JPH10107920A - Communication terminal equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain stable communication from the start to the end of communication by selecting and controlling a signal transmission level depending on a full duplex communication system for a communication protocol signal and on a half-duplex communication system for an image data signal. SOLUTION: In the facsimile communication, the full duplex communication system and the half-duplex communication system are selected sequentially as full, half, full, half. When the signal transmission level is kept constant, a sneak path of a transmission signal to a receiver side is increased in the full duplex and half-duplex communication. Then the transmission level is raised in the case of the half-duplex communication. Thus, a control circuit 6 controls an attenuator 1a in a MODEM 1 to attenuate or restores the signal level properly. Moreover, a parameter is set to a gain changeover circuit 7 via an I/O port 8 to change an amplification factor of an amplifier 3. Since all signals are surely sent/received, time-consuming process for signal re-transmission or the like is avoided and especially high section transmission is stably conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a communication terminal device capable of switching between full-duplex communication and half-duplex communication.

[0002]

2. Description of the Related Art At present, facsimile machines are widely used, but recently, as their use becomes more frequent,
There is a problem that the communication time becomes longer and the communication cost increases. In order to shorten the communication time, various full-duplex modem standards are recommended by ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) as an international standard, such as a facsimile apparatus equipped with this modem. Communication terminal devices have been developed, thereby enabling high-speed communication and reducing communication costs.

[0003] One of the ITU-T recommendations is V.2, a standard for a two-wire full-duplex modem. According to this, communication can be performed at a data transmission rate of up to 28.8 kbps.

[0004]

However, in the above-mentioned conventional communication terminal device, the exchange of procedure signals for facsimile communication is performed by full-duplex communication, and the transmission of image data is performed by half-duplex communication. Therefore, if the communication is performed at a fixed signal transmission level from the start to the end of the communication, the sneak (echo) of the transmission signal to the receiving side during full-duplex communication increases,
There is a problem in that the performance of the echo canceller function for eliminating this wraparound and the performance of the band separation function are further deteriorated.

The present invention has been made in view of the above circumstances, and controls the signal transmission level between full-duplex communication and half-duplex communication, so that the communication can be performed from the start to the end of communication. An object is to provide a communication terminal device capable of performing stable communication.

[0006]

In order to achieve the above object, a communication terminal according to the present invention is capable of switching between full-duplex communication and half-duplex communication. Means. According to the present invention, there is provided a transmission level switching means for switching a signal transmission level, and the transmission level switching means controls switching between a signal transmission level by full-duplex communication and a signal transmission level by half-duplex communication. .

[0007] The communication terminal device of the present invention includes, for example, IT
U.T. Recommendation V. There are 34 FAX modems, and the modem changes the signal transmission level between full-duplex communication of a communication procedure signal and half-duplex communication of an image data signal. According to the second aspect, the transmission level switching means of the first aspect controls the switching so that the transmission level of the signal by the half-duplex communication becomes higher than a predetermined level.

Here, the predetermined level may be a conventional transmission level preset in the communication terminal device, or may be a conventional transmission level at the time of half-duplex communication.
The predetermined level may be set lower than the conventional transmission level, and there is no limitation. According to a third aspect, in the first or second aspect, the transmission level switching means comprises an attenuator inside the modem or a gain control means outside the modem.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating an example of an internal configuration of the communication terminal device. Below,
Recommendation V.1 which enables full-duplex communication as one of the communication terminal devices. Although an example of a communication terminal device equipped with 34 FAX modems is shown, the present invention is applicable to any communication terminal device having a switching function of a full-duplex / half-duplex communication method.

In FIG. 1, reference numeral 1 denotes a modem (modem chip) for modulating and demodulating a signal for data communication via an analog line such as a telephone line L. Reference numerals 2 and 3 denote a reception signal and a transmission signal, respectively. Is a 2-4 wire conversion circuit for controlling a transmission signal and a reception signal in order to perform full-duplex communication in a 2-wire telephone line L, and 5 is connected to the telephone line L. NCU 6 for controlling the network, 6 is a control circuit composed of a CPU or the like, 7 is a gain switching circuit provided outside the modem 1 as gain control means, 8 is a control signal for controlling the gain switching circuit 7. Output I / O port. The attenuator 1a is provided inside the modem 1.
(Attenuator), and the attenuator 1a or the gain switching circuit 7 constitutes a transmission level switching means.

The present invention is characterized in that the signal transmission level is switched according to the change in the full-duplex and half-duplex communication systems. This switching control is performed by the control circuit 6
Is performed according to the communication sequence. In the case of facsimile communication, since the communication procedure signal is transmitted in full-duplex communication and the image data is transmitted in half-duplex communication, when transmitting image data, the transmission level should be higher than a predetermined level. I do.

This predetermined level can be determined according to the line state of each communication terminal device, and the transmission level in full-duplex communication before raising the transmission level affects the performance of the echo canceller function and the like. This predetermined level is determined as a level that does not exist. The control circuit 6 transmits a control signal to the attenuator 1a in the modem 1, and attenuates or returns the signal transmission level as appropriate. Also, I / O
Through the port 8, parameters are set in the gain switching circuit 7 configured by switching a resistance value or the like, and the amplification factor of the amplifier 3 is increased or restored.

As described above, the switching control of the signal transmission level reduces the probability of occurrence of a transmission error during full-duplex communication. Therefore, the case where the communication time is extended by repeating fallback and fallforward is considered. Can be prevented. Next, the basic operation of the communication terminal device according to the present invention will be described with reference to FIG. Here, V. 34 shows only the start-up sequence of facsimile communication by the F.34. (A) in the figure is a transmission signal on the transmission side,
(B) is a transmission signal on the receiving side.

When the transmitting side makes a call (CNG or CI), first, as phase 1, V.V. 8 procedure, Separate 34 modems from other modems. Thereby, the receiving side is set to V. 34
If it is determined that this is the modem, line probing (measurement) is performed as phase 2.

Here, the probing is to measure a line characteristic by transmitting a plurality of types of periodic signals called a probing tone.
Various parameters (data mode modulation parameters) for optimizing the line state, such as modulation parameters and power level parameters, are determined. Subsequently, as phase 3, a signal is transmitted based on various parameters set by line probing, and adjustment (training) of an equalizer (equalizer) and an echo canceller is performed. Here, the fallback during data transmission, the maximum value of the data communication speed required at the time of fallforward, and the like are also set.

Then, initial training of the control channel is performed, and modem parameters such as a communication speed are changed. Then, various control channel data for facsimile communication is transmitted and received, and handshaking is performed. The present invention
In particular, in the communication of the modem parameter change and the control channel data, a transmission level that does not cause an error in transmission is maintained, and when the communication is completed, the transmission level of the signal is increased, thereby effectively improving the transmission efficiency. Have improved.

Thereafter, the primary channel data is transmitted according to the set communication speed, and then the image data (image data) is transmitted. Although this image data is transmitted in a half-duplex system, procedure signals other than data transmission are transmitted and received in a full-duplex system.
The transmission level is switched and controlled. The procedure signal in the full-duplex communication includes a control signal between pages of image data, a control signal for terminating data communication, a control signal for changing a communication mode, and the like.

According to the present invention, since these signals are transmitted and received without fail, time is not spent on retransmission of signals, and the data communication can be performed more quickly in addition to the advantage of performing full-duplex communication.

[0019]

As can be understood from the above description, the communication terminal apparatus according to the present invention has the following effects. According to the first aspect, it is possible to control switching between the signal transmission level of full-duplex communication and the signal transmission level of half-duplex communication, so that stable transmission is maintained from the start to the end of communication. Can be done. That is, at the time of full-duplex communication, the performance of the echo canceller function, the band separation function, and the like is not adversely affected. Therefore, the transmission efficiency does not deteriorate, and the communication time is not prolonged, and the communication cost can be minimized.

According to the second aspect, in half-duplex communication, switching control is performed so as to increase the transmission level, so that error-free data communication can be performed in each of full-duplex and half-duplex communication systems. According to the third aspect, the signal transmission level is switched by the attenuator inside the modem or the gain control means outside the modem, so that the transmission level can be easily adjusted.
Transmission efficiency can be improved with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a main configuration of a communication terminal device according to the present invention.

FIG. 2 is a diagram illustrating an example of a basic operation of the communication terminal device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Modem 1a ... Attenuator 2, 3 ... Amplifier 4 ... 2-4 wire conversion circuit 6 ... Control circuit 7 ... Gain switching circuit

Claims (3)

[Claims] 1. A communication terminal device capable of switching between full-duplex communication and half-duplex communication, comprising: transmission level switching means for switching a signal transmission level; And a transmission level of a signal by half-duplex communication. 2. The communication terminal device according to claim 1, wherein said transmission level switching means performs switching control so as to raise the transmission level of a signal by half-duplex communication beyond a predetermined level. 3. The communication terminal device according to claim 1, wherein said transmission level switching means comprises an attenuator inside the modem or a gain control means outside the modem.