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Method and apparatus for automatic functional speed setting of a data circuit terminating equipment
| Details |
Inventors: Abbiate, Jean-Claude; Quenel, Lucien;
Assignee: International Business Machines Corporation (Armonk, NY)
Primary Examiner: Kuntz; Curtis
Assistant Examiner: Shankar; Vijay
Attorney, Agent or Firm: Duffield; Edward H.
A system implemented in a Data Circuit Terminating Equipment (DCE), interfacing between a user's data processing equipment and a digital network, comprises a detector for generating an Analog Carrier Detect (ACD) DCE internal signal as well as an Analog Squared Data (ASD) DCE internal signal, and an ASD WIDTH ERROR DCE internal signal from the flow of data transmitted by the network and received on the DCE receive line. The system also comprises new circuitry for generating a Lack of Receiver Timing (LRT) DCE internal signal, a Block Error ASD DCE internal signal, and a Block Error Bipolar (BEBIP) DCE internal signal. Finally, the system includes a logical decision process which leads the DCE to automatically adjust its functional speed to the rate of data transmitted by the network and received on DCE receive line. The process includes setting the DCE to the highest possible functional speed, and for that particular speed, checking all four of the ACD, LRT, BEASD and BEBIP DCE internal signals; and if one of the checkings is not satisfactory, setting the DCE to the next possible lower speed, or if all checkings are satisfactory, stopping the process as the DCE is ready to work. |
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Although the invention will be described in a preferred embodiment where the associated modem is hooked to a DDS network, it will be obvious for the man skilled in the art to extend implementation of the invention into a modem hooked to any kind of digital network providing the following features: Baseband connection between the modem and the user-network interface.
Bipolar Code used at interface (it is to be noticed that in the event a Biphase Code such as Frequency Shift Keying or Differential Frequency Shift Keying could be used such as a Biphase Code which could be easily transformed into Bipolar Code by means well-known to the man skilled in the art).
Data exchange rate at the interface is in a range of predefined rates as supported by the network Italian network CDN or Canadian network DATAROUTE for example provide those features.
Setting a modem's functional speed means setting all of its internal clocks so as to have the modem perfectly work when attached to a user-network interface at which data exchange rate corresponds to that functional speed.
The setting thus affects all parts of the modem, including the `transmit part` (which deals with the transmit pair of wires) and the `receive part` (receive pair) knowing that internal clocks for both those parts are at the same frequency, and are phase-related.
It will be assumed for sake of brevity that any modem comprises an internal processor capable of ensuring an automatic logical decision process.
Typical pulses as received on the receive pair of the modem after some low-pass filtering (See also FIG.
2) can be seen on FIG.
1.
Such a distorted waveform is commonly found despite the quasi perfect signal emitted by the network, due to the transfer function of the line between the actual user-network interface outlet and input of the modem, as well as all kinds of parasitic effects.
Nevertheless, one of the quality criteria for a modem will be its ability to handle very distorted waveforms and accurately differentiate between positive pulses, negative pulses and no-energy levels
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Finance 
