Communications: electrical – Continuously variable indicating – With meter reading
Patent
1993-08-19
1995-04-25
Hofsass, Jeffery A.
Communications: electrical
Continuously variable indicating
With meter reading
34082503, 3408255, 34082552, H04Q 1104
Patent
active
054103002
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to crossbar and crosspoint switches, and more particularly to an architecture for such switches that exhibits distributed and independent control of data routing elements.
BACKGROUND OF THE INVENTION
Crossbar switches are used in digital systems to provide communication between sources of data and sinks of data. A typical crossbar environment is shown in FIG. 1, wherein N sources of information and N sinks of information are shown connected by an N by N crossbar switch. At any given time, a data source may establish a connection to a data sink for data transmission. Connections may be terminated by either the source or the sink, and the crossbar switch allows several concurrent connections to operate. A crossbar switch should have the ability to establish a connection between one source and multiple sinks.
Crossbar switches see uses in many computer applications. In some parallel computers which share memories, the processors are placed on one side of a crossbar switch (acting as sources) and memory banks are placed on the other side (acting as sinks). As such, the switch allows any processor to access any memory bank and further allows multiple processors/memory bank connections to be in operation simultaneously. In such systems, one processor often wishes simultaneous access to data in several memory banks and as a result, the crossbar switch must support the notion of one source connecting to multiple sinks.
Crossbar switches are also found in nodes of distributed memory, parallel computer systems. In such systems, each node is directly connected to several other nodes, using data links. A crossbar switch at each node allows a message arriving along an inbound data link to be sent out over any set of outbound data links. In such systems, the initiating node merely wishes to know whether a message has been received at a receiving node and is unconcerned with how many copies of the message did not get through, so long as one does get through.
Attributes of an N by N crossbar switch are as follows: from sources and sinks in an uncorrelated manner. Sources must be able to generate connection allocation requests and once a connection is established, either the source or the sink should be free to terminate the connection. Multiple connections should be handled concurrently. Sources and sinks should not be required to wait several clock cycles for a connection request to be completed. Although physical constraints will limit the ultimate scalability of any design, the architecture itself should not impose any physical limits. manner. connection control path, but rather should employ the primary data path for both data and control signal transmission. In other words, connection allocation should be performed by signals transmitted over the primary data path. communication between a source and sink and one to many communication between a source and a set of sinks.
The prior art has attempted to achieve the above objectives through a number of design architectures. Several commercial digital crossbar switches provide data routing functions that are controlled by a configuration map. Examples of such switches are the Texas Instruments 74ACT8841 and 74AS8840. The configuration maps in those switches store connection information that details which sources are connected to which sinks. When a connection allocation or deallocation request is processed, the configuration map must be reloaded. This task is handled by a centralized controller that is implemented by the designer. Map reload takes several clock cycles in most implementations and, as a result, slows the data communication function.
In general, a centralized controller and data routing chip is expensive to implement and does not lend itself well to a dynamic switching environment where allocation and deallocation requests are received in an uncorrelated manner. While multiple crossbar switches can be cascaded to build larger switches, centralized controllers are not easily scalable.
In U.S. Pat. No. 4,852,08
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Gould Joel M.
Lackritz Neal M.
Hill Andrew
Hofsass Jeffery A.
International Business Machines - Corporation
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