VoIP spans access, distribution and core networks. This month, we’ll move the column’s focus to the access network, and we’ll look at how cable telephony installation is affected by VoIP. Within the access network, the embedded multimedia terminal adapter (EMTA) is the key network element of PacketCable. “Embedded” refers to the fact that the EMTA contains a built-in DOCSIS-compliant cable modem. This packaging has obvious implications. A cable company that can sell VoIP voice services automatically has its foot in the door for high-speed data. In practicality, however, the sequence of events is usually in the reverse order. Most cable companies offer data as the next service after video, followed by a voice offering. Plain vanilla data access has less support requirements than voice, and customer demand typically is stronger for data. Most of the time, this implies another truck roll to replace a cable modem with an EMTA. There are two types of EMTAs on the market today: outdoor and indoor. ARRIS is the only company that commercially offers an outdoor unit. Outdoor gear The ARRIS EMTA is called the Touchstone Telephony Port. Physically, it resembles its constant-bit-rate (CBR) cousin, the ARRIS Cornerstone Voice Port. Like the Voice Port, it requires professional installation. The process is very similar to installing any telephony network interface unit (NIU), with the obvious exception of new operational tests for data interfaces. When I began researching the Touchstone Telephony Port, I assumed that companies that had entered the telephone business via CBR technology would find it easiest to continue with an outdoor interface, especially if they already are using ARRIS voice ports. One reason is that installation procedures and installer training would require minimal change for new VoIP installations. I found out that in reality, existing telephony providers are opting for indoor EMTAs for new VoIP offerings, and the largest customer for the outdoor unit is GCI, who has not offered CBR cable telephony. Several factors influence a preference for indoor EMTAs over outdoor units. Because the outdoor unit is environmentally hardened, it costs more. In addition, the trend toward using the retail channel for cable modems makes it easier for an operator to consider a cap and replace strategy in anticipation of indoor EMTAs following the retail route. Perhaps the most negative factor, however, is that CableLabs requires an EMTA to be a “terminating device” to pass PacketCable certification. This requirement rules out certification for the ARRIS Touchstone Telephony port, as well as for any EMTA that provides cable TV passthrough. Indoor units The indoor EMTA is essentially an enhanced cable modem. The biggest difference is that most units have two RJ-11 jacks on the rear for attachment of up to two telephone lines and some provision for power backup. Most of the installation of the indoor EMTA is, therefore, about the same as installing a cable modem. Power is provided by connection to house AC. The data interface can be either Ethernet via an RJ-45 jack, or universal serial bus (USB). For USB interfaces, additional software may have to be installed on the customer’s computer. Indication of proper operation of the data interface is given by the status of lights on the face of the EMTA. Typically, none of these tasks are so complicated that they preclude customer self-install. What does get touchy, however, is the telephony installation. The easy part is attaching a telephone line cord between the EMTA and a house phone jack. The hard part is making sure the customer disconnects existing phone service prior to inserting that line cord. Cutting the cord In theory disconnecting existing phone service is not difficult. The easiest way is to go to the telephone company’s network interface unit (NIU) on the outside of the house, and unplug the home side of the wiring from the RJ-11 jacks within the NIU. The problem is that this leaves open the possibility that someone else, perhaps a telephone company installer or auditor, could replug the wires, not knowing that alternate service has been chosen. The correct way, if not the easiest way, to disconnect the existing phone service is to cut completely the home’s telephone wire connection at the exit from the NIU. This is not difficult, but the average consumer might have a problem with cutting telephone wires, not to mention possibly mistakenly cutting wires on the network side of the NIU, rather than on the customer side. I recently learned about a device that attempts to solve this problem. Sistellia LLC (www.sistellia.com) is offering a two component product called Netjax. The in-house part of Netjax is a three-inch square crossover switch that plugs into the EMTA and the wall jack. At the NIU, a pigtail-type crossover jack must be installed on the customer side of the network demarcation. The crossover jack moves the telephone company’s connection to the second pair on the NIU. The crossover switch makes cable VoIP the first choice for service and protects against electrical feedback from the old service. The upsides are that the crossover jack eliminates wire cutting, and provides a positive indication at the NIU that an alternative service is being provided, rather than just leaving the leads unplugged. The downsides are that installing the jack at the NIU might still be a stretch for some customers, and the incumbent telco still has a wired connection into the home. Backup power There is one more, very important issue for telephony installations of the indoor EMTA—power backup. Providing primary line telephony service generally means guaranteeing service continuity even when commercial power fails. That implies either correctly installing and maintaining a battery backup, or feeding EMTA power through an uninterrupted power supply. While feedback from Time Warner’s second line service offering indicates consumers are less concerned about telephone operation during power failures than we might have thought, carrier-grade service still means power backup. Whether the average consumer can be trusted to properly install and verify operation of backup power to the extent that it is carrier grade is open to discussion. The bottom line is that even with the new technology of VoIP, professional installation still will remain a critical piece of providing service to the cable industry’s customers. Justin J. Junkus is president of KnowledgeLink, Inc., an independent consulting firm. To discuss this topic further, you may email him at [email protected]

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