JP3048701B2 - Communication terminal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication terminal connected to a digital communication network.

[0002]

2. Description of the Related Art An analog communication network such as a public telephone line is not suitable for data communication since it is originally designed for transmitting voice signals. In order to make up for the drawbacks of the analog communication network, digital communication networks (for example,
SDN, integrated service digital network) are becoming widespread.

[0003] ISDN has two channels (B) for call information.
Channel) and one channel (D channel) for additional information, and each of the B channels is 64 Kbps (bit / s
ec). Thus IS
Since the speed of a DN is sufficiently higher than that of an analog network, there are many types of terminal devices that utilize the high speed. These terminals include terminal devices that simultaneously transmit voice and data. In this case, the communication of the terminals is generally based on having one channel for each of voice and data, that is, two B-channel lines.

Further, H.264, which is a standardized standard for data multiplexing, has been proposed. In the H.221, an attempt is made to multiplex voice, document data, and the like on one B channel line. This H. The H.221 standard is a framing standard. In the framing, frames are synchronized by detecting a specific bit pattern. As a result, multiplexing can be performed with one B channel line, and the communication speed can be changed during communication.
It is expected to be applied to various terminal devices in the future.

[0005] FIG. 1 shows a multiplexing terminal according to the H.221 standard.

That is, the received data enters the multiplexing unit 12 via the line interface unit 11, where the audio data,
It is separated into sub-channels such as non-audio data or high-level transmission control (HDLC) procedure data. Here, when the data of the HDLC procedure represented by, for example, G4 facsimile enters the multiplexing unit 12, the multiplexing unit 12 can detect the bit pattern of the multiplexed synchronization signal.
If the flag of the LC procedure is transmitted, it cannot be detected, so that it is forcibly assumed that all the data of 64 Kbps is the voice data, connected to the voice data channel, and no data is received.

[0007]

As described above, H.A. 22
In a terminal that conforms to the H.1 standard, When data having no H.221 frame is received, that is, when H.221 is received within a predetermined time. If the 221 frame is not detected, it is determined that the signal is an audio signal, and all the B channel signals are connected to the audio subchannel.
And H. Since the receiving terminal having the multiplexing unit 221 forcibly enters the communication state as all voice data, if all data is data, it cannot be received.

Accordingly, the present invention relates to H. It is an object of the present invention to provide a communication terminal device capable of receiving data even when data having no 221 frame is received.

[0009]

According to the present invention, a communication terminal apparatus includes a line interface unit for interfacing with a telephone line, and a frame synchronization signal for multiplexing from a data applied from the line interface unit. Multiplexing means for extracting voice data and non-voice data from each other and extracting the data, an HDLC flag detecting means for detecting an HDLC flag for a high-level transmission control procedure from data from the line interface unit, A switching unit for switching data from the line interface unit to bypass the multiplexing unit when the HDLC flag is detected by the flag detecting unit.

[0010]

The bit pattern of the synchronization signal for multiplexing is detected by the multiplexing means, and voice data and non-voice data are separated and extracted. On the other hand, the data transmitted by the HDLC procedure is detected by the HDLC flag detecting means, and the data from the line interface section is switched to bypass the multiplexing means. The data that has just been formed can also be detected and received as data.

[0011]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are explanatory diagrams for explaining a data flow based on an HDLC flag pattern in this embodiment.

In FIG. 1, reference numeral 21 denotes a line interface unit, and reference numeral 22 denotes a multiplexing unit. The multiplexing unit 22 includes a multiplexing circuit 22a, a switching circuit 22b, and a flag detecting circuit 2.
2c and a switching circuit 22d, and switching circuits 22b and 22d and a flag detecting circuit 22c are added to the conventional multiplexing unit.

The flag detection circuit 22c includes an 8-bit shift register latched by a data clock,
It is composed of a comparator that generates an output indicating that the data output from the shift register is true when the data is the HDLC flag pattern “01111110”, and is a flag detection unit dedicated to the HDLC flag pattern.

In such a configuration, when the HDLC flag pattern has not yet been detected by the flag detection circuit 22c, the data flow is as shown by the thick line in FIG. When the HDLC flag pattern is continuously detected by the flag detection circuit 22c for a predetermined period of time or more, the flag detection circuit 22c controls the switching circuits 22b and 22d to transfer the data from the line interface unit 21 as shown in FIG. , From the switching circuit 22b to the switching circuit 22d. As a result, all data transmitted according to the HDLC procedure can be received as data.

On the other hand, in the flag detection circuit 22c, HD
If no LC flag pattern is detected, as shown in FIG. 3, the flag detection circuit 22c controls the switching circuit 22b to input data to the multiplexing circuit 22a. The multiplexing circuit 22a continues to detect a bit pattern that is a synchronization signal for multiplexing. In accordance with the H.221 standard, for example, it is divided into audio data and non-audio data subchannels.

In the conventional multiplexing system, when a bit pattern for detecting a synchronization signal for multiplexing is not transmitted, communication is forcibly performed because all data is audio data. For this reason, there is a disadvantage that data of the HDLC procedure cannot be received. However, since this embodiment includes both the flag detection circuit 22c that detects the HDLC flag pattern and the multiplexing circuit 22a that is a bit pattern detection unit that takes a synchronization signal for multiplexing as in the present embodiment, multiplexing is performed. It is possible to discriminate whether the data string is a structured data string or a data string according to the HDLC procedure at an early time when the communication line is connected.

Further, in the conventional method, when data of the HDLC procedure is used, all of the data enters the communication as audio data. However, since the detection unit for the HDLC flag is provided, communication with a terminal that supports only the HDLC procedure is performed. can do.

[0018]

As described above in detail, according to the present invention, a line interface unit for interfacing with a telephone line, and a frame synchronization signal for multiplexing are extracted from data applied from the line interface unit. Multiplexing means for separating and extracting voice data and non-voice data from each other, HDLC flag detecting means for detecting an HDLC flag for a high-level transmission control procedure from data from a line interface unit, and detecting the HDLC flag. Switching means for switching the data from the line interface unit so as to bypass the multiplexing means when the HDLC flag is detected by the means. Even when data having no 221 frame is received, the data can be received. That is, at an early point in time when the communication line is connected, it is possible to determine whether the data is a multiplexed data sequence or data according to the HDLC procedure. As a result, when a specific bit pattern is not transmitted as in the related art, communication is forcibly performed because all data is audio data, and HDL is transmitted.
The inconvenience of not being able to receive data by the C procedure can be eliminated. In addition, communication can be performed with a terminal device that supports only the HDLC procedure.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining a data flow when an HDLC flag pattern is detected in FIG. 1;

FIG. 3 is an explanatory diagram for explaining a data flow when an HDLC flag pattern is not detected in FIG. 1;

FIG. 4 is a block diagram illustrating a general example of a communication terminal device.

[Explanation of symbols]

 21 line interface unit 22 multiplexing unit 22a multiplexing circuit 22b, 22d switching circuit 22c flag detecting circuit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04J 3/00-3/26 H04L 5/22-5/26 H04L 13/02-13/18 H04L 29/00-29 / 12 H04Q 3/52 H04Q 11/00-11/08

Claims (1)

(57) [Claims] 1. A line interface unit for interfacing with a telephone line, and a frame synchronization signal for multiplexing is extracted from data applied from the line interface unit to separate voice data and non-voice data from each other. Multiplexing means for extracting, and HDLC for a high-level transmission control procedure based on data from the line interface unit
HDLC flag detecting means for detecting a flag;
Switching means for switching the data from the line interface unit to bypass the multiplexing means when the HDLC flag is detected by the C flag detection means.