Multiplex communications – Communication techniques for information carried in plural... – Assembly or disassembly of messages having address headers
Reexamination Certificate
1999-06-15
2004-05-04
Pham, Chi (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Assembly or disassembly of messages having address headers
C370S352000
Reexamination Certificate
active
06731651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a voice relaying apparatus and a voice relaying method in order to carry out a digital voice communication in an asynchronous transfer mode (ATM).
2. Description of the Related Art
Conventionally, a digital voice communication network for carrying out an inter-office communication in an asynchronous transfer mode is well known. In this digital voice communication network, a voice signal is relayed and switched in accordance with a procedure described below. At first, a cell received from a relay line is disassembled. As a consequently, a low-bit-rate coding voice signal is produced. This low-bit-rate coding voice signal is further decoded into a PCM voice signal of 64 kbps that can be treated within a digital switch and sent to the digital switch. The digital switch switches this PCM voice signal and outputs the switched PCM voice signal. The PCM voice signal outputted by the digital switch is again encoded into the low-bit-rate coding voice signal, and then assembled into the cell, and further sent to the relay line.
In the above-mentioned relaying and switching method, each time the relay switch operation is carried out by the digital switch, the processes are carried out, such as the disassembling of the cell, the decoding of the low-bit-rate coding voice signal, the encoding of the PCM voice signal and the assembling of the cell. This results in deterioration of quality of the voice sent and received through the digital voice communication network and also leads to increase of a transmission delay time of the voice.
As a first conventional technique to solve this problem, Japanese Laid-Open Patent Disclosure (JP-A-Heisei 9-98169) discloses “VOICE RELAYING AND SWITCHING SYSTEM”. In this voice relaying and switching system, a cell received from a relay line is disassembled and converted into the low-bit-rate coding voice signal. Then, a predetermined synchronous signal is added to this low-bit-rate coding voice signal to thereby generate a pseudo digital voice signal, which is sent to a switch. If a digital voice signal switched by the switch includes the predetermined synchronous signal, only the low-bit-rate coding voice signal is extracted from the digital voice signal, and then assembled into the cell, and further sent to the relay line.
Accordingly, when a connection destination of the switch is the relay line, the process for decoding the low-bit-rate coding voice signal and the process for encoding the PCM voice signal can be omitted. As a result, this case can avoid the deterioration of call quality caused by these processes and the increase of transmission delay. However, in this voice relaying and switching system, because the digital voice signal must pass through the section for disassembling the cell, the switch and the section for assembling the cell at a speed of at least 64 kbps, the hardware which operate at high speed is required.
Also, Japanese Laid-Open Patent Disclosure (JP-A-Heisei 10-4415) discloses “DATA TRANSMITTING APPARATUS”, as a second conventional technique.
FIG. 1
shows the structure of this data transmitting apparatus. This data transmitting apparatus is provided with a switch (PBX)
704
, a transcoder
702
and an ATM multiplexer
701
. As the PBX
704
, a switch that can function as a relay station is employed. The ATM multiplexer
701
is composed of a cell assembling/disassembling device (CLAD)
715
for assembling the cell in accordance with data received from a transcoder
703
and a cell assembling/disassembling device (CLAD)
714
for assembling the cell in accordance with data received from another data transmitting apparatus and then transmitting to the transcoder
702
.
In this data transmitting apparatus, when the PBX
704
does not serve as the relay station, the transcoder
703
performs a band compression on the data received from the PBX
704
, and sends to the cell assembling/disassembling device
715
. Then, the transcoder
702
releases the band compression of the signal from the cell assembling/disassembling device
714
, and sends to the PBX
704
. However, when the PBX
704
serves as the relay station, the transcoder
703
does not perform the band compression on the data received from the PBX
704
, and sends to the cell assembling/disassembling device
715
. The transcoder
702
does not release the band compression of the data from the cell assembling/disassembling device
714
, and sends to the PBX
704
. Hence, when the PBX
704
serves as the relay station, the process for disassembling the cell and the process for assembling the cell can be omitted in the relay station to thereby avoid the deterioration of the call quality and the increase of the transmission delay caused by these processes, even in a case of a multiple-stage relay.
Moreover, Japanese Laid-Open Patent Disclosure (JP-A-Heisei 9-55753) discloses “METHOD FOR RELAYING AND SWITCHING COMPRESSED VOICE IN ATM”, as a third conventional technique. In this method for relaying and switching a compressed voice in ATM, it is detected whether or not a cell (digital compression voice data) received from an ATM network is relayed and switched by a digital switch, when it is relayed and switched by the digital switch and again transmitted to the ATM network. When a cell (digital compression voice data) is received from the ATM network, such a check is done that whether or not a relay switch operation is accomplished by the digital switch. Then, if such a fact that the relay switch operation is accomplished is detected, the cell is passed without the compression and expansion of the voice data and the assembling and disassembling of the cell.
SUMMARY OF THE INVENTION
Therefore, the present invention has an object to provide a voice relaying apparatus and a voice relaying method capable of further reducing a delay time when a voice signal is switched.
In order to achieve the above-mentioned object, a voice relaying apparatus according to a first aspect of the present invention includes a cell disassembling section to disassemble the cell received from a network and a detecting section to detect whether or not the voice relaying apparatus is carrying out a relay switch operation. The voice relaying apparatus assembles the cell disassembled by the cell disassembling section if the detecting section detects that the voice relaying apparatus is carrying out the relay switch operation and transmutes the assembled cell to the network.
Also, in order to achieve the above-mentioned similar object, a voice relaying apparatus according to a second aspect of the present invention comprises a receiving section for receiving a cell from an asynchronous transfer mode (ATM) network, a plurality of cell assembling/disassembling units for disassembling and assembling the cells and a transmitting section for transmitting the cell assembled by each of the plurality of cell assembling/disassembling units. Each of the plurality of cell assembling/disassembling units is composed of a cell disassembling section to disassemble the cell received by the receiving section, a detecting section to detect whether or not the voice relaying apparatus is carrying out a relay switch operation, a controller to select the cell disassembled by the cell disassembling section if the detecting section detects that the voice relaying apparatus is carrying out the relay switch operation and a cell assembling section to assemble the cell which is selected by the controller, and to supply the assembled cell to the transmitting section.
Accordingly, if the relay switch operation is being carried out, the low-bit-rate coding voice signal obtained by disassembling the received cell is not decoded into the PCM voice signal. In addition, the signal before the pass to the switch is immediately transferred to the relay destination. As a consequently, it is possible to omit the time when data is reciprocated between this voice relaying apparatus and the switch to thereby reduce the delay time when the voice signal is switched.
George Keith M.
NEC Corporation
Pham Chi
Scully Scott Murphy & Presser
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