Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
1997-09-10
2001-05-01
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Through a circuit switch
C370S362000
Reexamination Certificate
active
06226288
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the field of telecommunications and, more specifically, to a programmable telecommunication switch having programmable cards which dynamically provide call processing and communications services to any port in the switch.
BACKGROUND OF THE INVENTION
Conventional digital telecommunications switches often employ a time slot interchange (TSI) to effect switching using time division multiplexing (TDM) techniques. As known, a conventional TSI includes a memory device for storing digital information (i.e., voice, data, etc.), a counter and a control store. The counter cyclically generates consecutive addresses which are applied to the memory device. As each such address is applied to the memory device, a portion of digital information, known as a time slot (i.e., a byte) is stored in the location of the memory device corresponding to that address. In general, in prior art telecommunications switches each time slot is associated with a single, unique “port” of the switch, wherein each port represents a possible connection for a telephone line, trunk or other device.
The switching function is effected by the control store, which generates addresses simultaneously with the counter. However the addresses generated by the control store may be dynamically changed and are generally not consecutive. Thus, as these reordered addresses are applied to the TSI memory device during a read operation, the effect is to switch or interchange the order in which the previously stored information is retrieved from the memory device. In this fashion, information which is stored in the memory device after being received from any given port during a particular time slot may be subsequently read from the memory and transmitted to any other port during another time slot.
In addition to the basic time switching function just described, many digital telecommunications switches provide communications or call processing services. Such services typically include tone generation and tone detection, and other known services to meet the requirements of a particular system application.
A conventional technique for providing call processing services is to configure a switch with the necessary dedicated circuitry (e.g., one or more tone generators and one or more tone receivers of the appropriate protocols) and use the TSI to establish communication paths between such dedicated circuitry and the appropriate ports. For example, assume that a user lifts her handset and the switch detects that her line is now off-hook. The switch then responds by establishing a communication path through the TSI between an available tone generator and the off-hook line, and consequently, a dial tone produced by the tone generator is heard by the user.
There are, however, significant disadvantages with this conventional technique and a solution to those problems is articulately set forth in U.S. Pat. No. 5,349,579 entitled “Telecommunications Switch With Programmable Communications Services” (hereinafter the “'579 Patent”), assigned to the assignee of the present invention and incorporated herein by reference. Although the dynamic allocation of resources disclosed in the '579 Patent is a significant advancement in the state-of-the-art, the system disclosed therein switches or processes only whole time slots (e.g., an entire byte) of information. That is, during each time slot, pulse code modulated (PCM) data is written into and read from the TSI by the digital signal processing modules byte-per-byte. One aspect of this architecture is that only a single DSP can use each time slot. That is, even if a DSP wishes to use less than a byte of a time slot, the entire byte is effectively committed to the DSP. Therefore, several bits of the byte would not be used during the time slot.
With the emergence of digital wireless services and the expansive features available with these services, dedicating an entire time slot to a DSP may be inefficient if a number of the DSPs are using less than the entire byte of the time slot.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a programmable telecommunications switch which allows switching and processing of units of information ranging in size from a single bit to an entire time slot.
Briefly, according to the present invention, a programmable telecommunications switch includes a CPU/matrix card, one or more line cards, and one or more programmable communications services cards, all of which are connected in communicating relationship. The CPU/matrix card includes a time slot interchange (TSI), whose time slots correspond to ports of the switch, and a central call processor which processes messages received from a host computer and controls the line cards and the communications services cards. Each communications services card is independently programmable and processes messages received from the CPU/matrix card. The communications services card includes a plurality of digital signal processor (DSP) modules which are capable of being dynamically programmed to meet the requirements of a particular application.
The CPU/matrix card, the line cards and the communications services cards are interconnected via a plurality of buses which allows messages to be bi-directionally passed between the cards. Specifically, the CPU/matrix card and communications services cards are connected to a TDM bus, such that, these cards continuously receive all PCM information transmitted from the line cards during all time slots. However, during any given time slot, one and only one of the CPU/matrix card or available communications services cards is permitted to transmit PCM information to the line card having the port associated with that given time slot. Thus, for any given time slot, the PCM information that is transmitted to the corresponding port will originate from either the TSI on the CPU/matrix card, or from the communications services cards. As a result of this arrangement, the communications services cards are able to transmit PCM information directly to the line cards (ports) via the TDM bus without occupying time slots that would otherwise be available for other calls.
Preferably, each of the DSP modules resident on a communications services card includes its own TSI. Significantly, this allows each DSP module to simultaneously receive all information transmitted from the line cards. In addition, since each DSP module includes its own dedicated TSI and each of these TSIs is connected in parallel to the same TDM bus, one or more TSIs may output data onto that bus during a time slot. Advantageously, this allows multiple communication services card TSIs to be assigned to transmit during the same time slot. For example, if a first DSP module needs only three bits of an eight bit time slot, and a second DSP module needs five or less bits, then both DSP modules can be assigned to transmit during the same time slot. The first TSI would output data as, for example, the three least significant bits, while the second TSI would output its data as the remaining bits of the time slot. Advantageously, this provides the telecommunications switch with an ability to “sub-rate” multiplex time slots at the bit level. This system further facilitates the use of variable length PCM or other data.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.
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Cesari and McKenna LLP
Excel Switching Corporation
Kwoh Jasper
Nguyen Chau
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