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The Legacy of Proprietary Cabling Systems

Communications Cabling

Early cabling systems were unstructured, proprietary, and often worked only with a specific vendor's equipment. They were designed and installed for mainframes and were a combination of thicknet cable, twinax cable, and terminal cable (RS-232). Because no cabling standards existed, an MIS director simply had to ask the vendor which cable type should be run for a specific type of host or terminal. Frequently, though, vendor-specific cabling caused problems due to lack of flexibility. Unfortunately, the legacy of early cabling still lingers in many places.

PC LANs came on the scene in the mid-1980s; these systems usually consisted of thicknet cable, thinnet cable, or some combination of the two. These cabling systems were also limited to only certain types of hosts and network nodes.

As PC LANs became popular, some companies demonstrated the very extremes of data cabling. Looking back, it's surprising to think that the ceilings, walls, and floor trenches could hold all the cable necessary to provide connectivity to each system. As one company prepared to install a 1,000-node PC LAN, they were shocked to find all the different types of cabling systems needed. Each system was wired to a different wiring closet or computer room and included the following:

  • Wang dual coaxial cable for Wang word processing terminals
  • IBM twinax cable for IBM 5250 terminals
  • Twisted-pair cable containing one or two pairs, used by the digital phone system
  • Thick Ethernet from the DEC VAX to terminal servers
  • RS-232 cable to wiring closets connecting to DEC VAX terminal servers
  • RS-232 cable from certain secretarial workstations to a proprietary NBI word processing system
  • Coaxial cables connecting a handful of PCs to a single Novell NetWare server

Some users had two or three different types of terminals sitting on their desks and, consequently, two or three different types of wall plates in their offices or cubicles. Due to the cost of cabling each location, the locations that needed certain terminal types were the only ones that had cables that supported those terminals. If users moved (and they frequently did), new cables often had to be pulled.

The new LAN was based on a twisted-pair Ethernet system that used unshielded twisted-pair cabling called SynOptics LattisNet, which was a precursor to the 10Base-T standards. Due to budget considerations, when the LAN cabling was installed, this company often used spare pairs in the existing phone cables. When extra pairs were not available, additional cable was installed. Networking standards such as 10Base-T were but a twinkle in the IEEE's (Institute of Electrical and Electronics Engineers) eye, and guidelines such as the ANSI/TIA/EIA-568 series of cabling standards were not yet formulated (see the next section for more information on ANSI/TIA-568-C). Companies deploying twisted-pair LANs had little guidance, to say the least.

Much of the cable that was used at this company was sub–Category 3, meaning that it did not meet minimum Category 3 performance requirements. Unfortunately, because the cabling was not even Category 3, once the 10Base-T specification was approved, many of the installed cables would not support 10Base-T cards on most of the network. So three years into this company's network deployments, it had to rewire much of its building.

KEY TERM: Application

Often you will see the term application used when referring to cabling. If you are like us, you think of an application as a software program that runs on your computer. However, when discussing cabling infrastructures, an application is the technology that will take advantage of the cabling system. Applications include telephone systems (analog voice and digital voice), Ethernet, Token Ring, ATM, ISDN, and RS-232.

Proprietary Cabling Is a Thing of the Past

The company discussed in the previous section had at least seven different types of cables running through the walls, floors, and ceilings. Each cable met only the standards dictated by the vendor that required that particular cable type.

As early as 1988, the computer and telecommunications industry yearned for a versatile standard that would define cabling systems and make the practices used to build these cable systems consistent. Many vendors defined their own standards for various components of a cabling system.

Article source: China Cable Suppliers