Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
1997-07-17
2001-05-08
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Through a circuit switch
C370S540000
Reexamination Certificate
active
06229805
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to systems for switching time-multiplexed communication channels at different rates.
BACKGROUND OF THE INVENTION
Referring to
FIGS. 1 and 2
, typical modem telephone systems use a digital switch
4
to switch calls from one time-multiplexed channel onto several others. For example, time slots A and B from two different telephone calls may have been time-multiplexed onto a single input channel
1
, but are destined for different output at channels
2
and
3
. The digital switch completes a connection by transferring the signal portions A and B received from the particular time slots in the input channel
1
to specific time slots in the different output channels
2
and
3
.
A digital switch generally performs its switching operations by temporarily storing data samples received on one of its input channels I
0
-IN and then distributing them to its output channels O
0
-ON. To keep up with the demands of switching between a certain number of input channels
6
and a certain number of input channels
8
at a particular rate, a switch should include a sufficient amount of computational resources, such as switching circuitry, data paths, and temporary storage. The switching rate is often a standard rate, but there are a variety of such rates in use. Voice-over-Internet systems, for example, often employ vocorders, which translate between so-called “full-rate” (64 kbps) audio telephone channels and “sub-rate” channels in which the audio data has been compressed to a fraction of the full rate.
A switch that supports sub-rate switching for a given number of channels is substantially more expensive than one that supports only full-rate switching. This is because resources within the switch are required on a per connection basis, and a switch supporting sub-rate switching must support far more connections. For example, a non-blocking switch supporting 1024 full-rate channels must support 1024 connections. But if the same switch also supported 8 kbps sub-rate channels, it would have to support 8096 connections.
Switches supporting such high connection densities are necessary in dedicated sub-rate systems, but they may be wasted in systems with mixed requirements. Although in very large systems it is possible to mix full-rate and sub-rate switches, smaller systems may present more difficult design choices. And the choices involved in systems tailored for specialized interface applications may be particularly problematic.
SUMMARY OF THE INVENTION
In one general aspect, the invention features a communications switching station that includes a digital switch and a sub-rate interface circuit. The switch has signal terminals including inputs and outputs, and switching circuitry adapted to operate at a first rate operatively connected between the inputs and the outputs. The sub-rate interface circuit includes a first signal terminal operatively connected to at least one of the signal terminals of the digital switch, a second signal terminal, and programmable circuitry connected between the first signal terminal and the second signal terminal, the programmable circuitry being operative at a second rate, which is lower than the first rate.
In preferred embodiments, a plurality of jumpers can bypass the sub-rate interface circuit; the programmable circuitry of the sub-rate interface circuit includes at least one packing circuit, such as a packer or unpacker, operatively connected between the two terminals of the sub-rate interface circuit, and the second terminal is for connection to external signal channels operating at the second rate; the sub-rate interface circuit includes at least a third signal terminal operatively connected to at least one of the signal terminals of the digital switch and at least a fourth signal terminal for connection to external signal channels operating at the second rate, and the sub-rate interface circuit includes further programmable circuitry connected between the third signal terminal and the fourth signal terminal; the second and third signal terminals of the interface circuit are inputs, the first and fourth signal terminals of the interface circuit are outputs, and the interface circuit includes an unpacker operatively connected between the first signal terminal of the interface circuit and the second signal terminal of the interface circuit, and a packer operatively connected between the second signal terminal of the interface circuit and the first signal terminal of the interface circuit; the second signal terminal of the interface circuit is operatively connected to one of the signal terminals of the digital switch, and a packing circuit is operatively connected between the first and second terminals of the interface circuit; the second signal terminal of the interface circuit is operatively connected to one of the signal terminals of the digital switch, and the station further includes a further plurality of signal terminals operatively connected to a plurality of the signal terminals of the digital switch; packing circuits are each operatively connected between two of the terminals of the interface circuit; the packing circuits include at least a packer and an unpacker; and the programmable circuitry in the sub-rate interface circuit includes field-programamble logic, such as an electrically programmable logic device.
In another general aspect, the invention features a communications switching station that includes a digital switch and a sub-rate interface circuit. The switch has signal terminals including inputs and outputs, and switching circuitry adapted to operate at a first rate operatively connected between the inputs and the outputs. The sub-rate interface circuit includes a first signal terminal operatively connected to at least one of the signal terminals of the digital switch, a second signal terminal, and a packing circuit connected between the first signal terminal and the second signal terminal, the packing circuit being operative at a second rate, which is lower than the first rate.
In a further aspect, the invention features a communications switching method that includes communicating with sub-rate streams, converting between packed sub-rate and sparse full-rate streams, and switching the sparse channels. The step of communicating can receive sub-rate streams and the step of converting can unpack the sub-rate streams. The method can also include the step of packing the switched sparse streams to obtain packed sub-rate streams and further the step of sending the packed sub-rate streams. The switching can be performed by a full-rate switch.
The invention is advantageous in that it permits a versatile handling of mixtures of sub-rate and full-rate communications. By providing a variable mixture of sub-rate and full-rate channels, systems requiring some sub-rate capability can be accommodated, without requiring the expense of full sub-rate capabilities. And by governing the configuration of sub-rate capabilities with programmable logic, the exact nature of the communications mix can be finely tailored to fit a specific application.
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Boakye Alexander
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
Natural MicroSystems
Nguyen Chau
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