.
Anixter offers products in the Category 6 range (350 MHz) and also has a proprietary Level 7 cable (400 MHz). Graybar offers high performance cabling products, which can support 350 MHz, and another product in a still higher maximum speed range.
Customers, however, can select a fiber and copper hybrid cable run to each workstation, considering that, generally, copper wiring is still needed for voice circuits at a desk.
The final concern, however, is not choosing between copper or optical fiber on a project, but rather, being able to answer your customer's needs. The more knowledge you have on cabling products, the better you can help your customer.
Work location cabling is the short run of cable connecting the terminal equipment to the telecom-munications outlet. It is usually 10 ft long (3 meters).
Horizontal cabling consists of the run of cable from the tele-communications outlet to the distribution closet. Tie cables between closets on the same floor are considered as horizontal wiring, regardless of the type of media (fiber, unshielded twisted-pair).
Backbone cable is the central or feeder group of cables in a building. The cable is typically placed from the main cross-connect TC to other floors where it is terminated in intermediate TCs.
Equipment cabling consists of the cables and connectors that link communications systems, host computer, local area networks and other devices to shared equipment or cross- and inter-connects at the TC.