Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-11-30
2004-09-07
Rao, Seema S. (Department: 2666)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S412000
Reexamination Certificate
active
06788684
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
This invention relates to a cell bridge apparatus and a cell bridging method as well as an information transmission system having a cell bridge apparatus suitable for use with a multimedia transmission system for an ATM network which handles ATM cells as fixed length cells. Here, the term ATM is an abbreviation of Asynchronous Transfer Mode.
2) Description of the Related Art
In recent years, as one of services of a B-ISDN, an integrated video service such as a VOD (Video on Demand) service has been proposed. The integrated video service is provided to allow a subscriber to freely extract and utilize information such as video and audio information stored in a center. Such information is placed into ATM cells and communicated between the center and the subscriber using an ATM technique. In this instance, if a plurality of subscribers require the same information, in order to minimize the traffic on the network to reduce a burden to the center or a repeating unit which serves as a transmission source, it is demanded to deliver only one piece of information to the network and produce a number of copies of it equal to the number of requesting subscribers in each node.
FIG. 15
illustrates a concept of an integrated video service. Referring to
FIG. 15
, an ATM information transmission system
50
shown includes a center
51
which accepts a request from a customer and distribute video and image data of a movie and so forth, network node interface (NNI) apparatus
52
and
54
having a cell bridging function, an ATM network
53
for distributing cells to a plurality of stations, an ATM network access apparatus
55
, subscriber terminals
56
-
1
to
56
-
n
, and so forth.
The center
51
stores multimedia information of movies and so forth and extracts and distributes, in response to a plurality of requests for the same work from the subscriber terminals
56
-
i
(i=1 to n), only one video data of the work to the ATM network
53
, and the ATM network access apparatus
55
copies the video data cell to produce a number of copies equal to the number of requests, thereby minimizing the traffic of the ATM network
53
.
The ATM network access apparatus
55
described above is required to apply, to information to be transmitted, a priority degree in accordance with contents of the information and communicate the resulting information. The function of adding a priority degree is realized by bridging, where information D is distributed in a one to multiple fashion (1: multiples), the signal by means of the NNI apparatus
54
or the ATM network access apparatus
55
. FIG.
16
(
a
) illustrates an example of bridging by the NNI apparatus
52
or
54
, and FIG.
16
(
b
) illustrates an example of bridging by the ATM network access apparatus
55
. In both cases, the information D is copied to produce a required number of copies, and simultaneously, new headers H
1
, H
2
and H
3
are produced from the header H
0
of the ATM cell and outputted together with the copies of the information D to bridge the information D. The bridging illustrated in FIG.
16
(
a
) is called intra-port multicast, and the bridging illustrated in FIG.
16
(
b
) is called multicast.
However, in the technique described above, where it is intended to bridge an ATM cell in such a manner as seen in FIG.
16
(
a
) or
16
(
b
), where the method of copying a cell to produce a number of copies equal to the number of cells to be outputted is employed, a large number of buffers are required, which increases the circuit scale.
Japanese Patent Laid-Open Application No. Heisei 9-83522 discloses a novel technique of an ATM switch which functions as an exchange when data communication by an ATM is performed between terminals or nodes, or more particularly, an ATM switch which is connected to a communication network such as a B-ISDN and can reduce a burden to a transmission source node involved in transmission processing, can eliminate a temporary increase of the traffic of cells in the ATM switch and can prevent an increase of the circuit scale of the ATM switch without increasing the buffer capacity of the ATM switch.
FIG. 17
illustrates operation of a cell bridge apparatus disclosed in Japanese Patent Laid-Open Application No. Heisei 9-83522 mentioned above. Referring to
FIG. 17
, an ATM network access apparatus
55
or an NNI apparatus
54
(
52
) shown produces a plurality of headers H
1
, H
2
and H
3
based on the header part H
0
of a cell C
0
, copies the data part D
1
of the cell D which represents information to produce three copies, reads out data from a buffer based on the headers, composes them to produce new cells C
1
, C
2
and C
3
, and sends out the new cells C
1
, C
2
and C
3
. If, in
FIG. 17
, another cell C
4
having a higher priority degree is inputted during outputting of the cell C
1
corresponding to the cell C
0
, then the copying processing for the plurality of headers C
2
and C
3
for the copies having been produced already must be continued. Consequently, a cell C
5
of a higher priority degree originating from the cell C
4
is outputted after sending out of the copies is completed.
Referring back to
FIG. 15
, a multicast method where the cell bridge apparatus shown is used for a node between a point and multiple points is described. As seen from the inside of a frame A in
FIG. 15
, if a cell C
0
which has data D
1
and another cell C
4
which has data D
2
for system control and has a higher priority degree are inputted successively, then after the cell C
0
is copied to produce three copies and the thus copied cells C
1
, C
2
and C
3
are outputted to the subscriber terminals
56
-
1
,
56
-
2
and
56
-
3
, respectively, the cell C
4
is processed and a resulting corresponding cell C
5
is outputted to the subscriber terminal
56
-
4
. In other words, the cell C
4
having a higher priority degree is outputted after the multicast is completed.
Accordingly, the technique described above has a subject to be solved in that, when multicast processing is performed by a large amount, transmission of a cell of a higher priority degree is retarded by multicast cells.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a cell bridge apparatus and a cell bridging method as well as an information transmission system having a cell bridge apparatus by which a cell can be outputted in accordance with a priority degree of it even during multicast processing.
In order to attain the object described above, according to an aspect of the present invention, there is provided a cell bridge apparatus, comprising a buffer unit for storing cell data of input cells, a buffer control unit for controlling writing and reading out of the cell data into and from the buffer unit, a cell production control unit for managing multicast information of the cell data read out from the buffer unit by the buffer control unit and producing a cell to be outputted from header information of the cell data, and a cell outputting unit for outputting the cell produced by the cell production control unit and issuing a cell data readout request to the buffer control unit, the buffer unit storing the cell data in accordance with priority degrees of the input cells, the buffer control unit being constructed in such a manner as to read out, when the cell data readout request from the cell outputting unit is received, the input cell data of a high priority degree from among the cell data stored in the buffer unit.
Accordingly, the cell bridge apparatus is advantageous in that it can process a cell having a high priority degree even during multicast processing and moderates the burden to a transmission source by intra-port multicast on the ATM transmission apparatus. The cell bridge apparatus is advantageous also in that, since cells are transmitted in accordance with priority degrees thereof, the transmission efficiency of cells having high priority degrees can be raised.
The buffer unit may include a plurality of buffers provided individually for the different
Abe Hideo
Asano Hiroyuki
Makishima Hiromichi
Obana Yuji
Ookubo Toshiaki
Fujitsu Limited
Harper Kevin C.
Katten Muchin Zavis & Rosenman
Rao Seema S.
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