Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-12-02
2001-01-09
Pham, Chi H. (Department: 2731)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S352000, C370S353000, C370S354000
Reexamination Certificate
active
06172978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an audio tandem relay device for transmitting and exchanging an audio signal in a communication system which employs synchronous transfer mode (STM) and an asynchronous transfer mode (ATM).
2. Description of the Prior Art
FIG. 1
is a block diagram showing the structure of a conventional audio tandem relay device. In this structure, a cell disassembly
1
disassembles an ATM cell inputted from a line into an encoded audio signal; an audio decoder
2
decodes an encoded audio signal into an audio signal; an audio encoder
3
encodes an audio signal inputted from an exchange side into an encoded audio signal; a cell assembly
4
assembles an ATM cell from an inputted encoded audio signal, etc.; a pseudo
64
k
signal composer
5
a
generates a pseudo encoded audio signal of 64 kbit/s (a pseudo audio signal) by converting, without decoding, an encoded audio signal of 32 kbit/s or 16 kbit/s, etc., the pseudo audio signal maintaining the same data rate as that before the conversion and being usable by a relay exchange; a pseudo
64
k
signal decomposer
6
a
changes a pseudo
64
k
signal inputted from an exchange side into an encoded audio signal having the original data rate; a first pattern inserter
10
inserts a first pattern signal so that an audio tandem relay device which makes a pair with its own audio tandem relay device in relaying (a paired audio tandem relay device or a paired device) will acknowledge that the current signal transmission is a relay transmission; a second pattern inserter
11
inserts a second pattern signal so that a paired device will acknowledge that its own device is in a relay exchange state after detection of a first pattern signal; a first/second pattern detector
12
detects either a first or second pattern signal inserted by a paired device; a second switch
20
switches its connection from a contact point
2
to a contact point
1
upon detection of either a first or second pattern signal in a signal inputted from an exchange side, to thereby output a signal from a pseudo
64
k
decomposer
6
a
in place of that from an audio encoder; and a first switch
21
switches its connection upon detection of either a first or second pattern signal in a signal inputted from an exchange side, to thereby output a signal from the second pattern inserter
11
in place of that from the first pattern inserter
10
.
An operation will next be described based on the accompanying drawings.
FIG. 1
shows an audio tandem relay device in the initial state, in which first and second switches
20
,
21
are connected at contact points
2
. When a telephone makes a call, an exchange to which the phone is connected outputs a Pulse Code Modulation (PCM) audio signal of 64 kbit/s into an audio tandem relay device connected thereto. As this signal includes neither a first nor a second pattern signal, a first/second pattern detector
12
in that device detects neither pattern signal, and the state of the switches of the device thus remain in the same state. The signal which was then supplied to the audio encoder
3
is encoded into an encoded audio signal, and passes through a second switch
20
, proceeding to the cell assembly
4
, so that the cell assembly
4
assembles a cell out of the signal supplied and outputs the cell to the line side.
When this cell arrives at a station which happens to be a called station for that call, the cell is disassembled by the cell disassembly
1
into an encoded audio signal. The resulting signal which was then inputted into the audio decoder
2
is decoded into a PCM audio signal therein, and subsequently given a first pattern signal in a first pattern inserter
10
before being outputted via a switch
21
to the exchange side. The signal is further transmitted to the telephone addressed by the call, which is connected to that exchange.
Also, when the cell arrives at a relay station, the arriving cell is processed similarly to the above in an audio tandem relay device of that station. This device, i.e., a relay device, is connected to another audio tandem relay device via an exchange, and these two devices make a pair in relaying, each hereinafter being referred to as a paired audio tandem relay device or a paired device. In the paired device, after it has received a signal from its exchange side, a first/second pattern detector
12
detects a first pattern signal in the signal received, upon which switches
20
,
21
are switched so as to be connected at contact points
1
. As a result, an output from the pseudo
64
k
signal decomposer
6
a
passes through the switch
20
and proceeds to the cell assembly
4
, while an output of the pseudo
64
k
signal composer
5
a
passes through the switch
21
after being given a second pattern signal by the second pattern signal inserter
11
, and is outputted to the exchange side. Note that a signal in the opposite direction in a telephone communication, which is a bidirectional communication, is similarly processed.
As described above, an audio signal is neither encoded nor decoded in a relay station, where composition or decomposition of a pseudo
64
k
signal is performed instead. In other words, an audio signal is encoded or decoded only in calling and called stations. With this arrangement, degradation of audio quality due to repetition of encoding/decoding can be effectively prevented.
FIG. 2
is a block diagram showing the structure of a conventional audio compression converter disclosed in JP laid-open No. Hei 7-307706, and so on. This structure comprises a silent data generator
30
; a separator
31
for separating an audio signal (or an encoded audio signal) and a relay frame signal, both supplied from the exchange side; a multiplexer
32
for inserting a relay frame signal into an audio signal (or an encoded audio signal); an audio encoder
33
for encoding an audio signal; an audio decoder
34
for decoding an encoded audio signal inputted; selectors
35
,
36
; a relay frame detector
37
for detecting a relay frame signal which has been separated by the separator
31
; a relay frame inserter
38
for inserting a relay frame signal; and a timer
39
.
The operation will next be described based on the accompanying drawings. In normal call connection, the selectors
35
,
36
select outputs from the audio encoder
33
and the audio decoder
34
, respectively. With this, an audio signal supplied from the exchange side is encoded by the audio encoder
33
and outputted as an encoded audio signal to the line side, while an encoded audio signal from the line side is decoded by the audio encoder
34
and multiplexed with a relay frame signal by the multiplexer
32
before being outputted to the exchange side.
In relay call connection, on the other hand, the relay frame detector
37
detects a relay frame signal, upon which the selector
35
is switched so as to select silent data for output from the silent data generator
30
. A predetermined period of time after the detection, the timer
39
switches the selectors
35
,
36
such that they select and output signals which have bypassed the audio encoder
33
and the audio decoder
34
, respectively. With this arrangement, an audio signal is not encoded or decoded in a relay station, and is only encoded or decoded in calling and called stations. This can prevent degradation of audio quality due to repetition of audio encoding/decoding.
However, a conventional audio tandem relay device shown in
FIG. 1
has such a problem that callers may sometimes hear loud noises. To be specific, in relay connection where one audio tandem relay device of a pair detects either a first or second pattern signal later or earlier than the other, loud noises may be produced and heard by the caller. This happens because one device of a pair will stay in a relay connection state in which the first and second switches
21
,
20
remain connected at the contact points
1
until both detect either a first or a second pattern signal, whereas the other is then in a calling state in
Ebisawa Hideaki
Fushimi Wataru
Naito Yushi
Shirokura Yoshihiko
Sugino Yukimasa
Mitsubishi Denki & Kabushiki Kaisha
Pham Brenda H.
Pham Chi H.
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