One of the reasons why TCP/IP is so popular is that there are many simple and useful standard applications available. The TCP/IP on VSE/ESA for example provides standard applications such as Telnet, FTP, LPR/LPD and the HTTP Web server.

Using these standard TCP/IP applications and standard TCP/IP APIs for user written applications also allows an easy migration from one TCP/IP platform to another.

The VSE products on which the following migration discussion is based are TCP/IP for VSE/ESA 1.3 (which comes with VSE/ESA 2.3) and TCP/IP for VSE 1.3 from Connectivity Systems Inc..

The migration target system is OS/390 R3 with TCP/IP OpenEdition, OS/390 V2R4 with TCP/IP UNIX Services or the soon to come OS/390 V2R5 with eNetwork Communications Server for OS/390 V2R5 which includes TCP/IP.

All the standard TCP/IP applications such as Telnet, FTP, LPR/LPD or HTTP that are available with TCP/IP on VSE are also part of TCP/IP on OS/390. Since, generally speaking, TCP/IP functions on VSE are a subset of those on OS/390, migration from TCP/IP for VSE to TCP/IP on OS/390 can be accomplished without loss of functionality in most cases.

The topics you should look into if you want to migrate from a TCP/IP for VSE environment to TCP/IP on OS/390 include:

network attachments and definitions required to communicate with other TCP/IP systems

TCP/IP configuration

TCP/IP related user data

your TCP/IP batch jobs

your own TCP/IP based application programs

TCP/IP security.

In the next sections each of these topics will be addressed at a general level. No detailed checklist or migration guidelines are provided. This would go beyond the scope of this documentation. The purpose of this discussion is to make you aware of the areas which need to be studied in detail when you intend to migrate.

9.4.1 Network Definitions

The connectivity/network attachments supported by TCP/IP on OS/390 is a superset of what is supported by TCP/IP for VSE. This is why your networking environment basically does not have to be changed. However, since OS/390 TCP/IP supports more communication interfaces, your network can be changed or extended for example by an IBM 3746 attachment.

As on VSE/ESA, all the network attachments to be used by TCP/IP have to be defined to the OS/390 operating system first. The network attachments (for example CTCA, IBM3172, OSA-2) need to be defined before they can be specified in the TCP/IP configuration.

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IBM OS/390 manual Network Definitions

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.