Availability Guide for Change Management

Availability Guide for Change Management–125506
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5
Making Communications
Subsystem Changes Online
Overview
In the Tandem environment, a software product that provides users with access to a set
of communications services is called a communications subsystem. Because
connectivity is an important part of online transaction processing (OLTP), Tandem offers
a variety of communications products. These products extend the OLTP power of your
NonStop system by supporting a wide range of application and networking
configurations.
Making changes to a communications subsystem can involve adding new
communications lines or devices to accommodate business growth, connecting new
systems to the network, or reconfiguring certain attributes.
This section provides information to help you reduce or eliminate planned outages by:
•
Identifying common communications subsystem changes that you can perform
online. An Online change is any change that can be performed while your
NonStop system is still operational. In some situations, online changes may
temporarily affect application availability.
•
Describing the tools you can use to make communications subsystems changes
online.
•
Telling you which manuals contain communications subsystem change information.
Overview of Communications Subsystems
Communications subsystems vary in the functions they provide and in the resources they
manage. Many subsystems allow applications to communicate with specialized devices;
a few subsystems exist to perform management services or to provide management
interfaces to other communications subsystems.
The part of a Tandem communications subsystem that runs in the NonStop system is
implemented as one or more processes. A communications subsystem usually consists
of system and user processes provided by Tandem. The system processes that make up a
communications subsystem are called input/output (I/O) processes. To understand
how changes are made to communications subsystems, you first need to understand how
Tandem I/O processes work.
I/O Processes
I/O processes manage communication with I/O devices, such as disks, printers, or—in
the case of communications subsystems—communications lines. An I/O process pair
logically “owns” one or more I/O devices or communications lines. The devices or lines
are physically connected to the system through a ServerNet addressible controller
(SAC); the I/O process pair runs in the pair of processors to which the SAC is attached.