Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
1997-10-02
2001-02-20
Nguyen, Chau (Department: 2772)
Multiplex communications
Pathfinding or routing
Through a circuit switch
Reexamination Certificate
active
06192048
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates, in general, to the field of methods and apparatus for implementing hunt group support for a crosspoint controller. More particularly, the present invention relates to a method and apparatus for implementing hunt group support for a crosspoint controller within an Enterprise Systems Connection switch (“ESCON™” is a trademark of International Business Machines Corporation).
Current approaches, such as those used in the ESCON Director series of point-to-point switches provide only a single path between any source and destination port. In other words, there is a one-to-one association between an attaching port and the paths to all other ports within the switch. This architecture limits the routing between any two physical ports to one, and only one, path through the switch. As such, the particular path must be available (that is, neither port can be busy) for a connection to be established between the source and destination ports, and a “busy” condition at either the source or destination port will deny the connection from being established and force the requesting device attached to the port to retry the connection request. U.S. Pat. No. 5,107,489 describes a typical ESCON switch and port states in more detail, the disclosure of which is herein incorporated by this reference.
The present ESCON Director configurations utilize a dual-ported 256 bit busy array with the one-to-one relationship of a single busy bit associated with a single port. Busy bits are associated with the physical source/destination port number (“PNUM”) and during a connection request, two bits of the busy bit array are accessed, one associated with the source of the connection request (“SRC_PORT”) and the other associated with the destination (“DST_PORT”). These bits represent the state of each port, and if a connection can be made, then the busy bits addressed by the source and destination port numbers are updated to reflect the new “busy” condition. The individual ports thereafter return a “clear” pulse to the associated busy bits upon termination of the connection.
SUMMARY OF THE INVENTION
The method and apparatus of the present invention overcomes the significant throughput limitation of conventional approaches limited to a single path between any two ports. Through the use of a “hunt group” concept within the busy bit array, multiple paths can be provided between a participating group member and another port. This function significantly increases the likelihood of a port getting a connection established on the first request, thereby providing a performance increase by reducing the number of retries generated by busy conditions. This is effectuated by elimination of the one-to-one relationship of a given path between source and destination ports through the crosspoint switch.
In the embodiment disclosed herein, multiple paths through the crosspoint switch are provided for a given port and are associated in groups of, for example, eight. Each grouping of eight paths then comprise a “hunt group” and the first available member of the hunt group will be selected to enable the connection should the first be “busy”. All paths within the hunt group share the same attributes such that if one path is prohibited from making connections to another port then all paths in the hunt group will be likewise prohibited. The embodiment shown herein comprises a plurality of sequentially organized hunt groups starting on a boundary of eight associated with ports
0
-
7
,
8
-
15
, . . . through
248
-
255
. The method and apparatus of the present invention will support a source port hunt group connection to a destination port, a source port connection to a destination port hunt group as well as a source port to destination port connection although hunt group to hunt group connection requests may be implemented utilizing, for example, a two-dimensional array or content addressable memory (“CAM”) for the connection lookup table.
Disclosed herein is a method and apparatus for implementing hunt group support for a crosspoint controller in which an attribute is defined that identifies either a destination or a source as belonging to a hunt group. In either instance, one or more bits may be utilized in this regard and, in the particular embodiment disclosed, a hardware information block attribute (“HIB”) may be utilized in connection with a destination. In like manner, a single bit HIB could be utilized to identify the source.
In an implementation of the present invention for use in conjunction with an ESCON compliant switch, changes may be made to the busy bit array which include enlargement to a 256 bit array (as opposed to the present two 128 bit arrays) and tight coupling to the connect table (256 byte dual-ported memory). Additionally, logic for “Port Busy” and “Dialog-2” states may be included and provided as input to the decision logic. These indicators may be combined with the other attribute (HIB and prohibit dynamic connectivity mask “PDCM”) and address checks to determine an appropriate response to a connection request.
In operation, the source and destination port number that are returned to the ports and the crosspoint switches are generated in additional decision logic based on hunt group attributes and responses. These values may include the requesting Source Port Number (“PNUM”) and Destination Port Number, the output of the Destination Address to Port (“A2P”) translation table indexed by the destination address (“DST_ADDR”). The setting of the busy bits and updating of the connection table may remain the same as in conventional ESCON switches using, for example, a connect response from the decision logic to perform operations. The operation of clearing the busy bits may also remain unchanged.
Particularly disclosed herein is a method for coupling a first data bus to a second data bus, wherein the first data bus is selectively couplable through a subset of a first plurality of ports to a first side of a crosspoint switch and a second side of the crosspoint switch is couplable to an available one of a second plurality of ports coupled to the second data bus. The method comprises the steps of: defining the subset of the first plurality of ports as a hunt group, identifying a first available port of the hunt group and coupling the first data bus through the first available port of the hunt group and the available one of the second plurality of ports to the second data bus.
Further disclosed herein is a crosspoint controller for coupling a first data bus to a second data bus. The controller comprises a switch having an input and output thereof. A plurality of input ports are coupled between the first data bus and the switch input. A subset of the plurality of input ports comprise a hunt group of member ports wherein the first data bus is coupled to the switch input through a first member port if available and alternatively through a next available member port. At least one output port is coupled between the switch output and the second data bus. The crosspoint controller may also comprise a plurality of output ports coupled between the switch output and the second data bus with a subset of the plurality of output ports comprising a hunt group of member ports. In this embodiment, the switch output is coupled to the second data bus through a first member port if available and alternatively through a next available member port. At least one input port is coupled between the first data bus and the switch input.
Still further disclosed herein is a method for coupling a first data bus to a second data bus through a source port to a destination port path. The method comprises the steps of: determining if either the source port or the destination port is a member of one of a plurality of predefined source and destination hunt groups respectively, coupling a first available member of the source hunt group to the destination port if the source port is a member of one of the plurality of predefined source hunt groups and coupling a first available member of the destination
Fugere James P.
Jessop Ken N.
Nelson Jeffrey J.
Bachand Richard A.
McDATA Corporation
Nguyen Chau
Santiago Enrique L
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