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Rockwell Semiconductors looking for Indian chip makers

The PCM4 voice pairgain system allows four subscribers on one twisted pair with no voice compression, allowing high-speed fax and data modems to operate well above the 9.6 KBPS limit for older ADPCM (adaptive differential pulse code modulation) voice compression systems.

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The VPG-4 reference designs are available from RSS at $10,000. The company is currently negotiating with several interested parties in the country to sell the reference design for manufacturing. The street price of the PCM4 system is expected to be around $100.

RSS is also scouting around for buyers of the PCM4 modem chip. It has already given the reference design to the Technical Evaluation Committee of the Department of Telecommunications for approval of the design.

ADPCM systems, based on the older DPG-4 standard used predominantly in India, allows 64 KBPS uncompressed voice line but is limited to 9.6 KBPS fax/data transmissions when linked to an analog modem.

This deficiency will be overcome by the VPG-4 systems which offer four 64 KBPS voice channels and a fax/data clear channel (V.34 modem) operating at 28.8 KBPS, according to Mark Steenstra, product manager, voice pairgain systems, Rockwell Network Access Division.

"The RSS-DSL (digital subscriber line) solutions are ideally suited for India where access to the Internet is a major issue. Deployment of Rockwell's ZipWire family of solutions which enable multi-channel data, fax and Internet services would enable the Indian service providers to overcome infrastructure bottlenecks and offer better, reliable services to their customers,'' said Steenstra.

The new system utilises Rockwell's Bt8960 HDSL transceiver technology to achieve U-interface distances of greater than 5 km. The VPG-4's complete PCM4 voice pairgain system consists of two boards, a COT (central office terminal) and an RT (remote terminal). The four voices are transmitted over UTP (unshielded twisted pair) using 2B1Q based DSL technology in a TDM (time division multiplexed) format.

An additional clear channel of 32 KBPS is used to transmit ringing, power, metering and signaling between an RT and the CO. The COT is designed to generate a high-voltage power source, which is coupled to the UTP and is used to power the RT.

The COT analog interface connects directly to the SLIC (subscriber line interface circuits) from the CO switch or channel bank. This analog interface ensures compatibility with existing and new CO equipment. Four Codecs digitise the speech for each of the SLICs. It also ensures vendor independence and requires less training. The digitised PCM data (uncompressed) is then placed on a PCM bus connected to the Bt8954 framer chip. The Bt8954 has an on-chip analog PLL for low jitter PCM clock generation and a slip buffer to align TX and RX frame sync signals to the Codecs.

These two features ensure the best voice quality possible by reducing sampling noise on the Codec. The Bt8954 incorporates additional features such as a programmable signaling overhead (8-64 KBPS), programmable interrupt rate (1,2,3, and 6 ms) for low pulse dialing distortion and a flexible frame format that supports from PCM2 to PCM18.

The high voltage levels (200V) on the DSL has raised some concern about the safety of the system. But RSS has accommodated for this, said Steenstra. "It is inevitable that we use power on the SLIC since we would not want the RT to depend on the local power situation. The reason that we use such high power is to reduce losses on the line.

"A reduction in line-power would lead to a reduction in the reach of the system. Instead intelligent monitoring of the RTs is used to turn the power on from the CO only when the receiver is lifted off the hook. Continuous monitoring of the lines is also done and any fault in the line leads to an automatic shut down of power," Steenstra added.

- Compiled from the Indian media

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