U.S. patent application number 10/042188 was filed with the patent office on 2002-05-23 for atm communication terminal and atm communication system.
Invention is credited to Takeda, Hirokazu, Takizawa, Masaaki.
Application Number | 20020061023 10/042188 |
Document ID | / |
Family ID | 15302061 |
Filed Date | 2002-05-23 |
United States Patent
Application |
20020061023 |
Kind Code |
A1 |
Takizawa, Masaaki ; et
al. |
May 23, 2002 |
ATM communication terminal and ATM communication system
Abstract
A communication terminal and a communication system for
efficiently using the transmission capacity of a circuit and
reducing the circuits disposed between an ATM switch and
communication terminals. The communication terminal disassembles
multiplexed signals obtained by multiplexing data into cells of
fixed length, adds each of the cells with a header containing
destination information and transmits/receives a cell through a
communication line. The terminal includes a discriminator for
referring to the destination information of each cell to
discriminate a cell addressed to the ATM communication terminal, a
multiplexed signal generator for multiplexed unit data to be
transmitted from the communication terminal to generate a
multiplexed signal, a cell-forming unit for forming the multiplexed
signal into cells, and a cell re-multiplexed for re-multiplexing
the cell generated from the multiplexed data and the cells
addressed to the other communication terminal.
Inventors: |
Takizawa, Masaaki; (Tokyo,
JP) ; Takeda, Hirokazu; (Yokohama-shi, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
15302061 |
Appl. No.: |
10/042188 |
Filed: |
January 11, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10042188 |
Jan 11, 2002 |
|
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|
09087510 |
May 29, 1998 |
|
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Current U.S.
Class: |
370/395.1 ;
370/392; 370/474 |
Current CPC
Class: |
H04Q 11/0478 20130101;
H04L 2012/5672 20130101; H04L 2012/5664 20130101 |
Class at
Publication: |
370/395.1 ;
370/474; 370/392 |
International
Class: |
H04L 012/28; H04L
012/56 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 1997 |
JP |
9-141869 |
Claims
What is claimed is:
1. A communication terminal which has functions of disassembling
multiplexed signals obtained by multiplexing data into cells of
fixed length, adding each of the cells with a header containing
destination information and transmitting/receiving the cell added
to the header through a communication line, comprising: a
discriminator for referring to the destination information of each
of cells which are received through the communication line to
discriminate, with regard to the cells, whether the cell is
addressed to the communication terminal concerned (hereinafter
referred to as "self communication terminal") or other
communication terminals; a multiplexed signal generator for
multiplexing data to be transmitted from said self communication
terminal itself to generate a multiplexed signal; a cell-forming
unit for forming the multiplexed signal generated in the
multiplexed signal generator into a cell; and a cell re-multiplexer
for re-multiplexing the cells generated by said cell-forming unit
and the cells addressed to the other communication terminals which
are discriminated in said discriminator.
2. The communication terminal as claimed in claim 1, further
comprising first input and output terminals and second input and
output terminals, wherein said communication terminal discriminates
and re-multiplexes cells received through said first input terminal
through said communication line and then transmits the
re-multiplexed cells from said first output terminal, and also
discriminates and re-multiplexes cells received through said second
input terminal and then transmits the re-multiplexed cells from
said second output terminal.
3. The communication terminal as claimed in claim 1, further
comprising bypass means for directly transmitting said received
cells when abnormality occurs in said communication terminal.
4. The communication terminal as claimed in claim 2, further
comprising bypass means for short-circuiting said input terminal
and said output terminal to each other when abnormality occurs in
said communication terminal.
5. A communication system comprising n (n represents an integer)
communication terminals, each of which has functions of
disassembling into cells a multiplexed signal of fixed length
obtained by multiplexing data, adding a header containing
destination information to each of the cells and then
transmitting/receiving the cells through a communication line,
wherein each of said communication terminals comprises: a
discriminator for discriminating a cell addressed thereto and a
cell addressed to another communication terminal by referring to
the destination information of the cell received from an input
terminal through said communication line; a multiplexed signal
generator for multiplexing data to be transmitted from the self
communication terminal to generate a multiplexed signal; a
cell-forming unit for forming the multiplexed signal generated in
said multiplexed signal generator into a cell; and a cell
re-multiplexing unit for re-multiplexing the cell which is to be
transmitted from said self communication terminal and generated
from the multiplexed data, and cells which are discriminated by
said discriminator and addressed to the other communication
terminals, and transmitting the re-multiplexed cells from said
output terminal to said communication line, wherein: the output
terminal of a first communication terminal and the input terminal
of a second communication terminal in said plural communication
terminals are connected via a communication line, the output
terminal of an i-th (i represents an integer of 1 or more and (n-1)
or less) is connected to the input terminal of an (i+1)-th
communication terminal, the output terminal of an (n-1)-th
communication terminal is connected to the input terminal of an
n-th communication terminal, and the output terminal of the n-th
communication terminal is connected to the input terminal of said
first communication terminal, whereby a ring-shaped transmission
path is constructed among n communication terminals so that data
communication can be performed through said transmission path among
said n communication terminals.
6. The communication system as claimed in claim 5, wherein: said
communication terminal further comprises a pair of input and output
terminals, the output terminal of said n-th communication terminal
is connected to the (n-1)-th communication terminal, the output
terminal of said (i+1)-th communication terminal is connected to
the input terminal of said i-th communication terminal, and the
output terminal of said first communication terminal is connected
to the output terminal of said n-th communication terminal, whereby
a second ring is formed among said n communication terminals.
7. A communication terminal for disassembling a multiplexed signal
obtained by multiplexing data into cells of fixed length, and
transmitting/receiving the multiplexed signal through a
communication line, comprising: a multiplexed signal generator for
multiplexing data to be transmitted from said self communication
terminal, thereby generating a multiplexed signal; a
cell-disassembling unit for disassembling the cells received
through said communication line to assemble a multiplexed signal;
and a cell multiplexing unit for forming the multiplexed signal
assembled and the multiplexed signal generated in said multiplexed
signal generator into cells, and transmitting the cells through
said communication line.
8. The communication terminal as claimed in claim 7, further
comprising a bypass for short-circuiting a reception system and a
transmission system of said communication line when abnormality
occurs in said communication terminal.
9. The communication terminal as claimed in claim 7, wherein said
cell-disassembling unit assembles plural multiplexed signals, and
comprises first storage means for storing a first multiplexed
signal of the plural multiplexed signals, second storage means for
storing a second multiplexed signal, third storage means for
storing the multiplexed signal generated in said multiplexed signal
generator, fourth storage means for storing the data other than the
multiplexed signal to be transmitted from said communication
terminal, and read-out control means for controlling the read-out
of the multiplexed signals stored in said first to fourth storage
means, and wherein said cell multiplexing unit forms the
multiplexed signals read out by said read-out control means into
cells and transmits the cells thus obtained.
10. The communication terminal as claimed in claim 9, wherein, when
a multiplexed signal on a control signal is stored in said second
storage means, said read-out control means controls the read-out
timing of the multiplexed signal on the control signal stored in
said fourth storage means.
11. The communication terminal as claimed in claim 7, further
comprising first and second input terminals and first and second
output terminals, wherein said multiplexing unit cell-multiplexes
the multiplexed signal generated thereby and the multiplexed signal
corresponding to the cell received through said first input
terminal and then transmitting the cell-multiplexed signal through
said first output terminal, and cell-multiplexes the multiplexed
signal generated thereby and th multiplexed signal corresponding to
the cell signal received through said second input terminal, and
then transmits the cell-multiplexed signal through said second
output terminal.
12. A communication terminal having functions of disassembling a
multiplexed signal obtained by multiplexing data into cells of
fixed length, adding a header containing destination information to
each of the cells and transmitting/receiving the cells through a
communication line, comprising: a cell-disassembling unit for
disassembling cells received through said communication line and
assembling a multiplexed signal for every destination information
by referring to destination information; a multiplexed signal
generator for multiplexing data to be transmitted from the
communication terminal in question; a re-multiplexing unit for
re-multiplexing the multiplexed signal generated in said
multiplexed signal generator and the multiplexed signals addressed
to other communication terminals in the multiplexed signals
assembled; and a cell-forming unit for forming said re-multiplexed
multiplexed signals into cells and transmitting the signals formed
into the cells through a communication line.
13. The communication terminal as claimed in claim 12, further
comprising first and second input and output terminals, wherein
said communication terminal disassembles the cells received from
said first input terminal through said communication line and
re-multiplexes the multiplexed signals, and transmits the resulting
signals from said first output terminal while disassembling the
cells received through said second input terminal and
re-multiplexing the multiplexed signals and then transmitting the
resulting signals from said second output terminal.
14. The communication terminal as claimed in claim 12, further
comprising bypass means for directly transmitting the received
cells when abnormality occurs in said communication terminal.
15. A communication system comprising a plurality of communication
terminals for disassembling a multiplexed signal obtained by
multiplexing data into cells of fixed length and
transmitting/receiving the cells through a communication line,
wherein: said plurality of communication terminals are connected in
series on a communication path, communication terminals located at
both ends in said plurality of communication terminals connected in
series are respectively connected to each other through a
communication line to form a ring-configuration communication path
among said communication terminals, and each of said plurality of
communication terminals assembles a multiplexed signal from cells
received through said communication line, and receives a
multiplexed signal addressed thereto while cell-multiplexing and
transmitting multiplexed signals addressed to other communication
terminals and the multiplexed signal obtained by multiplexing data
to be transmitted from the communication terminal in question,
together with the assembled multiplexed signal.
16. A communication system comprising a plurality of communication
terminals for disassembling a multiplexed signal obtained by
multiplexing data into cells of fixed length and
transmitting/receiving the cells through a communication line,
wherein: said plurality of communication terminals are connected in
series to one another on two communication paths which are
different from each other in communication direction, communication
terminals located at both ends in said plural communication
terminals connected in series through said two communication paths
are connected to each other through two communication lines having
different communication directions, thereby forming a dual
ring-configuration communication path between said communication
terminals, and each of said plurality of communication terminals
assembles a multiplexed signal from cells received through said two
communication paths, and receives a multiplexed signal addressed
thereto while cell-multiplexing and transmitting multiplexed
signals addressed to other communication terminals and the
multiplexed signal obtained by multiplexing data to be transmitted
from the communication terminal in question, together with the
assembled multiplexed signal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an ATM communication system
containing plural ATM communication terminals and an ATM switch,
and more particularly to an ATM communication system which is
suitable for use when the transmission rate of a transmission path
for connecting an ATM communication terminal and an ATM switch is
higher than the transmission rate of data to be
transmitted/received by each ATM communication terminal and the
transmission path has extra capacity.
[0003] 2. Description of Related Art
[0004] Recent developments of digital information reducing
technologies have promoted international standardizing
organizations such as International Organization for
Standardization (ISO), International-Telecommunication
Union-Telecommunication Standardization Sector (ITUT), to advance
the works for standardization of multimedia coding techniques to
reduce multimedia information such as images, sound, etc. and
actually have completed some of this work. Of these multimedia
coding techniques, a system known as "MPEG-2 (Moving Picture
Experts Group-2) which is to be applied to broadcasting and storage
media has been known. MPEG-2 enables transmission of images of the
current television broadcasting quality at a transmission rate of
about 6 to 10 Mbit/s. It also enables transmission of HDTV (High
Definition Television) signals having a resolution of twice or more
of current televisions in horizontal and vertical directions to be
transmitted at a transmission rate of about several tens
Mbit/s.
[0005] B-ISDN (Broadband-ISDN) which can transmit signals at a
transmission rate of 155.52 Mbit/s has been known as a
communication infrastructure. ATM (Asynchronous Transfer Mode) has
been used as a system for transmitting multiplexed signals by using
the B-ISDN. ATM is suitable for use in handling multimedia data of
various bit rates which range from low bit-rate data such as audio
data to high bit-rate data such as image data. According to the ATM
system, a signal such as a video signal, an audio signal, a data
signal or the like is disassembled into 48-byte unit signals. Each
of the 48-byte unit signals thus obtained is added with a header
(describing a destination or the like) of 5 bytes and then
transmitted. The signal of 53 bytes in total, which is obtained by
adding the 48-byte unit signal with the header of 5 bytes, is
called a cell.
[0006] In ATM, when information to be transmitted does not reach
155.52 Mbit/s, null information called a null cell is transmitted
to match the transmission rate to the transmission rate of the
transmission path. In this case, a signal comprising a combination
of a cell containing data and a null cell, that is, a cell which is
matched with the transmission rate of the transmission path is
hereinafter referred to as "ATM signal".
[0007] In the conventional technique, when signals reduced by
MPEG-2 described above are transmitted in ATM by using B-ISDN, the
ATM signal of 155.52 Mbit/s contains cells having effective data of
only 6 to 10 Mbit/s, and thus the residual bits of 145 to 149
Mbit/s are allocated to null cells.
[0008] Further, in the conventional technique, when many ATM
communication terminals are mutually communicated to one another
through an ATM switch, a line 12 must be provided between the ATM
switch 5 and each of the plural ATM communication terminals 13, as
shown in FIG. 12. Therefore, work for laying new lines must be
performed with new ATM communication terminals, and the cost for
establishing the system is increased.
SUMMARY OF THE INVENTION
[0009] An object of the present invention is to provide an ATM
communication terminal and an ATM communication system which can
solve the above problem and efficiently use the transmission
capacity of a communication circuit.
[0010] Further, another object of the present invention is to
provide an ATM communication terminal and an ATM communication
system which can reduce the number of lines disposed between an ATM
switch and each of ATM terminals constituting the system
irrespective of the number of the terminals.
[0011] In order to solve the above problem, an ATM communication
terminal according to the present invention has a function of
disassembling multiplexed signals obtained by multiplexing data
into cells of a fixed length, adding each of the cells with a
header containing destination information and
transmitting/receiving the cells through a communication line, and
comprises a discriminator for referring to the destination
information of the cells which are received through the
communication line to identify a cell addressed to the
communication terminal which received the cell (or, hereinafter
referred to as "self communication terminal") and a cell addressed
to another communication terminal from each other, a
multiplexed-signal generator for multiplexing data to be
transmitted from the self communication terminal to generate
multiplexed signals, a cell forming unit for forming the
multiplexed signals generated in the multiplexed signal generator
into cells, and a cell re-multiplexer for re-multiplexing the cell
generated from the multiplexed data to be transmitted from the self
communication terminal and the cell addressed to another
communication terminal which is discriminated in the
discriminator.
[0012] Further, a communication network is formed in a ring shape
among plural communication terminals, and cells which are received
through the communication network by a communication terminal
concerned (self communication terminal) and are to be transmitted
to (i.e., are addressed to) other communication terminals are
multiplexed with cells obtained by forming data to be transmitted
from the communication terminal in question into cells, and then
the cell-multiplexed cells are transmitted to a transmission path,
whereby the cell-multiplexed cells transmitted from the plural
communication terminals are allowed to make the round on the
ring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Preferred embodiments of the present invention will now be
described in conjunction with the accompanying drawings, in
which:
[0014] FIG. 1 is a diagram showing the configuration of an ATM
communication system according to a first embodiment of the present
invention;
[0015] FIG. 2 is a diagram showing the configuration of an ATM
communication terminal 1 at a transmission side shown in FIG.
1;
[0016] FIG. 3 is a flowchart showing the operation of a controller
109 shown in FIG. 2;
[0017] FIG. 4 is a diagram showing the configuration of an ATM
communication terminal 2 at a reception side shown in FIG. 1;
[0018] FIG. 5 is a diagram showing a bypass device 6 according to a
second embodiment of the present invention;
[0019] FIG. 6 is a diagram showing the configuration of a mode
switching circuit 602 shown in FIG. 5;
[0020] FIG. 7 is a diagram showing the configuration of an ATM
communication system according to a third embodiment of the present
invention;
[0021] FIG. 8 is a diagram showing the configuration of an ATM
communication terminal 7 shown in FIG. 7;
[0022] FIG. 9 is a diagram showing a modification of the third
embodiment of the present invention shown in FIG. 7 in which a line
for transmitting the output of the ATM switch 5 is omitted;
[0023] FIG. 10 is a diagram showing the configuration of an ATM
communication system according to a fourth embodiment of the
present invention;
[0024] FIG. 11 is a diagram showing the configuration of an ATM
communication terminal 10 shown in FIG. 10;
[0025] FIG. 12 is a diagram showing the configuration of a
conventional ATM communication system; and
[0026] FIG. 13 is a diagram showing the configuration of an ATM
communication terminal according to a fifth embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] A first embodiment according to the present invention will
be described hereunder.
[0028] FIG. 1 is a diagram showing the construction of an ATM
communication system according to the first embodiment of the
present invention.
[0029] Here, reference numerals 1.sub.1 to 1.sub.4 represent ATM
communication terminals at a transmission side, reference numerals
2.sub.1 to 2.sub.4 represent ATM communication terminals at a
reception side, reference numerals 3.sub.1 to 3.sub.4 represent
B-ISDN lines, reference numerals 4.sub.1 to 4.sub.6 represent
connection lines (for example, optical fibers) which can transmit
signals at a transmission rate of B-ISDN, and a reference numeral 5
represents an ATM switch.
[0030] First, the connection of the lines 3.sub.1 to 3.sub.4 (or,
hereinafter merely referred to as "line 3") and the connection
lines 4.sub.1 to 4.sub.6 (or, hereinafter merely referred to as
"connection line 4") will be described.
[0031] The lines 3.sub.1, 3.sub.2 are used to connect the ATM
switch 5 to the respective ATM communication terminals 1.sub.1 to
1.sub.4. The line 3.sub.1 is connected to the ATM switch 5 at one
end thereof, and connected to the input terminal of the ATM
communication terminal 1.sub.1 at the other end thereof. The line
3.sub.2 is connected to the ATM switch 5 at one end thereof and
connected to the output terminal of the ATM communication terminal
1.sub.4 at the other end thereof.
[0032] The lines 3.sub.3, 3.sub.4 are used to connect the ATM
switch 5 to the respective ATM communication terminals 2.sub.1 to
2.sub.4. The line 3.sub.3 is connected to the ATM switch 5 at one
end thereof, and connected to the input terminal of the ATM
communication terminal 2.sub.1 at the other end thereof The line
3.sub.4 is connected to the ATM switch 5 at one end thereof and
connected to the output terminal of the ATM communication terminal
2.sub.4 at the other end thereof.
[0033] The connection lines 4.sub.1 to 4.sub.3 are used to connect
the ATM communication terminals 1.sub.1 to 1.sub.4 to one another.
The connection line 4.sub.1 is connected to the output terminal of
the ATM communication terminal 1l at one end thereof and connected
to the input terminal of the ATM communication terminal 1.sub.2 at
the other end thereof. The connection line 4.sub.2 is connected to
the output terminal of the ATM communication terminal 1.sub.2 at
one end thereof and connected to the input terminal of the ATM
communication terminal 1.sub.3 at the other end thereof. The
connection line 4.sub.3 is connected to the output terminal of the
ATM communication terminal 1.sub.3 at one end thereof and connected
to the input terminal of the ATM communication terminal 1.sub.4 at
the other end thereof.
[0034] The connection lines 4.sub.4 to 4.sub.6 are used to connect
the ATM communication terminals 2.sub.1 to 2.sub.4 to one another.
The connection line 4.sub.4 is connected to the output terminal of
the ATM communication terminal 2.sub.1 at one end thereof, and
connected to the input terminal of the ATM communication terminal
2.sub.2 at the other end thereof. The connection line 4.sub.5 is
connected to the output terminal of the ATM communication terminal
2.sub.2 at one end thereof and connected to the input terminal of
the ATM communication terminal 2.sub.3 at the other end thereof The
connection line 4.sub.6 is connected to the output terminal of the
ATM communication terminal 2.sub.3 at one end thereof, and
connected to the input terminal of the ATM communication terminal
2.sub.4 at the other end thereof Through the lines 3 and the
connection lines 4 of B-ISDN thus connected, the ATM communication
terminals 1.sub.1 to 1.sub.4 at the transmission side and the ATM
switch 5, and the ATM communication terminals 2.sub.1 to 2.sub.4 at
the reception side and the ATM switch 5 are respectively connected
in the ring configuration.
[0035] Next, the ATM communication terminals 1.sub.1 to 1.sub.4 at
the transmission side (or, hereinafter merely referred to as "ATM
communication terminal 1") will be described.
[0036] The ATM communication terminal 1 at the transmission side
re-multiplexes a multiplexed signal transmitted from the upstream
side thereof and a multiplexed signal generated by the ATM
communication terminal 1 itself, and then transmits the
re-multiplexed signal to the downstream side thereof.
[0037] FIG. 2 is a diagram showing the configuration of the ATM
communication terminal 1 at the transmission side.
[0038] Here, reference numeral 101 represents an input terminal for
ATM signals, reference numeral 102 represents an output terminal
for ATM signals, reference numeral 103 represents an ATM interface,
reference numeral 104 represents a buffer memory for reception,
reference numeral 105 represents a buffer memory for transmission,
reference numeral 106 represents an MPEG coding device, reference
numeral 107 represents a data generator, reference numeral 108
represents a multiplexer, reference numeral 109 represents a
controller, reference numeral 110 represents a camera, reference
numeral 111 represents a microphone, and reference numeral 112
represents a switch.
[0039] The ATM interface 103 receives an ATM signal through the
input terminal 101 to discard null cells from the ATM signal
received and assemble a multiplexed signal for every destination
information which is affixed to the header of each of the residual
cells. Thereafter, it stores the multiplexed signal thus assembled
into the buffer memory 104.
[0040] Further, the ATM interface 103 reads out a multiplexed
signal stored in the buffer memory 105 and disassembles the
multiplexed signal thus read into cells. Further, the ATM interface
103, if necessary, adds null cells to the cells thus generated so
as to match the transmission rate of the B-ISDN line, and then
transmits these cells from the output terminal 102.
[0041] The MPEG coding device 106 reduces TV signals obtained by
the camera 110 or audio signals obtained by the microphone 111 on
the basis of the MPEG system to generate a high-efficiency coded
signal.
[0042] The data generator 107 generates data according to a user's
instruction, for example.
[0043] The multiplexer 108 multiplexes the high-efficiency coded
signal of images or sounds (voices) generated in the MPEG coding
device 106 or the data generated in the data generator 107 to
generate a multiplexed signal.
[0044] The controller 109 switches the input to the buffer memory
105 to any one of the output of the buffer memory 104 and the
output of the multiplexing device 108 by changing over the switch
112.
[0045] FIG. 3 is a flowchart showing the operation of the
controller 109.
[0046] In step 1001, it is checked whether or not the multiplexed
signal is stored in the buffer memory 104. If no multiplexed signal
is stored in the buffer memory 104, the processing goes to step
1003. On the other hand, if it is detected that some multiplexed
signal is stored, the processing goes to step 1002 to change over
the switch 112 to connect the buffer memory 104 and the buffer
memory 105 to each other and shift the multiplexed signal stored in
the buffer memory 104 to the buffer memory 105.
[0047] In step 1003, it is checked in the multiplexer 108 whether
or not preparation for generation of a multiplexed signal is
started. For example, this check work can be achieved by checking
whether the signal is generated in the MPEG coding device 106 or
the data generator 107.
[0048] If the preparation is started, the processing goes to step
1004 to change over the switch 112 so that the multiplexing device
108 is connected to the buffer memory 105 and the multiplexed
signal generated in the multiplexer 108 is stored into the buffer
memory 105. On the other hand, if the preparation is not started,
the processing goes back to step 1001.
[0049] Next, the operation of the ATM communication terminal 1 at
the transmission side thus constructed will be described.
[0050] The ATM interface 103 extracts the multiplexed signal
transmitted from the upstream side thereof from the ATM signal
which is input through the input terminal 101, and stores the
extracted multiplexed signal into the buffer memory 104. The
controller 109 shifts the multiplexed signal stored in the buffer
memory 104 to the buffer memory 105 by changing over the switch
112. The controller 109 changes over the switch 112 to store the
multiplexed signal stored in the multiplexer 108 into the buffer
memory 105.
[0051] When the multiplexed signal transmitted from the upstream
side and the multiplexed signal generated in the multiplexer 108
are stored into the buffer memory 105, the ATM interface 103
disassembles each of these multiplexed signal into cells, adds null
cells to these cells, if necessary, and then transmits these cells
from the output terminal 102.
[0052] Through the above operation, the ATM interface 103
re-multiplexes and transmits the multiplexed signal transmitted
from the upstream side thereof and the multiplexed signal generated
by itself.
[0053] Next, the ATM communication terminals 2.sub.1 to 2.sub.4 at
the reception side (or, hereinafter referred to as "ATM
communication terminal 2") will be described.
[0054] The ATM communication terminal 2 at the reception side picks
up a cell addressed thereto from the ATM signal transmitted from
the upstream side thereof, and transmits the residual cells to the
downstream side thereof.
[0055] FIG. 4 is a diagram showing the configuration of the ATM
communication terminal 2 at the reception side.
[0056] Here, reference numeral 201 represents an input terminal for
the ATM signal, reference numeral 202 represents an output terminal
for the ATM signal, reference numeral 203 represents an ATM
interface, reference numeral 204 represents a reception buffer
memory, reference numeral 205 represents a transmission buffer
memory, reference numeral 206 represents a multiplexed signal
separating device, reference numeral 207 represents an MPEG
decoding device, reference numeral 208 represents a data obtaining
device, reference numeral 209 represents a monitor and reference
numeral 210 represents a speaker.
[0057] The ATM interface 203 receives ATM signals through the input
terminal 201. It discards null cells from the ATM signals thus
received, assembles multiplexed signals on the basis of each
destination information which is affixed to the header of each
cell, and then stores the assembled multiplexed signals into the
buffer memory 204.
[0058] Further, the ATM interface 203 investigates the destination
information of the multiplexed signals stored in the buffer memory
204 to shift multiplexed signals addressed to ATM communication
terminals 2 located at the downstream side thereof to the buffer
memory 205 and transmit the multiplexed signal addressed thereto
(that is, to the ATM communication terminals 2 which received the
ATM signals) to the multiplexed signal separating device 206.
[0059] Further, the ATM interface 203 reads out the multiplexed
signal stored in the buffer memory 205 and disassembles it into
cells. Each cell thus generated is applied with a null cell so as
to match the transmission rate of the B-ISDN line, if necessary,
and transmitted from the output terminal 202.
[0060] The multiplexed signal separating device 206 separates the
multiplexed signal transmitted from the buffer memory 204 into a
high-efficiency coded signal for TV signals, a high-efficiency
coded signal for audio signals and data.
[0061] The MPEG coding device 207 decodes each of the
high-efficiency coded signal for TV signals and the high-efficiency
coded signal for audio signals which are obtained in the
multiplexed signal separating device 206. The TV signals and the
audio signals thus decoded are output from the monitor 209 and the
speaker 210, respectively.
[0062] The data obtaining device 208 obtains the data which is
obtained in the multiplexed signal separating device 206. This data
is used in its own ATM communication terminals 2 or at the
outside.
[0063] Next, the operation of the ATM communication terminal 2 at
the reception side will be described.
[0064] The ATM interface 203 picks up multiplexed signals
transmitted from the upstream side thereof from an ATM signal which
is input through the input terminal 201, and stores these signals
into the buffer memory 204. Thereafter, it shifts multiplexed
signals which are contained in the multiplexed signals thus stored
and addressed to ATM communication terminals 2 located at the
downstream side thereof to the buffer memory 205, disassembles the
multiplexed signals in the buffer memory 205 into cells and then
outputs these cells from the output terminal 202.
[0065] On the other hand, the ATM interface 203 transmits a
multiplexed signal addressed thereto (that is, to the ATM
communication terminals 2 which received the ATM signals) to the
multiplexed signal separating device 206. The multiplexed signal
separating device 206 receives and separates the multiplexed
signal, and supplies the separated multiplexed signal to the MPEG
decoding device 207 and the data obtaining device 208.
[0066] With the above operation, the multiplexed signal which is
addressed to the ATM communication terminals 2 which received the
ATM signals (or self ATM communication terminals 2) is read out, as
well as the multiplexed signals which are addressed to the ATM
communication terminals 2 located at the downstream side thereof is
transmitted.
[0067] Next, the ATM switch 5 will be described.
[0068] An ATM switch which is used in the normal ATM communication
system may be used as the ATM switch 5. However, it is necessary to
set that when destination information affixed to the header of a
cell indicates the ATM communication terminals 2.sub.1 to 2.sub.4
at the reception side, the cell concerned is transmitted to the
line 3.sub.3 of FIG. 1. That is, virtual channel of the ATM
communication terminals 2.sub.1 to 2.sub.4 are allocated in the
line 3.sub.3.
[0069] According to the ATM communication system of the first
embodiment as described above, each of the ATM communication
terminals 1.sub.1 to 1.sub.4 at the transmission side
re-multiplexes the multiplexed signal transmitted from the upstream
side of the ATM communication terminal concerned and the
multiplexed signal which is generated by the ATM communication
terminal concerned and addressed to at least one of the ATM
communication terminals 2.sub.1 to 2.sub.4 at the reception side,
and transmits the re-multiplexed signal to the downstream side
thereof.
[0070] Finally, the signal obtained by re-multiplexing the
multiplexed signals generated in the respective ATM communication
terminals 1.sub.1 to 1.sub.4 is transmitted from the ATM
communication terminal 1.sub.4 to the B-ISDN line 3.sub.2. The
re-multiplexed signal which is transmitted onto the line 3.sub.2 is
transmitted onto the B-ISDN line 3.sub.3 through the ATM switch
5.
[0071] On the other hand, each of the ATM communication terminals
2.sub.1 to 2.sub.4 at the reception side separates the
re-multiplexed signal transmitted from the upstream side of the ATM
communication terminal concerned to obtain the multiplexed signal
address thereto, and the multiplexed signal addressed to at least
one of the ATM communication terminals 2.sub.1 to 2.sub.4 located
at the downstream is re-multiplexed and transmitted.
[0072] Accordingly, according to this embodiment, the multiplexed
signal generated by the ATM communication terminal 1 at the
reception side can be transmitted to the ATM communication terminal
2 at the reception side by using the route comprising the line
3.sub.2--the ATM switch 5--the line 3.sub.3.
[0073] As described above, according to this embodiment, the
multiplexed signals generated by a plurality of ATM communication
terminals 1 are transmitted to one B-ISDN line 3, and thus the
transmission capacity of B-ISDN can be efficiently used. Further,
the number of line to be disposed between the ATM switch and the
ATM communication terminals can be reduced as much as possible
irrespective of the number of the ATM communication terminals
constituting the system.
[0074] In the above-described first embodiment, both the group of
the ATM communication terminals 1 at the transmission side and the
ATM switch 5 and the group of the connection of the ATM
communication terminals 2 at the reception side and the ATM switch
5 establishes the ring-shaped connection separately and
independently. However, the present invention is not limited to
this mode. For example, the connection may be made so that the ATM
communication terminals 1 at the transmission side and the ATM
communication terminals 2 at the reception side coexist in one
ring.
[0075] Further, in the above-described first embodiment, the ATM
communication terminal 1 at the transmission side and the ATM
communication terminal 2 at the reception side are separately used,
as ATM communication terminals. However, the present invention is
not limited to this mode. For example, each of the ATM
communication terminals constituting the ATM communication system
may be designed to serve as an ATM communication terminal at the
transmission side and also serve as an ATM communication terminal
at the reception side.
[0076] In this case, an ATM communication system which is suitable
for use in an interactive communication system for handling images
on a real-time basis, such as a video phone, video conference
equipment, etc. can be constructed.
[0077] Next, a second embodiment according to the present invention
will be described.
[0078] The ATM communication system of the second embodiment is
characterized in that in the ATM communication system shown in FIG.
1, each of the ATM communication terminals at the transmission side
and the reception side is provided with a bypass device which forms
a transmission path for bypassing the ATM communication
terminal.
[0079] FIG. 5 is a diagram showing the configuration of the bypass
device 6 used in the second embodiment of the present
invention.
[0080] The bypass device 6 includes, as shown in FIG. 5, a switch
601 for connecting a transmission path at the upstream side of the
ATM communication terminal to the input terminal of the ATM
communication terminal concerned or a transmission path at the
downstream side of the ATM communication terminal concerned, and a
mode switching circuit 602.
[0081] The mode switching circuit 602 serves to control the switch
601.
[0082] FIG. 6 is a diagram showing the construction of the mode
switching circuit 602. Here, reference numeral 603 represents a
diode, reference numeral 604 represents a capacitor, reference
numeral 605 represents a resistor and reference numeral 606
represents a threshold value judgment circuit.
[0083] When a normal signal indicating that an ATM communication
terminal operates normally is output from the ATM communication
terminal concerned, the normal signal is stored as charge in the
capacitor 605 through the diode 603. When the output of the normal
signal is stopped because some abnormality such as failure or the
like occurs in the ATM communication terminal concerned, the charge
stored in the capacitor 605 is discharged through the resistor 605,
and thus the voltage applied across both ends of the capacitor 605
is reduced.
[0084] The threshold value judgment circuit 606 compares the
voltage across both ends of the capacitor 605 with a predetermined
value to detect presence or absence of the output of the normal
signal. When the output of the normal signal is detected, the
switch 601 is changed over so that the transmission path at the
upstream side of the ATM communication terminal is connected to the
input terminal of the ATM communication terminal concerned. On the
other hand, when no output of the normal signal is detected, the
switch 601 is changed over so that the transmission path at the
upstream side of the ATM communication terminal concerned is
connected to the transmission path at the downstream side of the
ATM communication terminal concerned.
[0085] For example, the normal signal may be generated and output
by the following manner. Each constituent element of the ATM
communication terminal is provided with detection means for
detecting abnormality of the constituent element concerned, and the
normal signal is output if some abnormality is detected by the
detection means.
[0086] According to the second embodiment of the present invention,
even when abnormality occurs in one of the ATM communication
terminals constituting the ATM communication system and it is
impossible to receive any ATM signal, the flow of the ATM signal at
the ATM communication terminal concerned being cut off can be
prevented.
[0087] Next, a third embodiment according to the present invention
will be described.
[0088] FIG. 7 is a diagram showing the configuration of an ATM
communication system according to a third embodiment of the present
invention.
[0089] Here, reference numerals 7.sub.1 to 7.sub.4 represent ATM
communication terminals, reference numerals 8.sub.1 to 8.sub.4
represent B-ISDN lines, and reference numeral 9.sub.1 to 9.sub.6
represent connection lines (for example, optical fibers) through
which signals can be transmitted at the transmission rate of
B-ISDN. In this embodiment, the elements having the same functions
as the first embodiment shown in FIG. 1 are represented by the same
reference numerals.
[0090] In this embodiment, as, shown in FIG. 7, each of the B-ISDN
lines 8.sub.1 to 8.sub.4 (or, hereinafter merely referred to as
"line 8") and the connection lines 9.sub.1 to 9.sub.6 (or,
hereinafter merely referred to as "connection line 9") are dually
wired so that the ATM switch 5 and the ATM communication terminals
7.sub.1 to 7.sub.4 (hereinafter merely referred to as "ATM
communication terminal 7") are connected to one another through a
dual ring with clockwise and counterclockwise transmission
paths.
[0091] The ATM communication terminal 7 serves as both the ATM
communication terminal 1 at the transmission side and the ATM
communication terminal 2 at the reception side which are used in
the first embodiment shown in FIG. 1.
[0092] FIG. 8 is a diagram showing the ATM communication terminal
7.
[0093] Here, reference numeral 701a, 701b represents an input
terminal for an ATM signal, reference numeral 702a, 702b represents
an output terminal for an ATM signal, reference numeral 703a, 703b
represents an ATM interface, reference numeral 704a to 704d
represents a buffer memory for reception, reference numeral 705a,
705b represents a buffer memory for transmission, and reference
numeral 712a to 712c represents a selector. The elements having the
same functions as the ATM communication terminals shown in FIGS. 2
and 4 are represented by the same reference numerals.
[0094] The input terminal 701a and the output terminal 702a are
used to input and output the ATM signal which is transmitted in a
counterclockwise fashion (in the ring comprising the line
8.sub.1--the connection lines 9.sub.1 to 9.sub.3--the line 8.sub.2)
in FIG. 7, respectively. The input terminal 701b and the output
terminal 702b are used to input and output the ATM signal which is
transmitted in a clockwise fashion (in the ring comprising the line
8.sub.3--the connection lines 9.sub.4 to 9.sub.6--the line 8.sub.4)
in FIG. 7, respectively.
[0095] The ATM interface 703a receives the ATM signal through the
input terminal 701a. Null cells are discarded from the ATM signal
received, and the multiplexed signals are assembled for the
residual cells for every destination information which is affixed
to the header of each cell. Of the multiplexed signals thus
assembled, the multiplexed signal addressed thereto (that is, ATM
communication terminal concerned) is stored in the buffer memory
704a, and the multiplexed signals addressed to the other ATM
communication terminals 7 are stored in the buffer memory 704b.
[0096] Further, the ATM interface 703a disassembles the multiplexed
signal transmitted through the selector 712a into cells. If
necessary, it adds null cells to the cells thus obtained so as to
match the transmission rate of the B-ISDN line, and outputs these
cells from the output terminal 702a.
[0097] The ATM interface 703b receives the ATM signal through the
input terminal 701b. The null cells are discarded from the ATM
signal received and the multiplexed signals is assembled for every
destination information affixed to the header of each cell for the
residual cells. In the multiplexed signals thus assembled, the
multiplexed signal addressed thereto (ATM communication terminal
concerned) is stored in the buffer memory 704c, and the multiplexed
signals addressed to the other ATM communication terminals 7 are
stored in the buffer memory 704d.
[0098] The ATM interface 703b disassembles the multiplexed signal
transmitted through the selector 712c into cells. If necessary, it
adds null cells to the cells so as to match the transmission rate
of the B-ISDN line, and then transmits these cells from the output
terminal 702b.
[0099] The operation of the ATM communication terminal 7 thus
constructed will be described.
[0100] The ATM interface 703a assembles the multiplexed signal for
every destination information from the ATM signal input to the
input terminal 701a. Of the multiplexed signals thus assembled, the
multiplexed signal addressed to the ATM communication terminal
concerned is stored in the buffer memory 704a, and the multiplexed
signals addressed to the other ATM communication terminals 7 are
stored in the buffer memory 704b.
[0101] The multiplexed signal which is addressed to that ATM
communication terminal itself and stored in the buffer memory 704a
is transmitted through the selector 712b to the multiplexed signal
separating device 206 to be multiplex-separated.
[0102] Further, the multiplexed signals which are address to the
other ATM communication terminals and stored in the buffer memory
704b are transmitted through the selector 712a to the ATM interface
703a. Further, when the multiplexed signal generated by this ATM
communication terminal itself is stored in the buffer memory 705a
for transmission, the multiplexed signal concerned is transmitted
through the selector 712a to the ATM interface 703a.
[0103] The ATM interface 703a disassembles into cells each of the
multiplexed signal stored in the buffer memory 704b and the
multiplexed signal stored in the buffer memory 705a, adds null
cells to these cells, if necessary, and then transmits the cells
from the output terminal 702a.
[0104] Through the above operation, each ATM communication terminal
obtains the multiplexed signal addressed thereto from the ATM
signal which is transmitted from the left side (that is, an upper
stream side in a counterclockwise direction) thereof, and
re-multiplexes the multiplexed signals addressed to the other ATM
communication terminals and the multiplexed signal generated by the
ATM communication terminals concerned to transmit the
re-multiplexed signal to the right side (that is, an lower stream
side in a counterclockwise direction) thereof.
[0105] Further, the ATM interface 703b assembles the multiplexed
signals from the ATM signal input to the input terminal 702a for
every destination information. Of these assembled multiplexed
signals, the multiplexed signal addressed to the ATM communication
terminal concerned is stored into the buffer memory 704c, and the
multiplexed signals addressed to the other ATM communication
terminals 7 are stored into the buffer memory 704d.
[0106] The multiplexed signal which is addressed to the ATM
communication terminal concerned and stored in the buffer memory
704c is transmitted through the selector 712b to the multiplexed
signal separating device 206 in which the multiplexed signal is
subjected to the multiplexed signal separation processing.
[0107] On the other hand, the multiplexed signals which are
addressed to the other ATM communication terminals 7 and stored in
the buffer memory 704d are transmitted through the selector 712c to
the ATM interface 703b. Further, when the multiplexed signal
generated by the ATM communication terminal concerned is stored in
the buffer memory 705b for transmission thereof, the multiplexed
signal concerned is also transmitted through the selector 712a to
the ATM interface 703b.
[0108] The ATM interface 703b disassembles each of the multiplexed
signal stored in the buffer memory 704c and the multiplexed signals
stored in the buffer memory 705b into cells, and adds null cells to
these cells, if necessary, to transmit the cells from the output
terminal 702b.
[0109] Through the above operation, the ATM communication terminal
concerned obtains the multiplexed signal addressed thereto from the
ATM signal transmitted from the right side (that is, an upper
stream side in a clockwise direction) thereof, and re-multiplexes
the multiplexed signals addressed to the other ATM communication
terminals and the multiplexed signal generated by the ATM
communication terminals concerned to transmit the re-multiplexed
signal to the left side (that is, an lower stream side in a
clockwise direction) thereof.
[0110] In this embodiment, even when the ATM communication terminal
72 fails, the ATM communication terminal 7.sub.1 and the ATM switch
5 can form a ring therebetween by the transmission paths 8.sub.1
and 8.sub.4. Further, the communication terminals 7.sub.3 and
7.sub.4 and the ATM switch 5 can form a ring therebetween by the
transmission paths 8.sub.3, 9.sub.4, 9.sub.3 and 8.sub.2.
[0111] Further, even when any one of the clockwise and
counterclockwise transmission paths is cut off, the communication
can be performed by using other transmission paths. Further, even
when a transmission path is cut off at any point, for example,
between the ATM communication terminals 7.sub.1 and 7.sub.2, the
ATM communication terminal and the ATM switch can form a ring
therebetween using the transmission paths 8.sub.1 and 8.sub.4. The
other ATM communication terminals 7.sub.2 to 7.sub.4 can form a
ring with the ATM switch by the transmission paths 8.sub.3,
9.sub.4, 9.sub.5, 9.sub.2, 9.sub.3, 8.sub.2. Accordingly, the ATM
switch can receive the data transmitted from all the communication
terminals.
[0112] In this embodiment, any one of the clockwise and
counterclockwise transmission paths may be used as a backup path.
In this case, the backup transmission path is used when the other
transmission path fails.
[0113] When such a dual ring structure as described above is
adopted, the system can be designed to have high resistance to
problems such as failure of the communication terminals, occurrence
of abnormality of the transmission paths, etc.
[0114] Further, in this embodiment, when the ATM communication
terminal 7 needs no information from the ATM switch 5 (for example,
when data transmission target is limited to a special one), the
lines 8.sub.1, 8.sub.3 for transmitting the output of ATM switch
can be omitted from the lines 8.sub.1 to 8.sub.4 which connect ATM
switch and ATM communication terminal 7 each other as shown in FIG.
9. This is also satisfied for the case of the first embodiment
shown in FIG. 1.
[0115] Next, a fourth embodiment according to the present invention
will be described.
[0116] In an ATM, an identifier which is called "VCI (Virtual
Channel Identifier)" is affixed to each cell to identify the type
of signals to be transmitted and the address of a destination.
Further, a handshaking procedure for starting communications is
required to be carried out between the ATM switch and the ATM
communication terminal when controlling the start of the
communications, etc. Normally, a signal used for the handshaking
procedure (handshake signal) is divided into plural cells, and
transmitted onto the transmission path while mixed with normal data
cells. The ATM switch collects cells having the same VCI number to
assemble the handshake signal, and performs the handshaking
procedures on the basis of the handshake signal.
[0117] A predetermined VCI number (for example, VCI=5) is
frequently used as the handshake signal.
[0118] Therefore, in the above-described embodiments, when plural
ATM communication terminals carry out the handshaking procedures
for starting the communications at the same time, the cells of
plural handshake signals having the same VCI number may be
transmitted onto the same line while mixed with one another.
[0119] In this embodiment, each of the plural handshake signals can
be reliably restored in the ATM switch even in such a
situation.
[0120] FIG. 10 is a diagram showing the configuration of the ATM
communication system according to a fourth embodiment of the
present invention.
[0121] Here, reference numerals 10.sub.1 to 10.sub.4 represent ATM
communication terminals. In this embodiment, the elements having
the same functions as the first embodiment shown in FIG. 1 are
represented by the same reference numerals.
[0122] Each of the ATM communication terminals 10.sub.1 to 10.sub.4
(or, hereinafter merely referred to as "ATM communication terminal
10") has both the functions of the ATM communication terminal 1 at
the transmission side and the ATM communication terminal 2 at the
reception side in the first embodiment shown in FIG. 1.
[0123] FIG. 11 is a diagram showing the configuration of the ATM
communication terminal 10.
[0124] Here, reference numeral 151 represents an input terminal for
the ATM signal, reference numeral 152 represents an output terminal
for the ATM signal, reference numeral 153 represents an ATM
interface, reference numeral 154a represents a buffer memory for
data reception, reference numeral 154b represents a buffer memory
for signal reception, reference numeral 155a represents a buffer
memory for data transmission, reference numeral 155b represents a
buffer memory for signal transmission, reference numeral 156a, 156b
represents a flip-flop, reference numeral 157a, 157b represents an
AND circuit, reference numeral 158 represents a selector, reference
numeral 159 represents a read-out controller and reference numeral
108a represents a multiplexer. The elements having the same
functions as the ATM communication terminals shown in FIGS. 2 and 4
are represented by the same reference numerals.
[0125] The ATM interface 153 receives the ATM signal through the
input terminal 151. It discards null cells from the ATM signal thus
received and assembles multiplexed signals from the residual cells
on the basis of the information which is affixed to the headers of
the cells. Of the multiplexed signals thus assembled, the
multiplexed signals concerning the normal data are stored in the
buffer memory 154a, and the signals such as the handshake signal,
etc. are stored in the buffer memory 154b.
[0126] The ATM interface 703a disassembles the multiplexed signals
transmitted through the selector 158 into cells, adds null cells to
the cells so as to match the transmission rate of the B-ISDN line,
if necessary, and then transmits these cells from the output
terminal 152.
[0127] The multiplexer 108a generates multiplexed signals
concerning normal data such as video data, audio data and
multiplexed signals concerning signals such as handshake signals.
The multiplexed signals on the normal data are stored into the
buffer memory 155a for data transmission, and the multiplexed
signals concerning the handshake signal are stored into the buffer
memory 155b for signal transmission.
[0128] The read-out controller 159 monitors a ready signal
(indicated by a dotted line in FIG. 11) output from each of the
buffer memories 154a, 154b, 155a, 155b, reads out the multiplexed
signal from the buffer memory which outputs the ready signal and
transmits it to the ATM interface 153 through the selector 158.
[0129] This embodiment is designed so that when the handshake
signal (multiplexed signal) is read out from any one of the signal
reception buffer memory 154b and the signal transmission buffer
memory 155b, the input of the ready signal output from the other
buffer memory into the read-out controller 159 is prevented,
whereby the handshake signal which is stored in the signal
reception buffer memory 154b and generated by another ATM
communication terminal 10 and the handshake signal which is stored
in the signal transmission buffer memory 155b and generated by the
ATM communication terminal 10 concerned are prevented from being
transmitted through the selector 158 to the ATM interface 153 at
the same time.
[0130] That is, when the read-out of the data reception buffer 154b
is started, the flip-flop 156a is reset, whereby the ready signal
output from the data transmission buffer memory 155b is interrupted
by the AND circuit 157a and thus it does not reach the read-out
controller 159. When the readout of the data reception buffer
memory 154b is completed, the flip-flop 156a is set, whereby the
ready signal output from the data transmission buffer memory 155b
reaches the read-out controller 159 through the AND circuit
157a.
[0131] Further, when the read-out of the data transmission buffer
memory 156a is started, the flip-flop 156b is reset, whereby the
ready signal output from the data reception buffer memory 154b is
interrupted by the AND circuit 157b and thus it does not reach the
read-out controller 159. When the read-out of the data transmission
buffer memory 155b is completed, the flip-flop 156b is set, whereby
the ready signal output from the data reception buffer memory 154b
reaches the read-out controller 159 through the AND circuit
157b.
[0132] Through the above operation, the cells constituting the
multiplexed signal of the handshake signal generated by the ATM
communication terminal concerned and the cells constituting the
multiplexed signal of the handshake signal generated by the other
ATM communication terminals 10 can be prevented from being
transmitted while mixed with each other.
[0133] Accordingly, the ATM switch 5 can reliably restore each of
the plural handshake signals which are generated by plural ATM
communication terminals 10.
[0134] Next, a fifth embodiment according to the present invention
will be described.
[0135] FIG. 13 is a diagram showing the configuration of the ATM
communication terminal device of the fifth embodiment according to
the present invention.
[0136] In the fifth embodiment, each ATM communication terminal has
both the functions of the ATM communication terminals at the
transmission and reception sides. The system is constructed so that
plural ATM communication terminals are connected to one another in
a ring shape through high-speed transmission paths, as shown in
FIGS. 7, 9 and 10. In the fifth embodiment, a mechanism of
discriminating data addressed to the ATM communication terminal
concerned and data addressed to ATM communication terminals located
at the downstream side of the ATM communication terminal concerned
is disposed before an assembling and disassembling device of ATM
cells.
[0137] First, a signal which is transmitted through an optical
fiber cable is converted to an electrical signal by an O/E
converter 1300. The electrical signal thus obtained is a signal
having such a format that ATM cells are packed in a frame for
transmission. In a physical interface 1301, the electrical signal
having such a transmission format is disassembled into ATM cells.
The physical interface uses a transmission rate which is
standardized as a synchronous digital hierarchy (SDH), for example.
The overhead of a frame of SDH is referred in order to pick up ATM
cells which are packed in a payload of SDH. The cells picked up
from the SDH frame are discriminated into the data addressed to the
ATM communication terminal concerned and the data addressed to ATM
communication terminals located at the downstream side of the ATM
communication terminal concerned in a discriminator 1303 of an ATM
cell re-multiplexer 1302. Specifically, VCI contained in the header
of each ATM cell is checked to judge whether the cell is a cell
addressed to the ATM communication terminal concerned or a cell
addressed to another ATM communication terminal at the downstream
side of the ATM communication terminal concerned. If the cell is
addressed to the ATM communication terminal concerned (i.e., the
self ATM communication terminal), the cell is transmitted to an ATM
cell disassembling/assembling unit 1306. In the ATM cell
disassembling/assembling unit 1306, the ATM cell received is
disassembled. Thereafter, a transport stream of MPEG is picked up
and transmitted to a transport stream multiplexing/disassembling
unit 1307. The transport stream multiplexing/disassembling unit
1307 disassembles the transport stream of MPEG to extract a coded
video signal, a coded audio signal and data. The coded video signal
is decoded by an MPEG image coding/decoding unit 1308 and displayed
on a monitor (not shown). The coded audio signal is decoded by an
MPEG audio coding/decoding unit 1309 and output from a speaker (not
shown). The data are transmitted to the data generating/obtaining
unit 1310. The data is a communication terminal control signal for
controlling a camera, for example. The communication terminal
controls the camera or the like on the basis of the received
communication terminal control signal. When the communication
terminal control signal is not multiplexed with the MPEG transport
stream and received by another cell, it is directly delivered from
the ATM cell disassembling/assembling device 1306 to the data
generating/obtaining unit 1310.
[0138] On the other hand, the video signal and the audio signal
which are to be transmitted from a communication terminal to
another communication terminal are first coded by the video
coding/decoding unit 1308 and the MPEG audio coding/decoding unit
1309.
[0139] The transport stream multiplexing/disassembling unit 1307
multiplexes the data generated in the data generating/obtaining
unit 1310, the coded video signal and the coded audio signal to
generate the transport stream. Alternatively, when the data is not
multiplexed with the transport stream, the data generated in the
data generating/obtaining unit 1310 are delivered to the ATM cell
disassembling/assembling unit 1306. The ATM cell
disassembling/assembling unit 1306 disassembles this transport
stream to assemble the ATM cells and store them into the buffer
memory 1305 of the ATM cell re-multiplexing unit 1302. The ATM cell
re-multiplexing unit 1302 re-multiplexes these cells with cells
which are transmitted from the discriminator 1303 and addressed to
the communication terminals located at the downstream side of the
ATM communication terminal concerned, and transmits the
re-multiplexed cells to the physical interface unit 1301. The
physical interface unit 1301 packs these cells in the frame of SDH,
performs electro-optical conversion on the packed cells and then
transmits them from the optical fiber.
[0140] The discrimination between the data addressed to the ATM
communication terminal concerned and the data addressed to the ATM
communication terminals at the downstream side of the ATM
communication terminal concerned may be considered to be carried
out between the physical interface and the ATM cell
disassembling/assembling unit.
[0141] In FIGS. 2, 4, 8, 11 showing the communication terminals
from the first to fourth embodiments, the O/E converter and the
physical interface unit are not illustrated. However, they are
provided in these embodiments in the same manner as shown in FIG.
13 when an optical fiber is used.
[0142] Further, the present invention is not limited to the above
embodiments, and various modifications may be made to these
embodiments without departing from the subject matter of the
present invention.
[0143] For example, the above-described embodiments use B-ISDN as
the line. However, the present invention is not limited to the
above embodiments, and any line may be used insofar as the
transmission rate thereof is higher than the transmission rate
which is needed to accurately reproduce the signals reduced
according to MPEG on a real-time basis.
[0144] The number of ATM communication terminals is not limited to
that described in each of the above-described embodiments. In the
present invention, the number of the ATM communication terminals
may be increased within the range which is permissible by the
transmission capacity of the line for connecting the ATM switch and
the ATM communication terminals.
[0145] Further, the ATM communication terminals described in the
above-described embodiments can be implemented by making a CPU
execute predetermined programs stored in a storage medium such as a
CD-ROM or the like in an information processing device having an
ATM communication function and an MPEG coding or decoding function,
such as a personal computer or the like.
[0146] The present invention is more effectively applied to
surveillance systems such as a river surveillance system. In the
river surveillance system, communication terminals are disposed at
several to several tens of surveillance places along a river, and
these communication terminals are connected to one another in a
ring shape. For example, when the terminals are connected to one
another by B-ISDN having a transmission rate of 155.52 Mbit/s and
an MPEG transport stream of 6 Mbit/s is transmitted from each
terminal, the number of the terminals on the ring is set to about
30 at maximum. Each communication terminal transmits a monitored
image of the river picked up by a camera through an optical fiber
to a surveillance center. The surveillance center monitors the
image and transmits a camera control signal and a control signal
for instructing an open/close operation of a floodgate to control
the water amount of the river, if necessary. The destination of the
control signal and the video signal is indicated by VCI. The VCI
indication of the destination may be performed by indicating a
number which is allocated to each of the terminals in advance. At
this time, the discrimination in numbering between the terminals at
the surveillance center and the terminals at the river side may be
made, for example, by allocating the tens to the terminals at the
surveillance center and allocating the hundreds to the terminals at
the river. Further, in addition to the destination information, VCI
may be added with information for identifying the data type of
video, audio, data, normal telephone data. The overall
configuration of the above applied system is the same as shown in
FIG. 7 or FIG. 10. In the case of the applied system, the ATM
switch 5 is replaced by the center terminal.
[0147] As described above, according to the present invention, the
transmission capacity of the line can be used efficiently, and the
number of lines disposed between the ATM switch and the ATM
communication terminals constituting the system can be reduced to
be as few as possible irrespective of the number of ATM
communication terminals.
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