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Feature Article
August 2000


Calling Over Cable: Will IP Catch On?


Carla picks up her home telephone and makes a long-distance call to her friend Marty. Nothing seems odd to them about having a long-distance conversation, which happens about 280 million times every day in this country, by the FCC's 1999 figures. But behind the scenes, there's a new story to tell: Our heroine's standard Trimline is plugged into a cable modem. Her voice is digitized and sent over the cable TV provider's IP network to Marty's location, where a gateway rebuilds the call and routes it over the PSTN through Marty's local loop.

The idea is not as far-off as it sounds. Working with equipment vendors like Lucent, Nortel, Samsung, Tollbridge, and Motorola, cable television providers in the U.S. and Canada are aggressively trying to make 2001 the year they become reborn as next-gen telcos.

Thanks to deregulation and advancements in class 5 replacement switches and IP telephony, the environment is ripe for providers with a fast enough Internet connection and the proper development sense to become CLECs or long-distance carriers, according to recent reports from the Cahners In-Stat and Strategis Group research firms.

Through this summer, the cable-meets-VoIP movement may not seem so obvious. All of the currently available cable telephony offerings use circuit-switched technology. These services come from providers like Cox Communications, AT&T, Cablevision, and Comcast. They've been successful, too: AT&T Broadband, for example, announced signing up more than 75,000 users as of last month. And Mike Paxton, a senior analyst for the Cahners In-Stat research firm, says that circuit-switched "is currently 90 percent of the cable telephony story, and will continue to be for the next 18 months."

However, Paxton and experts from equipment vendors, cable carriers, and other research firms agree that while circuit-switched is a unique interim revenue stream, IP telephony over cable -- specifically, over managed hybrid fiber/coaxial, or HFC networks -- is where the future of long-distance is at, until the day when native fiber-optic lines are common.

Longer-term forecasts are equally optimistic. According to the Strategis report, "Cable Telephony Forecasts," almost 12 percent of U.S. households will have cable-based IP telephony by the end of 2005. The report outlines how cable telephony subscriptions will transition from circuit-switched to non-lifeline IP to lifeline IP. Lifeline services will account for a quarter of that 12 percent, the report says.

"I don't think there's a company out there that doesn't think they're going to see IP telephony," said Lucent Technologies' John Slevin, director of strategy and business development for cable solutions. Regarding the timing of such rollouts, he said, "the question is their priorities. Some are more entrepreneurial than others."

Leading the research into IP cable telephony is the PacketCable working group, a part of the CableLabs organization. This is the same group who made DOCSIS 1.0 the cable modem standard. To address real-time applications like telephony, they're developing DOCSIS 1.1, which adds measures like dynamic quality of service (QoS). Because cable users share their pipes with neighboring households, the dynamic QoS switches itself on or off as needed, thus saving bandwidth for other callers.

Many other issues also face operators who want to become telephone companies. PacketCable director Ed Miller said that the new standards address many of these issues, such as voice quality in terms of latency, fidelity, jitter, and packet loss at the customer end, and legacy signaling support, data security and theft of service security, scale, and feature deployment at the provider end. Other issues are provider-specific, like implementing systems for PSTN gateways and gatekeepers, provisioning, billing, and network maintenance.

The current trials are small in scale, but important players are administering them. A trial began in Georgia late last year between Lucent and High Speed Access Corp., and trials throughout the northeastern U.S. are being conducted between Nortel Networks and Adelphia Communications. AT&T, which owns TCI and MediaOne, is working with both Lucent and Motorola. Set-top box maker Scientific-Atlanta partners with both Net2Phone and Cox Communications, a test that also includes a video-on-demand service. Time-Warner has trials underway in Portland, ME, as a value-added feature to their Road Runner cable modem service. In Canada, Samsung and Vid´┐Żotron are conducting one of the largest trials, reaching more than 2,200 users in greater Montreal.

If the trials seem slow to deploy, notes a Nortel white paper called "The Cable Telephony Opportunity," it's because developing IP telephony that's easy enough for consumers to use is much more involved than becoming a traditional CLEC or a cable modem service. The white paper makes noteworthy points: Some of the IP telephony considerations are technical architecture, PSTN-level reliability, PSTN-level feature set, and regulatory issues.

"Technical architecture" refers to the actual network infrastructure. Cable TV networks pass about two-thirds of the roughly 100 million U.S. households. About half of that network is currently equipped to handle two-way data; Paxton expects the majority of the transition to be complete in three years, since most rural households involve the most per capita expense to reach.

What's unique about implementing this technology in residences compared to an enterprise VoIP project, he said, is the distributed characteristic. "You're spreading it out to millions of nodes. You have one switch for each home instead of one switch for each office," he explained. For operators, this means laying underground cable or leasing someone else's, and dealing with federal environmental and labor issues.

By PSTN-level reliability, the issue referred to is "five-nines" of uptime, with levels of latency and jitter low enough to be imperceptible to the average human ear, and levels of fidelity clear enough to match the famous Sprint "pin drop" claim. Most voice-over-data networks use aggressive compression algorithms, reducing the standard of 64 KB per call down to 16, 12, or even eight KB. Add to that equation the issue of normal Internet traffic, and suddenly the time-sensitive voice packets are stuck in rush-hour gridlock on the information superhighway. The message to operators is clear: Only a well-managed semiprivate network is acceptable if you want users to get the PSTN experience.

The feature set issue is equally tough for operators to solve. Sending voice packets is one thing, but what about conference calls, caller ID, call waiting, and on-hold lamps? What of DTMF tones, fax signaling, stutter tones, and flash-hooks? These and other features need to be addressed before IP telephony over cable will be accepted into the mainstream. More vital features like government-regulated wiretapping and number portability are being dealt with in the DOCSIS 1.1 specification and various CableLabs/PacketCable projects, but end-user features will largely be proprietary solutions.

FCC regulation is another challenging issue facing IP telephony in general. This summer saw much fuss made over H.R. 1291, whereby the House of Representatives voted to exempt ISPs "or any provider of Internet access service" from Universal Service contributions. The controversy stemmed from a last-minute addition to the bill, which states, "Nothing in this subsection shall preclude the Commission from imposing access charges on the providers of Internet telephone services, irrespective of the type of customer premises equipment used in connection with such services."

This leaves the door ajar for Congress to treat any IP telephony provider as a standard competitive carrier. Some of the biggest vendors in this space -- including Net2Phone, ITXC, Dialpad.com, deltathree.com, and Phonefree.com -- even staged a Washington, D.C. rock-and-roll rally. They argue that being forced to pay into the Universal Service Fund at such a young and vulnerable stage in the IP telephony industry's growth will surely suffocate it, maybe even to the point of extinction. Some analysts went even further, arguing that the bill amendment was the work of lobbyists for the big-ticket telcos, who they say fear VoIP technology because it will undercut their price models and offer better enhanced services.

Regardless of your opinion on the roots of H.R. 1291 or what it may mean, one thing is certain: For new operators or for traditional cable TV operators entering the IP telephony space, FCC regulation will be an important issue to deal with in coming years.

Dan Middleton, vice president for cable media solutions at Nortel, cites other items for potential IP cable telephony operators to deal with. Among them are the ability to see, understand, and avoid RF interference in the HFC infrastructure, modulation techniques, and redundant network maintenance using SNMP methods. He also cited the possible capacity limits of DOCSIS 1.1, although he and other experts agree that DOCSIS 1.1 is a vast improvement over DOCSIS 1.0. For now, he said, "Getting footprint is more important than the technology you're using."

The trick to meeting that challenge, says analyst Bruce Rapport, is to roll out IP cable telephony systems with a better feature set and lower costs than normal competitive carriers. Rapport's company, DST Innovis, makes billing and other record-keeping software for cable telephony applications.

The expanded feature set must include a powered line or some other method of accomplishing primary line reliability levels, he said. Ensuring that reliability is not easy, wrote NetSpeak Corp. engineer Linden deCarmo in an article for TMCnet.com, but it can be done with prudent CMTS testing of bandwidth and packet collision issues. 

Other experts note that enhanced features can also include unified messaging, video-on-demand, and other real-time, multimedia applications, any of which could make IP cable telephony lines distinct from their circuit-switched competitors.

While many people still see Internet telephony as being a niche or hobbyists' technology outside of the enterprise, the promise of PSTN quality, phone-to-phone connections, converged voice, data, and video, no special dialing codes, and no special customer premise equipment other than a cable modem is an attractive package that can offer a new revenue stream for cable providers.

"This is a step closer to being a replacement for your traditional telephone," Lucent's Slevin said. 

Evan Koblentz is a technology editor for TMC Labs. TMC Labs is made up of an experienced staff of engineers who acquire, install, evaluate, and relay to readers the advantages and pitfalls of the latest hardware and software for the CTI, Internet telephony, and call center/telemarketing markets. They review products and services for Internet Telephony, Communications Solutions, and C@ll Center CRM Solutions magazines.

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PacketCable 1.0 Architecture

  • At the customer's location, a multimedia terminal adapter resides within a DOCSIS 1.1-compatible cable modem. The modem has a coaxial connection, an Ethernet port, an external power supply, and an analog telephone port (RJ-45).
  • The coaxial connection, through a standard splitter, shares its connection with your cable TV signal. From your house, the connection goes through a PacketCable zone and a PacketCable domain, all while traveling over a DOCSIS 1.1-compatible HFC network.
  • The signal reaches the cable modem termination system, located at the operator's head-end of hub. CableLabs cites 11 functions of the CMTS: It provides QoS, allocates bandwidth, classifies packets, polices the packets' type-of-service (TOS) fields, adjusts the TOS fields as needed, performs traffic shaping, forwards packets, converts and classifies QoS parameters, handles signaling and reserving backbone QoS, and records call resource usage.
  • The connection navigates a managed IP network. The network is connected to four subsystems -- the call management server, the announcement server, the media gateway and signaling components, and the OSS back-office applications.
  • From the media gateway and signaling gateway, the connection travels over the PSTN and the local loop of the called party. 

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Managing QoS From The Cable Modem To The Core


Quality of Service (QoS) can be delivered across cable infrastructure and core IP networks by leveraging industry specifications and next-generation router and CMTS equipment.

Data over Cable Service Interface Specification (DOCSIS) 1.1 defines interface requirements enabling QoS. This specification must be supported by the CMTS/router at the edge of the cable access network and by the cable modem. Cable operators can then ensure that QoS parameters such as latency and jitter are receiving the treatments required on a per-flow basis.

At the edge of the network, the CMTS/router needs the intelligence to isolate traffic flows and apply policy-based QoS treatments in real time. Traffic flows need to be isolated by service provider, application, and subscriber so that during times of congestion, flows within their SLAs are maintained and flows exceeding their SLAs are discarded first.

By implementing flow-based congestion control and traffic policing at the CMTS/router, operators can ensure that flows conform to SLAs and can deliver the QoS control required for voice applications. Operators can then map the DOCSIS-based flows to IP-based specifications such as DiffServ and MPLS to manage the handoff to the core IP network. By leveraging intelligence, performance, and standards-based interoperability in next-generation CMTS/routers, operators can deliver QoS from the cable modem to the core network and offer new and innovative services.

Gerry White is chief technology officer of RiverDelta Networks. RiverDelta offers next-generation switching and service provisioning solutions for broadband service providers building carrier-class networks to deliver voice, data, and entertainment services for residential and corporate subscribers. For more information, visit the company's Web site at www.riverdelta.com

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