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The Three-Tier Architecture
• Allows performance or geographic expansion while protecting
the investments made in existing hardware and application
software
The router tier contains no application software unless running
callout servers. This tier reduces the number of logical network
links required on frontend and backend nodes and helps ensure
good performance even in an unstable network. It also decouples
the backend tier from the frontend tier so that configuration
changes in the (frequently changing) user environment have
little influence on the transaction processing and database
(backend) environment.
The three-tier model can be mapped to any system topology.
More than one role may be assigned to any particular node. For
example, on a system with few frontends, the router and backend
tiers can be combined in the same nodes. During application
development and test, all three roles can be combined in one
node.
The nodes used by an application and their configuration
roles are specified using RTR configuration commands. RTR
lets application code be completely location and configuration
independent.
RTR Facilities Bridge the Gap
Many applications can use RTR at the same time without
interfering with one another. This is achieved by defining a
separate facility for each application. A facility can be thought of
as an application network.
For example, when an application calls the C++ API
RTRFacilityManager to manage a channel or the C API
rtr_open_channel( )
routine to declare a channel as a client or
server, it specifies the name of the facility it will use.
Refer to the HP Reliable Transaction Router System Manager’s
Manual for information on how to define facilities.
Architectural Concepts 2–3