Coba jelasin Fault tolerance dari Sentral telepon dalam bahasa sunda dong

Composite switches are inherently fault-tolerant.  If a subswitch fails, the controlling computer can sense it during a periodic test.  The computer marks all the connections to the subswitch as "in use".  This prevents new calls, and does not interrupt old calls that remain working.  As calls are ended, the subswitch then becomes unused.  Some time later, a technician can replace the circuit board.  When the next test succeeds, the connections to the repaired subsystem are marked "not in use", and the switch returns to full operation.

To prevent frustration with unsensed failures, all the connections between layers in the switch are allocated using first-in-first-out lists.  As a result, if a connection is faulty or noisy and the customer hangs up and redials, they will get a different set of connections and subswitches.  A last-in-first-out allocation of connections might cause a continuing string of very frustrating failures.