Stream communication system and stream transfer control method

Details Stream communication system and stream transfer control method Stream communication system and stream transfer control method

1998-12-23

2002-09-03

Yao, Kwang Bin (Department: 2664)

Multiplex communications

Data flow congestion prevention or control

Control of data admission to the network

C370S236000

Reexamination Certificate

active

06445679

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a stream communication system in which there is transferred an encoding stream for which real time mode of operation is required as in video, audio and the like and particularly, to a stream communication system and a stream transfer control method for automatically controlling parameters relating to stream transfer following load variations by a feed back system while giving consideration to a quality of a transfer stream.
In company with progress in a computer network technology and a communication technology for digital information, a communication system has, in recent years, been developed; the communication system is called a stream communication system, in which there is handled a multimedia stream represented by an encoding image stream, an encoding image stream including speech information and the like, in other words a real time stream which requires real time mode of operation.
There are known methods by which real time transfer adopted in communication systems of this kind is maintained.
A first method is to adjust a sending data volume by annulling (discarding) part of data in a stream, but there is a fear in the first method that important part is lost.
A second method is to execute stationary filtering processing based on data priorities and to maintain real time transfer while keeping back as much important part of the data as possible. As a concrete example of the second method, there has been known a method in which several levels (data priorities) are provided by picture types in a system in which a MPEG (Moving Picture Experts Group) video stream is handled. This method has a feature that there are executed rate control by stepwise specification including transfer of all data, annulment (discard) of B picture, annulment of B, P pictures and annulment of all video (transfer of audio only). According to this method, for example in a situation where transfer of all data cannot be continued, even one frame of the B picture cannot be transferred. In other words, since the second method adopts an extremely discrete rate control and besides a transmission rate is not constant, real time transfer is not to be maintained while keeping a quality at a highest level attainable in the second method.
As described above, methods which have conventionally been known in which real time transfer is maintained (the first and second methods) are not to dynamically adjust a transmission data volume while giving consideration to a stream quality in real time transfer of a multimedia stream (encoding stream) and a transmission rate cannot, accordingly, be specified.
A third method is to reserve a network band (transmission rate) in advance of performing steam transfer and thereby guarantee QoS (Quality of Service). In the third method, however, it is only judged whether or not a reservation is allowed and when there is no room in the band for use, no reservation is allowed and no transmission can thus be performed. This means to restrict the number of users and no control is performed in such a manner that there is attained a band as close to the user's desirable band as possible.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a stream communication system and a stream transfer control method in which dynamic adjustment of a transmission rate is enabled while not only is real time mode of operation maintained, but a quality is also maintained at a highest level attainable, even when load variations arise, by processing in which the load variations in a network or a system is fed back to an upstream side, the load variations is followed on the upstream side and a transmission data volume is decreased through automatic annulment of data part with a lower priority.
It is another object of the present invention to provide a stream communication system and a stream transfer control method in which a further feed back control is not applied in a time period of a transition state from starting of adjustment of a transmission rate till a requested transmission rate is attained and thereby a system is, with certainty, prevented from becoming unstable.
In order to solve the above problems, the inventor has proposed a method in which a dynamic quality control is enabled by not performing a discrete rate control but a continuous rate control. In this method, a packet with a lower priority (lower degree of importance) in a stream is positively annulled (discarded), and thereby a quality and a transmission rate are both adjusted, whereby an available transmission rate (transfer band) can be made to be as close to a transmission rate specified by a user as possible, while maintaining a quality at a highest level attainable.
The above described methods, however, give no consideration to variations of a load state of a network or a system and there are performed neither quality adjustment nor transmission rate adjustment which is most suitable for the load state. For this reason, it is difficult to maintain a transmission rate which a user specifies in a situation where a load state of a network or a system varies. Real time image stream transfer being taken up as an example, data transfer is generally performed while maintaining a bit rate (encoding rate, content rate) of a content. At this time, when a packet loss arises since a network band is not sufficiently secured or when decode processing of reception data is insufficiently performed due to shortage of a processing capability at a terminal, an image presented to a user is deteriorated in quality.
Therefore, the present invention has (claim
1
).
As a feature, in such a constitution, a parameter showing a transmission rate at which there is enabled real time transfer at a control target node is calculated at a node which is assigned with a role as a management node corresponding to the control target node and at least one node located on the downstream side from the control target node which is assigned with a role as a monitoring target node, based on information showing a load state of the at least one node which is notified from (internal state notification means of) the at least one node and on information showing a transmission rate set currently at the control target node, and the parameter is fed back to the control target node. Thereby, at the control target node, there is performed a stream shaping processing in which data part with a lower priority is automatically annulled in order to decrease a data volume, while a less transmission permissible priority is given stepwise and the number of transmission permissible data blocks with the same priority as the transmission permissible priority in the same cycle is increased stepwise so that an actual transmission rate is changed to a new transmission rate shown by the parameter fed back from a current transmission rate.
As a result, even if there are load variations in a network or a system, dynamic adjustment of a transmission rate can be performed while maintaining not only real time mode of operation but a quality at a highest level attainable.
According to (claim
2
), feed back control with higher precision can be realized. In the constitution (claim
2
-
1
), it is recommended that at least one module in which a data processing result can be calculated, among modules constituting a monitoring target node, is assigned with a role as a monitoring target module and a node load is judged from a module load obtained from data processing results at all the monitoring target modules in the monitoring target node.
Periodicity in a data structure can be detected with no stream analysis with complexity by adopting a constitution in which there is used an encoding stream in which transmission control reference information as a standard for transfer control is inserted and a transmission permissible priority is updated based on a transmission result in a previous cycle for each cycle when judgment is performed based on the transfer control standard information.
It is recommended that a sp

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