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The Three-Layer Model
Figure 2–1 The Three Layer Model
DB
BE
Server
BE
Server
TR
FE
Client
FE
Client
FE
Client
DB
Terminals
Frontends (FE) Routers (TR)
Backends (BE)
Database (DB)
DB
FE
Client
TR
BE
Server
ZKO-GS011-99AI
• Allows performance or geographic expansion while protecting
the investments made in existing hardware and application
software.
The router layer contains no application software unless running
callout servers. This layer reduces the number of logical network
links required on frontend and backend nodes. It also decouples
the backend layer from the frontend layer so that configuration
changes in the (frequently changing) user environment have
little influence on the transaction processing and database
(backend) environment.
The three layer 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
frontend layers 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.
2–2 Architectural Concepts