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January 2001 Issue

Training: Examining Cable Telephony, Part 2
By the NCTI

This month’s installment continues a series on cable telephony service. The material is adapted from a lesson in NCTI’s new Digital Installer Course. © NCTI

Inside telephone wiring begins either at the network interface device (NID) for plain old telephone service (POTS) or at the network interface unit (NIU) for cable telephony, but from there into the residence, they are essentially the same. Inside telephone wiring includes all the telephone wire and plugs with their matching jacks. It is therefore important to understand types of telephone wire, wire characteristics, tip and ring designations, type of telephone termination and telephone routing wiring topologies. This installment covers types of telephone wire and their characteristics.

NID/NIU and inside wiring

Customer premises with existing POTS usually have the NID mounted on an outside wall that provides the interface and demarcation point between the telephone company’s outside plant and the inside wiring and equipment (see Figure 1). A cable telephony NIU typically is mounted in a similar location and serves similar purposes between the broadband cable network and the premises’ telephone wiring.

Station wire types

Telephone station wire is always composed of a number of conductor pairs, with each pair having a specific color code. Quad station wire (see Figure 2) is the traditional one used for inside telephone wiring in older homes and contains four wires: green, red, black and yellow. Twisted-pair station wire (see Figure 3) is the most common wire used for inside telephone wiring today. Two- and three-pair twisted wire is found in residential buildings, while four-pair twisted wire is found in commercial buildings.

Wire characteristics

For describing unshielded twisted-pair (UTP) wire characteristics, the Electronic Industries Association and Telecommunications Industries Association developed their Commercial Building Wiring Standard EIA/TIA 568 as an industry-wide standard of categories for UTP. Category 1 UTP (CAT-1) was traditional quad (four-wire) telephone wire that was nontwisted. Category 3 (CAT-3) UTP consists of four twisted pairs.

The NIU also serves other purposes specific to the broadband cable network, such as providing power to the telephony inside wiring and synchronizing with the host digital terminal (HDT) at the headend.

Next month’s installment will continue our examination of telephone inside wiring.

 Back to January 2001 Issue

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