Port congestion notification in a switch

Abstract

A congestion notification mechanism provides a congestion status for all destinations in a switch at each ingress port. Data is stored in a memory subsystem queue associated with the destination port at the ingress side of the crossbar. A cell credit manager tracks the amount of data in this memory subsystem for each destination. If the count for any destination exceeds a threshold, the credit manager sends an XOFF signal to the XOFF masks. A lookup table in the XOFF masks maintains the status for every switch destination based on the XOFF signals. An XON history register receives the XOFF signals to allow queuing procedures that do not allow a status change to XON during certain states. Flow control signals directly from the memory subsystem are allowed to flow to each XOFF mask, where they are combined with the lookup table status to provide a congestion status for every destination.

Description

RELATED APPLICATION [0001] This application is a continuation-in-part application based on U.S. patent application Ser. No. 10 / 020,968, entitled “Deferred Oueuing in a Buffered Switch,” filed on Dec. 19, 2001, which is hereby incorporated by reference. [0002] This application is related to U.S. patent application entitled “Fibre Channel Switch,” Ser. No. ______, attorney docket number 3194, filed on even date herewith with inventors in common with the present application. This related application is hereby incorporated by reference.FIELD OF THE INVENTION [0003] The present invention relates to congestion notification in a switch. More particularly, the present invention relates to maintaining and updating a congestion status for all destination ports within a switch. BACKGROUND OF THE INVENTION [0004] Fibre Channel is a switched communications protocol that allows concurrent communication among servers, workstations, storage devices, peripherals, and other computing devices. Fibre C...

AI Technical Summary

Benefits of technology

[0016] The present invention utilizes a single cell credit manager to track the inputs to the memory subsystem for a plurality of ports. Since each port has its own XOFF mask, the XOFF signals must be sent to the XOFF mask for each port that the cell credit manager tracks. Other cell credit managers exist within the switch. The present invention utilizes a special bus to transfer XOFF signals between the various cell credit managers within a switch. In addition, the present invention provides a technique for a stop_all signal to be shared with all XOFF masks utilizing a single memory subsystem. This signal will ensure that when the gross_xoff signal is set, it will prevent all traffic from flowing into the memory subsystem.

Problems solved by technology

Sometimes, however, a switch encounters a frame that cannot be delivered due to congestion at the destination port.

However, this requires large amounts of memory and a good deal of complexity in large switches having many possible destination ports.

Congestion and blocking are especially troublesome when the destination port is an E_Port providing an interswitch link to another switch.

Unfortunately, the existing solutions for providing this information are not satisfactory, as they do not easily present accurate congestion status information to each of the ingress ports in a switch.

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