Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
1999-08-02
2003-07-08
Chin, Wellington (Department: 2664)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S235000, C370S236000
Reexamination Certificate
active
06590865
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a transmission system in which a bus-type or a loop-type transmission line is shared among plural communication apparatuses and data transmission is performed by using isochronous communication channels with bandwidths ensured. The present invention also relates to a bandwidth (resource) management apparatus and a bandwidth (resource) management method which are used in the transmission system, for managing resources such as the bandwidths or time slots for the transmission system.
BACKGROUND OF THE INVENTION
As a conventional resource management method, there is a method used by a bus-type network according to an IEEE(Institute of Electrical and Electronics Engineers) 1394 High Performance Serial Bus (IEEE 1394) standard. As for the IEEE1394, articles as well as standard textbooks have been published, for example, Japanese articles appearing in the Interface(published in Japan) 1996, April, or the Interface 1997, (published in Japan) January.
FIG. 9
shows a transmission system which realizes the conventional resource management method. In
FIG. 9
,
81
denotes a resource management table,
82
-
1
,
82
-
2
, and
82
-
3
denote communication apparatuses, and
31
denotes a transmission line.
The communication apparatuses
82
-
1
,
82
-
2
, and
82
-
3
use an isochronous communication channel which ensures bandwidths or an asynchronous communication channel which does not ensure the bandwidths, to transmit data. Each of these communication apparatuses can freely determine which of the isochronous communication channel and the asynchronous communication channel is to be used by itself. In general, the isochronous communication channel is used to transmit data of a large capacity which requires isochronous transmission, such as video data or audio data, while the asynchronous communication channel is used to transmit data of a small capacity which does not require isochronous transmission, such as command or file transfer.
There is one resource management table
81
on the transmission line
31
, which contains contents of allocation of network resources as the isochronous communication channels. The contents of resource allocation stored in the resource management table
81
can be overwritten for each of the communication apparatuses by communication using the asynchronous communication channel. The resource management table
81
contains the sum total of free bandwidths which are available as the isochronous communication channels, that is, which are not allocated to any communication apparatuses, BANDWIDTH_AVAILABLE (BW_A). The communication apparatus
82
-
1
, before starting data transmission using the isochronous communication channel, obtains a bandwidth to-be-ensured from BW_A as a resource to-be-ensured, and performs data transmission by using the ensured bandwidth. In this case, if the resource to-be-ensured exceeds the BW_A, the apparatus
82
-
1
cannot be ensured the bandwidth. When data transmission is completed and the resource is released, the released bandwidth is added to the BW_A. The above operation enables to allocate the bandwidth required for the communication apparatus
82
-
1
.
FIG. 10
schematically shows a data transmission format according to IEEE1394. In
FIG. 10
, reference numerals
91
,
92
, and
93
denote a cycle start, an isochronous packet, and an asynchronous packet, respectively. The format shown in
FIG. 10
illustrates a transmission format of one cycle as a basic unit for IEEE1394 transmission. This cycle is repeated to implement data transmission. One cycle is 125 micro seconds starting from the cycle start
91
. The isochronous packet
92
which implements data transmission using the isochronous channel and the asynchronous packet
93
which implements transmission using the asynchronous communication channel are used as packets to-be-transmitted. The maximum length of the isochronous packet which can be transmitted by the communication apparatus in each cycle is assumed to be an arbitrary length below a value determined by the ensured bandwidth which is obtained from the resource management table
81
. Thereby, respective communication apparatuses can share the transmission line by using set respective bandwidths.
Hence, according to the conventional transmission system, the bandwidth ensured in advance by each of the communication apparatuses is ensured until the end of communication with no change made. This is suitable for data transmission which requires that a constant bandwidth be always ensured. Such data is defined as CBR (constant bit rate) data. On the other hand, when transmitting a file or map data of a large capacity, isochronous transmission is not required but bandwidths needs to be ensured because of its large capacity, and therefore the isochronous communication channel is used to perform data transmission. Such non-isochronous data of a large capacity is defined as ABR (available bit rate)data. The ABR data has a request relating to the maximum bandwidth and the minimum bandwidth, and demands to ensure an arbitrary bandwidth between the maximum bandwidth and the minimum bandwidth. When transmitting the ABR data, a data rate of the data to-be-transmitted can be changed according to the ensured bandwidth. However, when transmitting the ABR data by using the isochronous communication channel in the conventional transmission system, a bandwidth which was initially ensured is used to perform data transmission. As a consequence, the bandwidth cannot be allocated flexibly.
SUMMARY OF THE INVENTION
The present invention is directed to solving the above problem, and an object of the present invention is to provide a transmission system which is capable of allocating resources more flexibly.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the spirit of and scope of the invention will be apparent to those skill in the art from the detailed description.
According to a first aspect of the present invention, there is provided a transmission system comprising a transmission line, a communication apparatus connected to the transmission line, and a bandwidth management apparatus for managing bandwidths on the transmission line, wherein the communication apparatus, when performing isochronous data transmission by using an allocated resource on the transmission line, outputs a resource allocation request including information indicating a minimum bandwidth and a maximum bandwidth to the bandwidth management apparatus before the isochronous data transmission, and wherein the bandwidth management apparatus includes an allocated-resource request table for storing plural allocated-resource requests; and resource management means which decides whether or not sum of minimum bandwidths of all allocated-resource requests stored in the allocated-resource request table and a minimum bandwidth of the resource allocation request is allocatable from resources on the transmission line when receiving the resource allocation request as an input, allocates a resource for each of the all allocated-resource requests and the resource allocation request such that a bandwidth between a corresponding minimum bandwidth and a corresponding maximum bandwidth is allocated when deciding that the sum is allocatable, and writes the minimum bandwidth and an allocated bandwidth of the resource allocation request in the allocated-resource request table as an allocated-resource request. Therefore, when making the resource allocation request, resource allocation for the request is performed with higher probability.
According to a second aspect of the present invention, in the transmission system of the first aspect, the resource management means, when an allocated resource of at least one allocated-resource request stored in the allocated-resource request table is released, reallocates a free resource for
Hattori Toshikazu
Ibaraki Susumu
Kurosaki Toshihiko
Burr & Brown
Chin Wellington
Matsushita Electric - Industrial Co., Ltd.
Schultz William
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