RSC/MP Programming Manual

8 Unsolicited Message Service
This section describes how to use the Unsolicited Message Service (UMS). Included
are examples of code that show how to send and receive messages.
Unsolicited Messages
The UMS lets host applications send messages to workstation-based applications. An
unsolicited message, originated by a host program, is routed by the TDP to the proper
workstation session. The TDP uses the terminal name, an alias name, and an alias
type to identify the recipient of an unsolicited message. The host program provides the
TDP with this information in a header that accompanies the UMS message.
You can use either of these host procedures to send messages:
The Guardian WRITE procedure to send messages to the workstation.
The Guardian WRITEREAD procedure to send messages to the workstation and
get a reply. When expecting a reply from the workstation, you must specify a
terminal name, an alias name, and an alias type. RSC/MP provides aliases that let
users address UMS messages to a particular workstation, to all workstations, or to
a named group of workstations (see Aliases and UMS on page 8-3).
Figure 8-1 shows the flow of messages from the NonStop system to the workstation
using the Guardian WRITE and WRITEREAD procedures.
To send an unsolicited message, a Guardian process opens the TDP process and
sends it a UMS request message (see Figure 8-1). The TDP forwards this UMS
message to the workstation. The workstation must be connected and have an active
RSC/MP session.
The UMS can be used concurrently with RscWrite or RscWriteRead I/O initiated by
RSC/MP clients.
HP NonStop Remote Server Call (RSC/MP) Programming Manual — 522360-006
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