Road to PacketCable Passes DOCSIS 1.1

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The first domino in standards-based voice-over-Internet protocol (VoIP) gear hitting the market fell in late September when two cable modems and two cable-modem termination systems (CMTSs) won Data Over Cable Service Interface Specification (DOCSIS) 1.1 certification and qualification from Cable Television Laboratories Inc.

DOCSIS 1.1 serves as the underlying platform for packet-based services, including voice, as outlined by CableLabs' PacketCable initiative.

CableLabs certified cable modems from Toshiba America Information Systems Inc. and Texas Instruments Inc. — whose reference design was used in Toshiba's modem — and qualified CMTSs from Arris Group Inc. and Cadant Inc.

Those certifications and qualifications represent a significant milestone in bringing a real-time transport layer to DOCSIS networks. The DOCSIS 1.1 spec, explained Glenn Russell, director of PacketCable, is a highly complex one, much more so than the 1.0 iteration. "This is a brand-new invention of a protocol that works," he added.

That complexity translated into a long and arduous process to certify 1.1 modems, which have been tested at CableLabs since January. The effort to produce DOCSIS 1.1 certified and qualified gear has been ongoing through successive certification waves.

But DOCSIS 1.1 certification is not the last step for vendors seeking Internet protocol (IP) voice standardization. Once modems and CMTSs win certification, they must then undergo a PacketCable qualification process to receive CableLabs' blessing for packet services, including IP voice.

Earlier this month, CableLabs announced it will be ready to begin PacketCable testing next year. Russell noted, though, that the company is still working on what definitions it will use for successful products and components to form a PacketCable network, including modems, CMTS, call management servers, media gateways, provisioning servers, signaling servers, media gateway controllers and record-keeping servers.

Yet despite the complexity of both the specifications and the certification and qualification process, there is light at the end of the tunnel for standards-based VoIP gear.

DOCSIS 1.1 adds key functionality to cable networks, including Quality of Service (QoS) and data fragmentation, both vital for voice applications, which require real-time delivery of information to ensure smooth voice calls. The standard serves as the transport layer for IP voice applications.

"DOCSIS 1.1 is really the foundation for Quality of Service on a DOCSIS environment," said Debbie Greenstreet, product management director for Telogy Networks Inc., a TI company that makes voice software.

With DOCSIS 1.1, a voice call or stream can be designated with service identifiers, or SIDs, and can be pegged with a higher priority than an e-mail message, for example, which is not as dependent on reaching its destination in real-time.

For now, the modem certifications give TI an advantage over its competitors, which include Broadcom Corp. and Conexant Systems Inc. However, the company's reference design, the TNETC405, is a data-only configuration. According to Peter Percosan, director of strategy for TI's cable broadband business, four items distinguish it from TI's voice-modem reference design, the TNETC401: a subscriber's line interface circuit (SLIC); a voice codec and digital signal processor to execute it; phone connectors; and memory for the PacketCable software load.

The TNETC401 is in the latest DOCSIS 1.1 certification wave. TI is relying on voice software technology developed by Telogy to provide the intelligence necessary to meet PacketCable specifications. That technology will add other features — such as fax relay, which lets the cable modem emulate a fax machine — to the TNETC401.

According to Goodstreet, application programming interfaces will also be built into the platform to allow TI customers to develop software above and beyond the PacketCable spec, such as example provisioning and feature upgrade capabilities.

The voice reference design includes a digital signal processor (DSP), a reduced instruction set computing (RISC) processor on-chip memory, an Ethernet interface and a direct connection to the DOCSIS 1.1 media access control (MAC) and physical (PHY) layer chip. The data-only design lacks the DSP core.

Toshiba's certified PCX 2500 is a data-only modem. According to Christopher Boring, Toshiba Network Products Division's marketing communications manager, the modem is geared toward so-called "tiered data services" that allow operators to offer various levels of data services. For example, operators could sell a low-end package that allows for slower speeds, such as 256 kilobits per second, at a reduced price, or, high-end packages that guarantee faster speeds.

Yet Toshiba also has developed a modem with voice features, the PCX 3000, which, according to Boring, takes the best implementation of PacketCable voice requirements and offers them to operators who are unwilling to wait for gear to gain CableLabs' approval. "There's a demand today for this technology," he said, who noted that the PCX 3000 is a part of the latest DOCSIS 1.1 certification wave.

According to Boring, the PCX 3000 is in at least three marketing trials with two operators in three systems, although he declined to name the MSOs. The trials involve secondary line services with some added features. Technical trials, said Boring, are underway with several other operators.

According to Carlos Oliveira, senior staff engineer for Toshiba, the PCX 3000 has been used in conjunction with call agents, or soft switches, from Telcordia Technologies Inc., Clarent Corp. and Cisco Systems Inc.

Oliveira pointed out that Toshiba is supporting voice codecs beyond the standard G.711 required by PacketCable, including G.729, G.729a, G.729e and G.728. These codecs support different, higher levels of compression, and can provide bandwidth for more than one call to take place.

In addition, Oliveira said Toshiba's cable-modem tuners, which it manufactures and designs, support "pre-equalization," a technique to overcome distortion in communications between the cable modem and cable modem termination system.

Chip giant Broadcom is also building voice features into its products. According to John Gleiter, director of marketing for cable modem and VoIP products for Broadcom's Broadband Communications Business Unit, the company was "very, very close" to receiving certification for modems containing its silicon in the last completed wave. However, he pointed out that DOCSIS 1.1-qualified CMTSs from Arris and Cadant contain Broadcom silicon. CMTS chips, he said, are a "lot more complex than on the modem side."

Gleiter pointed out that Broadcom supports G.711 and other voice codecs, and has developed sophisticated echo cancellation technology based on the International Telecommunications Union G.168 spec. "We've done a lot of engineering in that area to provide a superior echo canceller," Gleiter said.

In September, Broadcom introduced the BCM3351 cable-modem chip, which supports two lines of VoIP/fax-over-IP and 32-megabit-per-second home phoneline networking, and includes extensions for 802.11 and Bluetooth wireless networking. The BCM3352V cable modem supports four lines. Broadcom uses DSPs from LSI Logics and gained IP voice software through its 1999 acquisition of HotHaus Technologies.

"Broadcom made a big investment in PacketCable," said Gleiter, who expects the company to deliver PacketCable-based products to CableLabs early next year for testing.

Although unsuccessful in its quest for DOCSIS 1.1 certification so far, Conexant Systems Inc. has been building chips with voice functionality. While its flagship cable-modem chip, the CN9414, already supports voice extensions, the company demonstrated in June its CX24952 with an integrated DSP. The signaling processor is a pared down version that Conexant has designed that is used in concentrator boxes for telephone central office applications. The company expects to announce a new design soon.

Conexant has developed patented echo cancellation algorithms and supports multiple voice codecs, said Al Servati, Conexant's director of marketing for cable modem products. The company, while committed to PacketCable, is taking a cautious approach to integration of networking protocols and other levels of DSP integration until the VoIP market crystallizes, he said.

The newest chip company on the block is Terayon Communications System Inc.'s subsidiary, Imedia Semiconductor, which supplies its IM6000 chip for Terayon's TJ615 cable modem in the current DOCSIS 1.1 certification wave. According to John Giddings, senior public relations manager for Terayon, Imedia is developing DSP functionality for the IM6000.

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