Compaq Reliable Transaction Router Getting Started page 29

RTR Server Types
channels within a single process or as one channel in separate
processes.
Figure 1–17 Concurrent Servers
BE
Server1
Server2
Server3
A-N
Server4
LKG-11275-98WI
The callout server provides message authentication on
Callout server
transaction requests made in a given facility, and could be used,
for example, to provide audit trail logging. A callout server can
run on either backend or router nodes. A callout server receives
a copy of all messages in a facility. Because the callout server
votes on the outcome of each transaction it receives, it can veto
any transaction that does not pass its security checks.
A callout server is facility based, not partition based; any
message arriving at the facility is routed to both the server
and the callout. A callout server is enabled when the facility is
defined. Figure 1–18 illustrates the use of a callout server that
authenticates every transaction (txn) in a facility.
To authenticate any part of a transaction, the callout server must
vote on the transaction, but does not write to the database. RTR
does not replay a transaction that is only authenticated.
Introduction 1–19