Don't Forget the Wires

You’ve done your voice over Internet protocol (VoIP) homework, and it’s time for your region to implement. You’re confident the bases are covered because you’ve checked out the RF plant, you’re just as comfortable with a multimedia terminal adapter (MTA) as an F-connector, and you even know a bit about protocols, quality of service (QoS) and routing. What else do you need to cover? The answer is at the same place it was for video—the customer premises. Although customer premises wiring is a lot less complicated than other components of VoIP, it is perhaps the most vulnerable spot in the triple play. With video and data, our premises concerns are RF issues, namely ingress and leakage. With telephony, we inherit potential trouble areas in the copper pairs previously used by the incumbent telephone provider, and we pick up new concerns, driven by the attachment of new customer premises equipment (CPE) to our network. The good news is that these are relatively simple physical layer issues that can be avoided by a careful prequalification process. We’ll talk about two general areas: the drop and in-house wiring. The drop At the drop, surge protection becomes much more of a concern as services expand beyond video. While cable installation practices always have emphasized the need for proper grounding and bonding to avoid dangerous ground-related current paths, in-line surge protection has not automatically been a major consideration for video. In an analysis of potential surge risks, areas of vulnerability for an analog video environment are the premises wiring and the customer’s TV set. Should damage from lightning or power crosses be traced to the cable drop, an analog TV set is a relatively inexpensive item to replace. Prior to the triple play, the relatively low probability of a surge thus outweighed the economics of adding surge protection to each drop, except in geographies where lightning hits are exceptionally frequent. Telephony, digital services and consumer electronics change that picture by bringing the subscriber into close physical proximity with devices connected to a potential surge path. More than a hundred years ago, incumbent phone companies learned the hard way that the combination of a phone set next to a subscriber’s or operator’s head and a lightning strike was a dangerous combination. It became standard practice to install carbon block protectors on the phone drop so that the path of least resistance to ground was via the protector, rather than the subscriber. Since then, technology has moved to gas tube protectors, but telephone industry practice remains to protect consumers and employees by installing surge protection on each phone line at the drop. In cable, even if safety were not an issue, the changed economics of digital services and consumer electronics fuel a business case for in-line surge protection. A typical high-end home contains more than $4,000 worth of consumer electronics and computer equipment that will be connected to the cable drop. Excellent in-line surge protection now costs less than $4 per line. A recent white paper I authored points out that in-line surge protection on each drop has a payback of about one year in areas where lightning flash density is four or more flashes per square kilometer per year. This flash density pertains to most of the Midwest and is even greater in Florida. The details of the calculation and the flash density map are available from TII Network Technologies (tiinettech.com). In-home wiring Beyond the drop and the MTA, we have an entire network of in-home copper wire. The type of wire will be one factor that determines the capability of the network for services beyond plain old telephone service (POTS). Ideally, in-home wiring should be twisted copper pair. Twisting improves the data transmission capabilities of copper wire by canceling the effects of crosstalk between pairs. Whether your particular installation is twisted pair depends to a certain extent upon the age of the residence. Older telephony wiring is not twisted, but is constructed with two to four insulated conductors randomly placed in a common jacket. This medium, known as Category 1 (CAT-1) wire, is good for POTS service, but will not be adequate for high-speed data or multimedia. Category 3 (CAT-3) wire is the next step up and is now the minimum mandated by the Federal Communications Commission for all new projects. This grade has eight conductors in four pairs, with twist rates of two to six per inch. Its usable bandwidth is 10 MHz. The gold standard for residential wiring is Category 5 (CAT-5). You usually can recognize this type of wire by its blue jacket. CAT-5 wire has four pairs, each twisted together at least three twists per inch, resulting in 100 MHz bandwidth. Because prices for CAT-5 wiring have decreased substantially, it is increasingly displacing CAT-1 and -3 for new construction. Although the presence of CAT-5 cable is the right step toward offering advanced services, poor installation practices can negate the performance of CAT-5. Many problems of this nature can be identified and removed when cable telephony is first installed, alleviating the need for later truck rolls when new services such as multimedia are added. Good installation procedure is to verify dialtone presence and line locations at each phone jack prior to disconnecting existing phone service. As you check for dialtone at each jack, remove the wall plate and inspect the connections. The connectors should be good quality, with no loose components. A common mistake with CAT-5 cable is excessive jacket removal and undoing the twist at the outlet connection. The CAT-5 standard specifies that no more than 1 inch should be stripped from the cable jacket, and the connection should be reinstalled if this is not met. If cable runs are visible in the basement or attic, also check that any bends are no sharper than a 1-inch radius and that any staples do not crimp the cable tightly. New residential construction is beginning to avoid many of these problems by using structured wiring systems. This type of installation, although initially more expensive, tends to adhere more closely to standards and makes it easier to install new services. A full discussion of structured wiring is beyond the scope of this column, but for now it is worth noting that structured wiring systems provide for a centralized access point for all communications media, as well as for standardized outlet connections. Attention to detail and the future The bottom line of this discussion is attention to detail and a view toward future services. Although it may be tempting just to swap service providers and be happy with POTS, the extra attention now will save headaches in a year or two, when POTS alone becomes insufficient to maintain a competitive edge. Justin J. Junkus is president of KnowledgeLink and telephony editor for Communications Technology. Reach him at [email protected].