Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
1998-08-13
2002-04-30
Ton, Dang (Department: 2732)
Multiplex communications
Pathfinding or routing
Through a circuit switch
Reexamination Certificate
active
06381239
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention pertains to a communications switch preferably for use in telephone switching systems. In particular, the present invention pertains to a distributed architecture telephone switching platform that processes telephone call requests by establishing connections between a communication source and a communication destination without the use of a centralized processor, centralized resources or a centralized switching matrix.
2. Discussion of Prior Art
Generally, modem switching systems (e.g., of the kind employed within central offices and/or private or private automatic branch exchanges) include a time division multiplexed (TDM) bus as a common medium to transport information (e.g., voice or data signals) between multiple sources and destinations on a time-shared basis. Information is typically transported over the time division multiplexed (TDM) bus in units commonly referred to as frames wherein each frame typically includes at least thirty-two time slots within a 125 microsecond frame period. Thus, the bus accommodates 8,000 frames during each one second interval. A connection between a communication source and a communication destination is typically accomplished by notifying the communication source and communication destination of the particular time slot the other is utilizing for transmission of data over the time division multiplexed (TDM) bus. The communication source transmits data during its designated time slot period and examines information received during the time slot utilized by the communication destination in order to retrieve information from the communication destination. Similarly, the communication destination transmits data during its designated time slot period and examines information received during the time slot utilized by the communication source to retrieve information from the communication source. The designated time slots, in effect, provide a connection between the communication source and communication destination and further enable multiple connections, via the different time slots within a frame, for facilitating communications between multiple communication sources and communication destinations. Larger systems frequently use several such buses, each providing a connection between one or a few sources and destinations, and a central time slot interchange unit (i.e., matrix) which makes connections between sources and destinations attached to different buses.
In order to establish a connection between a communication source and communication destination (e.g., processing a telephone call), switching systems frequently utilize a systemwide common database containing information relating to time slot availability (i.e., time slots that are currently available for establishing connections). The database is typically consulted by the communication source and communication destination to ascertain available time slots during which the communication source and communication destination may transmit information across the time division multiplexed (TDM) bus. The database is maintained in real time and may reside within two independent processors when redundant processors are utilized to enhance system fault tolerance. When a time slot is utilized to establish a connection, or when a time slot becomes available subsequent to termination of a connection, the database is updated to reflect the current availability status of the respective time slots. The manner in which connections are facilitated between any communication source and communication destination via a switching system is fairly sophisticated since each communication source potentially requires a connection to each communication destination. A central switching matrix is commonly employed to establish these connections wherein a redundant or spare matrix is frequently employed to automatically replace the original matrix in response to an original matrix failure. Further, several switching systems include common resources and/or utilize a common or central processor to perform substantially all of the connection activity and control for the switching system.
Switches having common or central resources suffer from several disadvantages. Specifically, common processors tend to create bottlenecks, thereby restricting processor throughput and switch efficiency. System enhancement to a common processor switching system via addition of hardware and/or software tends to be difficult due to numerous time critical concurrent processes typically executing within the common processor. Further, a central processor performs several tasks, typically in a multi-tasking environment, thereby complicating programming, debugging and portability of tasks, increasing the chance of real time problems and reducing the processing power for each task. Moreover, a spare or redundant processor is commonly utilized in a central processor switching system since failure of the common processor tends to disable the switching system. The spare processor usually requires real time updates, to coincide with the central processor thereby reducing the central processor throughput.
Common matrices employed within switching systems typically require real time connection maps to indicate the status of matrix connections wherein the connection maps are constantly maintained and updated to accurately reflect the matrix connection state. The maintenance of connection maps is usually performed by a processor, thereby distracting the processor from handling connection requests and reducing switch efficiency. Further, since the size of a centralized matrix increases in relation to an increase in communication sources, expansion of the switch becomes expensive and may exceed cost efficiency. Moreover, since failure of a matrix essentially disables switch operation, an additional redundant matrix is often utilized to automatically replace the original matrix in response to an original matrix failure, thereby substantially increasing the costs and complexity of a switching system. In addition, centralized matrices commonly have a particular quantity of matrix ports (i.e., time slots) physically connected or permanently assigned to a slot or a group of slots within a backplane, thereby restricting the quantity of ports that may be utilized by a source or communication destination connected to the switch through that backplane slot. The matrix port assignment may prevent calls from immediately being processed (i.e., increase blocking) when an insufficient quantity of ports have been assigned to a particular backplane slot (i.e., the quantity of possible simultaneous calls to or from lines or trunks connected to that backplane slot exceeds the quantity of assigned ports). Conversely, the matrix port assignment may waste resources when the quantity of ports assigned to a particular backplane slot exceeds requirements of that backplane slot (i.e., the quantity of assigned matrix ports exceeds the quantity of possible calls from attached lines or trunks, thereby having idle ports that are unavailable to process calls received on other backplane slots).
Generally, switching systems employing common resources for control and/or matrix switching have limited growth potential since the maximum capacity of the central resources governs the switch growth capacity. These systems are typically replaced with larger switching systems to attain increased switching capacity. Further, common resources tend to be expensive, thereby compromising switching system growth potential in favor of lower start-up costs for a small installation. Thus, a common resource switching system may either far exceed switching requirements for an installation (i.e., having more capacity than required), or be insufficient to handle increased switching requirements within a short-term, thereby necessitating replacement by a larger switching system. Moreover, incorporating fault tolerance into a switching system, via redundancy, by duplicating the common resources dramatically increases system costs and require
Ashley William
Atkinson Roger F.
Beckman Kenneth A.
Klein Raymond
Ng Simon S.
Taqua Systems, Inc.
Ton Dang
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