Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
2000-05-23
2004-08-31
Vu, Huy D. (Department: 2663)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S516000, C370S519000
Reexamination Certificate
active
06785230
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a real-time audio transmission apparatus for transmitting audio data in real time on a network of asynchronous communication such as Ethernet.
BACKGROUND OF THE INVENTION
Recently, in bus-format Local Area Network (LAN) or asynchronous communication such as Ethernet and Asynchronous Transfer Mode (ATM ), improvement of quality is demanded in the real-time audio transmission apparatus for transmitting audio data in real time.
FIG. 10
is an explanatory diagram showing a first example of communication system using a conventional audio transmission apparatus, which shows an example of audio transmission by packet data using a communication network with a constant delay time.
The communication system in
FIG. 10
comprises a transmission side audio transmission apparatus
1001
a
, a reception side audio transmission apparatus
1001
b
, a communication network
1011
with a constant delay time, and a receiving buffer
1003
. Generally, in the case of the communication network
1011
with a constant delay time, the audio packet transmitted at a specific interval is also received at a specific interval at the reception side, so that a continuous audio reproduction is realized.
FIG. 11
is an explanatory diagram showing a second example of communication system using a conventional audio transmission apparatus. Referring now to this diagram, a communication system using a communication network involving delay time fluctuation is explained. A communication network
1111
is an asynchronous communication network such as Ethernet. In the case of the asynchronous communication network
1111
, since an irregular change of delay time, that is, a delay time fluctuation occurs, if the delay is significant, the audio data of the receiving buffer
1103
is empty, the sound is lacking, and the audio quality deteriorates.
As a countermeasure of this problem, assuming a maximum delay time fluctuation of the communication network, the audio data for this time duration is stored in a receiving buffer
1103
in advance. Then, in the event of a delay time fluctuation, the audio data stored in the receiving buffer
1103
is reproduced, so that a continuous audio reproduction without pause is realized.
This countermeasure, however, needs to determin the maximum delay time fluctuation of the communication network. At present, since there is no standard of tolerance level of delay time fluctuation in communication network, it is not clear how much the maximum delay time fluctuation is, that is, it is not clear how much audio data should be stored in the receiving buffer
1103
. The capacity of the receiving buffer
1103
(the maximum capacity of storing the audio data) has been determined uniformly on the basis of the assumption of the maximum delay time fluctuation of the communication network.
FIG. 12
is a block diagram showing a conventional audio transmission apparatus, in which an audio packet is received by using an asynchronous communication network such as Ethernet. In
FIG. 12
, a real-time audio transmission apparatus
1201
comprises a network-interface (communication network I/F unit)
1202
, a receiving buffer
1203
, an audio decoder
1204
, a D/A converter
1206
, a buffer controller
1208
, an asynchronous communication network
1211
such as Ethernet, and an audio reproduction switch
1213
.
In thus composed audio transmission apparatus, an outline of operation is described below. The buffer controller
1208
, initially, turns off the audio reproduction switch
1213
until a specific amount of audio data is stored in the receiving buffer
1203
, and does not reproduce the sound. When storage of specific amount of audio data in the receiving buffer
1203
is detected, the buffer controller
1208
turns on the audio reproduction switch
1213
. Then, the audio decoder
1204
and D/A converter
1206
start their operation, and sound reproduction begins. As far as the delay time fluctuation in the communication network
1211
is within the reproduction time of the audio data stored in the receiving buffer
1203
, the continuous reproduction is possible by reproducing the stored audio data until the next audio packet gets into the receiving buffer
1203
.
In this countermeasure, the capacity of the receiving buffer (the maximum capacity of storing audio data) has been fixed uniformly on the assumption of the maximum delay time fluctuation of the communication network. This is, however, merely a prediction. If a delay time fluctuation more than a reproducing time of stored audio data actually occurs, the stored audio data becomes empty until next audio packet is received, and audio data under-run occurs and then a lack of reproduced sound happens, and the reproduced audio quality deteriorates.
An amount of audio data stored in the receiving buffer itself may cause more audio delay time. Therefore, it should be avoided to store too much data, so as to keep the delay time low. Accordingly, the storing amount of audio data has been determined by actually investigating the communication network or by a method depending on experiences. If the storage amount is thus determined, in the case of worsening of operation condition of communication network, audio quality deterioration occurs. Therefore in order to maintain audio reproduction of high quality, the quality of communication network must be maintained higher than a specific level, but it means higher cost and it is difficult to realize.
If the delay time fluctuation of communication network is constant, in the case of failure in achieving clock synchronism between communication devices, the audio data may becomes empty or overflow in the receiving buffer when the reception state lasts for a long time, and the sound may lack audio quality.
Between devices for real-time audio data communication, in order to synchronize in clock, it is general that both sides clock synchronize with the communication network. However, in the case of asynchronous communication network not having clock synchronizing means in the communication network itself such as Ethernet, a portion of audio data denoting sound is detected, and only this portion is sent out in packet, and the timing is adjusted at the receiving side in duration of audio data stream denoting no sound, so that the real-time reproduction is maintained.
Referring now to
FIG. 13
, the problem occurring due to a difference between the transmitting clock frequency and receiving clock frequency in the case of communication through an asynchronous communication network is explained.
FIG. 13
shows a transition state of buffer storage amount in the receiving audio transmission apparatus
1201
when the transmission coding clock frequency is larger than the receiving decoding clock frequency in the conventional audio transmission apparatus. Reference numerals
1310
and
1312
at the upper side of the diagram show data blocks in time duration when writing the audio data received in the network-interface
1202
in
FIG. 12
into the receiving buffer
1203
,
1311
and
1313
show data blocks of time duration when reading out audio data from the receiving buffer
1203
into the audio decoder
1204
. First, the time duration
1301
and
1305
in the diagram represent the time from the start of reception of audio data from the communication network
1211
in a state not having data to be read out from the receiving buffer to the time when reading is started from the receiving buffer
1203
as the buffer amount exceeds a certain threshold (START)
1308
.
Time duration
1302
is the time duration of simultaneous writing and reading of the receiving buffer
1203
, in which the transmitting coding clock frequency is higher than the receiving side decoding clock frequency, and therefore the storage amount of the receiving buffer is slightly increased along with the lapse of time. During the time duration
1303
, only the reading is made and the writing is terminated. In the time duration
1304
, the receiving buffer is empty, and no sound is reproduced.
As shown in
FI
Ogata Keisuke
Takeda Yutaka
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
Ryman Daniel
Vu Huy D.
LandOfFree
Audio transmission apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Audio transmission apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Audio transmission apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3356346