Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-09-17
2004-05-11
Olms, Douglas (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S395210
Reexamination Certificate
active
06735204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ATM (asynchronous transfer mode) cell multiplexing apparatus, and particularly to such an apparatus and method suitable for providing functions for performing multiplexed transmissions of AAL (ATM adaptation layer) type-2 ATM cells.
2. Description of Related Art
Referenced Literature: Kawakami, et. al.: “IMT-2000 mobairu maruchimedeia wo jitsugen suru ATM akusesu seigyo hoshiki [ATM access control scheme for implementing IMT-2000 mobile multimedia],” Denshi Joho Tsushin Gakkai Kenkyu Hokoku [Research Report of The Institute of Electronics, Information and Communication Engineers (IEICE)], Vol. 98, No. 18, pp 41-48, “Kokan shisutemu [Switching systems],” Shingaku Giho, SSE98-6 RCS98-6 (April, 1998).
In regard to research done conventionally on multiplex-transmission functions of this type, the literature cited above is available. In particular, in
FIG. 15
on page 48 in the literature cited, the configuration of a multiplex-transmission apparatus comprising functions for generally controlling the multiplexed transmission of AAL type-1, type-2, and type-5 ATM cells is disclosed. This configuration is shown in
FIG. 1
in the present specification.
In general, in AAL type-1 and type-5 ATM cells, it is possible to provide various quality of service (QoS) levels in response to user demand. More specifically, ATM cells are divided into a plurality of QoS classes (priorities), and, by implementing band control according to each class, that QoS class is guaranteed.
The details of this process are now described. With the ATM cell multiplexing apparatus shown in
FIG. 1
, when an AAL type-1 or type-2 ATM cell is input, the QoS class thereof is identified by a distribution module
1
. The distribution module
1
distributes ATM cells to corresponding buffers
2
i (where i=1, 2, . . . n) for cells to be sent, provided beforehand for each class, based on the QoS class identified. An ATM multiplexer
3
fetches ATM cells held in the buffers
2
i (where i=1, 2, . . . n) for cells to be sent, in accordance with established fetch order and output timing, and transmits them on a transmission path.
In the case of AAL type-2 cells, when the user requires different QoS levels, the QoS levels are divided into classes that represent priorities. In such cases, however, CPS (common part sublayer) packets are input to the ATM cell multiplexing apparatus.
When CPS packets are input to the ATM cell multiplexing apparatus, a CPS packet distribution module
4
identifies the QoS classes of the packets. Then, the CPS packet distribution module
4
distributes the input CPS packets into corresponding buffers
5
i (where i=1, 2, . . . n) for packets to be ALL multiplexed, provided beforehand for each class, based on the QoS class identified. The AAL multiprocessing timing and ATM cell transmission timing are synchronized by a timing controller
6
. When it is time to output ATM cells, irrespective of the input traffic volume, the timing controller
6
sends a multiprocessing start request to the AAL multiplexer
7
. The AAL multiplexer
7
reads out CPS packets according to the receiving timing of processing start request, and performs AAL multiplexing in ATM cell format. When this is done, even when there are not enough CPS packets present in the buffers for packets to be AAL multiplexed to sufficiently fill out an ATM cell payload, the AAL multiplexer
7
sends an ATM cell (AAL
2
) partially carrying CPS packets to a buffer
8
for ATM cells (AAL
2
) to be sent. Thus the configuration is such that CPS packets of the same QoS are AAL multiplexed in one ATM cell.
However, the prior art is subject to a technical difficulty that will now be described. That is, in the apparatus configuration as described in the foregoing, in guaranteeing QoS levels, there is a problem in that a phenomenon called uncontrolled priority inversion may occur, making it impossible to satisfy the most critical QoS demands of multimedia services.
By priority inversion here is meant a phenomenon whereby data of high priority are made to wait by data of low priority. When, moreover, the maximum value of this forced wait time cannot be logically predicted, this is called an uncontrolled priority inversion. Such uncontrolled priority inversions become serious hindrances in real time systems and multimedia services and the like.
An example of uncontrolled priority inversion is now described, with reference to FIG.
1
. In this description, the priority is higher the smaller the number of the QoS class.
Let it be assumed that an AAL type-2 CPS packet for which the QoS class is 1 is held in a buffer
51
for packets to be AAL multiplexed at the point in time when an AAL type-2 CPS packet for which the QoS class is 3 is input to the buffer
8
for ATM cells to be sent.
Conventionally, when QoS levels are guaranteed, a QoS class-1 CPS packet must be AAL multiplexed in ATM cell and sent out after the ATM cells in the buffer
8
for ATM cells to be sent are transmitted. However, when the QoS class in AAL type-5 ATM cells is 2, the priority is higher for the AAL type-5 ATM cells than for the AAL type-2 ATM cells, wherefore the AAL type-5 ATM cells are successively transmitted. Until that transmission is completed, the transmission of AAL type-2 ATM cells is made to wait.
It does not matter that AAL type-2 ATM cells are made to wait because their priority is itself low. However, so long as AAL type-2 ATM cells are not transferred, with the ATM multiplex-transmission apparatus shown in
FIG. 2
, the AAL type-2 CPS packets of the highest priority (QoS class
1
) held in the buffer
5
for packets to be AAL multiplexed may be made to wait for unlimited times, causing uncontrolled priority inversions. In other words, with the conventional apparatus, the buffer
8
for ATM cells (AAL
2
) to be sent becomes a bottleneck.
SUMMARY OF THE INVENTION
One object of the invention is to provide an ATM cell multiplexing apparatus and method which can be implemented wherewith uncontrolled priority inversions do not occur.
Another object of the invention is to provide an ATM cell multiplexing apparatus and method which can be implemented wherewith not only do uncontrolled priority inversions not occur, but the cell loss ratio can also be guaranteed.
A further object of the invention is to provide an ATM cell multiplexing apparatus and method which can be implemented wherewith the multiplexing efficiency is superior to that obtainable with the conventional ones.
(A) According to one aspect of the invention, there is provided an ATM cell multiplexing apparatus comprising: an AAL multiplexer for generating ATM cells from AAL type-2 user data; a buffer for cells to be sent for temporarily holding generated ATM cells; and an ATM multiplexer for ATM-multiplexing ATM cells read out from the buffer for cells to be sent; wherein the buffer for cells to be sent comprises functions for discarding ATM cells when the transmission waiting period exceeds a time-over period; and the AAL multiplexer comprises functions for giving priority to user data for which a higher quality of service is demanded than for the discarded ATM cells, which data are ATM cells generated immediately after the discarding.
According to the second aspect of the invention, there is provided an ATM cell multiplexing apparatus comprising: AAL multiplexers for generating ATM cells from AAL type-2 user data; and buffers for cells to be sent for temporarily holding generated AAL type-2 ATM cells; wherein: said AAL multiplexers and said buffers for cells to be sent are comprised in a plurality of sets for each quality of service; ATM cells read out from said buffers for cells to be sent are ATM-multiplexed by said ATM multiplexers; and said buffers for cells to be sent, respectively, comprise functions for discarding ATM cells when transmission waiting periods thereof exceed time-over periods set for each quality of service.
According to the third aspect of the invention, the
Fukuyoshi Makoto
Furuhashi Toru
Ishizuka Masaru
Wang Cai Dong
Burdett James R.
Oki Electric Industry Co. Ltd.
Olms Douglas
Pizarro Ricardo M.
Venable LLP
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