RAS SERVER IMPLEMENTATION

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DESIGNING A DSP-BASED RAS SERVER

Lessons from the Trenches Part 2: Implementation
by Shawn Arnold

Start ı Network I/F ı Telco I/F ı Sources and PDF

TELCO I/F

The Telco I/F involves the connection of the DSP's serial port to the Telco PCM stream. This connection gives rise to two important design considerationsıthe number of ports and serial connections.

Because the Telco I/F is usually sent via a channelized TDM stream, the number of ports, bus width, and bus bandwidth is fixed by the specific form of data delivery. Take, for example, a T1 trunk. A T1 trunk contains 24 channels on PCM data, and therefore a single T1 trunk would require termination into 24 DSP ports. In this case, the bus width is fixed at 24 ports. Also, a T1 trunk delivers data at a fixed rate of 1.544 MBps. And, the required bus bandwidth is 1.544 MHz.

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The physical bus restrictions of static loading, dynamic loading, and power dissipation are not difficult to meet and design to.

The serial connections are straightforward. The Telco transceiver chip is responsible for physically interfacing to the Telco trunk and interpreting the sophisticated serial signal. Telco trunk transceivers are designed to provide the types of serial signals that are built into today's DSP serial ports.

In most cases, the Telco interface connection to the DSP's serial port is a relatively painless connection. In many cases, it is the direct connection of the trunk line transceiver's serial signal to the DSP's serial port signals.

SUMMARY

The DSP is the best solution for the RAS port because it is specifically designed to handle the computationally intense data processing required by the port, meets all the critical RAS port specifications, and includes the required features.

The integration of a DSP into the RAS server is a fairly simple task. Most DSPs include integrated I/O subsystems, which significantly reduce the complexity of the logic design. Because RAS servers contain dozens of bused DSP ports, some connection issues do arise. However, most of these issues are easily dealt with.

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