Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Utility Patent
1998-12-17
2001-01-02
Marcelo, Melvin (Department: 2739)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S282000, C714S011000
Utility Patent
active
06169726
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to communications systems, and more particularly to a network access redundant duplex system and method for providing switching between an active controller and a standby controller without the need for retransmission of messages in progress.
2. Description of the Related Art
Conventional network access products, such as a digital network access telephone system, typically comprise at least one central switch which is capable of handling many simultaneous communications, such as telephone calls. The central switch typically is connected to a number of interface units, each of which provides access to the telephone system for one or more subscribers. A switch controller is provided to control the switching and routing of the telephone calls from one subscriber to another through the network.
As the telephone and other types of communication links which require access to a network have become more and more indispensable in every day life and the costs reduced to make such services possible for all, the number of subscribers to the network access systems has increased. As the number of subscribers increases, so to must the number of subscribers allotted to each interface unit or the number of interface units allotted to each switch increase to provide the necessary service access. Typically, each switch is capable of handling up to twenty-four access interface units, with each access interface unit capable of handling several subscribers. Correspondingly, each central switch must be able to handle the routing and switching of ever increasing numbers of communication paths. Thus, if the control unit of the switch fails, the resulting loss of service may not affect only a few subscribers but may affect numerous subscribers.
To prevent the loss of service to the numerous subscribers connected through a specific central switch should the controller in that switch malfunction, network access service providers have been utilizing redundant duplex carrier systems. In a redundant duplex carrier system, a pair of controllers are provided within each central switch. The first controller, initially designated as the active controller, provides the necessary switching and routing of the communications during normal operation. A second controller, designated as the standby controller, is provided within the system. To maintain a high degree of reliability, control of the system is periodically “soft switched,” i.e., switched not under a failure condition, between the two controllers. A switch made under a failure condition is referred to a “hard switch.” Statistically, if the system waits until the first controller fails before switching control to the second controller, there is a fifty percent chance that the second controller will have also failed during the same time period, thus leaving both controllers inoperative. To avoid the disruption of service caused by both controllers being inoperative, the system is “soft switched” frequently relative to the life of a controller so there is a good chance of detecting that one of the controllers is inoperative and repairing or replacing it before both controllers become inoperative at the same time.
There are problems, however, associated with the conventional switching of control from an active controller to a standby controller. The periodic switching from the active to standby controller is most difficult because it may occur frequently, such as for example, once every twenty-four hours, and must be done without disrupting operation. For example, it is possible that during the change from the active controller to the standby controller a data message may be in the progress of being sent from an interface unit to the switch. Should the control of the switch be changed from the active controller to the standby controller during this data message, there is a high probability that the message may be lost during transmission. One common approach to solve these problems is to send messages to both the active and standby controllers. This, however, has its own problems including the possibility of acting twice on the same message. While there are standard ways of dealing with the problem, that too adds to the cost and complexity of the system.
To prevent the possible loss of a message, conventional systems will re-send messages that were in progress during a switch from the active controller to the standby controller, resulting in additional delays for receipt of the message and corresponding delays to the subscriber.
Thus, there exists a need for an apparatus and method that will allow the switching of control from an active controller to a standby controller without the need for retransmission of messages or the risk of loss of data in the messages that may have been in progress during the change.
SUMMARY OF THE INVENTION
The present invention overcomes the problems associated with the prior art and provides a unique method and apparatus for switching between an active controller and a standby controller in a redundant duplex system without the need for retransmission of messages or the risk of loss of data in the messages that may have been in progress during the switching.
In accordance with the present invention, when a change between the active controller and standby controller is required, active controller will stop sending messages to the interface units. After a specified period of time, the main processor in the active controller stops running and signals a main processor in the standby controller to become active. The main processor in the standby controller waits for a fixed period of time before initiating any communications, thus ensuring that the sending of any current messages between the interface units and the switch have been completed before the switch from the active to standby controller is completed. In this manner, there will be no loss of messages and no need for the retransmission of messages which were in progress during the switch between controllers.
These and other advantages and features of the invention will become apparent from the following detailed description of the invention which is provided in connection with the accompanying drawings.
REFERENCES:
patent: 5408462 (1995-04-01), Opoczynsi
patent: 5434998 (1995-07-01), Akai et al.
patent: 5487149 (1996-01-01), Sung
patent: 5491787 (1996-02-01), Hashemi
patent: 5544077 (1996-08-01), Hershey
patent: 5652833 (1997-07-01), Takizawa et al.
patent: 5663949 (1997-09-01), Ishibashi et al.
patent: 5774642 (1998-06-01), Flon et al.
patent: 5983360 (1999-11-01), Ugajin
Dempsey Peter A.
Stern Clifford B.
Woods Gordon D.
Dickstein , Shapiro, Morin & Oshinsky, LLP
Lucent Technologies - Inc.
Marcelo Melvin
Nguyen Phuongchau Ba
LandOfFree
Method and apparatus for error free switching in a redundant... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for error free switching in a redundant..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for error free switching in a redundant... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2461352