JPH0218799B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a line termination circuit using ping-pong transmission in a private branch exchange system that accommodates subscriber lines (transmission lines) of widely varying lengths.

(2) Background of technology In recent years, terminals in private branch exchange systems have been digitized and private branch exchanges (hereinafter referred to as PBXs)
It has become common to connect branch exchanges (branch exchange) and terminals using digital transmission. FIG. 1 is a block diagram of such an exchange system, and in the figure, a PBX 1 accommodates a plurality of digital terminals 2 via subscriber lines 3.
The PBX 1 includes a network 5 for making call connections between the subscriber circuit 4 corresponding to each digital terminal 2 and the central office line, and is controlled by a control circuit 6. The digital terminal 2 accommodates a voice telephone 7 and a data terminal 8, and handles voice signals in the digital form. and digital terminal 2 and subscriber circuit 4
and are connected via the subscriber line 3 by line termination circuits 9 and 9' provided on both sides facing each other.
In such switching systems, the subscriber line 3 is part of the logic circuitry and therefore generally cannot propagate in both directions at the same time. Therefore, a ping-pong transmission method is used in which transmission in each direction is performed in a time-division manner.

(3) Prior art and problems The conventional line termination circuit in the ping-pong transmission system will be described below.

FIG. 2 is a block diagram of a conventional line termination circuit 9. In the figure, the line termination circuit 9 includes a transmission buffer 10 for temporarily storing transmission data, a reception buffer 11 for temporarily storing reception data, and a transmission buffer 10 for temporarily storing transmission data. A timing circuit 12 that generates a clock for reading out transmission data, and a phase locked oscillator (hereinafter referred to as PLO) that generates a clock for writing reception data into a reception buffer.
13, and a 2-wire/4-wire converter 14 that connects the subscriber line 3 with the transmitting buffer 10 and the receiving buffer 11.

Figure 3 is a time chart when transmitting and receiving in units of one frame. In the figure, a is a signal from the network, 15 is data sent on a time-sharing basis with other digital terminals, and b is a short subscriber signal. c is the signal on the subscriber circuit side on the short subscriber line, d is the signal on the subscriber circuit side on the long subscriber line, and e is the signal on the digital terminal side on the long subscriber line. . If the subscriber line is short, the data 15 from the network is stored in the transmission buffer 10 and is received from the subscriber circuit 4 after a guard time T ₁ (16) and by the digital terminal 2 after a delay time T ₂ (17). ). The data from the digital terminal 2 is transmitted after a guard time T ₃ after the end of reception (18), and is received by the subscriber circuit 4 after a delay time T ₄ (19), completing one frame with a margin of time T ₅ . Here, the guard times T ₁ and T ₃ are provided to prevent transmission data and reception data from colliding on the subscriber line, and are assigned a fixed time regardless of the length of the subscriber line 3. However, if the subscriber line 3 is long, the delay times T ₂ ′ and T ₄ ′ become longer, so that the received data 19 from the digital terminal and the transmitted data 16 from the subscriber circuit are This will result in a collision, making normal transmission and reception impossible.

Conventionally, when the subscriber line is long, the guard times _T1 and _T3 are reduced by sending and receiving the transmission data 15 from the network a as two frames at a time, as shown in b and c, as shown in Figure 4. Since the delay times T ₂ and T ₄ can be omitted by one for every two frames, there is no collision between the received data 19 from the digital terminal and the transmitted data 16 from the subscriber circuit. 4 if the subscriber line is even longer
Transmission and reception is possible by transmitting and receiving frames or eight frames at a time.

In the past, the number of frames to be sent and received at one time was determined according to the longest subscriber line, and was applied to all line termination circuits.
A line termination circuit that can transmit and receive frames one by one has the disadvantage that the transmission and reception buffers for (n-1) frames become redundant and are wasted.

(4) Object of the Invention The object of the present invention is to solve the above-mentioned conventional drawbacks and to provide a line termination circuit that can cope with the length of subscriber lines.

(5) Structure of the Invention In order to achieve the above object, the present invention includes a basic part having a function of performing ping-pong transmission in units of one frame, and a basic part having a function of performing ping-pong transmission in units of one frame, in a line termination circuit using a ping-pong transmission method. A function to convert between transmission and reception in units of n (n is an integer of 2 or more) frames and at least (n-1)
A line termination circuit for a short transmission line is provided with only the basic part, and a line termination circuit for a long transmission line includes both the basic part and the extension part. has been established.

(6) Examples of the invention Examples of the present invention will be described below.

FIG. 5 is a block configuration diagram of a line termination circuit according to an embodiment of the present invention, in which 20 is a basic part, 21 is an extension part, 22 and 27 are transmission buffers for one frame, and 23 and 28 are timing circuits. , 24 is a 2-wire 4-wire converter, 25 and 29 are
PLO, 26 and 30 indicate reception buffers for one frame.

In the embodiment of the present invention, only the basic section 20 is provided in a line termination circuit capable of transmitting/receiving in units of one frame, and both the basic section 20 and the extension section 21 are provided in a line termination circuit capable of transmitting/receiving in units of two frames.

In the case of only the expansion section, as in the past, data sent from the network is written into the sending buffer 22 using the timing and clock from the network, and read out one frame at a time using the read clock from the timing circuit 23. The received data from the subscriber line 3 is written to the reception buffer by the write clock from the PLO 25, and read by the timing and clock from the network. put out.

When an extension section is added to perform transmission and reception in units of two frames, the transmission data read out from the transmission buffer 22 is sent to the extension section 21 instead of being sent to the 2-wire/4-wire conversion section. Within the expansion unit 21, this transmission data is accumulated in a transmission buffer 27. The write clock and read clock are created by the timing circuit 28 of the extension section 21 which receives the frame signal from the timing circuit 23 of the basic section 20.

The transmission data read from the transmission buffer 27 is transmitted to the subscriber line 3 via the 2-wire/4-wire conversion section of the basic section. Received data from subscriber line 3 is sent to line 2 4
It is sent to the extension section 21 via the line conversion section 24,
The write clock generated by PLO 29 writes to the receive buffer. This received data is read out by the read clock from the timing circuit 28 and sent to the basic section 20, and written into the receive buffer by the write clock generated by the PLO 25.

Next, the timing when transmitting and receiving data in units of two frames will be described.

FIG. 6 is a time chart of transmission and reception in units of two frames according to the embodiment of the present invention, and in the same figure,
a is the output from the transmitting buffer 22, b is the output from the transmitting buffer 27, c is the input to the receiving buffer 30, d is the input to the receiving buffer 26, and 3
1 to 34 indicate transmission data, and 35 to 38 indicate reception data, respectively.

The transmission data for each frame from the transmission buffer 22 is grouped in pairs, and the first transmission data 31 is stored in the transmission buffer 27, and the next transmission data 3 is stored in the transmission buffer 27.
Sent when 2 arrives (33). The next transmission data 32 is accumulated in place of the first transmission data 33 when it is transmitted, and is transmitted continuously after the transmission data 33 is transmitted (34).

Successive received data 35 and 36 from the subscriber line 3 are sequentially stored in the receiving buffer 30, and the first received data 35 is sent to the receiving buffer 26 when the next received data 36 is stored (37). Then, one frame later, the next received data is sent to the reception buffer 26 (38).

That is, when transmitting/receiving in units of two frames, the transmitting buffer 22 for one frame and the transmitting buffer 27 for one frame are used as a pair as the transmitting buffer for two frames, and the receiving buffer 30 and one for one frame are used as a pair. The reception buffer 26 for frames is combined and used as a reception buffer for 2 frames, and the extension unit 21 converts transmission in units of 1 frame to transmission in units of 2 frames, and reception in units of 2 frames to reception in units of 1 frame. is converting. Therefore, the basic unit 20 always transmits and receives one frame at a time.

As described above, in the embodiment of the present invention, the line termination circuit that transmits and receives in units of one frame is provided with only the basic part that has the function of transmitting and receiving in units of one frame, and the line termination circuit that transmits and receives in units of two frames is provided with only the basic part that has the function of transmitting and receiving in units of one frame. has a transmit/receive buffer for 1 frame and 1
By also providing an extension unit that mutually converts transmission/reception in frame units and transmission/reception in units of 2 frames,
The line termination circuit can be configured to correspond to the length of the subscriber line, eliminating wasted transmission and reception buffers.

(7) Effects of the Invention As described above, the present invention has the great effect of reducing unnecessary transmission buffer in the line termination circuit for short subscriber lines and reducing the cost per line.

In the embodiment of the present invention, the extension unit is for sending and receiving in units of 2 frames, but it can be used for sending and receiving 4 frames as needed.
An additional unit for transmission and reception in units of frames or units of 8 frames may be provided.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a switching system to which the present invention is applied, Fig. 2 is a conventional line termination circuit, and Fig. 3 is a diagram of a switching system to which the present invention is applied.
A time chart of transmission and reception in units of frames, FIG. 4 is a time chart of conventional transmission and reception in units of two frames, and FIG. 5 is a line termination circuit according to an embodiment of the present invention.
FIG. 6 is a time chart of transmission and reception in units of two frames according to an embodiment of the present invention. In the drawing, 20 is the basic part, 21 is the expanded part,
22 and 27 are transmitting buffers, 23 and 28 are timing circuits, 24 is a 2-wire/4-wire converter, and 26 and 30 are receiving buffers, respectively.

Claims (1)

[Claims] 1. In a line termination circuit using the ping-pong transmission method, there is a basic part that has the function of performing ping-pong transmission in units of one frame, transmission and reception in units of one frame, and units of n frames (n is an integer of 2 or more). an extension section having a function of converting between transmitted and received data and a buffer for storing at least (n-1) frames of transmitted and received data, and only the basic section is provided in a line termination circuit for a short transmission line;
A line termination circuit using a ping-pong transmission method, characterized in that a line termination circuit for a long transmission line is provided with both the basic part and the extension part.