International Business Machines Corporation

Alan E Baratz

Diane Phylis Pozefsky

James P Gray

Lee M Rafalow

George A Grover

Melinda R Pollard

John E Drake, Jr

Andrew Hilliard Arrowood

Inder Sarat Gopal

Mark Pozefsky

William E Siddall

Kathryn E Clarke

John L Eisenbies

Philip F Chimento, Jr

Jeffrey M Jaffe

Karla J Norsworthy

Jean A Lorrain

Enhanced type 2.1 nodes for SNA networks provide network routing of information between non-adjacent network nodes and program-to-program linkage across the network. These nodes are called 'advanced peer to peer networking' (abbreviated APPN) nodes. Network state information, describing the topology and resources of the network is disseminated betweeen APPN nodes by a first data link control exchange of identification (XID) information indicating node type (and thereby distinguishing APPN nodes from other nodes) and other exchanges conducted over a newly defined control point to control point (abbreviated CP--CP) session having a message architecture unique to APPN type nodes. The XID exchange is conducted whenever a link between nodes is activated, and when the exchanging nodes are both APPN, and if both are available to participate in as CP--CP session, they automatically engage in a second exchange of session binding signals which establish a pair of sessions between the nodes. By internal conventions, the node components which use the session pair for exchanging their network state information adapt the sessions to be used in simplex modes with one session flowing from one node to the other and the other flowing in reverse from the other node to the one node. Within these sessions, for the sake of efficiency, communications are not directly acknowledged. Instead, a process transparent to the sessions monitors for link failure and upon such occurrence notifies all affected components to terminate their use of the session and deactivate the session.

Node initiating XID exchanges over an activated link including an

In a computer network a logical duplex session between control points of adjacent network nodes is comprised of two physical half duplex sessions. Each half duplex session includes the send session of one node and the receive session of the adjacent node. In the event of a session failure at either node, the session from the other node is also deactivated so the nodes may begin recovery in phase with each other. Unique messages are exchanged between the adjacent nodes to distinguish new from old messages, such that the nodes are resynchronized only when new messages are present on each session.

Control point session synchronization in a network

A LOCATE search dynamically locates resources (e.g., logical units (LUs) and transaction program and files associated with LUs) in a computer network so that a session can be established between the origin and the destination of the search. In a network which includes end nodes associated with server nodes, a resource contained in any node is located by a requesting node. The requesting node initiates a search of the resources residing within itself. If the resource does not reside in the requesting node, the server node searches the resources known to the server node that reside anywhere in the nework. If the resource is not known by the server node, it searchers all resources that reside in its associated end nodes. If the resource does not reside in the associated end nodes, either a request is sent to a central directory if one exists or a search of all resources in the network is made.

Locating resources in computer networks

When computing a least weight path from an origin node to a destination node in a data communication network, a route-computing network node uses information provided by the origin and destination nodes to compute least weight routes from those nodes to adjacent network nodes. The route-computing network node uses information in the topology database to compute least weight routes from network nodes adjacent the origin node to network nodes adjacent the destination node. The results of the computations are concatenated to determine an optimum route from the origin node to the destination node. The topology database need not include information about the transmission groups connecting the origin/destination nodes to network nodes.

Method for selecting least weight end node to end node route in a data

Each network node in a communications network maintains its own copy of the network topology database defining network resources. Each resource record contains a 'timer' field which is initially set to a maximum value but which may be decremented on a daily basis. If the timer field is decremented to zero without being reset, the node unilaterally removes the resource record from its copy of the database. The timer field will normally reach zero only for obsolete resource records since each network node responsible for a resource broadcasts a timer-resetting message for the resource (1) each time the resource status changes, (2) when the node first joins or rejoins the network, and (3) on a periodic (weekly) basis regardless of whether conditions (1) or (2) have occurred.

Method of maintaining a topology database

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Chappaqua, NY, United States of America

Alan E Baratz