Availability Guide for Application Design

Availability in the Pathway Transaction-Processing
Environment
Availability Guide for Application Design—525637-004
6-13
How Does RSC/MP Work?
On the workstation:
•
The client process uses the RSC/MP application program interface to establish
connections and sessions with the Transaction Delivery Process (TDP) on the
server system and to send requests through the TDP to server processes.
•
The communications subsystem (CSS) supports multiple Transmission Control
Protocol/Internet Protocol (TCP/IP), Failsafe TCP/IP, NETBIOS, or asynchronous
communications lines to provide communication between the client workstation
and the HP server.
On the server:
•
The TDP controls message flow and provides a gateway between the client
process and the server process.
•
NonStop TS/MP works with RSC/MP by managing communication between the
TDP and the server class as it would for any Pathsend application. Refer to
Availability Through Pathsend on page 6-18.
•
RSC/MPCOM is the system administrator’s command interface to RSC/MP for
configuring and controlling the RSC/MP subsystem.
The TDP is multithreaded, providing message control to several clients. In Figure 6-4
on page 6-12, the TDP is shown as a Pathsend requester, converting RSC/MP
procedure calls to Pathsend procedure calls, Guardian procedure calls, or Transaction
Management Facility (TMF) procedure calls. For example, an RSC/MP write to the
server is converted to the equivalent Pathsend call and passed to NonStop TS/MP
through the Pathsend interface.
The following sequence shows the skeletal outline of a typical RSC/MP application
when operating normally. Familiarity with this sequence will be helpful in understanding
the recovery requirements and procedures described later in this subsection. The
RSC/MP function calls for C are shown in parentheses.
1. The client process makes a request to the communications subsystem to establish
a connection with the server system (RscConnect() function).
2. The communications subsystem establishes the connection with the TDP and
returns to the client, which now has a connection to the TDP.
Note. This discussion focuses on Pathsend interprocess sessions, which is the recommended
way to access a Pathway server class from an RSC/MP client.
A TDP process can also act as a front end to an intelligent device support (IDS) requester
managed by a TCP. The IDS program contains the requester logic, while the TDP handles the
protocol with the client. Such a design is inherently less efficient than the Pathsend interface
because it uses more interprocess messages and executes interpreted code rather than
compiled code.
The TDP can also provide message control between an RSC/MP client process and a
Guardian process by converting RSC/MP procedure calls into Guardian procedure calls and
TMF procedure calls.