Pathway/iTS TCP and Terminal Programming Guide

Designing Your Application
Compaq NonStop™ Pathway/iTS TCP and Terminal Programming Guide—426751-001
2-19
Clients Using RSC/MP
•
Write nested servers, which act as requesters by making requests to servers in other
server classes, perhaps server classes managed by a different PATHMON process.
•
Write context-sensitive servers (servers that retain information about the processing
of previous requests).
Pathsend procedure calls give you more flexibility than WRITEREAD calls for server-
to-server communication. The application gets all the advantages of server classes,
including advantages not readily available with WRITEREAD; for example, load
balancing, adjusting the number of servers to fit response-time requirements, and
configuration and operations management. You can use the Pathsend procedure calls in
C, C++, COBOL85, Pascal, and TAL programs.
The Pathsend procedures and the LINKMON process, however, do not provide
multithreading, fault tolerance, device configuration, or operations management for
requesters. Therefore, if you need these capabilities in a Pathsend requester, you must
provide the programming for them.
In addition, Pathsend procedure calls that send messages to server classes must be
protected by the TMF subsystem to ensure data integrity in your Pathway application.
The Pathsend procedures and the LINKMON process do not support the checkpointing
of Guardian interprocess message synchronization IDs. This lack of checkpointing
support is an important consideration when writing fault-tolerant requester programs
that do not use the TMF subsystem.
For more information about designing and coding Pathsend requesters, refer to the
NonStop™ TS/MP Pathsend and Server Programming Manual.
Clients Using RSC/MP
The RSC/MP product facilitates client/server computing, allowing workstation
applications to access Pathway server classes and Guardian processes. This product
supports a number of different transport protocols and workstation platforms. For
detailed information about the supported platforms and protocols, refer to the Compaq
NonStop™ Remote Server Call (RSC/MP) Programming Manual.
Transactions are transmitted from the workstation application (the client) to a Pathway
application running on a Compaq NonStop™ Himalaya system (the server) by means of
a supported communications protocol, such as NETBIOS, TCP/IP, or an asynchronous
connection.
RSC/MP includes a process called the Transaction Delivery Process (TDP), which
resides on the NonStop™ Himalaya system. The TDP is a multithreaded process that
can handle multiple workstations. It routes request messages from workstations to
Pathway server classes by using either the Pathsend API and the LINKMON process or
the terminal control process (TCP) provided in the Pathway/iTS product. If the TCP is
used, it can route a request message to a Pathway server by using either the intelligent
device support (IDS) requester supplied as part of RSC/MP or an IDS requester that you
develop yourself. The TDP can also send request messages from a workstation to a
Guardian process.