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IMS Version 9 Support for z/OS Sysplex Distributor

A look at the new functionality.

A look at the new functionality.

IMS*, IBM's hierarchical database-management system, continues to improve its availability and performance with enhancements specifically designed for z/OS* Sysplex Distributor. This article explores some of those enhancements made available with Version 9 as well as an overview of some IMS functionality and a look ahead to what we can expect next for IMS.

z/OS Communications Server Sysplex Distributor

Sysplex Distributor, a feature of z/OS Communications Server, is IBM's strategic solution for balancing TCP/IP connections across multiple z/OS servers in a Parallel Sysplex*.

Sysplex Distributor uses a dynamic virtual IP address (DVIPA) to present to external network clients a single IP address for all participating servers in a Parallel Sysplex. The single IP address and the internal distribution of incoming TCP/IP connections within the Parallel Sysplex allows multiple instances of a server application program to appear as a single instance to the client applications. The client applications are unaware that they are connected to any server other than the server on which the primary Sysplex Distributor function resides.

The Sysplex Distributor can distribute new TCP/IP connections to different servers in the Parallel Sysplex based on a variety of criteria, including:

  • The current availability of the various instances of the server application program
  • The current workload of the TCP/IP stacks and the servers themselves
  • A Quality of Service (QoS) policy maintained by a Service Policy Agent
  • A round-robin distribution strategy that distributes incoming connections evenly among the participating servers

Sysplex Distributor further ensures high availability (HA) by performing automatic takeover and take back functions between a primary Sysplex Distributor on one z/OS image and a backup Sysplex Distributor on another z/OS image. In the event of a failure, client applications lose their connections, but they can immediately reconnect through the backup Sysplex Distributor.

The Sysplex Distributor is a key element of the HA, scalability and performance of the TCP/IP support provided by z/OS Communications Server.

In addition to z/OS Sysplex Distributor, the super member solution supports the WebSphere Edge Components Load Balancer and the z/OS DNS/WLM Connection Optimization function.

Ben Johnson is an IBM information developer. He has been writing about IMS since 2003, focusing on both IMS database administration and IMS communications and connections, with a particular interest in OTMA and IMS Connect. He can be contacted at

Jack Yuan is a senior software engineer for IMS development. He can be contacted at

Leilei Li is a development team lead for IMS On Demand solution at IBM's Silicon Valley Lab. Leilei can be reached at



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