Envoy Configuration and Management Manual

Configuration Quick Start

Envoy Configuration and Management Manual—429861-001

1-7

Reconfiguring Existing Communications Lines

Once the process exists in the configuration database (as a DEVICE object) and you

start the process by using START DEVICE, you can start, stop, and change the

associated line OBJECT’s attributes directly through the Envoy subsystem. (You can

also start, stop, and change the DEVICE object in the WAN subsystem.)

You must consider the scope of line attribute changes. To change a line attribute and

have it remain intact even after the system has been cold-loaded, issue an SCF ALTER

DEVICE command specifying the altered modifier to the WAN subsystem. (See

Table 1-2

for a summary of line attribute modification persistence.)

Once the various lines have been characterized, you interact with them by issuing

Guardian 90 file-system procedure calls. You first open (activate) each line by calling

the OPEN procedure. Once the line is opened, you use WRITE calls to transmit data and

READ calls to accept incoming data. You can also use other file-system procedures such

as WRITEREAD, CONTROL, SETMODE, DEFINELIST, CHANGELIST, AWAITIO,

and so on. When you have finished using a line, you close (deactivate) that line by

calling the CLOSE procedure. For information on file-system procedures, refer to the

Envoy Application Programming Manual.

When Guardian 90 passes I/O requests to application programs, an Envoy I/O process

acquires the necessary system buffer space, monitors the state of all open lines for which

it is responsible, and returns completion status (and data for read operations) to the

application process.

Figure 1-1

shows the flow of SCF commands to the Envoy subsystem. For more

information about using SCF to change line attributes, see Section 4, Subsystem Control

Facility (SCF) for Envoy.

Example 1-4. Starting the Line

-> START LINE $ENV01

Table 1-2. Persistence of Line Attribute Changes

Change Method

Persistence

SCF commands to the WAN subsystem. Changes persist until you change the

DEVICE and/or the PROFILE object in the

WAN subsystem.

SCF commands to the Envoy subsystem. Changes persist until you change the

attributes, change the modifiers in the

PROFILE, stop the DEVICE in the WAN

subsystem, or until the system is cold-

loaded.

Guardian procedure calls from an

application program to the Envoy

subsystem.

Changes persist only during the application

session.