Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-10-26
2003-03-04
Olms, Douglas (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S535000
Reexamination Certificate
active
06529529
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multiplexing digital communications system, and more particularly to a multiplexing device having a digital 1-link relay capability for preventing the deterioration of voice quality or a delay of data, when multiplexing devices are connected via a digital relay exchange with multiple links.
2. Description of the Related Art
Currently, a multiplexing device for lowering the bit rate of a coded voice signal or a fax signal by performing data conversion is frequently used, for example, in an in-house dedicated line network so as to reduce a line cost, etc.
When a voice system network is configured by using a dedicated line, etc., the line is effectively used by coding and multiplexing a voice signal (a coded voice signal is hereinafter referred to as a coded signal) on some occasions. If the scale of such a network becomes large, an exchange may sometimes serve as a relay exchange, which relays a voice signal to a different point. When a connection is made via such a relay exchange, a non-reversible data conversion system may be sometimes used as a system for coding/decoding a voice signal. Therefore, the coding/decoding of a voice signal is repeated by the number of times that the voice signal is relayed by a relay exchange. As a result, the voice quality deteriorates. Additionally, a delay caused by repeating the encoding/decoding may become large. If only the multiplexing devices which are respectively closest to a call originating unit and a call terminating unit can be opposed to each other in order to overcome the above described problems, the coding and decoding operations are respectively performed only once. As a result, the deterioration of data and a delay can be reduced to a minimum. For example, a hearing difficulty in a voice transmission can be eliminated. As described above, the system for keeping the multiplexing device existing between the multiplexing devices, which are respectively closest to the call originating and terminating units, from performing the coding/decoding operations, and for directly relaying a coded signal to the multiplexing device closest to the call terminating unit via a digital relay exchange is referred to as a digital 1-link relay connecting system.
FIG. 1A
is a block diagram showing the network configuration for explaining a digital 1-link relay capability. In
FIG. 1A
, for example, a voice signal, which is transmitted from an exchange A to an exchange C via a digital relay exchange B
100
, is coded by a multiplexing device
101
, propagated over a transmission line, decoded by a multiplexing device
102
arranged in the stage preceding the digital relay exchange B
100
, and switched by the digital relay exchange B
100
. Then, the signal is again coded by a multiplexing device
103
, propagated over a transmission line, and decoded by a multiplexing device
104
arranged in the stage preceding the exchange C.
In such a network, a synchronous bit for relay exchange switching, which is referred to as an F bit to be described later, is inserted in, for example, the signal transmitted from the multiplexing device
102
to the relay exchange B
100
. The multiplexing device
103
which has received the F bit via the digital relay exchange B
100
recognizes that it must only relay the voice signal by detecting the synchronization establishment with the F bit. The multiplexing device
103
therefore performs relay exchange mode operations for fundamentally outputting the signal transmitted from the digital relay exchange B
100
to the multiplexing device
104
side unchanged and not via its coder
103
b
, and for outputting the signal input from the multiplexing device
104
to the digital relay exchange B
100
side unchanged.
When the multiplexing device
102
detects the F bit which is inserted in the voice signal by the multiplexing device
103
, it performs the relay exchange mode operations in a similar manner. That is, the multiplexing device
102
outputs the signal input from the digital relay exchange B
100
to the multiplexing device
101
unchanged, and also outputs the signal input from the multiplexing device
101
to the digital relay exchange B
100
unchanged. As a result, the voice signal input from the exchange A is coded only by the multiplexing device
101
and decoded only by the multiplexing device
104
, thereby implementing the digital 1-link relay capability.
Provided below are the explanations about the configuration of a conventional multiplexing device, and the insertion of an F bit as the synchronous bit for relay exchange switching.
FIG. 1B
is a schematic diagram explaining the operations of a multiplexing device. This multiplexing device is hereinafter referred to as a conventional type (a). For example, a multiplexing device
102
is composed of a decoder
102
a
, a coder
102
b
, a bypass data transmitting unit
102
c
for fundamentally outputting a signal input from a transmission line to a digital relay exchange
100
side unchanged, and a bypass data receiving unit
102
d
for outputting the signal input from the digital relay exchange
100
side unchanged. F bit detection
102
e
operations are performed for the data input from the exchange side, while F bit insertion
102
f
operations are performed for the data output to the exchange side. The bypass data receiving unit
102
d
performs an in-phase operation due to the difference between the bit rates of a PCM (Pulse Code Modulation) signal and coded data, and performs control in order not to generate a lot of noise.
FIG. 1C
is a schematic diagram showing the details of the configuration of the constituent elements of the multiplexing device
102
shown in FIG.
1
B. Its configuration is almost the same as that of the multiplexing device
102
shown in
FIG. 1B
except for an adder
102
f
for inserting the F bit in a voice signal, which is arranged on the output side of the decoder
102
a.
FIG. 1D
is a diagram explaining the method for inserting the F bit as the synchronous bit for relay exchange switching in a PCM voice signal. In
FIG. 1D
, an F bit is periodically inserted in a selected position among the LSBs (DOs) of the 8 bits (D
7
through DO) of the voice signal on every 8 KHz clock cycle (cycle T=125 &mgr;s).
FIG. 1E
exemplifies a PCM signal after the switching to relay exchange mode is performed. Generally, “1” is assigned to an unused bit in order not to generate a lot of noise after the signal is converted into an analog signal while running in the relay exchange mode. Here, also all the values of the LSBs at the positions in which F bits are not inserted are “1”.
FIG. 1F
is a diagram explaining the method for establishing synchronization with an F bit in the multiplexing device of the conventional type (a). In
FIG. 1F
, for example, one of 4 consecutive LSBs (Least Significant Bits) is used for an F bit after F bits are started to be inserted. Accordingly, 500 &mgr;s is recognized to be one cycle of an F bit for a 64-Kbps voice signal (8 KHz clock). When a voice path is connected within a digital relay exchange and the voice data in which the F bit from the multiplexing device on an opposing side is inserted is input, the detection of a synchronous pattern, “10” in this case, is started. To improve the accuracy of the detection, the switching to the relay exchange mode is performed when 4 synchronous patterns are consecutively detected.
FIGS. 1G and 1H
are diagrams for explaining the details of the method for inserting an F bit. In
FIG. 1G
, F bits are inserted in the positions “b”, “f”, “j”, “n”, . . . among the LSBs of voice data, and one of 4 LSBs is used for an F bit. Therefore, its cycle will become 500 &mgr;s. “0”, “1”, “0”, “1”, “0”, . . . are inserted in the positions “b”, “f”, “j”, “n”, “r”, . . . as F bits of actual LSBs.
FIG. 1H
is a diagram explaining data arrangement of an actual PCM signal.
FIG. 1H
shows the case where a data clock is 64 KHz. The LSB of the initial 8 bits of the voice data corresponds to “a” s
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Olms Douglas
Sam Phirin
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