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Cabling for the next five years
As the demand for faster networks increases, so does the need to provide the best and most efficient medium for the data to travel. Not long ago, terms like “thin” and “fat” cable described networks using coaxial cable as the primary medium to connect computers. Twisted-pair cable has been around since the early days of the telephone, but was only considered a viable medium to carry voice or very low-speed data. Topologies dictated the type of data protocol to be used on a particular network. For example, arc net networks connected computers in series across a thin coaxial cable, while Ethernet topologies used coaxial cable terminated to a central hub. Fortunately, there are fewer network protocols to worry about now.
Fiber cabling offers a higher raw data throughput capacity.
Ethernet has the greatest installed user base. Ethernet technology permits data throughputs in excess of 1Gb/s. There are also fewer topologies to concern ourselves with as the majority of Ethernet networks in place use the classic star, where each device is connected to a central hub, or the ring which uses two concentric data paths connected to form a ring to which individual network devices can be inserted. The increased throughput of Ethernet over simple and easy-to-install twisted-pair cable has all but eliminated the Ring's twin-ax network. The ring topology is far from gone, however, because all fiber-based networks use a ring topology.
There are also fewer types of transmission media. Coaxial cable is almost never used as cabling in modern networks. We now have three choices: twisted-pair, fiber or wireless. Wireless networks are gaining in popularity due to recently implemented standards, which permit seamless and reasonably secure transfer of data between devices of different manufacturers. The technology is still in its infancy and hindered by relatively low data throughput performance; however, with pricing of wireless networking dropping to levels near that of wired, and the ability to deploy a large network quickly without the added expense of cable installation, a lot of attention is now being drawn by network administrators.
Fiber. In terms of raw data speed capabilities, fiber cabling is still the best choice. You may ask how this can be possible since we can now pass 1Gb/s data over a twisted pair. This is a misconception shared by many network administrators. It is true that Ethernet networks can conceivably pass data at this rate for a short interval; however, in reality, Ethernet inherently limits the amount of data traffic permitted over the medium. For example, you may expect a 10baseT Ethernet network to pass data at 10Mb/s; however, if you were to measure the actual throughput with a proper analysis tool, it is unlikely that you would measure more than approximately 3Mb/s. The high-speed varieties of Ethernet boast better performance, mainly due to full-duplex transmission, but still suffer performance degradation. In contrast, data communications protocols such as DS1 (T1) or higher represent full always on bandwidth; for example, a DS3 connection requires and uses a bandwidth of about 45Mb/s whether data is present or not.
Twisted-pair cables are categorized to evaluate their data-handling capabilities.
I make this comparison to illustrate the basic reason why fiber cabling is the superior choice for large bandwidth requirements — fiber can easily carry a DS3 (or several DS3s) signal several miles. Twisted pair cable would require a series of repeaters to maintain reliable communications for long distances.
The technology behind fiber cabling hasn't changed a great deal. There are two types of fiber cabling: single-mode and multi-mode. Single-mode fiber is more efficient at passing lightwave signals, thus making it well suited for long-haul applications. Single-mode cable is fragile and, thus, difficult to work with. Multi-mode fiber was created as a more bendable, rugged and cost-effective alternative to single-mode, albeit at the expense of efficiency. Multi-mode fiber has become the standard type of cabling used with LANs. Both types of fiber cabling are rated to carry more than 1Gb/s.
Although the cabling itself hasn't changed, connectors used for fiber cabling have seen a great deal of improvement in the area of size, ease of installation and durability.
As with wireless, the price of fiber cabling and the associated hardware is dropping. In most cases, fiber may not be a practical substitute to twisted-pair cable, but it should be considered as a backbone between servers and hubs. Since fiber cables do not conduct electricity, one major benefit to using them in a broadcast facility is their natural resistance to lightning — potentially saving damage and lost airtime.
Twisted-Pair Cables. Unshielded twisted-pair (UTP) cabling used for LANs comprises four pairs of wires, each pair twisted together wrapped within a common sheath. As the name implies, UTP cable does not contain any shielding, which is not a problem in most areas. Shielded twisted-pair (STP) is available for locations such as those with transmitter sites.
There have been significant advances in UTP cable design over the past few years. Building upon the technological advances of networking hardware, standards have been developed not only for the manufacture of the cable, but also for the methods and criteria used in its installation.
UTP and STP cables are manufactured and certified to meet minimum performance criteria. The rating system, which defines those criteria, is established and maintained by the Telecommunications Industry Association/Electronic Industries Association (TIA/EIA). Cables are classified in a specific category. The category (CAT) system is as follows:
CAT1: basic telephone wire rated less than 1Mb/s
CAT2: used with Token-Ring networks rated 4Mb/s
CAT3: used for 10baseT Ethernet networks rated 16Mb/s
CAT4: used for 16Mb/s Token-Ring
CAT5: used with 100baseT Ethernet networks rated 100Mb/s
CAT5 level 5: expanded specification of CAT5 rated for 200Mhz
CAT5+level 6: expanded specification of CAT5 rated for 350Mhz
CAT5 level 7: expanded specification of CAT5 rated for 400Mhz
As you will note, CAT5 cable specifications are also broken into levels, reflecting a more stringent performance criteria. Although not officially a standard, some manufacturers are producing cabling that they call CAT6. As the performance criteria differs between manufacturers, you must be careful to compare specifications. New standards are already in the works. In fact, CAT7 is presently in discussion and will most likely define an STP cable.
One of the few sure things we can expect with networking — networks will get faster. Given the speed with which all things technological grow, the medium that the data will travel upon should be selected and installed to accommodate that growth.
Kevin McNamara, BE Radio's consultant on computer technology, is president of Applied Wireless Inc., New Market, MD.
All of the Networks articles have been approved by the SBE Certification Committee as material that may assist your preparation for the SBE Certified Broadcast Networking Technologist. Contact the SBE at (317) 846-9000 or go to www.sbe.org for more information on SBE Certification.
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