Availability Guide for Problem Management

Problem Management Tools
Availability Guide for Problem Management–125509
9-21
How NSAN Works
A status message stating that “I am alive” status packets have stopped arriving indicates
that one of the controller pair has a problem. TLAM can determine whether the problem
lies in the controller receiving or sending the status messages by noting whether the
media packets are still being received. TLAM also monitors the state of the controller
and the channel controls for signals of failure.
Automatic Switching to Alternate Plan
Using the information from the controllers, TLAM maintains the status of its current and
alternate paths to the network. If TLAM detects a failure of its current path, it switches
to the alternate path. If TLAM detects a failure of both paths, it sends an operator
message notifying the system administrator of the failure.
NSAN is described in the NonStop Access for Networking System Note.