U.S. patent application number 11/260358 was filed with the patent office on 2006-02-23 for data transmission method and data trasmission system.
Invention is credited to Daisuke Hiranaka, Yoshiyuki Ito, Haruyoshi Murayama, Hideyuki Narita, Masatoshi Takashima.
Application Number | 20060038878 11/260358 |
Document ID | / |
Family ID | 18598723 |
Filed Date | 2006-02-23 |
United States Patent
Application |
20060038878 |
Kind Code |
A1 |
Takashima; Masatoshi ; et
al. |
February 23, 2006 |
Data transmission method and data trasmission system
Abstract
A data transmission method and a data transmission system not
requiring a large delay unit for multiplexing and composition and
capable of reducing the hardware scale, wherein when transmitting
data among multiple points from a plurality of terminals arranged
in a network, when the data at multiple points are transmitted to
the terminals, in the network, identical packets are added
different time stamps in accordance with the transmission delays,
whereby the data shifted in accordance with the transmission delays
are transmitted.
Inventors: |
Takashima; Masatoshi;
(Tokyo, JP) ; Narita; Hideyuki; (Kanagawa, JP)
; Murayama; Haruyoshi; (Kanagawa, JP) ; Ito;
Yoshiyuki; (Tokyo, JP) ; Hiranaka; Daisuke;
(Kanagawa, JP) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL LLP
P.O. BOX 061080
WACKER DRIVE STATION, SEARS TOWER
CHICAGO
IL
60606-1080
US
|
Family ID: |
18598723 |
Appl. No.: |
11/260358 |
Filed: |
October 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09811099 |
Mar 16, 2001 |
|
|
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11260358 |
Oct 27, 2005 |
|
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Current U.S.
Class: |
348/14.08 ;
348/14.09; 348/E7.084; 375/E7.268 |
Current CPC
Class: |
H04N 21/2365 20130101;
H04L 65/605 20130101; H04N 21/2665 20130101; H04N 21/23608
20130101; H04N 7/152 20130101; H04L 65/607 20130101; H04N 21/2187
20130101 |
Class at
Publication: |
348/014.08 ;
348/014.09 |
International
Class: |
H04N 7/14 20060101
H04N007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2000 |
JP |
P2000-081851 |
Claims
1-7. (canceled)
8. A data transmission method for transmitting a plurality of data
streams having different degrees of importance among multiple
points from a plurality of terminals arranged in a network,
comprising demultiplexing said plurality of data streams having
different degrees of importance in the middle of the transmission
line, transmitting data where continuity is regarded as important
through a network having a higher quality of service and
transmitting data for which discontinuity is permitted through a
network having a lower quality of service, and combining the
plurality of data transmitted through the different networks again
before the data arrive at the destination terminals and
transmitting the same to the terminals.
9-15. (canceled)
16. A data transmission system for transmitting a plurality of data
streams having different degrees of importance among multiple
points from a plurality of terminals arranged in a network,
comprising; a first network having a higher quality of service, a
second network having a lower quality of service than the first
network, a first device for demultiplexing said plurality of data
streams having different degrees of importance in the middle of the
transmission line, transmitting data where continuity is regarded
as important through the first network, transmitting data for which
discontinuity is permitted through the second network, and a second
device for combining the plurality of data transmitted through the
different networks again before the data arrive at the destination
terminals and transmitting the same to the terminals.
Description
RELATED APPLICATION DATA
[0001] The present application claims priority to Japanese
Application No. P2000-081851 filed Mar. 17, 2000, which application
is incorporated herein by reference to the extent permitted by
law.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a data transmission method
and a data transmission system for transmitting a plurality of
streams over a network when communicating, streaming, etc. among a
plurality of terminals.
[0003] Below, an explanation will be made of a conventional method
for transmitting a plurality of streams over a network when
communicating, streaming, etc. among a plurality of terminals in
relation to the drawings.
[0004] FIG. 1 is a view of an example of a television (TV)
conference system.
[0005] In this TV conference system, a conference is simultaneously
carried out by using five terminals of a terminal 1 to a terminal 5
with cameras CMR mounted thereon.
[0006] The terminals 1 to 5 are connected via switches SW1 to SW4,
routers RT1 to RT3, and an ISDN network NTW1.
[0007] The signals (video and audio) from the terminals 1 to 5 are
assembled at a multipoint control unit (MCU) 6 where they are
combined to the signal to be reproduced at each terminal.
[0008] The MCU 6 has mainly two functions. One is that of a block
of a multipoint controller (MC) 6A for controlling which terminals
are attending the conference, while the other is that of a
multipoint processor (MP) 6B for combining signals assembled from
multiple points for every terminal.
[0009] FIGS. 2A and 2B are views of the structure of data flowing
over the network and an amount of transmission in the TV conference
system of FIG. 1.
[0010] As shown in FIG. 2A, signals (A1, V1) transmitted from the
terminal 1 pass through the switch SW1, router RT1, ISDN network
NTW1, router RT2, and switch SW4 to be transmitted to the MCU
6.
[0011] Similarly, the signals transmitted from the terminals 2, 3,
4, and 5 are transmitted to the MCU 6. The signals assembled at the
MCU 6 are combined as follows for every terminal. [0012] Terminal
1: (A2-3-4-5, V2-3-4-5) [0013] Terminal 2: (A1-3-4-5, V1-3-4-5)
[0014] Terminal 3: (A1-2-4-5, V1-2-4-5) [0015] Terminal 4:
(A1-2-3-5, V1-2-3-5) [0016] Terminal 5: (A1-2-3-4, V1-2-3-4)
[0017] Here, A denotes audio, and V denotes video. Further, (,) of
(A1,V1) indicates that each signal is separated, and (-) of
(A1-2-3-4) indicates that the signals are combined. "Combined"
means that the signals are added in a baseband state (for example
PCM) in the case of the audio.
[0018] In the case of the video, it means that the signals are
combined to one having the same image size by reducing the sizes of
the images in the baseband (pixel) state and joining the plurality
of images with each other in one frame.
[0019] The data structure of the signal flowing over the network
shown in FIG. 2A becomes as shown in FIG. 2B.
[0020] Namely, the data has the same amount of information before
and after the composition. The audio and video are formed into
different packets and multiplexed (MUX) in packet units. Further,
data is also multiplexed in addition to the audio and video.
[0021] When arranged in this way, it is understood that, as the
amount of information of the signals flowing over the network of
the TV conference system, signals of 20 times the data structure
flow in all layers.
[0022] Next, a case where the TV conference system is applied to
wireless telephones will be considered.
[0023] FIG. 3 is a view of the topology in the case where the TV
conference system is applied to wireless telephones. In other
words, FIG. 3 is a view of an example of the configuration of
multipoint communication. In this example as well, the case where
five terminals MT (Mobile Terminal) 1 to MT5 communicate is
shown.
[0024] The terminals MT1 to MT5 are connected via mobile base
stations (MBS) 11A to 11D arranged in the network, mobile switching
centers (MSC) 13A to 13C with the MCUs 12A to 12C connected
thereto, and further gateway mobile switching centers (GMSC) 14A to
14E having home location registers (HLR).
[0025] The center portion is a network wherein the GMSCs 14A to 14E
are connected in a so-called mesh state (for example circuit
switched network or a packet switching network).
[0026] A great difference from the TV conference system resides in
that there are many MCUs in the network, and the MCU located
nearest each terminal multiplexes the signals of the multiple
points.
[0027] That is, in the MCU, in the same way as the time of the TV
conference, there are the function of an MC and the function of an
MP. However, one MC among the plurality of MCUs controls one
communication, while a plurality of MPs are controlled by this one
MC and perform the multiplexing.
[0028] FIGS. 4A and 4B are views of the structure of the data
flowing in the network and the amount of transmission in the
multipoint communication of FIG. 3.
[0029] As shown in FIG. 4A, unlike the TV conference system, there
are a plurality of MCUs, so the signals of the multiple points must
all be transferred to a plurality of MCUs 12A to 12C. Accordingly,
the signals (A1,V1) transmitted from for example the terminal MT1
are transmitted to the MCU 12A, MCU 12B, and MCU 12C.
[0030] The data structure of the signals (A1, V1) becomes as shown
in FIG. 4B. The channel is narrow, so, unlike the time of the TV
conference system, the image sent from each terminal is transmitted
matching with the size after composition.
[0031] Further, when looking at the MCU 12A, two patterns are
combined in the following way from the collected five signals for
the terminals MT1 and MT2: [0032] MT1: (A2-3-4-5, V2-3-4-5) [0033]
MT2: (A1-3-4-5, V1-3-4-5)
[0034] The data structure of this signal is indicated by numeral 15
in FIG. 4B. This becomes the same as the combined one in the TV
system. Note, due to a difference of thicknesses of the wireless or
other channels, the size of the images, quality of audio, etc. are
different from those of the TV conference utilizing an ISDN
network.
[0035] In this way, behind the existence of the GMSCs, since the
composed signals do not flow over the network, the structure of the
data flowing at this layer becomes the format as indicated by
reference numeral 16 in FIG. 4B. The amount of transmission also
becomes 15 times this data structure.
[0036] In this way, it is understood that the amount of the data
flowing over the entire network is improved a little in comparison
with the TV conference by arranging a plurality of MCUs.
[0037] Further, by giving the terminal side the function of
simultaneously decoding a plurality of streams, the MCU side can
multiplex the data in packet units without composition at the
baseband level. This situation will be shown in FIGS. 5A and
5B.
[0038] In this case, looking at the MCU 12A, the signals combined
for the terminals MT1 and MT2 become as follows: [0039] MT1: (A2,
3, 4, 5, V2, 3, 4, 5) [0040] MT2: (A1, 3, 4, 5, V1, 3, 4, 5)
[0041] This data structure becomes as shown in FIG. 5B. The example
of FIG. 5B shows the situation where the data is multiplexed in
packet units.
[0042] Next, an explanation will be given of the operation of an
MCU in multipoint communication.
[0043] FIG. 6 is a view of an example of the configuration of a
conventional MCU used for multipoint communication.
[0044] Note that, in this example, the explanation will be made
treating the three existing MCUs as one MCU 12.
[0045] There is a time difference by which each of the signals
collected from the terminals MT1 to MT5 reach the MCU 12.
[0046] In order to make these constant, the MCU 12 inserts delay
units DLY1 to DLY5 for the signals to match their phases, then
demultiplexes the plurality of signals at the demultiplexers DMX1
to DMX5 provided in the MP, passes them through a switcher (buffer)
BF, and combines them at the multiplexers MX1 to MX5 for every
terminal.
[0047] This delay amount and the demultiplexing and multiplexing at
the MP are performed according to instructions of the MC.
[0048] Next, how this delay time is controlled will be
explained.
[0049] FIGS. 7A, 7B and 7C and FIGS. 8A, 8B and 8C are views for
explaining a situation where the video and audio are encoded and
decoded.
[0050] (Explanation of Video Encoding)
[0051] First, an explanation will be made of the video encoding in
relation to FIG. 7A.
[0052] 1) in FIG. 7A indicates a vertical synchronization signal V
Sync. The bold lines represent frames. This frame is an access unit
of the video. Generally, this is used as the unit for compression
of the amount of information. Further, according to the method of
compression, there may be I-pictures and P-pictures. An I-picture
is a picture compressed utilizing the correlation with a frame,
while a P-picture is a picture compressed utilizing the correlation
among frames. The numerals after the picture type indicate the
sequence of input frames.
[0053] The picture input as in 2) in FIG. 7A is encoded at a time
4).
[0054] 5) in FIG. 7A indicates the image of the buffer existing
inside the encoder. An inverse form to a virtual decoder buffer
(VBV buffer) is described rather than the operation of the actual
buffer. This corresponds to a virtual buffer existing inside a
controller for controlling the rate.
[0055] Accordingly, this buffer is instantaneously generated when
the encoding is terminated. The bold line shows this situation.
[0056] 3) in FIG. 7A indicates the value of an STC (system time
clock) when each access unit of the video is input to the encoder.
This STC illustrates an absolute clock in a telephone network. All
systems and terminals are assumed as operating with the same clock
and time.
[0057] 6) in FIG. 7A indicates an STS (decoding time stamp) which
indicates the timing when the access unit finished being encoded at
5) starts being decoded at the reproduction side.
[0058] This value is transmitted together when the access units of
the video are formed into packets and multiplexed. Accordingly, for
10 pictures, a value such as STC_V6 is transmitted. When the system
reaches this time, the decoding is started.
[0059] (Explanation of Encoding of Audio Related Information)
[0060] Next, an explanation will be made of the audio encoding in
relation to FIG. 7B and FIG. 8A.
[0061] In audio, unlike video, there is no concept of discrete
access units such as frames. However, the audio is fetched in the
form of access units for every certain number of sample number.
[0062] 8) in FIG. 7B and FIG. 8A show the situation where an AAU
(audio access unit) is input into the encoder. 7) is the time when
the AAU is input. 9) is the time when the encoding is actually
carried out, while 10) indicates the situation where data is
generated in the virtual buffer at the instant when the encoding is
completed. 11) is the timing when each AAU is decoded. This value
is multiplexed together with the AAU and transmitted to the decoder
side.
[0063] (Explanation of Video Decoding)
[0064] Next, an explanation will be made of the video decoding in
relation to FIG. 7C and FIG. 8B.
[0065] The bit stream (compressed signal) generated in the buffer
in 5) of FIG. 7A starts to be transmitted while the state of the
buffer on the decoder side is monitored. The data is accumulated in
the decoder buffer.
[0066] This situation is shown in 12) of FIG. 7C and FIG. 8B. Here,
the state of the virtual buffer (VBV buffer) is illustrated.
[0067] 13) of FIG. 7C and FIG. 8B indicate the timing when the
decoding is carried out matching with the time of the STC of 15).
Here, it is supposed that the decoding is ideally instantaneously
completed and, simultaneously with the completion of the decoding,
the data is output as shown in 14).
[0068] Here, the time from the instant when the signal is input to
the encoder (terminal) to when the signal is output from the
decoder (terminal) is defined as the end-to-end delay. Namely, that
time is shown in 15) of FIG. 7C and FIG. 8B. This becomes the same
in all access units both video and audio.
[0069] The state where the video and audio become out of phase is
defined as "lip-sync deviation". Deviation between the same video
or between the same audio is defined as "jitter".
[0070] (Explanation of Decoding of Audio Related Information)
[0071] Next, an explanation will be made of the audio decoding in
relation to FIG. 8C.
[0072] As shown in 16) in FIG. 8C, the audio is transmitted with a
delay so as to match the end-to-end-delay of the video. The data is
accumulated in the decoder buffer.
[0073] The timing of decoding is determined for every AAU shown in
17) matching with the value of the STC of 19) in FIG. 8C. The
decoding is instantaneously completed matching with this. The data
is output from the decoder immediately after that.
[0074] As described above, the information concerning the video and
audio are synchronized by transmitting a time stamp such as a DTS.
Further, they are controlled so that no underflow or overflow of
the buffer occurs in the system.
[0075] By utilizing the DTS shown in FIGS. 7A to 7C and FIGS. 8A to
8C, it is possible to achieve synchronization among multiple
points. This situation is shown in FIG. 9.
[0076] In the example of FIG. 9, the signals of the terminals MT1
and MT2 reach the MCU 12A without through the GMSC 14.
[0077] Contrary to this, the signals of the terminals MT3, MT4, and
MT5 reach the MCU 12A after passing through the GMSC 14.
[0078] Accordingly, it is learned that the signals of the terminal
MT3 (T3-AU1, AU2), terminal MT4 (T4-AU1, AU2), and terminal MT5
(T5-AU1, AU2) arrive delayed in comparison with those of the
terminal MT1 (T1-AU1, AU2) and the terminal MT2 (T2-AU1, AU2) as
shown in the situation of the time difference of the packets
transmitted from the terminals indicated by symbol TM1 in FIG.
9.
[0079] The MCU 12A analyzes this DTS from each packet, controls the
delay units in the MCU to match the phases of the signals from the
terminals, then multiplexes and combines the signals.
[0080] In this way, it becomes possible to make the phases of the
signals from all of the terminals completely match at each of the
terminals MT1 and MT2 as shown in the situation of reproduction and
display at each terminal shown by the reference symbol TM2 in FIG.
9.
[0081] Further, in recent years, Internet telephone and other
services using the Internet have been started.
[0082] In the Internet, the band is often not compensated.
Therefore, it is an area where the quality of service (QoS) is low.
When using such a network, it is necessary to monitor the state of
congestion and control a signal to be transmitted to the network in
accordance with the state of congestion.
[0083] FIG. 10 is a view of an example of the configuration of a
multipoint communication system utilizing only a network having a
low QoS.
[0084] As a network having a low QoS, here, the case of utilizing
the Internet is shown.
[0085] In FIG. 10, the terminals are indicated by MT1 to MT4 in the
same way as the above. Further, 21A to 21C denote MBSs, 22A and 22B
denote MSCs, 23A and 23B denote MCUs, 24A and 24B denote packet
switching networks, 25A and 25B denote Internet exchanges (IX), and
26 denotes the Internet.
[0086] The signals rising from the terminals are all transmitted to
the packet switching networks 24A and 24B at the MSCs 22A and 22B.
Here, the MCUs 23A and 23B for multiplexing the signals of the
multiple points are arranged in this packet switching networks.
[0087] The MCU 23A preparing the signals to be transmitted to the
terminals MT1 and MT2 receives the signals from the terminals MT1,
MT2, MT3, and MT4, multiplex them, and send them to the terminals
MT1 and MT2.
[0088] Here, the data of the terminals MT3 and MT4 are transmitted
through the Internet 26, so the transmission delay is greatly
influenced in accordance with the state of congestion of the
network.
[0089] At this time, in order to confirm the congestion, an RTCP
(real-time control protocol) is utilized to monitor the RTT (round
trip time).
[0090] When the RTT widely fluctuates by more than the amount of
allowable end-to-end jitter, the amount of the data transmitted
over the network is controlled to ease the congestion state so as
to avoid congestion.
[0091] Summarizing the problem to be solved by the invention, there
are the following problems.
[0092] (Problem 1)
[0093] Conventionally, all of the signals of the multiple points
have been gathered at the MCU (multipoint control unit) for
combining the signals of the multiple points which then composed
the signals required for each terminal. For this reason, many
signals had to be transmitted over the network.
[0094] (Problem 2)
[0095] Conventionally, when combining signals of multiple points,
in order to match the times of the signals of the multiple points,
the times taken for the transfer were canceled and the phases
matched by inserting delay. In order to realize this, delay units
compensating for large delays were necessary.
[0096] (Problem 3)
[0097] When transferring a plurality of signals such as video and
audio signals among two or more multiple points, signals of more
importance and signals of less importance from the viewpoint of the
continuity of the signals are frequently mixed together among these
plurality of signals.
[0098] For example, when comparing the video and audio, the
continuity is more important in the audio.
[0099] These signals are transmitted over bands having the same
QoS, so the transmission cost becomes high.
[0100] Further, from the viewpoint of effective utilization of the
bands, the utilization efficiency was low.
[0101] (Problem 4)
[0102] When utilizing different bands, a plurality of signals (for
example audio and video) are transmitted through a plurality of
transmission lines. At this time, since the delay values of the
signals flowing over the transmission lines are different, if the
signals are recombined as they are, a plurality of signals will end
up out of phase. In the case of audio and video, this will result
in lip-sync deviation and an extremely strange feeling. In some
cases, the signals could become even more out of phase than with
lip-sync deviation.
[0103] (Problem 5)
[0104] When communicating by utilizing only a network having a low
QoS, there is a possibility of large jitters or large delay
occurring in accordance with the state of congestion of the
network.
[0105] In order to enlarge the permissible value of such jitter in
the network, a large delay unit (buffer) becomes necessary
somewhere in the system. In one-way streaming, delivery of a
continuous signal is made possible by this method.
[0106] Further, if a large delay is inserted, in the communication,
a deviation occurs in the responses to each other and conversation
ends up becoming impossible.
[0107] Further, if a state of congestion occurs in the network, the
audio will be interrupted. Not only it is then difficult to use
this system as a communication tool, but also there is the problem
that once congestion occurs, the system cannot be restored for a
long time.
SUMMARY OF THE INVENTION
[0108] An object of the present invention is to provide a data
transmission method and a data transmission system capable of
reducing traffic of signals flowing over the entire network.
[0109] A second object of the present invention is to provide a
data transmission method and a data transmission system not
requiring a large delay unit in the MCU performing the multiplexing
and composition and therefore capable of reducing the hardware
size.
[0110] A third object of the present invention is to provide a data
transmission method and a data transmission system achieving an
improvement of a utilization efficiency of the transmission bands
and a reduction of the transmission cost.
[0111] A fourth object of the present invention is to provide a
data transmission method and a data transmission system capable of
synchronizing a plurality of signals transmitted over different
bands.
[0112] A fifth object of the present invention is to provide a data
transmission method and a data transmission system capable of
avoiding the trouble of enormous amount of signals being
accumulated in the transmission line and the data not being updated
for a long time.
[0113] According to a first aspect of the invention, there is
provided a data transmission method for transmitting video data and
audio data among multiple points from a plurality of terminals
arranged in a network, comprising transmitting the video data by
multiplexing it as a stream encoded for every point and
transmitting the audio data by combining at least one audio signal
in a baseband in the network.
[0114] According to a second aspect of the invention, there is
provided a data transmission method for transmitting data among
multiple points from a plurality of terminals arranged in a
network, comprising shifting data in accordance with transmission
delays when transmitting data at multiple points to the
terminals.
[0115] In the present invention, identical packets are transmitted
given different time stamps in accordance with the transmission
delays in the network.
[0116] According to a third aspect of the invention, there is
provide a data transmission method for transmitting a plurality of
data streams among multiple points from a plurality of terminals
arranged in a network, comprising transmitting each of the
plurality of data streams through a network having a different
property and recombining them after transmission over the networks
and transmitting them to the terminals.
[0117] Preferably, when a network having a superior property is
defined as a master network, and the others are defined as slave
networks, the delay values of the slave networks are monitored
based on the master network as the standard and the transmission of
data through a slave network is restricted when that slave network
has more than a certain delay in comparison with the master
network.
[0118] Further, preferably, when restricting the transmission of
data to a slave network, if the data transmitted over the slave
network employs a compression method utilizing correlation among
access units, the data transmitted to the network is controlled for
every unit of interruption of the correlation.
[0119] Further, in the present invention, when restricting the
transmission of data to a slave network, data for restricting a
frame rate and a bit rate is transmitted from the network to the
terminals.
[0120] According to a fourth aspect of the invention, there is
provided a data transmission method for transmitting a plurality of
data streams having different degrees of importance among multiple
points from a plurality of terminals arranged in a network,
comprising demultiplexing the plurality of data streams having
different degrees of importance in the middle of the transmission
line, transmitting data where continuity is regarded as important
through a network having a higher quality of service, transmitting
data for which discontinuity is permitted through a network having
a lower quality of service, combining the plurality of data
transmitted through the different networks again before the data
arrive at the destination terminals, and transmitting the same to
the terminals.
[0121] According to a fifth aspect of the invention, there is
provided a data transmission system for transmitting video data and
audio data among multiple points from a plurality of terminals
arranged in a network, comprising a device for transmitting the
video data by multiplexing it as a stream encoded for every point
and transmitting the audio data by combining at least one audio
signal in a baseband in the network.
[0122] According to a sixth aspect of the invention, there is
provided a data transmission system for transmitting data among
multiple points from a plurality of terminals arranged in a
network, comprising a device for shifting data in accordance with
transmission delays when transmitting data at multiple points to
the terminals.
[0123] In the present invention, the device transmits identical
packets given different time stamps in accordance with the
transmission delays in the network.
[0124] According to a seventh aspect of the invention, there is
provided a data transmission system for transmitting a plurality of
data streams among multiple points from a plurality of terminals
arranged in a network, comprising a plurality of networks having
different properties, a first device for transmitting each of the
plurality of data streams through a network having a different
property, and a second device for recombining them after
transmission over the networks and transmitting them to the
terminals.
[0125] Preferably, when a network having a superior property is
defined as a master network, and the others are defined as slave
networks, the first device monitors delay values of the slave
networks based on the master network as the standard and restricts
the transmission of data through a slave network when that slave
network has more than a certain delay in comparison with the master
network.
[0126] Further, preferably, when restricting the transmission of
data to a slave network, if the data transmitted over the slave
network employs a compression method utilizing correlation among
access units, the first device controls the data transmitted to the
network for every unit of interruption of the correlation.
[0127] Further, in the present invention, when restricting the
transmission of data to a slave network, the first device transmits
data for restricting a frame rate and a bit rate from the network
to the terminals.
[0128] According to a eighth aspect of the invention, there is
provided a data transmission system for transmitting a plurality of
data streams having different degrees of importance among multiple
points from a plurality of terminals arranged in a network,
comprising a first network having a higher quality of service, a
second network having a lower quality of service than the first
network, a first device for demultiplexing the plurality of data
streams having different degrees of importance in the middle of the
transmission line, transmitting data where continuity is regarded
as important through the first network, transmitting data for which
discontinuity is permitted through the second network, and a second
device for combining the plurality of data transmitted through the
different networks again before the data arrive at the destination
terminals and transmitting the same to the terminals.
[0129] According to the present invention, when combining and
transmitting a plurality of data (signals), the system adds only
the information concerning the audio at the baseband (PCM) to
obtain a signal of one channel. It transmits the video by bundling
a plurality of channels while keeping the packet form.
[0130] At that time, the information concerning the audio is
greatly reduced in size by assembling the same in one channel. Note
that, in the video, since the amount of information is determined
in accordance with the image size, even if the images are returned
to the baseband and combined, the amount of information is not
reduced. On the contrary, a high performance is required in order
to return the images to their original form and combine them.
[0131] Further, by sending the data signals as described above to
each other when transferring the data required for multiplexing,
the amount of information of the signals flowing among the MCUs is
reduced.
[0132] Further, when transmitting the multiplexed signals to the
terminals, by adding only the information concerning the audio at
the baseband (PCM) and transmitting signals multiplexed by bundling
a plurality of channels as the video while keeping the packet form,
the amount of information flowing over the transmission lines is
reduced.
[0133] Due to this, the traffic of the signals flowing over the
entire network can be reduced.
[0134] Further, according to the present invention, the data
transmitted from the multiple points are deliberately shifted in
accordance with the transmission delays for reproduction and
display instead of matching the phases of the signals input to the
terminals at the same time.
[0135] In this case, when for example transmitting the same access
units to a plurality of multipoint control devices, they are
transmitted by adding different delay values to the time stamps in
accordance with the transmission delays.
[0136] Further, according to the present invention, a plurality of
data signals having different degrees of importance (for example
the video and the audio) are demultiplexed in the middle of the
transmission lines, the signals where continuity is regarded as
important (for example, information concerning the audio) are
transmitted through the network having a higher QoS (quality of
service), while signals for which discontinuity can be permitted
(for example video) are transmitted through the network having a
lower QoS.
[0137] Further, before the signals arrive at the destination
terminals, they are recombined and delivered to the terminals.
[0138] Further, the signals transmitted through the network having
a high QoS (for example the audio) are used as the reference, and
the signals transmitted through the network having a lower QoS (for
example the video) are multiplexed and combined matching with the
display time of the former and transmitted to the target
terminals.
[0139] Further, according to the present invention, where the
signals transmitted over the network having a lower QoS (for
example the video) are delayed more than a certain predetermined
level in comparison with the signals transmitted over the network
having a high QoS (for example the audio), the timing of the
display is shifted on the receiver side. For this purpose, the
value of the time stamp (for example DTS) is delayed by that
amount.
[0140] Further, where the signals transmitted over the network
having a lower QoS (for example the video) are delayed more than a
certain predetermined level in comparison with the signals
transmitted over the network having a high QoS (for example the
audio), the transmission to the network is restricted on the
transmitter side.
[0141] As the method for control, there are a method of lowering
the bit rate and a method of lowering the frame rate.
[0142] Further, when the congestion of the network having a low QoS
is not eased, the end-to-end delay of the system is delayed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0143] These and other objects and features of the present
invention will become clearer from the following description of the
preferred embodiments given with reference to the accompanying
drawings, in which:
[0144] FIG. 1 is a view of an example of a television (TV)
conference system;
[0145] FIGS. 2A and 2B are views of the structure of the data
flowing over a network in the TV conference system of FIG. 1 and
the amount of transmission;
[0146] FIG. 3 is a view of a topology in a case where the TV
conference system is applied to wireless telephones (example of the
configuration of the multipoint communication);
[0147] FIGS. 4A and 4B are views of the structure of the data
flowing in the network in the multipoint communication of FIG. 3
and the amount of transmission;
[0148] FIGS. 5A and 5B are views of another example of the
structure of the data flowing in the network in the multipoint
communication of FIG. 3 and the amount of transmission;
[0149] FIG. 6 is a view of an example of the configuration of a
conventional MCU used for multipoint communication;
[0150] FIGS. 7A to 7C are views for explaining a situation where a
video and an audio are encoded and decoded;
[0151] FIGS. 8A to 8C are views for explaining the situation where
a video and an audio are encoded and decoded;
[0152] FIG. 9 is a view for explaining a flow and a timing of the
signals in a case where a DTS shown in FIGS. 7A to 7C and FIGS. 8A
to 8C are utilized for the multipoint communication;
[0153] FIG. 10 is a view of an example of the configuration of
multipoint communication utilizing only a network having a low
QoS;
[0154] FIG. 11 is a view for explaining a first embodiment of a
data transmission system employing a data transmission method
according to the present invention and a view of a signal
transmission state of a case of multipoint communication;
[0155] FIG. 12 is a view for explaining the first embodiment of the
data transmission system employing the data transmission method
according to the present invention and a view of a state where
signals in the case of multipoint communication are reproduced and
displayed at terminals;
[0156] FIGS. 13A to 13E are views for explaining a second
embodiment of the data transmission system employing the data
transmission method according to the present invention and a view
of the situation of adding information concerning an audio at a
baseband;
[0157] FIGS. 14A and 14B are views for explaining the second
embodiment of the data transmission system employing the data
transmission method according to the present invention, in which
FIG. 14A is a view of an example of the configuration of a data
transmission system 40 in a case where such multiplexed signals are
transmitted among MCUs and between the MCU and the terminals, and
FIG. 14B is a view of a data structure and an amount of
transmission in the system of FIG. 14B;
[0158] FIGS. 15A and 15B are views for explaining the second
embodiment of the data transmission system employing the data
transmission method according to the present invention, in which
FIG. 15A is a view of an example of the configuration of a data
transmission system 40A in a case where the multiplexed signals are
transmitted among MCUs and between the MCU and the terminals, and
the MCU is not a layer of an MSC, but the layer of a GMSC, and FIG.
15B is a view of a data structure and an amount of transmission in
the system of FIG. 15A;
[0159] FIG. 16 is a view for explaining a third embodiment of the
data transmission system employing the data transmission method
according to the present invention and a view of a first example of
the configuration thereof;
[0160] FIG. 17 is a view for explaining the third embodiment of the
data transmission system employing the data transmission method
according to the present invention and a view of a second example
of the configuration thereof;
[0161] FIG. 18 is a view for explaining the third embodiment of the
data transmission system employing the data transmission method
according to the present invention and a view of a third example of
the configuration thereof;
[0162] FIGS. 19A to 19C are explanatory views of monitoring and
control of a transmission delay according to a fourth embodiment;
and
[0163] FIG. 20 is a flowchart of monitoring and control of the
transmission delay according to the fourth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0164] Below, preferred embodiments will be described with
reference to the accompanying drawings.
First Embodiment
[0165] FIG. 11 and FIG. 12 are views for explaining a first
embodiment of a data transmission system employing a data
transmission method according to the present invention. FIG. 11
shows a signal transmission state in a case of multipoint
communication, while FIG. 12 shows a state where the signals in the
case of multipoint communication are reproduced and displayed at
the terminals.
[0166] A data transmission system 30 according to the first
embodiment is configured based on the following
characteristics.
[0167] 1) The signals transmitted from multiple points are
deliberately shifted for reproduction and display in accordance
with the transmission delays instead of matching the phases of the
data (signals) input to the terminals at the same time.
[0168] 2) In order to realize 1), when transmitting the same access
units to a plurality of MCUs (multipoint control devices),
different delay values are added to the DTS (decoding time stamp)
in accordance with the transmission delays and transmitted.
[0169] In FIG. 11 and FIG. 12, MT31 to MT35 denote mobile terminals
(hereinafter, simply referred to as terminals), 31A to 31C denote
MBSs (mobile base stations), 32A to 32C denote MSCs (mobile
switching centers), 33A to 33C denote MCUs, and 34 denotes the
gateway mobile switching center (GMSC).
[0170] FIG. 11 shows the situation when the signals of the
terminals MT31 to MT35 are transmitted to the MCU 33A.
[0171] Specifically, an audio signal A1 and a video signal V1 from
the terminal MT31 and an audio signal A2 and a video signal V2 from
the terminal MT32 pass through the MBS 31A and the MSC 32A, but do
not pass through the GMSC 34, and arrive at the MCU 33A.
[0172] As opposed to this, an audio signal A3 and a video signal V3
from the terminal MT33 pass through the MSB 31B, MSC 32B, and the
MCU 33B, an audio signal A4 and a video signal V4 from the terminal
MT34 and an audio signal A5 and a video signal V5 from the terminal
MT35 pass through the MSB 31C, MSC 32C, and the MCU 33C and further
pass through the GMSC 34 and arrive at the MCU 33A.
[0173] Further, the portion indicated by the symbol MT31 of FIG. 11
indicates the situation of the time difference of the packets
transmitted from the terminals MT31 to MT35.
[0174] (T1-AU1, T1-AU2, . . . , T1-AU5) denote packet signals from
the terminal MT31, (T2-AU1, T2-AU2, . . . , T2-AU5) denote packet
signals from the terminal MT32, (T3-AU1, T3-AU2) denote packet
signals by the terminal MT33, (T4-AU1, T4-AU2, . . . , T4-AU4)
denote packet signals from the terminal MT34, and (T5-AU1, T5-AU2,
. . . , T5-AU4) denote packet signals from the terminal MT35.
[0175] Note that, T31 denotes the timing of the transmission of
each packet signal.
[0176] Further, the portion indicated by the symbol MT32 in FIG. 11
indicates the situation where the transmitted packet signals are
reproduced at the terminals MT31 and MT32 and displayed.
[0177] Note that, T32 denotes the timing of reproduction and
display.
[0178] In the data transmission system 30 having the above
configuration, in the MCU 33B, the signals (A3, V3) of the terminal
MT33 transmitted from the MCU 33B to the MCU 33A are transmitted
delayed by exactly the delay 1.
[0179] For this reason, the value of the DTS of the signals (A3,
V3) transmitted to the MCU 33A is set up as follows.
DTS=DTS+delay1
[0180] Note that since a transmission line having a high QoS is
assumed, the delay value is known in advance.
[0181] Similarly, in the MCU 33C, the values of the DTSs of the
signals (A4, V4), (A5, V5) of the terminals MT34 and MT45
transmitted from the MCU 33C to the MCU 33A are replaced as
follows. DTS=DTS+delay2
[0182] By this, in the MCU 33A, it becomes possible to multiplex
the signals sent from the terminals MT33, MT34, and MT35, without
delaying the signals sent from the terminals MT31 and MT32, and
send them out via the MSC 32A and MBS 31A. They are reproduced and
displayed at the terminals MT31 and MT32 according to the
designated times.
[0183] Similarly, the situation of the reproduction and display at
the terminals MT31 to MT35 is shown in FIG. 12.
[0184] In FIG. 12, the portion indicated by the symbol MT32
indicates the situation where the signals are reproduced and
displayed at the terminals MT31 and MT32, the portion indicated by
the symbol MT33 indicates a situation where the signals are
reproduced and displayed at the terminal MT33, and the portion
indicated by the symbol MT34 indicates a situation where the
signals are reproduced and displayed at the terminals MT34 and
MT35.
[0185] Note that, T32 to T34 denote the timings of the reproduction
and display.
[0186] In the example of FIG. 12, the timing when the packet
signals (T1-AU1, T1-AU2, . . . T1-AU5) of the terminal MT31 are
displayed differs according to the terminal.
[0187] In order to realize this, the signals (A1, V1) of the
terminal MT31 sent from the MCU 33A to the MCU 33A (MCU 1), MCU 33B
(MCU 2), and MCU 33C (MCU 3) are transmitted so that the DTSs are
replaced by the following three types according to the delay values
of the transmission lines. [0188] MCU 1-->MCU 1: DTS=DTS+0
[0189] MCU 1-->MCU 2: DTS=DTS+delay1 [0190] MCU 1-->MCU 3:
DTS=DTS+delay2
[0191] Note that, in FIG. 12, each of the MCU 33A, MCU 33B, and MCU
33C is shown divided into two, but physically the parts are the
same. Accordingly, a signal transmitted to itself will not pass
through the GMSC 34.
[0192] In this way, according to the present first embodiment, even
for the same signals, the display times at the terminals can be
controlled by controlling the DTSs in accordance with where are
they transmitted. By this, in each MCU, the multiplexing can be
simply and smoothly achieved.
[0193] Further, a signal from a near position can be output in the
shortest time. Quick display of even a signal from a far position
is enabled after only the transmission delay.
[0194] According, overall, communication with the shortest delay
value becomes possible.
Second Embodiment
[0195] FIGS. 13A to 13 E, FIGS. 14A and 14B, and FIGS. 15A and 15B
are views for explaining a second embodiment of a data transmission
system employing a data transmission method according to the
present invention.
[0196] A data transmission system 30A according to the second
embodiment is configured based on the following
characteristics.
[0197] 1) When combining and transmitting a plurality of signals,
only the information concerning the audio is added at the baseband
(PCM) to obtain a signal of one channel. The video is transmitted
by bundling a plurality of channels while keeping the packet
form.
[0198] 2) When transferring the data required for the multiplexing
among the MCUs, by sending the signals as in 1) to each other, the
amount of information of the signals flowing among the MCUs is
reduced.
[0199] 3) When transmitting the multiplexed signals from the MCU to
the terminals, by transmitting the signals multiplexed as in 1),
the amount of the information flowing through the transmission
lines is reduced. 4) By combining 2) and 3), the traffic of the
signals flowing over the entire network can be reduced.
[0200] FIGS. 13A to 13E are views of the situation when adding the
information concerning the audio at the baseband.
[0201] FIG. 13A shows the information concerning the audio, FIG.
13B shows the video information, FIGS. 13C and 13E show the data
structures, and FIG. 13D shows the flow of the signals.
[0202] As shown in FIG. 13A, by adding the audio, audio of a
plurality of channels can be converted to one channel. When it is
not necessary to demultiplex and reproduce the same later, the
amount of information can be reduced by combining them.
[0203] In the video, spatial information cannot be superposed at
the same position. Therefore, it is possible to view it by putting
together the videos.
[0204] However, the amount of information is greatly influenced by
the image size. Therefore, even if they are combined at the
baseband, the amount of information does not change so much.
[0205] Therefore, in the video, as shown in FIG. 13B, the signals
are multiplexed in packet units as encoded.
[0206] In this way, when transmitting the signals fetched into the
MCUs to each other among the MCUs, by transmitting them in such a
combined state, the amount of the information flowing through the
network is reduced and thus the traffic can be reduced.
[0207] Further, even when transmitting the signals from the MCU to
the terminals, by performing similar multiplexing, the amount of
the information flowing over the transmission lines can be
reduced.
[0208] FIG. 14A is a view of an example of the configuration of a
data transmission system 40 in a case when transmitting such
multiplexed signals among the MCUs and between the MCU and the
terminals described above, while FIG. 14B shows the data structure
and the amount of transmission in the system of FIG. 14A.
[0209] In the data transmission system 40 of FIG. 14A, the
terminals are indicated by the symbols MT31 to MT35 in the same way
as FIG. 11 and FIG. 12.
[0210] Further, in FIG. 14A, 41A to 41E denote MBSs, 42A to 42C
denote MSCs, 43A to 43C denote MCUs, and 44A to 44C denote
GMSCs.
[0211] Further, the MBSs 41A and 41B, MCU 43A, and GMSC 44A are
connected to the MSC 42A, the MBS 41C, MCU 43B, and GMSC 44B are
connected to the MSC 42B, and the MBS 41D, MBS 41E, MCU 43C, and
the GMSC 44C are connected to the MSC 42C.
[0212] In the data transmission system 40 of FIG. 14A, when looking
at the MCU 43A, the signals (A1, V1) of the terminal MT31 and the
signals (A2, V2) of the terminal MT32 are multiplexed (A1-2, V1,
2), that is, transformed to the data structure as indicated by a
symbol X6 in Fig. 14B, pass through the GMSCs 44A to 44C, MSC 42B,
and MSC 42C, and are transmitted to the MCU 43B and the MCU
43C.
[0213] Further, for the terminals MT31 and MT32, the signals are
transformed to (A2-3-4-5, V2, 3, 4, 5) and (A1-3-4-5, V1, 3, 4, 5),
that is, the data structure as indicated by numeral 411 in FIG.
14B, and transmitted.
[0214] In this way, in the data transmission system 40, the amount
of transmission of the data flowing through the network is reduced
in comparison with the conventional data transmission system shown
in FIG. 4A.
[0215] Further, FIG. 15A shows the case where the multiplexed
signals are transmitted among the MCUs and between the MCU and the
terminals as described above and shows an example of the
configuration of a data transmission system 40A in a case where the
MCU is not a layer of the MSC, but the layer of the GMSC, while
FIG. 15B shows the data structure and the amount of transmission in
the system of FIG. 15A.
[0216] The transfer of the data between the MCU 43A (MCU 1) and the
MCU 43B (MCU 2) in the data transmission system 40A of FIG. 15A
becomes as follows. [0217] MCU 1-->MCU 2: (A1-2, V1,2): Data
structure of numeral 421 of FIG. 15B [0218] MCU 2-->MCU 1:
(A3-4-5, V3,4,5): Data structure of numeral 422 of FIG. 15B
[0219] In this way, in the data transmission system 40A as well,
the amount of information of the signals flowing over the entire
network can be reduced, and the traffic can be reduced.
Third Embodiment
[0220] FIG. 16, FIG. 17, and FIG. 18 are views for explaining a
third embodiment of a data transmission system employing a data
transmission method according to the present invention.
[0221] The data transmission system according to the third
embodiment is configured based on the following
characteristics.
[0222] The signals where continuity is regarded as important (for
example the information concerning the audio) are transmitted over
a network having a higher QoS (quality of service), while the
signals for which discontinuity can be permitted (for example the
video) are transmitted over a network having a lower QoS.
[0223] A network having a high QoS includes a circuit switched
network at present, while a network having a low QoS includes a
packet switching network.
[0224] Therefore, in the third embodiment, the information
concerning the audio is transmitted to the circuit switched
network, and the information concerning the video is transmitted to
the packet switching network.
[0225] The information concerning the audio has a smaller amount of
information in comparison with the video, but the continuity is
regarded as important. Conversely, in the video, the amount of
information is large, but the continuity is not regarded as so
important in comparison with the audio.
[0226] FIG. 16 is a view of a first example of the configuration of
a data transmission system according to the third embodiment.
[0227] In this data transmission system 50 as well, the terminals
are indicated by the symbols MT31 to MT34 in the same way as FIG.
11 and FIG. 12.
[0228] Further, in FIG. 16, 51A to 51C denote MBSs, 52A and 52B
denote MSCs, 53A and 53B denote MCUs, 54 denotes a circuit switched
network, and 55 denotes a packet switching network.
[0229] In the circuit switched network 54, GMSCs 541 and 542 having
home location registers (HLR) are arranged.
[0230] The MBSs 51A and 51B, MCU 53A, GMSC 541 of the circuit
switched network 54, and the packet switching network 55 are
connected to the MSC 52A, while the MBS 51C, MCU 53B, GMSC 542 of
the circuit switched network 54, and the packet switching network
55 are connected to the MSC 52B.
[0231] In this data transmission system 50, when transferring
signals containing information concerning for example the video and
the audio from the terminal MT31 and MT32 side to the terminal MT33
and MT34 side, under the control of the MCU 53A, the MSC 52A
transmits the information concerning the audio where continuity is
regarded as important to the circuit switched network 54 having a
higher QoS (quality of service) and transmits the video signal for
which discontinuity can be permitted to the packet switching
network 55 having a low QoS.
[0232] Then, the information concerning the audio and the video
signals transmitted through the circuit switched network 54 and the
packet switching network 55 are combined to a single signal at the
MSC 52B and transmitted via the MBS 51C to the terminals MT33 and
MT34.
[0233] In this way, according to the data transmission system 50
according to the third embodiment, since information concerning the
audio where continuity is regarded as important is allocated to a
switching network having a high QoS and few bands, and information
concerning the video for which the continuity is not regarded as so
important is allocated to a switching network having a low QoS and
many bands, there are the advantages such that the transmission
cost can be greatly enhanced, and the effective utilization of the
network becomes possible.
[0234] When comparing the amount of transmission, the packet
switching network 55 is more expensive than the circuit switched
network 54. However, if CoS (class of service) is introduced in the
future, it is projected that the cost will be lowered all at once
in the "best effort" region.
[0235] FIG. 17 is a view of a second example of the configuration
of a data transmission system according to the third
embodiment.
[0236] The difference of this data transmission system 50A
according to the second example of the configuration from the first
example of the configuration of FIG. 16 resides in that the
Internet 56 is utilized for the network having a low QoS, and the
Internet 56 is connected to the packet switching networks 55A and
55B via Internet exchanges (IX) 57A and 57B.
[0237] In this data transmission system 50A as well, the
information where continuity is regarded as important is
transmitted to the circuit switched network 54, while the
information for which the continuity is not regarded as so
important is transmitted through transmission lines formed by the
packet switching networks 55A and 55B and the Internet 56.
[0238] In the second example of the configuration, similar effects
to the effects of the first example of configuration can be
obtained.
[0239] FIG. 18 is a view of a third example of the configuration of
the data transmission system according to the third embodiment.
[0240] This third example of the configuration assumes the case of
international roaming.
[0241] Specifically, systems A and B resembling FIG. 16 are present
in for example two countries. The data transmission system 50B is
configured by the packet switching networks 55A and 55B of the
systems A and B connected by the Internet 56.
[0242] Note that, in this third example of the configuration, as a
network having a low QoS and cheap cost, a path that passes through
the packet switching network from the layer of GMSC, passes through
the packet switching network of the other country via the Internet,
and returns to the circuit switched network is formed.
[0243] In the third example of the configuration as well, similar
effects to the effects of the first example of the configuration
mentioned above can be obtained.
Fourth Embodiment
[0244] FIGS. 19A to 19C and FIG. 20 are views for explaining a
fourth embodiment of the present invention.
[0245] In the fourth embodiment, as the data transmission system,
use is made of one which allocates information concerning the audio
where the continuity is regarded as important to a switching
network having a high QoS and few bands and allocates information
concerning the video for which the continuity is not regarded as so
important to a switching network having a low QoS and many bands,
shown in FIG. 16 to FIG. 18.
[0246] Further, in the fourth embodiment, the transmission delays
are monitored and controlled as explained below.
[0247] 1) Using the signals transmitted over the network having a
high QoS (for example the audio) as a reference, the signals
transmitted over the network having a low QoS (for example the
video) are multiplexed and combined matching with the display time
and transmitted to the intended terminals.
[0248] 2) When the signals transmitted over the network having a
low QoS (for example the video) are delayed more than a certain
predetermined level in comparison with the signals transmitted over
the network having a high QoS (for example, the audio), the timings
of the display are shifted at the receiver side. For this purpose,
the values of the time stamp (for example DTS) are delayed by that
amount.
[0249] 3) When the signals transmitted over the network having a
low QoS (for example the video) are delayed more than a certain
predetermined level in comparison with the signals transmitted over
the network having a high QoS (for example the audio), the
transmission to the network is controlled at the transmitter
side.
[0250] As the method for control, there are the method of lowering
the bit rate and the method of lowering the frame rate.
[0251] Where the congestion of the network having a low QoS is not
eased, the end-to-end delay of the system is delayed.
[0252] FIGS. 19A to 19C are explanatory views of the monitoring and
the control of the transmission delays according to the fourth
embodiment, while FIG. 20 is a flowchart of the monitoring and the
control of the transmission delays according to the fourth
embodiment.
[0253] In FIG. 19A, 1) indicates a situation where the video is
input to a terminal, 2) indicates a situation where the input
signals are encoded in units of access units, 3) indicates a
situation where the audio is input to a terminal, 4) indicates a
situation where the input audio signals are encoded in units of
access units, and 5) and 6) indicate situations where the video and
audio are reproduced and displayed at the same timing according to
the end-to-end delay.
[0254] In order to enable this, using the signals transmitted over
the network having a high QoS (for example the audio) as the
reference, the signals transmitted over the network having a low
QoS (for example the video) are multiplexed and combined matching
with the display time and transmitted to the intended
terminals.
[0255] Further, as shown in FIGS. 19B and 19C, the delay value of
the network having a low QoS is observed and monitored. When it
becomes larger than the estimated end-to-end delay value, it is
possible to add this delay value to the DTC of the video
transmitted to the network having a low QoS on the receiver side so
as to display the data with a delay by that amount at the
terminal.
[0256] Further, where congestion occurs in the network having a low
QoS, in order to quickly ease this, it is possible to decide if the
delay value is increasing and is larger or smaller in comparison
with the estimated end-to-end delay value and thereby have the
receiver side, as previously mentioned, replace the value of the
DTS and the transmission side control of the information to be
transmitted to the network.
[0257] The flow of the above series of operations is shown in the
flowchart of FIG. 20.
[0258] Namely, first, the delay values among the MCUs in the
network having a low QoS are observed (ST1).
[0259] Next, it is decided whether or not a delay value is larger
than that of the previous time (ST2).
[0260] When it is decided at step ST2 that a delay value is larger
than that of the previous time, it is decided whether or not the
delay value is larger in comparison with the estimated end-to-end
delay (ST3).
[0261] When it is decided at step ST3 that the delay value is
larger than the estimated-end-to-end delay value, it is assumed
that the delay value is increasing and is exceeding the permissible
value, the DTSs of the signals flowing through the network having a
low QoS are replaced, and the transmission of the signals to the
network having a low QoS is controlled (ST4).
[0262] When it is decided at step ST3 that the delay value is
smaller than the estimated end-to-end delay value, it is assumed
that the delay value is increasing but not exceeding the
permissible value and the transmission of the signals to the
network having a low QoS is controlled (ST5).
[0263] Further, when it is decided at step ST2 that the delay value
is smaller than that of the previous time, it is decided whether or
not the delay value is larger than the estimated end-to-end delay
value (ST6).
[0264] When it is decided at step ST6 that the delay value is
larger than the estimated end-to-end delay value, it is assumed
that the delay value is decreasing and exceeds the permissible
value, the DTSs of the signals flowing through the network having a
low QoS are replaced, and the control of the transmission of the
signals to the network having a low QoS is eased (ST7).
[0265] When it is decided at step ST6 that the delay value is
smaller than the estimated end-to-end delay value, it is assumed
that the delay value is decreasing and does not exceed the
permissible value, the DTSs of the signals flowing through the
network having a low QoS are returned to the original values, and
the transmission of the signals to the network having a low QoS are
returned to the original level (ST8).
[0266] According to the fourth embodiment, it becomes possible to
synchronize a plurality of signals (for example the audio and the
video) transmitted over different bands.
[0267] Summarizing the effects of the invention, as explained
above, according to the present invention, the traffic of the
signals flowing over the entire network can be reduced.
[0268] Further, according to the present invention, a large delay
unit becomes unnecessary in the MCU for performing the multiplexing
and composition, so the size of the hardware can be reduced.
[0269] Further, the delay among multiple points at the time of
multipoint communication can be made as short as possible.
[0270] Further, according to the present invention, all signals can
be continuously transmitted without interpolation and thinning for
more important signals and signals where continuity is regarded as
important (for example the audio). Further, it becomes possible to
set the total transmission cost cheap by utilizing bands having a
low QoS for signals having a lower degree of importance and for
which continuity is not regarded as important (for example the
video).
[0271] Further, the utilization efficiency can be improved from the
viewpoint of the effective utilization of the bands.
[0272] Further, according to the present invention, it becomes
possible to synchronize a plurality of signals (for example the
audio and the video) transmitted over different bands.
[0273] Further, according to the present invention, the trouble of
an enormous amount, of signals building up in the transmission
lines and the data not being updated for a long time can be
avoided.
[0274] While the invention has been described with reference to
specific embodiment chosen for purpose of illustration, it should
be apparent that numerous modifications could be made thereto by
those skilled in the art without departing from the basic concept
and scope of the invention.
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