LOUISVILLE, Colo. — CableLabs Inc. on Thursday (Dec. 19) announced its certification of equipment from six suppliers that complies with the International Telecommunication Union's Docsis 2.0 specification, fulfilling a promise to complete its first certifications this year.
The industry group certified a chip set from Texas Instruments, modems from Motorola, Scientific-Atlanta, Terayon and Xrosstech, and the cable modem termination system (CMTS) of Terayon.
Docsis 2.0, the third generation of the data over cable service interface specification, requires equipment to include two separate modulation schemes — advanced time-division multiple access (A-TDMA) and synchronous code-division multiple access (S-CDMA). Texas Instruments Inc. is the first chip vendor to put a product through CableLabs' certification process, though others, including Conexant Systems Inc., have sampled chips that implement both A-TDMA and S-CDMA.
Dennis Rauschmayer, director of marketing in TI's broadband cable group, said that certification is not much tougher for a semiconductor company than an OEM, because CableLabs uses a core reference design in its certification testing. With certification in hand, TI can spin the chip into a standard data-only cable modem platform, a voice gateway system that uses Telogy Systems' voice packetization software, or a wireless-LAN gateway that includes TI's 802.11 media-access controller and physical-layer chips.
Since hybrid fiber/coax networks are inherently asymmetric, cable modems have delivered higher bandwidth downstream while offering significantly slower speeds in the upstream. But with Internet users more likely to exchange larger files such as MP3 audio files, the cable industry has seen a need to increase upstream performance. The Docsis 2.0 specification was developed with these requirements in mind, increasing upstream performance from a peak data rate of 10 Mbit/second to a peak rate of 30 Mbit/s.
"The significance of Docsis 2.0 is that it opens the upstream channel for the future expansion," Rauschmayer said. By supporting the higher data rates, cable modems can better support online gaming, peer-to-peer services and future high-bandwidth Internet applications, he said.
"The future is wide open," Rauschmayer said.
Modulation compromise
That future was slowed somewhat by Terayon Communication Systems Inc.'s promotion of S-CDMA, which it claimed was inherently more bandwidth-efficient that A-TDMA. Most customer premises OEMs and chip-set vendors elected to include S-CDMA as an option, which led to CableLabs' double-modulation approval scheme for Docsis 2.0 equipment, which requires customer-premises equipment (CPE) modems to support both S-CDMA and A-TDMA, while operators can choose between the two in the network architecture. Terayon has since made efforts to move into an S-CDMA chip-licensing business, without much traction.
A-TDMA, promoted by Broadcom Corp., adds additional quadrature amplitude modulation (QAM) densities and bandwidths, including 64-level QAM, to existing Docsis architectures. S-CDMA can use the same MAC, but requires different modulation.
"S-CDMA hashes users in the time and frequency domain," Rauschmayer said. "It assigns codes to users and users employ one or more of these codes during transmission." As long as the users are synchronized, this approach enables multiple users to transmit data at the same time, Rauschmayer said.
So far, Toshiba Corp., Motorola Inc.'s broadband products group, and Arris Networks have announced their intent to use TI's Docsis 2.0-compatible chip sets. Even so, all system vendors must go through Docsis 2.0 certification independently for their systems, Rauschmayer said.
CableLabs also announced Thursday that the the International Telecommunication Union has accepted Docsis 2.0 as J.122. This enhances the international acceptance of Docsis, which already had won acceptance in Europe through the EuroDocsis initiative. The ITU will use the J.122 recommendations as the basis for offering packet telephony services, dubbed IPCablecom in ITU parlance.
At the BroadbandPlus conference in early December, several cable operators predicted that the move from Docsis 1.1 to 2.0 will be far smoother than the shift from Docsis 1.0 to 1.1, which required upgrades in headend switching to support quality-of-service. That won't create a mad dash to implement 2.0, Rauschmayer said, but he added that several OEMs should have cable modems ready to introduce by the second half of 2003.
Robert Keenan is editor-in-chief of CommsDesign.com, an online sister publication of EE Times.
