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Race Resolution in Tdm Any-To-Any Path Connections in a Space Division Switch

IP.com Disclosure Number: IPCOM000061802D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

King, A: AUTHOR [+2]

Abstract

This invention relates to a method for time division multiplexed controlling the any-to-any independent path connections among pairs of ports attaching a space division switch. The ports subtend diverse channels and storage control units (SCUs), and permit the "packet-like" transmission and switching of data streams therebetween. The "packets" arise out of the asynchronous connect and disconnect modes of attaching SCUs while a DASD arm is dispatched as, for example, in executing a seek. The feature of interest concerns the resolution of race among calling ports for a common called port and the avoidance of circular waiting (deadlock) among concurrent calling ports.

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Race Resolution in Tdm Any-To-Any Path Connections in a Space Division Switch

This invention relates to a method for time division multiplexed controlling the any-to-any independent path connections among pairs of ports attaching a space division switch. The ports subtend diverse channels and storage control units (SCUs), and permit the "packet-like" transmission and switching of data streams therebetween. The "packets" arise out of the asynchronous connect and disconnect modes of attaching SCUs while a DASD arm is dispatched as, for example, in executing a seek. The feature of interest concerns the resolution of race among calling ports for a common called port and the avoidance of circular waiting (deadlock) among concurrent calling ports. Since each port is assigned a time slot, then upon the occurrence of a slot for port j, the race among calling ports i and k is resolved by priority circuits, while deadlock avoidance uses line- finding logic distributed among the ports. This logic is operative on a first-come, first-served arbitration basis. The logic ascertains whether (a) a called port j is being connected to calling port i; (b) called port j is busy (or already connected) to another port k; or (c) port j is already connected to calling port i over another path. In order to establish a connection between two ports, that is, when port i attempts to connect to port j, port i drops a predetermined "Control/Response i" control line connected to a switch in time slot j. The requested connection may or may not be established, depending on such factors as priority of the requestor in the event of multirequests and availability of the requested port, as described below. Whether port i succeeds in connecting to port j, the switch will normally acknowledge the receipt of the connection request by port i by keeping the "Control/Response i" line down in time slot j+1. Lack of such acknowledgement by the switch will be detected as a switch failure. The switch will inform port i that the requested connection is made, and inform port j that it is connected to a requesting port. The two ports need to explicitly maintain the connection until a disconnection takes place. While the connection is active, the switch will make unsuccessful any attempt to connect to either port by some other port; that is, ports i and j will appear busy. If port j is available and no higher-priority port (including port j itself) is requesting to connect to port j in the same time slot j, the switch will connect port i to port j in the requesting time slot j+1 (referred to as "time slot j delayed") by closing two crosspoints (i,j) and (j,i). Thus, a two-way data transfer path b...