Changing the recipe for telephony?

Sat, 07/31/1999 - 8:00pm
David Iler, Associate Editor

The table is nearly set for the cable TV industry to implement one of the most appetizing choices in its expanding pantry of subscriber services: Internet Protocol-based telephony. However, before the party begins and IP telephony is actually brought to the table and made available to hungry subscribers, several key "ingredients" need to be added to the mix, including:

Improved voice quality


The full set of CLASS (custom local area signaling service) features

Reduced cable modem/multimedia terminal adapter (MTA) power consumption.

Technically, the obstacles to broad-scale deployment of full-featured VoIP are fairly complex and will take some time to iron out. Exactly how long that process will take is tough to predict, but 18 months seems to be the consensus. "We're not where we need to be," says Ham Mathews, director of marketing for the broadband networks division of ADC Telecommunications Inc., "but we're pretty far from where we started." A look at the steady stream of telephony industry product announcements and alliances is a good indicator of the amount of engineering talent devoted to solving these issues, and the industry remains generally optimistic that the challenges over IP voice in the cable world can be met.

"I think these issues are going to be solved," says Jim Rice, general manager of telecommunications strategy for Charter Communications. "I'm a great believer in the technology." Charter recently conducted a very small, but successful technical trial of IP voice in its Fitchburg, Wis. system. But despite the minuteness of the trial, which involved just five employees, the test garnered some unexpected (for Charter) attention after Cisco Systems Inc. issued a press release about the "event." If one is allowed to read a bit into the clamor, it almost seems Cisco is trumpeting rather loudly the fact that VoIP works on a cable plant-certainly news the industry is eager to hear.

A more advanced series of VoIP tests will be conducted very shortly by Groupe Videotron in Quebec, Canada this year. According to Francois Laflamme, vice president of IP telephony for Videotron, the company will use Samsung's CableLabs Certified cable modems, Cisco routing and cable modem termination system (CMTS) equipment and Telcordia Technologies Inc. call agent software in a test that will take place "within the next couple of weeks," says Laflamme. "The goal of the trial," which will involve about 200 friends and family members, "is to look at network reliability and voice quality," says Laflamme.

But not all the focus is on pure technology. Later this fall, Videotron will scale up its test to include 2,000 people in Quebec to determine if its VoIP telephony business processes and the overall Videotron "machinery" are well-tuned. The telephony services, says Laflamme, will include 911, local number portability, 411 directory services, call-waiting, caller ID and other CLASS services.

Videotron is not alone. Fellow Canadian operator Cogeco is also planning a VoIP trial this year.

Asked what's driving Videotron's move into VoIP, Laflamme says it's simple economics. He notes that the telephony business is a "10-times bigger market than what we're in now (video). It's straightforward for us."

Clearly, the appetite for both MSOs and vendors to make VoIP a reality is strong.

The Arris cable modem termination system rack.
Hearty stew, not thin soup

Almost universally, both vendors and MSOs alike believe that, in the words of Wade Carter, director of development for Arris Interactive LLC, VoIP must offer "equivalent or better quality service to end subscribers" than the circuit-switched flavor of telephony they're accustomed to. Thus, recreating the public switched telephone network infrastructure on an IP backbone is the ambitious challenge of VoIP.

Arris, the joint venture 20 percent owned by Antec Network Technologies and 80 percent owned by Nortel Networks, is supplying the constant bit rate, or circuit-switched technology for AT&T Broadband & Internet Services' telephony trials, the first of which began May 12 in Fremont, Calif.

AT&T, according to spokesman Mark Siegel, will initiate circuit-switched telephony trials over its hybrid fiber/coax plant this year in Portland, Ore.; Seattle, Wash.; Salt Lake City, Utah; Denver, Colo.; Dallas, Texas; St. Louis, Mo.; Pittsburgh, Pa.; and Chicago, Ill. Echoing Carter, Siegel says that despite the advantages of IP telephony ("routers cost less than Class 5 switches"), "we're not going to introduce IP until we think it's ready for prime-time." This will occur, says Siegel, not this year, not next year, but in the first quarter of 2001, when AT&T will start to deploy VoIP on a trial basis.

The first attribute Siegel mentions when discussing VoIP is voice quality. Arris' Cornerstone circuit-switched technology, says Carter, produces low delays of less than 5 milliseconds (ms) roundtrip between caller and receiver. VoIP delays right now, he says, are between 60 and 80 ms roundtrip. (It's generally agreed that delays of 250 ms result in a broken-up conversation.)

Complicating the voice quality issue is the fact that echo cancellation is necessary for voice quality, but can be compromised by ambient background noise. Consequently, Carter says Arris is working with digital signaling processor vendors (such as Telogy Networks Inc. and HotHaus Technologies Inc.) to address the issue of echo cancellation.

One key component of voice quality and latency will be the emergence of DOCSIS 1.1 cable modems, which will address two-way Quality of Service, guaranteeing dedicated bandwidth for voice, which Carter says, "almost mimics circuit-switched" constant bit rate calls. Importantly, DOCSIS 1.1 "is a very big piece of reducing latency," says Peter Sherlock, senior director of telecommunications systems engineering for General Instrument Corp.

The rigorous certification process of DOCSIS 1.1 modems is expected to begin early next year, according to officials from Cable Television Laboratories, which runs the tests.

Another burning issue facing MSOs as they try to match the quality of today's circuit-switched telephony is the exact nature (and ownership) of the IP networks on which voice traffic will travel. Clearly, the public Internet is not a candidate because of the high traffic volume. Mathews says that "packet prioritization occurs on private networks much better than the public Internet."

He points out that 50 ms of latency is added to a voice call each time a router is encountered on a typical IP network. And because a typical U.S. Internet user is eight router hops from the core of the Internet, the latency additions would make voice conversations practically impossible. Thus, a "flat infrastructure with very few router hops" is what Mathews considers optimal.

As examples, he points to the networks built by Qwest Communications International Inc., Level 3 Communications Inc., AT&T and Road Runner. But while Road Runner and Excite@Home's data networks may seem natural conduits for MSOs' IP voice traffic, one industry source who asked not to be identified said those data networks "are not architected to provide seamless, end-to-end Quality of Service." Conversely, Level 3's network, says the source, employs a "very sweet architecture" in which data traffic is split off from voice traffic to ensure its integrity.

Additionally, Level 3's network is "self-healing," meaning it employs a loop architecture that automatically senses fiber cuts and can re-route traffic within 40 ms.

Extra portions are good

To achieve the vaunted "five nines" (99.999 percent up time) reliability so often attributed to regional Bell operating companies, redundancy is a key component to implementing VoIP on a cable network. Mathews says that redundancy is actually a component of the larger question: How do you maintain a reliable system?

8x8's Audacity chip architecture.

To answer that question, the primary line group of CableLabs' PacketCable initiative is addressing both redundancy (and network powering) issues, says David Bukovinsky, director of PacketCable. The group is addressing redundancy by establishing "reliability guidelines" for all network components, such as CMTSs, call agent servers, PSTN gateways and database servers, operating at four- or five-nines reliability. This "partitioning out of components" to understand the role of each in terms of reliability is not meant to be incorporated into a formal specification by PacketCable, says Bukovinsky, but is designed to provide MSOs with a set of requirements that they may in turn present to vendors in requests for proposals. For example, the primary line group will study what is required of a cable modem in a network to achieve four-nines reliability. This set of requirements is expected to be completed in four to six months.

Perhaps the most important component to backup at the headend is the CMTS because of its role in communicating with cable modems and/or MTAs at the customer premise and vice versa.

Connecting and placing calls

There is more than one type of CMTS redundancy, says Mark Bakies, manager of the cable communications group for Cisco. Pure one-to-one redundancy lets a second CMTS take over if the primary fails, and the cable modems are "none the wiser" about the handing off. This type of redundancy, says Bakies, is good for Data-Over-Cable Service Interface Specification (DOCSIS) 1.0-based cable modems and CMTSs because there's no support in the spec for CMTS failure. However, DOCSIS 1.1, Bakies points out, allows for cable modems to be aware that there is a backup CMTS and gives instructions and message sets about how to find it.

Thus, with DOCSIS 1.1 gear, a redundancy scheme in which a spare CMTS serves four or five CMTSs as backup becomes possible. Under this scenario, the backup CMTS has access to information, such as Quality of Service details, being processed by the other CMTSs, allowing it to come online immediately. How this is implemented will vary between vendors.

Spicing up VoIP

It's almost taken for granted today how many advanced calling features are available to residential and business telephony customers. Mark Effinger, executive director and chief OSS architect for Telcordia, says that over the decades that companies such as his (formerly known as Bellcore) have been creating so many services for traditional Class 5 switches that between 3,000 and 10,000 features now exist in various permutations.

What's important to determine, says Effinger, is to prioritize and pick those features that are most important to a specific demographic that's being targeted for VoIP service.

Although he expresses satisfaction with his company's numerous circuit-switched deployments, Jeff Turner, director of IP telephony for MediaOne, believes, "Most common services will move over to an IP platform."

Turning down the heat

With the Videotron and Cogeco trials utilizing batteries placed at the customer premise for backup in the event power is lost, the issue of powering the cable modem/MTA device at the customer premise has not been completely solved, but can be addressed by looking at the power consumption of cable modems. The cost of network powering (as opposed to local battery powering) is prohibitive, given the 10-25 watts consumed by today's cable modems, a fact not lost on MTA/cable modem chip manufacturers.

"Clearly, in the cable modem today," says Rich Nelson, director of marketing for cable TV for Broadcom Corp., "the power consumption is typically driven by the silicon." The key, he says, is higher levels of chip integration. "The more advanced the processor technology … the (lower the) supply voltage." Today, there are two main chips for voice and data, in addition to memory chips, chips for analog to digital (and vice versa) conversion and compression. An MTA, says Nelson, "adds more circuitry on top of that."

All that silicon makes it tough to reduce power consumption to the 2.5 watt level deemed desirable for cable modem chipsets.

However, innovative technology and engineering can help solve that problem. Scott St. Clair, director of corporate communications for 8x8 Inc., says the company's Audacity chipset, for example, can be "throttled" down in power consumption to the point that it uses just 0.3 watts when idle and 1.5 when running.

Late-arriving guests

Still, other questions about VoIP remain and must be answered before cable operators can really whet their appetites. These include:

How does one bill for an IP telephony call?

What is the optimum node size, given a 30 percent take-rate for IP telephony?

Using encoding/decoding compression schemes too many times (as voice calls move from one IP network to another and/or are brought into voice mail) affects voice quality. Also, the G.711 audio codec, which uses a 64 kilobit-per-second bit rate, may be a bandwidth hog.

Also of importance is the use of existing home phone wiring to connect multiple IP phone lines off of the same twisted pair. Coming to the rescue here is the snowballing HomePNA standard, the home networking spec that's been embraced by more than 70 telecommunications and consumer electronics companies. In fact, the issue of multiple IP phone connections is a reason why CableLabs is devoting some of its resources toward home networking.

"We're very focused on alternative ways to distribute voice and data inside the home," says Arris' Carter. HomePNA, he adds, "looks very attractive" because of its Quality of Service attributes.

In addition, Carter notes that any home-wiring standard that's adopted by the industry should be "fairly ubiquitously deployed in PCs and other devices."

With CableLabs ready to release PacketCable 1.0 in September, the initiative will continue to evolve as future iterations of the spec will address how a subscriber on a Comcast voice network calls a Time Warner subscriber across a managed IP backbone.

With movements on several fronts of the IP voice equation coming together this year and next to field test technologies, it remains to be seen whether VoIP can indeed deliver the type of quality and feature set that today's telephone users are accustomed to.

"The world has not seen this yet," says Mathews. However, in late June, CableLabs hosted the first of a series of interoperability "events" with 11 vendors participating. The group of equipment included five MTAs, four call agents and two test equipment platforms.

Still, there's nothing, as they say, like the real thing, and real-world deployments of VoIP may turn up nuances in usage patterns.

For example, Turner notes that in the PSTN world, phone usage patterns are fairly well-established, with peaks such as Mother's Day well-known. But on the Internet, "Who's to say when the Starr Report (or similar phenomenon) is going to be published?," he asks. MediaOne will soon discover some of those nuances as it's expected to begin VoIP trials at the beginning of next year.

With plenty of hungry guests sitting at the table, all eyes will be on the "engineers" in the kitchen and the real-world engineers at Videotron and Cogeco.




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