Error recovery method in a system constituted by nodes connected by lienks which transfer error control fames

Claim 1

An error recovery method for use in an information communication system which comprises a plurality of nodes connected by links, information being transferred between the nodes, using one or more of said links, in frames of predefined types, including at least a first frame type used to transfer data and a second frame type used for error recovery, the information transfers being initiated by more than one node, the nodes having at least a first and a second mode of operation, the method comprising the steps of: defining a master node for controlling error recovery; on detecting an error on a link connecting a first and second node; switching one or both of the first and second nodes from a first to a second mode of operation wherein frames of the first type are discarded by the node at all of its ports and frames of the second type are accepted by the node at any of its ports; transmitting by one or both of the first and second nodes, to the master node, of a second frame type containing first error information; transmitting by the master node, to all nodes capable of initiating information transfer, of a second frame type containing second error information; transmitting by other nodes which have initiated frames of a first type using said link connecting first and second nodes, to each node to which said first type frames were sent, of instructions causing said first frame types to be discarded; on successful completion of said transmitting steps; transmitting by the master node, to the first and second node frames, causing the nodes to switch to the first mode of operation, where frames of all types are accepted; and transmitting by the master node, to all nodes capable of initiating information transfer, of a second frame type cancelling said second error information.

Claim 4

A method as claimed in any preceding claim wherein said error recovery method further comprises the steps, prior to switching one or both of said first or second nodes to said second mode of operation, of: retransmitting by said first or second nodes, to the respective other node, of the frames being transmitted when an error was detected; checking whether said retransmitted frame is received without error by said respective other node; and if said retransmitted frame is received without error, terminating the error recovery method.

Claim 5

A method as claimed in any preceding claim wherein said first error information identifies that an asynchronous event has occured on one of the ports of the node from which the first error information is transmitted.

Claim 6

A method as claimed in any preceding claim wherein said error information identifies that a link state change has occurred.

Claim 7

A method as claimed in any preceding claim further comprising: on a first node detecting the addition of a third node to a port on said first node; switching the first node from a first to a second mode of operation wherein frames of the first type are discarded by the node at all of its ports and frames of the second type are accepted by the node at any of its ports; transmitting by the first node, to the master node, of a second frame type containing first error information; transmitting by the master node, to the third node, of a second frame type containing the unique identity of the master; on successful completion of said transmitting steps; transmitting by the master node, to the first and third node, frames, causing the nodes to switch to the first mode of operation, where frames of all types are accepted; and transmitting by the master node, to all nodes capable of initiating information transfer, of a second frame type containing the unique identity of the third node.

Claim 8

A method as claimed in any preceding claim wherein said link is a serial link.