Tooling the Network for Voice:

The conventional thinking is that cable operators need to get voice over Internet protocol (VoIP) telephony right the first time. The idea is that while telephone companies’ circuit-switched services are vulnerable, they are reliable, and people are comfortable with them. Folks may go for operator bundles that include video, data and phone, but will bolt at the first sign of trouble. "I think the most important thing to remember is that we have to deliver the same carrier-class services as TDM or the legacy phone system," says Bill Dame, Cox’s director of network switch engineering. Vendors are positioning their products to confront that challenge. DOCSIS test phone The Cheetah division of Tollgrade, for instance, has added VoIP status monitoring to its DOCSIS transponder, according to director of marketing Hamid Qayyum. The devices go hand-in-glove with the quickly evolving world of transponder communications protocols. These transponders—traditionally used to monitor the status of power supplies—communicate with the headend in one of three ways: via proprietary protocols, via older frequency shift key (FSK) protocols or via DOCSIS. The latter approach, which is being developed in the SCTE’s Hybrid Management Sublayer (HMS) subcommittee, is picking up steam. One of the advantages of the DOCSIS approach is that it permits a tremendous amount of other information to be carried from the field to the headend, and some of this information can be about the latency and jitter the network is experiencing. "It not only manages power supplies, but becomes a test phone within the network," Qayyum says. "It is an industrially hardened phone that allows you to find out what’s happening in the network." Qayyum says that the device can measure packet loss, delay, jitter and mean opinion score. He says that the firmware can be collocated with power supply transponders or, in areas with less penetration, used as a standalone device. The firmware is about to enter field trials with operators, he says. Double trouble Another product tooled for VoIP is Auspice’s voice services manager, which is built upon the company’s TLX cross-platform foundation. Director of Marketing David Hayward says that the software monitors all aspects of VoIP operations. On the HFC plant, the software monitors plant outages and performance. The elements of the system covered include cable modems, the MTA, the CMS, the CMTS, switches, provisioning and billing systems and trouble ticketing systems. There is no shortage of technical challenges to cable operators’ ability to win—and hold on to—VoIP subscribers. One area of challenge is that cable’s VoIP initiatives are built on an open platform in which hardware and software from different companies must interoperate. This makes meeting the tight tolerances of VoIP an even trickier business. Perhaps the bigger challenge is on the networking side. VoIP transmissions utilize the user datagram protocol (UDP), which lacks the error correction features of the transmission control protocol (TCP) traditionally used to deliver data over the Internet. Thus, there is double trouble: voice communications are more demanding than data—but at the same time don’t have the same built-in advantages in the protocols used to deliver it. Cox’s Dame says that effective test equipment—which can delve deeper than monitoring tools—is available. And that’s a good thing. "The plant is going to be a headache from this point on," Dame adds. "Cable operators who have legacy plant out there are going to really see a lot more trouble than they have on the data side. The big reason is that data transport is forgiving." —Carl Weinschenk I Want My Multiplex:
Supporting PSIP Has Bandwidth Management Implications One thing that stood out in the scramble to meet the July 1 deadline on supporting program and system information protocol (PSIP) data was operators’ jealous regard for multiplexing technologies. Broadcasters had developed PSIP to provide guide information related to the delivery of multiple streams within a broadcast. Early on, operators flagged the potential for these data to consume bandwidth. A February 2000 agreement between the NCTA and CEA limited PSIP’s scope, as well as set expectations for its implementation. The FCC referenced that agreement in its adoption last September of the plug-and-play agreement involving the one-way, digital CableReady TV sets and related CableCards. To meet the July 1 deadline, operators faced additional challenges, such as reconciling the in-band PSIP program identification numbers (PIDs) with those already in use via out-of-band signaling, teaching both new and legacy equipment to speak PSIP, and not upsetting multiplexed efficiencies. Advanced modulation and multiplexing techniques, for instance, enable operators to combine two HD broadcasts in a single 6 MHz slot. But PSIP data collided in that scenario, and that was a problem. "We need to be able to multiplex that with other services, so we can get the best bang for the buck," Steve Watkins, Cox Communications director of digital video technology, says. Accordingly, Cox worked with Terayon and Bigband Networks on ways to protect PSIP data in the multiplexer. Leading up to the deadline, Sylvain Riviere, director of product marketing for Bigband Networks says his team was "upgrading headends like crazy, going non-stop." Lost efficiency? Basil Badawiyeh, advanced video engineer at Adelphia Communications, said that broadcast QAM modulators posed another challenge. A software upgrade allows operators to configure them manually to pass through the PIDs, but that could disable other functionality, such as the ability to encrypt. A headend controller, software release upgrade is required to enable some devices both to encrypt and pass PIDs, Badawiyeh says. Without that ability to encrypt, an operator’s strategy for statistically multiplexing in-the-clear HD signals "unfortunately has to be re-done, not based on efficiency, but on the limitations of the box," he says. Another alternative is using a basic, clear-QAM modulator which passes all PIDs. But operators who pass through PSIP data without resolving the conflicts with existing PIDs on the plant will negatively impact customers, Watkins says. Specifically, the small but important group of customers that buy plug-and-play TV sets. "What we’re trying to do here at Cox is ensure that the transition period or experience of moving from a digital CableReady television without a CableCard to having a CableCard is pleasant and positively reinforced," he says. —Jonathan Tombes