3COM I-MODEM EXT FORCED ANALOG PROFILE DRIVER DETAILS:

Type: Driver
File Name: 3com_i_26788.zip
File Size: 906.2 KB
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Supported systems: Windows 7/8/10, Windows XP 64-bit, Mac OS X 10.X
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3COM I-MODEM EXT FORCED ANALOG PROFILE DRIVER



The procedures for reading and writing data between the Supervisor and the serial port and for managing the buffer are contained in the serial interrupt handler SERIAL. The Supervisor additionally controls and responds to the serial port by sending and receiving signals on its various control lines, and controls other portions of the modem including particularly the analog telephone interface network which is controlled via control lines indicated diagrammatically by in FIGS. AT commands from the DTE supplied to the Supervisor via the serial port are handled by the routine PARSE which interprets the command and calls the appropriate routine for performing the requested function. Additional 3Com I-Modem EXT Forced Analog Profile line parsing and user interface procedures are contained in 3Com I-Modem EXT Forced Analog Profile collection of subroutines named SUBS.

The Supervisor is provided with a read only memory for program storage and for the storage of a variety of "factory default" values for use by the software. The modem further advantageously includes a programmable, nonvolatile random access memory NRAM-not shown in the drawings for storing a number of user-defined default values. When the modem is powered ON, these user-defined default values are loaded from NRAM for use by the software, or alternatively the factory-defined defaults in ROM storage are loaded, depending on the setting of a DIP-switch option.

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The overall supervision of the modem when operating in its high-speed bps mode is handled by the routine HS while the routine LS handles the same function for the low-speedand bps modes. The routine LS also handles 3Com I-Modem EXT Forced Analog Profile initial "handshaking" which takes place with the remote modem. It is the task of the Supervisor to monitor certain conditions in the "outside world" as evidenced by the signals appearing at the serial port to the DTE and at the telephone line circuit This mechanism utilizes two signals developed by the analog telephone network seen generally in FIG. Secondly, the CARRIER DETECT signal provides a second two-level logical signal which indicates whether or not the full-wave-detected absolute value of the received signal within the passband of the lowpass filter is above or below the threshold level applied the threshold input of the threshold amplifier The resulting frequency count is then used to indicate the line status in accordance with the following algorithm: Baud rate detection is accomplished by using the internal counter Timer 0 in Supervisor to measure the width of the start bit in the "A" character of each "AT" command received from over the serial port The resultant count is then available when it is determined that the start bit measured is the leading start bit in the AT command, to provide a measure of the 3Com I-Modem EXT Forced Analog Profile port speed.

By utilizing a hardware timer which is directly controlled by the start bit, it is possible to detect higher baud rates shorter start bits up to the bps maximum port speed, a rate which could not be detected if the processor were to take repeated samples of the received data line and perform the count in software. When originating or answering a call, the modem and the remote modem negotiate the highest possible link rate. For example, if the AT-- DETECT routine 3Com I-Modem EXT Forced Analog Profile an AT command at bps and the modem calls a remote modem which is operating at bps, the originating modem automatically falls back to bps, and notifies the DTE of the link rate by sending a result code e. If the flow rate on the phone link is lower than the data rate at the serial port, the modem buffers the data from the serial port to enable the phone link to catch up.

The modem monitors how full the buffer is, and sends the agreed hardware or software flow control command to the DTE to terminate the reciept of further data until more room is available in the buffer.

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Still another mechanism for managing the flow of data occurs on the data link itself when the modem is operation in its asymmetric, high-speed mode in which data is sent at bps in one direction over the wideband channel defined by forward channel filter seen in FIG. This mechanism, which operates automatically, is illustrated in FIG. As seen in FIG. These two modems are shown operating in the high speed mode with local modem sending over the high speed channel illustrated by the path at bps. Since the 3Com I-Modem EXT Forced Analog Profile modem has been assigned the highest speed channel for transmission, it merely needs to monitor the amount of data in its forward channel transmit buffer to insure that buffer is not being overloaded. When the transmit buffer is emptied to less than half-full, the modem signals the DTE to resume transmitting.

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At the remote end, the modem also monitors the amount 3Com I-Modem EXT Forced Analog Profile data pending for transmission in the reverse direction over the backchannel As will be discussed later, under the extended MNP protocol used in the present invention, data is transmitted in frames over the backchannel and largest frame that can be sent contains 64 bytes. In the event that more than 64 bytes of data is ready to be sent over the backchannel, the modem using the backchannel for transmission just verifies that the far modem has had the benefit of the high speed channel for transmission for at least a predetermined minimum period of time e.

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In standard MNP, there are six types of frames: As in all error checking protocols, the standard MNP protocol maintains a continuous dialogue between the two ends of the data link to insure the integrity of the data transmission. Error detection is achieved by dividing the information into the above-noted LPDU's or frames, each of which begins and ends with a unique flag codes and each of which includes CRC cyclic redundancy checking codes.

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In standard MNP as well as in the protocol used in connection with the present invention, every frame of data being sent is processed by a cyclic algorithm which computes a bit check value and inserts it into the frame being transmitted. At the receiving end, the same cyclic computation is performed on the received data and the resulting computed value is then compared against the received check value.

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The receiving station then transmits either a positive or negative acknowledgment based on the result of the comparison. If errors are detected, the receiving station accepts no more data until the defective frame is retransmitted and correctly received.

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In the simplest case, one LT frame is sent in a first direction over the link and an LA frame is then returned in the opposite direction over the link to communicate correct receipt of the LT frame. In the more general case, a single LA may acknowledge the receipt of several LT frames. Moreover, in addition to simple data transfer over the link, additional mechanisms control the flow of data to pace transmission so that the receiver is not overwhelmed with data, and a retransmission mechanism is employed to prompt the sender to retransmit frames which were received in error. In accordance with a feature of the present invention, improved error-rates are achieved under the control of an extension of this MNP link protocol without the degradation in speed exhibited by other systems. The present modem's 3Com I-Modem EXT Forced Analog Profile of trellis coded modulation TCM makes the data transmitted less vulnerable to errors cause by telephone network impairments TCM can tolerate twice the telephone channel noise power as conventional quadrature amplitude modulation and consequently requires fewer error-correcting transmissions.

Moreover, the asymmetric architecture of the system a wide forward passband and narrow backchannel passband allows error-control retransmission requests to be sent from the high-speed receiver to the high-speed transmitter without requiring the "ping-ponging" direction reversals which characterize of half-duplex systems.

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An improved control protocol is used to for more efficient error signalling over the limited bandwidth backchannel, allowing the backchannel to simultaneously supervise the operation of the highspeed forward channel while handling interactive communication at keyboarding speeds. The improved error control protocol contemplated by the present invention is compatible with, and represents 3Com I-Modem EXT Forced Analog Profile extension to, the Microcom Networking Protocol MNP which is widely used in the industry, particulary in bps systems, and which is described in MNP Networking Protocol Specification, cited above. To reduce signalling overhead, frame formats have been streamlined to eliminate redundant bytes and new frame types not present in the standard protocol 3Com I-Modem EXT Forced Analog Profile been added for use on the back channel.

The basic structure and operation of the standard MNP protocol operates in the usual way in the present invention and, with the exception of the differences noted below, standard MNP rules and formats are followed. The differences will be more apparent by comparing the frame formats of the present, extended version depicted in FIG. In particular, it may be noted that:speed from Windows if you have an external I-Modem and a serial card that. I-Modem EXT (Forced Analog Profile) 3ComFacts is a service mark of 3Com.

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