This paper reviews the evolution of routing mechanisms in IBM's Systems Network Architecture (SNA) since its inception in 1974 to the present. Routing mechanisms are related to changes in the application and communications environment. Also discussed are possible evolutionary paths that may be taken in the future to address the problems of large heterogeneous networks. This paper traces the evolution of SNA routing from adsiract, but no other portions, of this paper may be copied or distributed royalty free without further permission by computerpresent and speculates on possible directions that republish any other portion of this paper must be obtained from may be taken to meet future needs. In addition to the Editor. _the introduction Of the architecture in 1974 to the based and other information-service systems. Permission to IBM SYSTEMS JOURNAL,

Recent technological advances have increased the size and number of teleprocessing networks as well as broadened their scope and complexity. This added size and complexity has magnified the need for communications network management. One approach to communications network management is to provide centralized control which is integrated into the Systems Network Architecture user network. This approach is described in this paper by focusing on two program products that provide centralized operator control and problem determination capabilities for a network.

Problem determination on a Systems Network Architecture network has dealt mostly with error detection on physical network components. Adequate logical error-detection mechanisms associated with the logical network (software-related) errors have been only recently provided with the announcement of a new on-line interactive package called the Network Logical Data Manager (NLDM). This paper discusses the physical and logical network environments, logical network problems, and functions provided by the two releases of NLDM for logical problem determination. This paper first describes in more detail the differences between the physical and logical networks and how they intersect. Next it discusses the difficulties associated with logical problem determination and how NLDM can be used to aid in identifying logical @Copyright 1983 by International Business Machines Corporation. Copying in printed form for private use is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract, but no other portions, of this paper may be copied or distributed royalty free without further permission by computerbased and other information-service systems. Permission to republish any other portion of this paper must be obtained from the Editor.

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