Multiplex communications – Fault recovery – Bypass an inoperative channel
Reexamination Certificate
1998-02-18
2001-01-30
Hsu, Alpus H. (Department: 2738)
Multiplex communications
Fault recovery
Bypass an inoperative channel
C370S251000, C370S465000, C375S267000, C379S015050
Reexamination Certificate
active
06181677
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to digital communications in a T1 or E1 digital communications network environment. More particularly, it is directed toward protection against loss of data in a fractional T1/E1 communication environment due to an out-of-service condition occurring within a digital communications carrier network.
BACKGROUND OF THE INVENTION
In a corporate (i.e., non-fractional) T1 or E1 digital communications network environment, communication line conductivity and signal/data quality assertion is provided by conventional T1/E1 protocol maintenance signals. These maintenance signals provide assurance against data loss occurring anywhere from the customer's data service unit/channel service unit (DSU/CSU) equipment, continuing through the commercial carrier's central office (CO), the carrier network itself, other connecting central offices of the carriers, and finally through to the customer unit at the destination. Unfortunately, these maintenance signals do not provide the same end-to-end coverage in a fractional T1/E1environment.
In a “fractional” T1/E1 environment, the conventional T1/E1 maintenance signaling techniques will only cover the connection between customer equipment and the carrier network. Consequently, an interruption of service resulting in data loss may go undetected if it occurs within the commercial carrier network. For example, conventional T1/E1 maintenance signals cannot detect the loss of a DS0 channel or an out-of-service condition (OSS) (assuming the integrity of the customer-to-central office connection is maintained). Merely attempting to detect an absence of data is not feasible in a traditional T1/E1 environment because a DS0 time slot in a fractional T1/E1 network is not guaranteed to be a constant when data is not present. One solution has been proposed that entails initiating a Unix-type “ping” messaging arrangement wherein one unit sends a query or test message to another unit which upon receiving the message then reciprocates with a return message indicating that the query was received. A major drawback with this arrangement is that it incurs unavoidable network transmission path delays for each message (i.e., the “ping” must travel through the T1/E1 network twice) in addition to some processing delay at the remote unit. The cumulative delay incurred is often unacceptable for meeting various user requirements. Accordingly, there is a long-felt need for a more efficient signaling arrangement that would allow a user of a fractional T1/E1 digital communications carrier network to protect against a loss of data in the event of a data interruption in the carrier network without incurring unacceptable delays. The present invention solves this problem by utilizing a unique “heartbeat” signalling arrangement that incurs only a single path delay through the T1/E1 network, thus permitting a much faster detection of a loss of communication condition in fractional networks.
SUMMARY OF THE INVENTION
The present invention addresses the problem of detecting and contending with data interruptions that may occur within a carrier network of a fractional T1/E1 communications environment. In a fractional T1/E1 environment, when service is interrupted in the carrier network, a user of the network has no way of efficiently detecting the interruption. A method and apparatus disclosed herein allows the user of a fractional T1/E1 network to quickly determine when such interruptions occur so that corrective actions may be immediately taken.
In accordance with an embodiment of the present invention, each active data service unit or channel service unit (DSU/CSU) making up a user's network is adapted to generate and send a periodic indication that the unit is active. This periodic indication or “heartbeat” message is sent to other receiving units through the digital carrier network via a bit-stealing in-band dedicated channel. Each DSU/CSU is also adapted to monitor the message transmission activity of one or more remote units. If a heartbeat signal message is not received within a predetermined amount of time a service interruption condition is declared. Accordingly, the user of a carrier network in a fractional T1/E1 environment is notified when data interruptions occur in the network and when the network is non-responsive.
In an example embodiment of the invention, a digital communications network is comprised of conventional DSUs/CSUs interconnected via a fractional T1 carrier network. Each DSU/CSU is programmed to generate and send a “heartbeat” signal to other DSUs/CSUs within the network. This heartbeat signal is sent periodically at a predetermined selectable rate and is carried as a proprietary message on a dedicated embedded T1 service channel. Each DSU/CSU also maintains at least one programmable watchdog timer mechanism, implemented in either hardware or software. When a heartbeat signal message is received from a remote unit, the receiving DSU/CSU resets its corresponding watchdog timer mechanism. If the heartbeat message is not received before the predetermined duration of the timer expires, the affected DSU/CSU locally provides a “loss of remote communications” (LRC) indication and/or enters a “dial back-up” mode wherein alternate communications channels are automatically established. Once the primary communications channel through the T1 carrier network is restored and remains established for a predetermined amount of time, the affected DSU/CSU reverts to its normal operation.
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Hitchcock Sam
Sala Ulises
Valli Ron
Hsu Alpus H.
Milgo Solutions, Inc.
Nixon & Vanderhye P.C.
Qureshi Afsar M.
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