JPH0744741B2 - Relay exchange method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a relay exchange system in which a PCM signal (pulse code modulation signal) is encoded at a low bit rate and a plurality of high speed digital lines are multi-link connected by a digital exchange. , Encoding between low bit rate encoded signals and PCM signals,
Multilink connection can be performed without degrading information quality by relaying and exchanging low bit rate coded signal and code with remaining bits vacant instead of PCM signal by digital exchange. It was done like this.

[Industrial application field]

The present invention relates to a relay exchange system, and more particularly to a system for relay exchange of a low bit rate encoded signal instead of a PCM signal by a digital exchange.

In a corporate network that connects long-distance headquarters, branch offices, and businesses with high-speed digital lines, an encoding device for transmitting low bit rate encoded signals has been introduced in order to use the high-speed digital lines more economically. Tend to Therefore, even when such a low bit rate encoder is used, there is a need for a relay exchange system that enables multilink connection with good information quality by a digital exchange.

[Conventional technology]

A general concept of multilink connection is shown in FIG. In the figure,
1-1 to 1-5 are high-speed digital lines, 2-1 to 2-4
Is a demultiplexer (MUX), 3-1 to 3-4 are private branch exchanges (PBX) with relay switching function and terminal switching function, 4 and A
And B are subscribers (telephones), respectively.

In case of multi-link connection, high-speed digital line 1-1 to 1-
A PCM signal input to any of the demultiplexers 2-1 to 2-4 from any one of 5 will always enter one of the private branch exchanges 3-1 to 3-4.
Then, it is again transmitted to any of the high-speed digital lines 1-1 to 1-5 through the corresponding demultiplexers 2-1 to 2-4.

For example, when calling from subscriber A to subscriber B, A
→ 3-1 → 2-1 → 1-2 → 2-2 → 3-2 → 2-2 →
1-3 → 2-3 → 3-3 → 2-3 → 1-4 → 2-4 → 3
-4 → Follow the route B.

The demultiplexing devices 2-1 to 2-1 in such multi-link connection
2-4 and the private branch exchange (PBX) 3-1 to 3-4 are connected as shown in FIG. 7 when the private branch exchange is an analog exchange, and as shown in FIG. 8 when it is a digital exchange. become. In FIG. 7, an A / D / D / A converter 5 for performing mutual conversion between an analog audio signal and a 64 kbps PCM signal is provided in the demultiplexer 2a.
The voice signal between the analog exchange 3a and the analog exchange 3a is exchanged as an analog signal. In addition, 6 shows a data terminal.

On the other hand, in the connection form shown in FIG. 8, the A / D / D / A converter 7 is provided in the digital exchange 3b, and the voice signal between the demultiplexer 2b and the digital exchange 3b is a digital signal. Exchanged with.

When performing multi-link connection in the connection form shown in FIG. 7, A / D conversion and D / A conversion are performed by the A / D / D / A conversion unit 5 every time relay exchange is performed. As the number of links increases, the voice quality deteriorates due to the generation of quantization noise due to / D conversion and the mixing of noise in the analog section.

On the other hand, when the multi-link connection is performed in the connection state shown in FIG. 8, since the digital signal is relayed and exchanged as it is, the voice quality is hardly deteriorated as compared with the case of one link. Therefore, it can be seen that the digital exchange is superior to the analog exchange in the case of multilink connection.

By the way, of the signals transmitted through the high-speed digital line in the conventional multi-link connection, the PCM audio signal is a signal having a sampling frequency of 8 kHz per channel and a quantization bit number of 8 bits, and its transmission bit rate is 64 kbps.
And is fast.

Further, in recent years, in order to use the existing high-speed digital line more economically, the transmission bit rate per voice channel is 32 kbps, 16 kbps, or 8 kbps.
Voice coding schemes for compressing 1/2, 1/4, or 1/8 of kbps PCM voice signals are being put to practical use.

FIG. 9 shows a block diagram of an example of a connection form between a multiplexer / demultiplexer and an exchange, in which the low bit rate voice encoding system is introduced. FIG. 9 shows a connection form for one channel, and a codec (CODEC) 8 is provided in the demultiplexer 2c. The CODEC 8 described above converts (decodes) the low bit rate coded voice signal from the high speed digital line 1 into a 64 kbps PCM voice signal and supplies it to the digital exchange 3b, and also supplies the 64 kbps PCM voice signal from the digital exchange 3b to the low bit rate code. The converted voice signal is converted (encoded) and output to the high-speed digital line 1.

The private branch exchange (PBX) may be an analog exchange,
In that case, an A / D / D / A converter is provided in the demultiplexer in addition to the CODEC.

[Problems to be solved by the invention]

When a multi-link connection is made by introducing the above low bit rate voice coding system, a 64 kbps PCM voice signal or a 64 kbps PCM voice signal is transmitted to the private branch exchange (PBX) as described above.
Since it is necessary to transmit the analog voice signal obtained by A conversion, a CODEC 8 is required in the demultiplexer 2c, and a low bit rate coded voice signal and 64 kbps PC are required every time relay exchange is performed.
Since encoding and decoding are repeated with the M voice signal, there is a problem that the voice quality is deteriorated even if the digital exchange 3b is used. This tendency of voice quality deterioration becomes more remarkable as the bit rate becomes lower, such as 8 kbps rather than 16 kbps.

For this reason, the low bit rate voice coding methods such as 16 kbps and 8 kbps have a limited number of links and can be used only for one link.

The present invention was created in view of the above points, and it is an object of the present invention to provide a relay exchange system that can relay exchange a low bit rate coded signal with multi-link connection with little deterioration in quality.

[Means for solving problems]

FIG. 1 shows a block diagram of the principle of the present invention. In the figure, a terminal exchange 11 sends an analog signal supplied from a plurality of terminals 12-1 to 12-n or a PCM signal in which one time slot consists of N bits to the relay exchange 15 by pulse code modulation of the analog signal. The analog signal supplied from the repeater exchange 15 or the analog signal obtained by pulse code demodulating the PCM signal is supplied to a predetermined terminal.

The demultiplexing device 13 performs low bit rate encoding of the analog signal or PCM signal supplied from the terminal switch 11 with M bits (where M <N) in one time slot, and sends it to the relay switch 15 through a predetermined channel. Supply and relay exchange
A low bit rate coded signal of a predetermined channel supplied from 15 is decoded into the analog signal or PCM signal and supplied to the terminal exchange 11 through a predetermined channel, which has a coding / decoding unit 14 and a relay exchange 15 The low bit rate coded signal supplied from the specified channel from the high speed digital line 16
-1, 16-2, high-speed digital line 16-1,
The low bit rate coded signal coming from 16-2 is supplied to the repeater exchange 15 through a predetermined channel.

The relay exchange 15 is provided between the demultiplexing device 13 and the terminal exchange 11, and performs relay exchange according to the channel.

The demultiplexer 13 is the high-speed digital line 16-1, 16-2
The incoming low bit rate coded signal is relayed through a predetermined channel as a digital signal in which one time slot consists of N bits by adding (N−M) bit vacancy to M bits forming one time slot. The high-speed digital signal is sent to the exchange 15 and a low bit rate coded signal in which one time slot is M bits is separated by separating M bits from a digital signal in which one time slot of a predetermined channel is N bits through the relay exchange 15. Lines 16-1, 16-2
To relay exchange.

[Action]

When a multi-link connection relay exchange is performed between a plurality of high-speed digital lines 16-1 and 16-2 by a digital exchange consisting of a terminal exchange 11 and a relay exchange 15, a high-speed digital line
In the low bit rate encoded signal input from 16-1 or 16-2, of the N bits forming one time slot by the demultiplexing device 13, M bits are the input low bit rate encoded signal, and the remaining ( The (NM) bits are sent to the repeater exchange 15 as a vacant digital signal, and further supplied to the demultiplexing device 13 via the repeater exchange 15.

When the digital signal has 8 bits for N bits and 2 bits for M bits, the signal format of one time slot is as shown in FIG. In FIG. 2, b ₁ and b ₂ are low bit rate PCM signals, and 6 bits each have a value of “0” and are empty. Therefore, in the above low bit rate encoded signal, one time slot has 8 bits, and the demultiplexer 1 has the same bits as the PCM signal in appearance.
It is transmitted between 3 and the repeater exchange 15.

The demultiplexer 13 demultiplexes only the low bit rate PCM signal parts of b ₁ and b ₂ from the digital signal of which one time slot is 8 bits and sends it to the high speed digital line 16-2 or 16-1.

In this way, the low bit rate encoded signal is not encoded or decoded by the encoding / decoding unit 14 (N−
By adding and separating the empty bits of M) bits, they are relay-exchanged as they are.

〔Example〕

FIG. 3 shows a block diagram of an embodiment of the present invention. In the figure, the same components as those in FIG. 1 are designated by the same reference numerals.
In FIG. 3, reference numeral 18 denotes an exchange (TLS) having both functions of the terminal exchange 11 and the transit exchange 15. Further, the encoding / decoding unit 14 in the demultiplexing device 13 is 64 kb in the present embodiment.
Performs mutual conversion between psPCM audio signals and 16kbps coded audio signals.

Further, the demultiplexing device 13 sets not only the voice data, but also the line controller 19 for setting the route of various data, multiplexing and demultiplexing, and 64 kbps × 30 channels of 64 kbps PCM data and 16 kbps encoded voice signal. The general data terminal 22 has a built-in demultiplexing unit 20 for demultiplexing the data of the above and demultiplexing the data, and an interface unit (INF) 21.
Is externally connected.

Further, the demultiplexer 13 is connected to the interface unit (INF) 24 in the exchange 18 via the line 23. In the exchange 18, in addition to the interface unit 24 described above, a demultiplexing unit 25 that multiplexes 64 kbps PCM data into data of 64 kbps × 30 channels and demultiplexes the same, and an exchange unit 26 that performs exchange processing in units of 64 kbps. , A / D / D / A converters 27-1 to 27-n are provided.

One line 2 at 2 Mbps between the demultiplexer 13 and the exchange 18.
Although connected in 3, the logical path is exactly the same as in Fig. 1. An example of the frame format of the line 23 is shown in FIG. One time slot consists of 8 bits,
One frame consists of 32 time slots. Since one frame is composed of 8 kHz, the transmission rate of the line 23 is 8 bits × 32 × 8 kHz = 2048 (kbps).

In FIG. 4, the first time slot TS1 is used for synchronization bits and signaling, and the 17th time slot TS17 is not used. Also time slots TS2-TS16 and T
S18 to TS32 are used as voice channels CH1 to CH30 and have a transmission bit rate of 64 kbps (= 8 bits × 8 kHz) per channel.

The above audio channels are divided into A station, A station, B station, and A station, C station, and the channel for A station is 64 kb.
It is divided into a psPCM audio signal and a 16kbps encoded audio signal. Here, as an example, as shown in FIG. 5 (A), the channels for the 64 kbps PCM audio signal in the A station are CH1 to CH5.
5 channels CH6 to CH10 are assigned as channels for 16 kbps coded voice signals in station A as shown in FIG. Also, as shown in FIG. 5 (C), the voice channels for A station and B station are 10 channels of CH11 to CH20,
The voice channel for station C between stations is CH
It is assigned to each of 10 channels from 21 to CH30. In the data format of each audio channel shown in FIGS. 5B to 5D, the first 2 bits b ₁ and b _{2 of} 8 bits are 16 kbp.
sPCM audio signal data, the remaining 6 bits are empty,
The value is always "0".

Next, the operation of the embodiment shown in FIG. 3 will be described. First, in order to explain a call from station A shown in FIG. 3 to station B (not shown) (station B and station C described later have the same structure as in FIG. 3), a terminal (a telephone here) 12- 1-12-
The analog voice signal from any of the n
After analog-to-digital conversion by one of the corresponding A / D / D / A conversion units 27-1 to 27-n in 18 and converted into a 64 kbps PCM audio signal, CH1 from exchange section 26
It is connected to one of the audio channels of CH5 (here, as an example, it is assumed that it is connected to CH1).

The CH1 64 kbps PCM audio signal is multiplexed by the demultiplexing unit 25, then transmitted to the line 23 via the interface unit 24, received by the interface unit 21, and further demultiplexed by the demultiplexing unit.
20 and the 64 kbps PCM audio signal of audio channel CH1 is separated. The separated 64 kbps PCM voice signal is decoded by the encoding / decoding unit 14, and the decoded signal is encoded by the 16 kbps code and converted into the 16 kbps coded voice signal (16 kbps code). The channel CH6 is multiplexed by the demultiplexing unit 20, and further the interface unit 21
Is sent to the line 23 via the line and reaches the exchange 18.

Here, in the demultiplexing unit 20, since one channel of the 2 Mbps line 23 has 8 bits, 2 bits of the 16 kbps coded voice signal are inserted into bit 1 and bit 2, and the remaining bits 3 to 8 are blank ( Multiplexed as "0") to obtain 8 bits of CH6 digital signal in the format shown in FIG. 5 (B). The CH6 digital signal is demultiplexed by the demultiplexing unit 25 and supplied to the switching unit 26, where the audio channels CH11 to CH for station A and station B in the format shown in FIG. 5 (C).
It is connected to any one of 20 (probably CH11), returned to the demultiplexing unit 25 again and multiplexed this time, and then sent again to the 2 Mbps line 23 via the interface unit 24.

The CH11 PCM voice signal received by the interface unit 21 is 16 kbps encoded by separating and extracting only the required 2 bits of bit 1 and bit 2 in the signal format shown in FIG. After being converted into a voice signal, the line control unit 19 multiplexes it with other data and then sends it to the high-speed digital line 16-1 to reach the B station.

To summarize the signal path from station A to station B, Becomes

The signal path during a call from station B to station A is opposite in the direction of the arrow. In addition, station B and station A go through the same route.
Both telephones of the station are connected.

Next, a case where the relay exchange is performed at the A station for the call from the B station to the C station will be described. It is generated by the B station in the same manner as described above when talking between the A station and the B station.
The PCM voice signal coded in kbps passes through the high-speed digital line 16-1 together with other data, etc.
Come in 13. In the demultiplexer 13 of station A, the line controller 19
The 16 kbps coded voice signal from station B is separated and extracted from other data, but the 16 kbps coded voice signal is CH11 to CH20.
One of the voice channels (here, tentatively CH12) is in.

The CH12 16 kbps coded voice signal from the rotation control unit 19 is a signal shown in FIG. 5 (C) which is 8 bits as a whole by adding a blank 6 bits to the data 2 bits by the demultiplexer 20. After being formatted and then multiplexed, it is sent to the 2 Mbps line 23 through the interface section 21 and reaches the exchange 18.

The CH12 PCM audio signal is supplied to the demultiplexing unit 25 through the interface unit 24, separated and extracted there, and the exchange unit 26 selects one of the channel A to C station audio channels CH21 to CH30 (for example, CH21. And then connected to
It is returned to the demultiplexer 25 again and is multiplexed this time. The PCM voice signal of the signal format of the voice channel CH21 multiplexed by the demultiplexing unit 25 as shown in FIG. 5 (D) together with other data passes through the interface unit 24 and the 2 Mbps line 23.
To the A / C audio channel CH21 signal format shown in FIG. 5 (D) by the demultiplexing unit 20 via the interface 21.
Of the required 2 bits are separated and extracted as a 16 kbps encoded voice signal.

The 16 kbps coded voice signal is multiplexed with other data by the line controller 19 and then sent to the high speed digital line 16-2 to reach the C station.

When the signal path of the relay exchange at the station A during the call from the station B to the station C is arranged, Becomes Further, the relay exchange at the station A at the time of the call from the station C to the station B is only opposite in the direction of the arrow.

In this way, at the time of relay exchange, with the 16kbps coded voice signal
16kbps without mutual conversion with 64kbps PCM audio signal
The relay exchange is performed with the encoded voice signal as it is.

Therefore, in the case of multi-link connection, the encoding / decoding for mutual conversion between the 16 kbps encoded voice signal and the 64 kbps PCM voice signal is performed by the encoding / decoding unit 14 of the desired receiving station.
Only once, the voice quality is the same as that of one-link connection, and high quality is obtained.

Note that the present invention is not limited to the above embodiments, the transmission bit rate may have other values, and the same can be applied to other information signals such as image signals other than audio signals. Of course.

〔The invention's effect〕

As described above, according to the present invention, the low bit rate encoded signal is relay-exchanged as it is without being encoded / decoded for mutual conversion with the PCM signal.
Even if the multi-link connection is made, the information quality is exactly the same as that of the one-link connection, and the quality deterioration due to the multi-link connection can be eliminated.

[Brief description of drawings]

1 is a block diagram showing the principle of the present invention, FIG. 2 is a diagram showing an example of a signal format relayed and exchanged according to the present invention, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG. 4 is a frame. FIG. 5 is a diagram showing an example of a format, FIG. 5 is a data format diagram of each part of FIG. 4, FIG. 6 is a conceptual diagram of multilink connection, and FIG. 7 is a diagram showing an example of a connection form between an exchange and a demultiplexer. FIG. 8 is a diagram showing another example of the connection form between the exchange and the demultiplexing device, and FIG. 9 is a diagram showing an example of the low bit rate speech coding system. In the figure, 11 is a terminal switch, 12-1 to 12-n are terminals, 13 is a demultiplexer, 14 is a coding / decoding unit (CODEC), 15 is a relay switch, and 16-1 and 16-2 are High-speed digital lines, 20, 25 are demultiplexing units, and 26 is a switching unit.

Claims (1)

[Claims] 1. A relay switching system in which a plurality of demultiplexing devices are multi-link connected by a high-speed digital line, and an analog signal supplied from a plurality of terminals (12-1 to 12-n) or a pulse code of the analog signal. A PCM signal that is modulated and consists of N bits in one time slot is relayed (1
5), and the analog signal supplied from the repeater exchange (15) or the analog signal obtained by pulse code demodulating the PCM signal to a predetermined terminal, and the terminal switch (11) Analog signal or PC
One time slot of the M signal is M bits (however, M <
N), which is subjected to low bit rate coding and is supplied to a relay exchange (15) through a predetermined channel.
A coding / decoding unit (14) for decoding the low-bit-rate coded signal of a predetermined channel supplied from 5) into the analog signal or PCM signal and supplying it to the terminal exchange (11) through a predetermined channel. And having the low bit rate encoded signal supplied from the transit exchange (15) on a predetermined channel to the high-speed digital line (16-1, 16-2),
A demultiplexer (13) for supplying a low bit rate coded signal coming from a high speed digital line (16-1, 16-2) to the transit exchange (15) through a predetermined channel, and the demultiplexer (13) ) And the terminal exchange (11), and a relay exchange (15) for performing a relay exchange according to a channel, wherein the demultiplexing device (13) is the high-speed digital line (16-
1, 16-2), the low bit rate coded signal is converted into M bits forming one time slot (N−
M) A vacant bit is added, and one time slot is sent as a digital signal consisting of N bits to the relay exchange (15) through a predetermined channel, and one time slot of the predetermined channel is passed through the relay exchange (15). Is separated from the digital signal consisting of N bits and a low bit rate coded signal having M bits in one time slot is sent to the high speed digital line (16-1, 16-2) for relay switching. A relay exchange method characterized in that