Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
1998-06-25
2001-07-31
Marcelo, Melvin (Department: 2733)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S219000
Reexamination Certificate
active
06269077
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a system switching over process for duplicated ATM (asynchronous transfer mode) switch as an active system and a stand-by system.
DESCRIPTION OF THE RELATED ART
FIG. 5
outlines the constitution of a conventional duplicated ATM switch which is disclosed in Japanese Unexamined Patent Publication No. Hei 6-6372.
In
FIG. 5
, the ATM switch is duplicated as an active system, currently in operation, and a stand-by system, waiting for being switched over as active system of the next time, and each system comprises a temporary cell storage unit
510
or
520
and a supervisory unit
511
or
521
.
An incoming cell flow to the ATM switch from an input is directed to the active system by an input selector, and an outgoing cell flow switched by the active system is selected a route to an output by an output selector. The temporary cell storage unit temporarily stores incoming cells in each storage area depending on a delay class provided with each cell, and reads out each cell for switching from storage area in the order of higher delay priority to maintain the delay priority qualities of individual cells. For example, cells with CBR (Constant Bit Rate) are usually for real time data such as voice or moving pictures, and allowance of delay time is very severe for those cells. Therefore, high delay priority is allocated to those cells and the delay priority quality is maintained by the foregoing operation.
When the active and stand-by systems are switched over, the input selector changes the direction of incoming cell flow from the active system to the stand-by system (system newly to be put in an operation state), and as the result, incoming cells are now temporarily stored in the temporary cell storage unit
520
instead of the temporary cell storage unit
510
. On the other hand, remaining cells being stored in the temporary cell storage unit
510
of the active system (system previously in the operation state) should be output even in this state in order to prevent any cell from being lost. Therefore, the supervisory unit
511
supervises contents of the temporary cell storage unit
510
if all cells having been output and no cell is remained.
When the supervisory unit
511
has confirmed that no cell being remained in the temporary cell storage unit
510
, the supervisory unit
511
sends this state to the supervisory unit
521
of the stand-by system (system in operation state now) to allow to start operation as new active system, and also this state is transferred to the output selector to instruct to switch over output cell flow route from the active system to the stand-by system.
Through these procedures, it is possible to switch from one system to the other or vice versa over duplicated ATM switch without causing any loss in cell transmission during switching over operation.
In the conventional example described above, generally it is no problem as long as the temporary cell storage unit of the active system has no cell left at the time of switching over operation. However, if the temporary cell storage unit of the active system has any cells left at the time of switching over operation, it causes the following problem. For example, let's assume that the temporary cell storage unit of the active system is still storing cells with a low delay priority at the time of system switching over. In this case, although incoming cells with a high delay priority are stored in the temporary cell storage unit of the stand-by system (system newly put in the operation state), they should be waited for outputting until all cells with a low delay priority stored in the temporary cell storage unit of active system (system previously in operation) have been completely flowed out.
Namely, as long as the time period during system switching over being performed is concerned, the delay priority of individual cells is ignored, and cells stored in the temporary cell storage unit of active system (system previously in operation) always flow out first even if they have a low delay priority. As a result, even a cell with a high delay priority becomes to have a large CDVT (Cell Delay Variation Tolerance), and is degraded in its delay quality.
SUMMARY OF THE INVENTION
The present invention intends to provide an apparatus and method of an ATM link switching over from an active system to a stand-by system for a duplicated ATM switch for solving above problems and maintaining the delay qualities of involved cells.
To attain above object, the present invention provides an apparatus of an ATM link switching over for a duplicated ATM switch comprises a temporary cell storage unit in each of active and stand-by systems for storing incoming cells in accordance with a delay priority provided with each cell, and control means for arbitrating cell reading from which temporary cell storage unit is to be performed depending on cell storage condition and delay priority in each temporary cell storage unit at the time of system switching over.
In more detail, the apparatus of an ATM link switching over a duplicated ATM switch comprises an input selector for transferring incoming cells from an input line to a system currently being operated, an output selector for transferring outgoing cells from a system currently being operated to an output line, a temporary cell storage unit in each of active and stand-by systems for storing incoming cells in accordance with a delay priority provided with each cell transferred from said input selector, and system-switching control means for detecting cell information including delay priority stored in each temporary cell storage unit in both of active and stand-by systems, for instructing one of temporary cell storage units storing a cell having the highest delay priority among both of active and stand-by systems to read out the cell, and for outputting the read out cell from one of temporary cell storage units selectively to said output selector.
Further, the system-switching control means comprises a system-switching control unit in each of active and stand-by systems for communicating with the system-switching control unit in the other system each other and detecting cell information including delay priority stored in each of temporary cell storage units in both of active and stand-by systems, and for instructing the temporary cell storage unit of own system if storing a cell having the highest delay priority among cells in both of own and the other systems to read out the cell, and outputting system information indicating the system from which a cell being read out, and a delay priority selector in each of active and stand-by systems, which is connected to both of temporary cell storage units in own system and in the other system each other, for outputting a read out cell from either of temporary cell storage unit selectively according to the system information output from the system-switching control unit.
The system-switching control unit outputs the system information to the delay priority selector of own system if own system state is currently in operation, and outputs the system information to the delay priority selector of the other system through the system-switching control unit of the other system if the other system state is currently in operation.
The system-switching control unit further comprises a cell management section, a selector control section and an inter-system communication section.
The cell management section is provided for memorizing cell information including length of queue to be read out for each delay priority stored in the temporary cell storage unit of own system and other system, for providing an instruction of cell reading out to the temporary cell storage unit of own system if a cell having the highest delay priority among cells in the both systems being stored in own system, and for outputting the system information when the cell being read out from own system.
The selector control section is provided for instructing the delay priority selector of own system for allowing to pass the read o
Matsumura Kenji
Yamamoto Toru
Marcelo Melvin
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
ATM link switching over method and 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 ATM link switching over method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and ATM link switching over method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2459275