U.S. patent application number 10/356725 was filed with the patent office on 2003-06-26 for cell multiplexing apparatus handling multiple items of information.
This patent application is currently assigned to Fujitsu Limited. Invention is credited to Kajiwara, Masanori, Mase, Hideki, Nobuyasu, Kosuke, Norizuki, Reiko, Takashima, Tomonobu, Tanaka, Kenji, Tanaka, Takeshi, Toyofuku, Hidetoshi.
Application Number | 20030117957 10/356725 |
Document ID | / |
Family ID | 26333333 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030117957 |
Kind Code |
A1 |
Takashima, Tomonobu ; et
al. |
June 26, 2003 |
Cell multiplexing apparatus handling multiple items of
information
Abstract
A cell multiplexing apparatus including call monitors and
multiplexers. The call monitors monitor a plurality of channels for
their call setting status and select at least two channels for
their call setting status and select at least two channels for
which the same cell may be assembled, i.e., for which the
destination of the calls is the same. The multiplexers receive
audio information or information already assembled in asynchronous
transfer mode (ATM) cells from the channels selected by the call
monitors, and disassemble and multiplex the received information
for assembly into the payload of a new ATM cell.
Inventors: |
Takashima, Tomonobu;
(Kawasaki-shi, JP) ; Tanaka, Takeshi;
(Kawasaki-shi, JP) ; Norizuki, Reiko;
(Kawasaki-shi, JP) ; Toyofuku, Hidetoshi;
(Kawasaki-shi, JP) ; Mase, Hideki; (Kawasaki-shi,
JP) ; Kajiwara, Masanori; (Tokyo, JP) ;
Nobuyasu, Kosuke; (Kawasaki-shi, JP) ; Tanaka,
Kenji; (Kawasaki-shi, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
700 11TH STREET, NW
SUITE 500
WASHINGTON
DC
20001
US
|
Assignee: |
Fujitsu Limited
Kawasaki-shi
JP
|
Family ID: |
26333333 |
Appl. No.: |
10/356725 |
Filed: |
February 3, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10356725 |
Feb 3, 2003 |
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08835995 |
Apr 11, 1997 |
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08835995 |
Apr 11, 1997 |
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08510121 |
Aug 1, 1995 |
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08510121 |
Aug 1, 1995 |
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08004134 |
Jan 13, 1993 |
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5509007 |
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Current U.S.
Class: |
370/232 ;
370/535 |
Current CPC
Class: |
H04L 2012/5649 20130101;
H04L 2012/5672 20130101; H04J 3/247 20130101; H04L 2012/561
20130101; H04Q 11/0478 20130101; H04L 2012/5661 20130101; H04L
2012/563 20130101 |
Class at
Publication: |
370/232 ;
370/535 |
International
Class: |
H04L 012/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 16, 1992 |
JP |
4-5378 |
Jan 5, 1993 |
JP |
5-363 |
Claims
What is claimed is:
1. A cell multiplexing apparatus for receiving communication
information over a minimum of two channels and for transmitting the
communication information to a transmission line, said cell
multiplexing apparatus comprising: call monitoring means for
obtaining call setting information from said communication,
indicative of monitor control information for each channel; and at
least one multiplexing means, each of said at least one
multiplexing means for multiplexing said communication information
received over said minimum of two channels into a single cell of a
fixed length comprising a header and a payload, having recognize
information to recognize each channel and length of the
communication information, in accordance with said call setting
information obtained by said cell monitoring means, and
transmitting said single cell to the transmission line.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Ser. No. 08/835,995
filed Apr. 11, 1997 now pending, which is a continuation of U.S.
Ser. No. 08/510,121, filed Aug. 1, 1995, now abandoned, which is a
continuation of U.S. Ser. No. 08/004,134, filed Jan. 3, 1993, now
U.S. Pat. No. 5,509,007, and claims priority to Japanese
Application 4-5378 filed Jan. 16, 1992 and Japanese Application
5-0363 filed Jan. 5, 1993, incorporated by reference herein. This
application is also related to U.S. Ser. No. 09/467,759, filed Dec.
20, 1999.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an asynchronous transfer
mode (ATM) transmission apparatus for multiplexing coded audio
signals into a cell for transmission over a transmission network an
ATM mode.
[0003] Research is progressing on the so-called ISDN (integrated
services digital network). This is a branch of technologies for
concurrently transmitting over a single network multiple pieces of
information that have different characteristics, such as audio
information and dynamic image information. Drawing attention in
this area presently is asynchronous transfer mode (ATM), a
switching technique indispensable for implementing a broadened ISDN
(B-ISDN). This technique involves dividing communication
information into packets called cells of a fixed length for
transmission.
[0004] The most commonly utilized method today for coding telephone
voice signals in digital format is pulse code modulation (PCM) at a
transmission rate of 64 kilobits per second. Where it is desired to
lower the transmission rate (also known as the bit rate) without
degrading the quality of voice transmitted, one known method
employed is ADPCM (adaptive differential pulse code modulation) at
a transmission rate of 32 kilobits per second.
[0005] About to be put into practice is what is known as low delay
code excited linear prediction (LD-CELP:CCITT G728). This is a
method for converting every five values sampled at 8 kHz into a
predetermined code of 10 bits, whereby a transmission rate of 16
kilobits per second is provided.
[0006] Where voice signals are transmitted as communication
information, the quality of voice sound deteriorates if the
transmission delay time involved is prolonged. Thus there are
strict limits as to how long the transmission delay time is allowed
to be.
[0007] Described below is a typical setup of the abovementioned ATM
transmission using voice signals. FIG. 2 is a block diagram of a
typical prior art ATM transmission apparatus, and FIG. 3 is a of an
ATM cell used by the conventional apparatus of FIG. 2. In FIG. 2,
an exchange 1 accommodates subscriber lines from a plurality of
subscriber terminals 2 and is connected to the ATM transmission
apparatus 4 via a plurality of channels 5.
[0008] Suppose that one of the subscriber terminals 2 (i.e.,
calling subscriber) makes a call to communicate with another
subscriber terminal (i.e., called subscriber) via an ATM
transmission line 3. In that case, the exchange 1 first connects
the terminal 2 of the calling subscriber to the ATM transmission
apparatus 4 over a given channel 5.
[0009] In turn, the ATM transmission apparatus 4 converts into a
predetermined digital code (called coded information) the voice
signal transmitted from the subscriber terminal 2 (calling
subscriber) through the exchange 1 and channel 5. The ATM
transmission apparatus 4 then generates an ATM cell 10, multiplexes
it with another cell made of the voice signal from the subscriber
terminal 2, and transmits the multiplexed result over the ATM
transmission line 3.
[0010] As depicted in FIG. 3, cells generated by the ATM
transmission apparatus 4 are each composed of 53 octets. The first
five octets constitute an ATM header 7. The ATM header 7 includes a
virtual path identifier (VPI) and a virtual channel identifier
(VCI). The remaining 48 octets make up a payload 8 comprising coded
information.
[0011] Of the 48 octets constituting the payload, the first octet
contains a sequence number identifier (SN) and a data type
identifier (IT), the last two octets make up an effective data
length identifier (LI) and a cyclic redundancy check identifier
(CRC). The remaining 45 octets (i.e., 360 bits) constitute a
payload user information part 11 for transmitting the coded
information.
[0012] The ATM transmission apparatus 4 of FIG. 2 is equipped for
each channel 5 with a coder-decoder 41, a code buffer 42, a payload
assembler 43 and an ATM multiplexer 13. The channels 5 are provided
commonly with a cross connection multiplexer 45. These components
work as follows:
[0013] The coder-decoder 41 digitizes a voice signal illustratively
according to the LD-CELP method. The voice signal has been
transmitted from a subscriber terminal 2 (calling subscriber) over
a channel 5 and through the exchange 1. The signal in digital
format is stored in the code buffer 42 downstream.
[0014] The payload assembler 43 monitors the amount of coded
information in the code buffer 42. On detecting an accumulation of
36 items of coded information (i.e., 360 bits, or 45 octets) in the
code buffer 42, the payload assembler 43 gets the accumulated 36
items of coded information from the code buffer 42 and assembles
them into a payload 8. The payload 8 is then transferred to the ATM
multiplexer 13 downstream.
[0015] Upon receipt of the payload 8 from the payload assembler 43,
the ATM multiplexer 13 composes a cell by adding an ATM header 7 to
the payload coming from the payload assembler 43. The cell when
composed is transferred to the cross connection multiplexer 45.
[0016] The cross connection multiplexer 45 stores temporarily in a
queue (i.e., buffer) the cells transferred from the ATM
multiplexers 13 upstream. The cells are then output onto the ATM
transmission line 3 in the order in which they were stored into the
buffer.
[0017] As described, in the prior art ATM transmission apparatus 4,
the coded information made of the voice signals coming from
subscriber terminals 2 is transmitted over the ATM transmission
line 3 after 36 items of the coded information are accumulated in
the code buffer 42 and are assembled into a cell for
transmission.
[0018] It takes 625 microseconds (.mu.s) for the coder-decoder 41
to generate one item of coded information (i.e., 125
.mu.s.times.5). That is, a delay time of 22,500 .mu.s occurs by the
time 36 items of coded information are accumulated in the code
buffer 42 (i.e., 625 .mu.s.times.36). This often makes it difficult
to comply with the time constraints on transmission delay under the
LD-CELP method. As a result, a serious adverse effect on the
quality the transmitted voice may occur.
[0019] Presently, there is a possibility that in-house LAN's (local
area networks), based on the DQDB (distributed queue dual bus)
system proposed under IEEE (Institute of Electrical and Electronics
Engineers) 802.6, will gain widespread acceptance. If that happens,
the congestion of different types of communication information,
which will affect transmission, can be a severe disadvantage to the
system.
[0020] Packet data transmitted over the LAN's have variable lengths
while ATM cells 10 have a fixed length. When communication
information is divided, the divided items are multiplexed into an
ATM cell 10. If a fraction of the cell 10 constitutes the
information, the remaining vacant parts are filled with dummy
patterns so that the finished cell will be a complete cell. The
smaller the fraction and the higher the frequency at which a
fractionally complete cell occurs, the more dummy patterns are
needed to fill the gap. As a result, the transmission efficiency
decreases.
[0021] More and more terminals connected to in-house LAN's
including those in compliance with the DQDB system will likely be
multi-media terminals such as TV telephone sets and audio/visual
output devices. There is little doubt that the number of available
channels will not keep up with the growing number of multi-media
terminals. Furthermore, if equipped with a transmitter-receiver for
each different medium, the multi-media terminal will bloat in size
and cost and will run counter to today's trend toward downsized
terminals with compact functions.
[0022] Certain kinds of communication information such as motion
pictures require synchronism between dynamic image information and
audio information when transmitted. Ensuring synchronism between
the different kinds of information is necessary so as to keep the
received information meaningful. It may be arranged technically
that each cell comprises either audio or image information alone.
In that case, a relatively small amount of audio information is in
disproportionate contrast with large quantities of dynamic image
information. This can result in what is known as image cell
drop-out, i.e., the rate of dynamic image information transmission
failing to keep up with the rate of audio information transmission.
The image cell drop-out can be a major cause of deterioration in
image quality.
SUMMARY OF THE INVENTION
[0023] It is therefore an object of the present invention provide a
cell multiplexing apparatus operating in asynchronous transfer mode
(ATM), the apparatus minimizing the delay time required to transmit
communication information of a single or a plurality of kinds over
an ATM transmission network while collectively handling
communication information of different media with no data
drop-out.
[0024] In carrying out the invention and according to one aspect
thereof, there is provided a cell multiplexing apparatus which
receives communication information over at least two channels of
any one of the same and different kinds, and assembles the received
information into an asynchronous transfer mode cell made of a
fixed-length header and a payload, and which transmits the
assembled cell. The apparatus comprises call monitoring means for
obtaining call setting information from individual items of the
communication information and multiplexing means for multiplexing
the communication information received over the minimum of two
channels into a single asynchronous transfer mode cell of a fixed
length in accordance with the call setting information obtained by
the call monitoring means.
[0025] In a preferred structure according to the invention, the
multiplexing means 200 may multiplex control and alarm information
from the channels 5 selected by the call monitoring means together
with, say, audio information into a cell. Alternatively, the
multiplexing means 200 may assemble a cell using audio signals
obtained by converting a plurality of sampled values into a code of
a predetermined number of bits. Because the communication
information 6 from the multiple channels 5 is multiplexed, as
described, into a single cell according to the invention, the
transfer delay is minimized.
[0026] When a plurality of items of information are multiplexed
into a single cell, the payload part of the cell may be formed to a
fixed or variable length. How the payload part is formed may be
expressed as payload control information that is prefixed to the
beginning of the payload 8.
[0027] The same kind of communication information (e.g., audio
information) may be multiplexed into a single cell. Alternatively,
communication information of different characteristics (audio and
image information) may be multiplexed into a single cell.
[0028] In a further preferred structure according to the invention,
a plurality of ATM cells 10 received as communication information 6
may be divided and the divided parts may be multiplexed into a new
ATM cell 10.
[0029] These and other objects, features and advantages of the
invention will become more apparent upon a reading of the following
description and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a view illustrating the operating principle of the
present invention;
[0031] FIG. 2 is a block diagram of a typical prior art ATM
transmission apparatus;
[0032] FIG. 3 is a view showing the constitution of an ATM cell
used by the conventional apparatus of FIG. 2;
[0033] FIG. 4 is a block diagram depicting the overall system
configuration of a first embodiment of the invention;
[0034] FIG. 5 is a block diagram of an ATM transmission apparatus
in the first embodiment;
[0035] FIG. 6 is a view showing the format of an ATM cell used by
the first embodiment;
[0036] FIG. 7 is a conceptual view indicating how data items are
multiplexed by the first embodiment;
[0037] FIG. 8 is a detailed view showing how call monitors are
illustratively structured in the first embodiment;
[0038] FIG. 9 is a view depicting typical sequences of control
operations in effect when a call is connected by the first
embodiment;
[0039] FIG. 10 is a view portraying the sequence of operations
between a code buffer controller and a code buffer on the calling
side where a call is connected by the first embodiment;
[0040] FIG. 11 is a view showing the sequence of operations between
a code buffer controller and an ATM multiplexer on the called part
where a call is connected by the first embodiment;
[0041] FIG. 12 is a view depicting the sequence of operations
between a code buffer controller and a code buffer on the called
side where a call is connected by the first embodiment;
[0042] FIG. 13 is a view illustrating the overall system
configuration of a second embodiment of the invention;
[0043] FIG. 14 is a function block diagram of a cell mapping part
in the second embodiment;
[0044] FIG. 15 is a conceptual view showing how ATM cells are
multiplexed by the second embodiment;
[0045] FIG. 16 is a view depicting the format of a channel
identifier in a new ATM cell produced by the second embodiment;
[0046] FIG. 17 is a block diagram portraying the overall system
configuration of a third embodiment of the invention;
[0047] FIG. 18 is a view illustrating the format of a channel ID
part in a new ATM cell produced by the third embodiment;
[0048] FIG. 19 is a block diagram depicting the overall system
configuration of a fourth embodiment of the invention;
[0049] FIG. 20 is a conceptual view showing how ATM cells are
multiplexed by the fourth embodiment;
[0050] FIG. 21 is a block diagram sketching the overall system
configuration of a fifth embodiment of the invention;
[0051] FIG. 22 is a block diagram of an interface part that handles
the transmission and reception of ATM cells in the fifth
embodiment;
[0052] FIG. 23 is a function block diagram showing how a buffer
controller and an ATM multiplexer operate on the transmitting side
of the fifth embodiment;
[0053] FIG. 24 is a function block diagram depicting how a buffer
controller and an ATM multiplexer operate on the receiving side of
the fifth embodiment;
[0054] FIG. 25 is a conceptual view illustrating how ATM cells are
multiplexed by the fifth embodiment;
[0055] FIG. 26 is a view showing typical contents of payload
control information parts in ATM cells in connection with the fifth
embodiment;
[0056] FIG. 27 is a view describing how the ATM cells multiplexed
by the fifth embodiment as shown in FIG. 25 are restored back to
the original information;
[0057] FIG. 28 is a view showing a detailed format of an ATM cell
in connection with the fifth embodiment;
[0058] FIG. 29 is a view indicating what is typically meant by a DB
header stored in a payload control information part in connection
with the fifth embodiment;
[0059] FIG. 30 is a view depicting typical contents of a DC header
stored in a payload control information part in connection with the
fifth embodiment; and
[0060] FIG. 31 is a view showing the format of an ATM cell that
actually contains information in connection with the fifth
embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0061] In FIG. 1, call monitoring means 100 monitors each of the
multiple channels 5 for the call setting status in order to select
a plurality of channels 5 for which the same cell may be assembled
(i.e., for the same destination). The coder-decoder 41 for each
channel 5 converts to coded information the audio signal
transmitted over the corresponding channel 5. Cell multiplexing
means 200 takes audio information or ATM cells from the multiple
channels 5 selected by the call monitoring means 100, through the
coder-decoder 41, divides a received information or ATM cells, and
assembles the divided parts in a-multiplexing manner into a new
cell (containing a payload 8). The cross connection multiplexer 45
places in a queue the cells coming from the multiplexing means
200.
[0062] First Embodiment:
[0063] The first embodiment of the invention is arranged to divide
audio information from plurality of channels into ATM cells 10 of a
fixed length each for multiplexing. FIG. 4 depicts the overall
system configuration of the first embodiment, FIG. 5 is a block
diagram of an ATM transmission apparatus in the first embodiment,
and FIG. 6 shows the format of an ATM cell used by the first
embodiment.
[0064] FIG. 7 is a conceptual view indicating how data items are
multiplexed by the first embodiment. FIG. 7 shows how audio
information from a plurality of channels 5 (data A, data B, data C,
. . . ) is multiplexed into ATM cells 10.
[0065] In FIG. 4, an exchange 1 accommodating subscriber lines from
subscriber terminals 2 is connected to an ATM transmission
apparatus 4. The ATM transmission apparatus 4 on the calling side
is in turn connected via an ATM transmission line 3 to another ATM
transmission apparatus 4 on the called side.
[0066] In FIG. 5, call monitors 46 constituting call monitoring
means 10 are provided in the ATM transmission apparatus 4. The call
monitors 46 are respectively connected to ATM processors 44. Each
ATM processor 44 comprises coder-decoders 41, a data multiplexer 36
and an ATM multiplexer 13, the latter two constituting multiplexing
means 200.
[0067] Referring again to FIG. 4, suppose that a subscriber
(calling subscriber) wishes to make a call to another subscriber
(called subscriber). In that case, the exchange 1 connects the
calling subscriber's terminal 2 to the ATM transmission apparatus 4
via a given channel 5. In FIG. 5, the calling subscriber sends to
the ATM transmission apparatus 4 call setting information for
setting up the call.
[0068] In the ATM transmission apparatus 4, the call monitor 46
monitors the call setting information coming from calling
subscribers over the channels (data A-n). From the call setting
information, each call monitor 46 obtains the settings needed to
determine a virtual path identifier VPI and a virtual channel
identifier VCI for the relevant ATM processor 44. The settings are
transferred along with identification information of each channel 5
to the data multiplexer 36. The transfer is made to a buffer
controller 12 (buffer control means 12) in the data multiplexer 36
via a control line 37 provided independently the data communication
lines.
[0069] How each call monitor is typically structured will now be
described with reference to FIG. 8. As shown in FIG. 8, each call
monitor comprises call monitor units 38 provided for the respective
channels, a control signal transmitter-receiver 15 for recognizing
a channel control signal received over the channels 5, and a
transmission path selector 16 for obtaining path information from
the channel control signal.
[0070] The control information including the channel control
information may be obtained on an in-slot basis (i.e., the
information is contained in the audio signal from the channels 5),
or on an out-slot basis (the information is received over a
separate control line 37 independent of the audio information).
[0071] In the data multiplexer 36 of FIG. 5, the buffer controller
12 analyzes the information sent from the call monitor 46,
determines the virtual path identifier VPI and virtual channel
identifier VCI for identifying the call, selects up to six channels
5 that determined the identifiers VPI and VCI, and forms a group of
communication data accordingly. This group of communication data is
a group which comprises communication information received over
different channels 5 and which complies with the virtual path
identifier VPI and virtual channel identifier VCI of the next
stage.
[0072] When the calling subscriber starts transmitting
communication information (audio signal in this example), the
coder-decoder 41 provided for each channel 5 converts to coded
information the audio signal transmitted over the corresponding
channel 5 and through the exchange 1. The conversion is carried out
on the basis of the LD-CELP method. The coded information is
accumulated in the code buffer 42 of the data multiplexer 36.
[0073] The buffer controller 12 monitors the amount of coded
information being accumulated in each code buffer 42. A point is
eventually reached where the buffer controller 12 finds that the
code buffers 42 corresponding to the six channels 5 forming the
same group have each accumulated five sets of coded information (a
total of 50 bits). At that point, the buffer controller 12 obtains
the accumulated five sets of coded information from the buffers and
stores them into a user information part 11 of each channel 5 in
the payload 8 of the cell shown in FIG. 6.
[0074] In addition, the buffer controller 12 collects through the
call monitor 46 the control information on the connection status of
six subscribers forming the same group (e.g., on-hook/off-hook
information) as well as alarm information in connection therewith.
The collected information is stored in a 10-bit control/alarm
information area assigned each of the six channels 5 in the payload
8.
[0075] Five sets of coded information (a total of 50 bits) and
control/alarm information (10 bits) are allocated to the six
channels 5. These sets of coded information constitute part of the
360-bit payload 8.
[0076] In the setup of FIG. 6, each coded information area of the
payload 8 is formed to a fixed length (50 bits). Alternatively,
these information areas may be formed to a variable length each.
How this can be achieved will be described later in connection with
the fifth embodiment (FIG. 25).
[0077] The payload 8 is assembled under control of the buffer
controller 12. The payload data are then output to the ATM
multiplexer 13 in accordance with the virtual path identifier VPI
and virtual channel identifier VCI determined commonly for those
channels 5 constituting the same group.
[0078] The ATM multiplexer 13 assembles a cell by supplementing the
payload 8 from the upstream multiplexing part with an ATM header 7
containing the virtual path identifier VPI and virtual channel
identifier VCI. The assembled cell is transmitted to a cross
connection multiplexer 45. The cross connection multiplexer 45
places in a queue (i.e., buffer) the cells coming from various ATM
multiplexers 13. These cells are then output over the ATM
transmission line 3 in the order in which they arrived.
[0079] Described below with reference to FIGS. 9 through 12 are the
sequences of control operations in effect when a call is made by
the first embodiment. In FIG. 9, the upper half shows the sequence
of control operations on the calling side of the ATM transmission
apparatus 4, and the lower half indicates the sequence of control
operations on the called side of the ATM transmission apparatus
4.
[0080] On the calling side of the ATM transmission apparatus 4, as
shown in the upper part of FIG. 9, the control signal
transmitter-receiver 15 in the call monitor 46 receives call
information, i.e., a start signal and a selection signal, from a
calling subscriber's terminal 2 belonging to the same exchange I.
At that point, the control signal transmitter-receiver 15 extracts
a channel control signal from the received information and sends
the signal to the transmission path selector 16.
[0081] Based on the channel control signal received, the
transmission path selector 16 selects an appropriate transmission
path, generates channel path information, and sends the information
to the code buffer controller 12. In turn, the code buffer
controller 12 determines the path of an ATM cell to be generated on
the basis of the channel path information. With the cell path
determined, the code buffer controller 12 sends cell transmission
path information to the ATM multiplexer 13.
[0082] Concurrently, the code buffer controller 12 reads coded
information from the code buffer 42. If any of the channels
involved is busy with a call, the code buffer controller 12
notifies the ATM multiplexer 13 with only the control signal such
as cell transmission path information until an acknowledge signal
is received from the opposite exchange. It is only after the
opposite exchange 1 acknowledges receipt and completion of the call
and its connection that the coded information is transmitted to the
ATM multiplexer 13.
[0083] FIG. 10 portrays the sequence of operations performed
between the code buffer controller 12 and the code buffer 42 in the
above setup. As described, upon receipt of the channel path
information from the transmission path selector 16, the code buffer
controller 12 determines the cell path and makes a read request to
the code buffer 42 by designating an appropriate address thereto.
The coded information is read from the code buffer 42 in response
to the read request and is transferred to the code buffer
controller 12. When one cell of coded information has been read out
by the code buffer controller 12, the controller 12 outputs a cell
generation complete notice to the ATM multiplexer 13. The cell
generation complete notice prompts the ATM multiplexer 13 to make a
read request. In turn, the code buffer controller 12 supplies the
ATM multiplexer 13 with payload information made of the channel
control signal and of the coded information.
[0084] When the ATM multiplexer 13 prefixes the header 7 to the
payload information, the result is an ATM cell 10 that is
transferred through the cross connection multiplexer 45 of FIG. 5
and on to the ATM transmission line 3.
[0085] FIG. 11 shows the sequence of operations in effect when call
information sent from the ATM transmission apparatus 4 on the
calling side is received as the ATM cell 10 by the ATM transmission
apparatus 4 on the receiving side. Upon receipt of the ATM cell 10,
the ATM multiplexer 13 sends a cell receipt acknowledge signal to
the code buffer controller 12 within the receiving-side ATM
transmission apparatus 4. In turn, the code buffer controller 12
makes a read request to the ATM multiplexer 13. The read request
prompts the ATM multiplexer 13 to read the payload information
(coded and control information) from the ATM cell 10. The code
buffer controller decodes the channel path and the decoded channel
path information is sent by the code buffer controller 12 to the
control signal transmitter receiver 15. The channel path
information received by the control signal transmitter-receiver 15
is sent both to the call monitor units 38 (FIG. 8) and to the
transmission path selector 16.
[0086] In parallel with the above process, the code buffer
controller 12 writes the coded information to the code buffer 42.
The sequence of the write operation is shown in FIG. 12.
Specifically, upon receipt of the path information from the
transmission path selector 16, the code buffer controller 12
decodes the channel path and makes a write request to the code
buffer 42. When the code buffer 42 grants permission to write, the
code buffer controller 12 writes to the code buffer 42 the coded
information obtained from the payload 8 in the ATM cell 10.
Subsequent operations, not shown in FIG. 12, include outputting the
coded information that came from the code buffer 42 onto the ATM
transmission line 3 and transmitting the information to the called
subscriber's terminal.
[0087] The lower half of FIG. 9 depicts the sequence of operations
performed by the ATM transmission apparatus 4 on the called side
when the call is acknowledged by the called subscriber.
Specifically, when the called-side ATM transmission apparatus 4
receives acknowledge information (acknowledge signal) from the
called subscriber, a call connection signal is extracted by the
control signal transmitter-receiver 15 from the received
information and is sent to the code buffer controller 12 via the
transmission path selector 16. Then in the same sequence as shown
in FIG. 10, the coded information is read from the code buffer 42
for cell generation. The payload information is forwarded to the
ATM cell multiplexer 13.
[0088] The ATM multiplexer 13 prefixes the header 7 to the payload
information. The payload information prefixed with the header 7 is
sent to the cross connection multiplexer 45. In turn, the cross
connection multiplexer 45 transmits the acknowledge information as
an ATM cell 10 to the ATM transmission apparatus 4 on the calling
side.
[0089] As described, the first embodiment works roughly as follows:
when the code buffers 42 corresponding to the six calls that share
a virtual path identifier VPI and a virtual channel identifier VCI
have each accumulated five sets of coded information, the data
multiplexer 36 (buffer controller 12) in the ATM transmission
apparatus 4 starts assembling one set of payload information using
separately collected control and alarm information. At this point,
it takes 3,125 .mu.s (i.e., 625.times.5) for each of the code
buffers 42 to accumulate five sets of coded information. That is,
the coded information accumulation time with the code buffers 42 is
reduced to 5/36 of the time normally calculated with the prior art
ATM transmission apparatus 4 (22,500 .mu.s).
[0090] Second Embodiment:
[0091] The second embodiment is arranged to further multiplex ATM
cells 10 into a new ATM cell 10 through remapping in an ATM node
(i.e., ATM transmission apparatus 4), the new ATM cell being output
onto the ATM transmission line 3. Among the plurality of ATM cells
10 to be multiplexed, the VCI value of a given ATM cell 10 is taken
as the VCI value of the header 7 for the new ATM cell 10. The VCI
values of the old ATM cells 10 are stored as channel identification
information in the payload 8 of the new ATM cell 10.
[0092] As depicted in FIG. 13, the system configuration of the ATM
transmission apparatus 4 in the second embodiment includes ATM
converters (AAL's) and a path distributor 50. The path distributor
50 contains a path identifier 17 and a cell mapping part 18, the
path identifier operating as the call monitoring means 100. FIG. 4
is a function block diagram of the cell mapping part 18. The cell
mapping part 18 comprises a cell mapping controller 22, a timer 20
controlled by the cell mapping controller 22, a mapping buffer 32,
a VCI detector 21 and a cell output part 52.
[0093] What characterizes the second embodiment is that the signals
from subscriber terminals 2 are converted by the ATM converters
(AAL's) into ATM cells which are then remapped by the path
distributor 50 into a newly multiplexed ATM cell 10 for output.
[0094] In FIG. 13, the path identifier 17 acts as a kind of
selector. While receiving information in the form of ATM cells 10
from the ATM converters (AAL's), the path identifier 17 detects VPI
values from these cells. If ATM cells 10 found destined to the same
path based on VPI detection are received within a predetermined
period of time, the path identifier 17 inputs these ATM cells into
the cell mapping part 18. In FIG. 15, cells #1 and #2 have the same
VPI value.
[0095] When a first ATM cell 10 (i.e., first cell #1 given after
timer reset) arrives from an ATM converter (AAL), the timer 20 is
activated and the VCI detector 21 is fed with a pulse signal
indicating the input of the first ATM cell 10 (cell #1). The VCI
detector 21 detects the VCI value from the cell, and notifies the
cell mapping controller 22 of the VCI value of the first ATM cell
10 (cell #1).
[0096] The cell mapping controller 22 then assembles a new ATM cell
10 (cell #A) with its VCI value taken from the first ATM cell 10
(cell #1). That VCI value is also stored in a channel ID part 24 of
the payload 8.
[0097] When the path identifier 17 detects the arrival of an ATM
cell (cell #2) having the same VPI value as that of the first cell
before time is up on the timer 20, the VCI detector 21 reads the
VCI value from the header 7 of the ATM cell 10 (cell #2). The cell
mapping controller 22 writes the VCI value of the ATM cell (cell
#2) only to the channel ID part 24 in a payload control information
part 23 of the payload 8. Thereafter, whenever an ATM cell 10 is
input of which the VPI value is the same as the above, the VCI
value is stored successively into the channel ID part 24 of the
payload 8. The successive storage of VCI values into the channel ID
part 24 continues until a timeout is reached on the timer 20.
[0098] Concurrently with the storage of the VCI values, the
information on the ATM cells 10 (cells #1, #2, etc.) is stored
consecutively into a user information part 11 of the payload 8.
[0099] FIG. 15 illustrates how ATM cells (cells #1, #2, etc.) are
related in format to the new ATM cell (cell #A) in connection with
the second embodiment. As shown, the VPI and VCI values of the
first ATM cell (cell #1) are adopted as those of the new ATM cell
10 (cell #A). The VCI information of the second and subsequent ATM
cells is stored successively into the channel ID part 24. The
control information and user information of the ATM cells 10 are
placed for each channel into areas of a fixed length each within
the user information part 11 of the payload 8 in the new ATM cell
10 (cell #A).
[0100] The channel ID part 24 accommodates, in addition to the VCI
values of the ATM cells 10 (cells #1, #2, etc.), data length
information indicating the amount of information (significant bit
count or byte length) of each old ATM cell 10. If the control
information is the same or common to the channels 5, the
information may alternatively be written to an appropriate address
of the new ATM cell 10 (cell #A). Where one sampled data item is
fixed to a data length of eight bits, as with 64-kbps PCM audio
information, the data length information may be stored as a single
item or may be omitted altogether.
[0101] When a predetermined period of time has elapsed on the timer
20 (i.e., upon time-out), the timer 20 outputs a trigger signal to
the cell output part 52 through the cell mapping controller 22.
With the trigger signal output, the VPI value is written to the
header 7 of the new ATM cell 10 (cell #A) via the cell output part
52. The ATM cell 10 (cell #A) is then output onto the transmission
line.
[0102] Even before the time-out of the timer 20, the cell mapping
part 18 outputs the trigger signal to the cell output part 52 if
the user information part 11 of the ATM cell 10 (cell #A) has been
filled to capacity with information. This prompts the output of the
ATM cell 10 (cell #A). At this point, the timer 20 is reset
regardless of the time-out that may or may not be reached on the
timer.
[0103] In the receiving side ATM node, the old VCI values of the
old ATM cells (cells #1, #2, etc.) are extracted from the channel
ID part 24 in the payload 8 of the new ATM cell 10 (cell #A). At
the same time, the data length information is read out to determine
the allocation of the information for the respective old cells. The
operations combine to reassemble the old ATM cells 10 (cells #1,
#2, etc.).
[0104] Although the above setup involves storing the VCI value of
the first ATM cell (cell #1) in the channel ID part 24 of the
payload 8, the channel ID part 24 may alternatively accommodate the
VCI values of the second and subsequent ATM cells 10 (from cell #2
on). In the latter case, the VCI value in the header 7 of the ATM
cell 10 (cell #A) that has arrived may be used unchanged as the
first user information on the receiving side.
[0105] Although the above setup uses the VCI value of the first ATM
cell 10 (cell #1) as the VCI value of the new ATM cell 10 (cell
#A), an alternative arrangement may be employed. Specifically, the
maximum or minimum VCI value of the old ATM cells 10 (cells #1, #2,
etc.) may be detected by the VCI detector 21. Then the cell mapping
part 18 may write the maximum or minimum VCI value to the header 7
of the new ATM cell 10 (cell #A). In this case, the writing of the
VCI value to the header 7 of the new ATM cell 10 (cell #A) is
accomplished after mapping.
[0106] As described, the second embodiment assembles old ATM cells
10 (#1, #2, etc.) regardless of their many dummy patterns (see FIG.
15) into a new ATM cell (#A) with no dummy pattern. In this manner,
the payload 8 of the new ATM cell 10 is utilized efficiently.
Because the assembly of the new ATM cell 10 is monitored by the
timer 20, there is no delay in the output of that cell.
[0107] FIG. 16 depicts the format of a channel ID part in a new ATM
cell (#A) produced by a variation of the second embodiment. One way
to apportion VPI and VCI values of ATM cells in the channel ID
format is to set low-order n bits as per the number of paths or
channels needed by the user while the high-order bits are fixed
(e.g., all bits fixed to zero). In the example of FIG. 16, the
channel ID part 24 of the new ATM cell 10 (#A) accommodates only
the low-order n bits and VCI significant bit count of the VCI
values from the old ATM cells 10 (#1, #2, etc.).
[0108] According to the preceding method, three bits are enough
when it comes to expressing, say, five channels for use by a single
path (VPI). Even if the use of "000" is prohibited by the user, a
three-bit format provides expressions of up to seven channels
(001-111).
[0109] Where the above method is employed, the cell mapping part 22
takes the significant bit count n (n=7 in the above example) of the
VCI values from the input ATM cells 10 (#1, #2, etc.) and stores
the count into a significant bit count storage part of the channel
ID part 24 in the payload 8. Following the bit count storage part,
the cell mapping part 22 stores consecutively the low-order n bits
of the VCI values from the input ATM cells 10.
[0110] The value n may be determined in one of two ways: either it
is set when entered initially through the network, or it is
determined as needed based on the information obtained from the VCI
detector 21. In any case, the format of FIG. 16 allows the channel
ID part 24 to be used efficiently so that an extensive user
information part 11 will be secured in the payload 8.
[0111] Third Embodiment:
[0112] In the third embodiment, an ATM node (i.e., ATM transmission
apparatus 4) further multiplexes the information in the form of ATM
cells 10 into a new ATM cell 10 through remapping, and outputs the
new ATM cell to another ATM node. Among the plurality of ATM cells
10 to be multiplexed, the VCI value of a given ATM cell 10 is taken
as the VCI value of the header 7 for the new ATM cell 10. The VCI
values of the old ATM cells 10 are converted to channel numbers
through a management table 25 for storage into the channel ID part
24 of the new ATM cell 10.
[0113] FIG. 17 portrays the system configuration of the third
embodiment. In FIG. 17, the cell mapping controller 22 is basically
the same in composition as that of the second embodiment except for
the management table 25 shown in the figure. The other components
that are functionally identical to those described in connection
with the second embodiment are designated by the same reference
numerals, and any repetitive description thereof is omitted. As
depicted in FIG. 17, the management table 25 is made of conversion
tables each converting the VCI numbers under a given VPI into
channel numbers.
[0114] When notified of the VCI values of the old ATM cells 10 (#1,
#2, etc.) by the VCI detector 21, the cell mapping controller 22
references the conversion table of the applicable VPI in the VCI
management table 25, and reads the corresponding channel numbers
therefrom. The channel numbers thus read out are written
consecutively, together with data length information, to the
channel ID part 24 of the new ATM cell 10 (#A).
[0115] FIG. 18 illustrates the format of the channel ID part 24 in
a new ATM cell produced by the third embodiment. As with the second
embodiment, if the data length is the same throughout the payload
user information part 11 of this format, only one data length may
be stored, or the storage of data lengths may be omitted
altogether.
[0116] Fourth Embodiment:
[0117] In the fourth embodiment, an ATM node (i.e., ATM
transmission apparatus 4) further multiplexes the information in
the form of ATM cells 10 into a new ATM cell 10 through remapping,
and outputs the new ATM cell to another ATM node. What
characterizes the fourth embodiment is that a representative VCI
indicating a plurality of multiplexed cells is stored as the VCI
value of the new ATM cell 10.
[0118] FIG. 19 depicts the system configuration of the fourth
embodiment which includes a representative VCI prefixing part 53.
The other components that are functionally identical to those
described in connection with the second embodiment are designated
by the same reference numerals, and any repetitive description
thereof is omitted.
[0119] With the fourth embodiment, the cell mapping controller 22
sends a trigger signal to the representative VCI prefixing part 53
immediately after reset or time-out of the timer 20 or when the
user information part 11 of the payload 8 has been filled with
information. This causes the representative VCI value to be written
to the header 7 of the new ATM cell 10 (#A). The representative VCI
stands for a plurality of cells being multiplexed and is preferably
reserved as a special number. FIG. 20 shows how old ATM cells 10
(#1, #2, etc.) compare in format with the new ATM cell 10 (#A) in
connection with the fourth embodiment.
[0120] Upon receipt of the multiplexed ATM cell 10 (#A) prefixed
with the representative VCI, the ATM node on the receiving side
disassembles the ATM cell 10 (#A) into the original plurality of
ATM cells 10 (#1, #2, etc.). The disassembled ATM cells 10 are
transferred to the terminals corresponding thereto. If an ATM cell
10 (#B) has no representative VCI prefixed thereto, the cell is
transferred intact to the corresponding terminal or ATM
transmission apparatus 4.
[0121] The prefixing of the representative VCI may be implemented
by combining the methods of the second and third embodiments.
[0122] Fifth Embodiment:
[0123] The fifth embodiment involves dividing into variable lengths
a plurality of items of information generated by terminals (i.e.,
terminal equipment; TE) in an in-house setup and multiplexing these
items in the payload 8 of an ATM cell 10.
[0124] FIG. 21 sketches the overall system configuration of the
fifth embodiment. In the in-house setup of FIG. 21, terminals 31
(TE) connected to in-house bus means 28 coming from network transit
switching equipment 26 are illustratively multimedia terminals.
Each of these terminals incorporates a pair of interface parts 30
(See FIG. 22) that transmit and receive image information, audio
information, text data and other data in the form of ATM cells 10.
FIG. 22 illustrates an interface part 30 in more detail. As
depicted, the interface part 30 comprises an ATM multiplexer 13, a
buffer controller 12 and a buffer 54. In each terminal (TE), one
interface part 30 is located on the upward-bound bus side and the
other interface part 30 on the downward-bound bus side.
[0125] FIG. 23 is a function block diagram showing how the buffer
controller 12 and the ATM multiplexer 13 operate on the
transmitting side of the fifth embodiment, and FIG. 24 is a
function block diagram depicting how the same components operate on
the receiving side.
[0126] What takes place on the transmitting side of the fifth
embodiment in FIG. 23 is as follows: data items (A, B, C, . . . ,
N) from terminals are first written to the buffer 54. When a buffer
input counter 2302 has counted written data of each of the data
items up to a predetermined value, the counter notifies an input
transmission rate calculation part 2303 that the predetermined
count value of one of the data items is reached. Based on that
input count value, the input transmission rate calculation part
2303 calculates the transmission rate of the input data of the one
and notifies a payload assembly ratio calculation part 2305 of that
rate. At the same time, a desired transmission rate request
processing part 2304 receives desired transmission rate requests
from the terminals (TE) and notifies the payload assembly ratio
calculation part 2305 of these requests.
[0127] Based on the received information on the data from a bus
monitoring and processing part 2312, the payload assembly ration
calculation part 2305 determines how the different data items are
to be allocated in the payload 8. The data allocation thus
determined is sent to a sub-header assembly part 2309 and to a read
order and amount controller 2306 of the payload control information
part 23.
[0128] In turn, the read order and amount controller 2306 activates
individual input buffer reading part 2307 which reads necessary
amounts of data from the buffer 54 in a predetermined order. The
read-out data are handed over to a payload data assembly part 2308
of the ATM multiplexer 13.
[0129] After the sub-header assembly part 2309 prefixes the payload
control information part 23 as a sub-header 7 to the payload 8, an
ATM header prefixing part 2310 prefixes the other items of the
header 7 (e.g., VPI, VCI) to the ATM cell 10. The completed ATM
cell 10 is then sent to a transmission buffer 2311 (first-in
first-out memory) in the ATM multiplexer 13. From the buffer 2311,
the ATM cell 10 is output onto the in-house bus means 28.
[0130] What takes place on the receiving side of the fifth
embodiment in FIG. 24 is as follows: when an ATM cell 10 is
received through the in-house bus means 28 (FIGS. 21 and 22), cell
receipt information is sent from an ATM header Identification part
2413 to a bus monitoring and processing part 2412 within the ATM
multiplexer 13. This causes necessary processing to take place
according to the protocol (e.g., DQDB protocol) of the in-house bus
means 28.
[0131] The ATM cell thus received is accumulated in a reception
buffer 2414 (first-in first-out memory) in the ATM multiplexer 13.
Thereafter, the ATM cell is sent both to a sub-header removal part
2416 and to a sub-header analysis part 2415, the latter analyzing
the sub-header 7 held in the payload control information part 23.
In accordance with the result of the analysis on the sub-header 7,
the payload control information part 23 is removed and the user
information part 11 of the payload 8 is disassembled by a payload
data disassembly part 2417. Following disassembly, image
information, audio information, text data and other data are
transferred to individual data transmission buffer writing parts
2419 via individual data buffers 2418 (first-in first-out memory).
These kinds of information are read from the buffers according to
the transmission rate determined by a desired transmission rate
request processing part 2421.
[0132] What characterizes the fifth embodiment is that, as
discussed, with reference to FIG. 23, the relative ratio at which
to assemble different data into the payload 8 is varied (by the
payload assembly ratio calculation part 2305) in accordance with
the desired transmission rates requested and with the actually
input transmission rate. While the first through the fourth
embodiment allocate data in a fixed length format within the
payload 8 upon multiplexing of information in the ATM cell 10, the
fifth embodiment allocates data in a variable length format within
the payload 8.
[0133] FIG. 25 is a conceptual view illustrating how ATM cells are
multiplexed by the fifth embodiment. In FIG. 25, transmitted
information composed of four data types (data A through data D in
the upper part of the figure) is a shown multiplexed in variable
lengths (in the lower part of the figure) within the payload 8 of
an ATM cell 10. These four kinds of data (data A-D) may be data for
a different channel each (e.g., data A representing image, data B
sound, data C text data). The fifth embodiment is particularly
effective when used with an in-house setup wherein multimedia
terminals connected to an in-house LAN are often required to
transmit and receive information of different channels in
synchronism.
[0134] Generally, the ATM cell 10 comprises the ATM header 7,
payload control information part 23 and payload user information
part 11. The ratio of assembling each of different types of
information into the payload user information part 11 is calculated
by the payload assembly ratio calculation part 2305. The ratio is
determined after consideration of such factors as whether or not
the information to be transmitted needs to be processed at high
speed and whether or not the information is to be handled on a
burst basis.
[0135] FIG. 26 shows typical contents of payload control
information parts in ATM cells (i.e., lower half of what is
depicted in FIG. 25) in connection with the fifth embodiment, and
FIG. 28 gives a detailed format of one of such ATM cells. As
illustrated in FIG. 28, the payload control information part 23
contains a DB header (first control area 34) and a DC header
(second control area 35). The DB header comprises identifiers each
indicating the beginning, an intermediate portion or the end of the
information in question. The DC header includes identifiers
indicating the data length of each item of information held in this
ATM cell 10.
[0136] Take, for example, the first ATM cell 10 (cell 1) shown in
the lower half of FIG. 25. This ATM cell contains the beginning of
each of data A through data C, while data D is not stored. Thus the
DB header contains an identifier (e.g., "01") indicating the
beginning of each of data A through data C, and includes another
identifier (e.g., "00") indicating the absence of data D (see FIG.
29, to be discussed later). The DC header stores the data length of
each of the different data (Al, B1, C1; see FIG. 30, to be
discussed later).
[0137] On the receiving side, the DB and DC headers are read out of
the payload control information part 23. The information contained
in the headers allows the receiving side ATM transmission apparatus
to recognize what kinds of information are held and how they are
allocated in the payload user information part 11 of the ATM cell
10 in question. With the necessary information thus revealed, the
original data A through D are restored precisely. FIG. 27 describes
how the ATM cells multiplexed by the fifth embodiment as shown in
the lower half of FIG. 25 are restored back to the original data
(data A through D).
[0138] In the ATM cell format shown in FIG. 28, what characterizes
the fifth embodiment is that, as mentioned above, the payload user
information part 11 is headed by the payload control information
part 23 which comprises the first control area 34 and second
control area 35. The first and the second control areas 34 and 35
accommodate the DB header and DC header, respectively, as
identifiers. The DB header may store up to four, two bits in length
each. The meanings of these identifiers (DCF's) are listed in FIG.
29.
[0139] In FIG. 29, a bit string "00" held in-a DCF means that no
data is stored in the corresponding payload user information part
11, a bit string "01" means that the beginning of transmitted data
is stored; a bit string "10" means that an intermediate portion of
the transmitted data is stored, and a bit string "11" means that
the end of the transmitted data is stored.
[0140] The DC header may contain up to four pairs of identifiers,
each pair indicating a data length (DL) and a data sequence (DSN,
or data sequence number). The DL identifier denotes the length of
the corresponding data accommodated in the payload user information
part 11 (to be described below), and the DSN identifier designates
the data sequence number of the applicable data as counted from the
first data.
[0141] The payload user information part 11 ranges from the
eleventh octet to the fifty-second octet. Actual data are allocated
in this part according to the ratio determined for the respective
data. FIG. 31 shows the format of an ATM cell that contains actual
data in connection with the fifth embodiment.
[0142] As described and according to the fifth embodiment, numerous
kinds of data are multiplexed in each ATM cell 10 in which the
payload 8 is apportioned in variable lengths. This feature boosts
the efficiency of data transmission and makes effective use of the
available traffic capacity thanks to the high concentration of
transmitted data.
[0143] Because there is no need to classify data types on a network
27 (in FIG. 21), the structure of the network can be
simplified.
[0144] With no need to change transmission and reception protocols
on any terminal (TE) for each different type of data to be
transmitted in an in-house setup, the terminal may be made smaller
in size and simpler in structure than before.
[0145] Since it is not necessary to repeat call settings for each
set of data to be transmitted, the call setting procedure becomes
more efficient. As a result, transmission costs are reduced.
[0146] The ease of keeping synchronism between a plurality of kinds
of data for simultaneous transmission contributes to preventing the
voice or image drop-out during multimedia information
transmission.
[0147] As many apparently different embodiments of this invention
may be made without departing from the spirit and scope thereof, it
is to be understood that the invention is not limited to the
specific embodiments thereof except as defined in the appended
claims.
* * * * *