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NAME

ltpclock - LTP daemon task for managing scheduled events

SYNOPSIS

ltpclock

DESCRIPTION

ltpclock is a background "daemon" task that periodically performs scheduled LTP activities. It is spawned automatically by ltpadmin in response to the 's' command that starts operation of the LTP protocol, and it is terminated by ltpadmin in response to an 'x' (STOP) command.

Once per second, ltpclock takes the following action:

First it manages the current state of all links ("spans"). In particular, it checks the age of the currently buffered session block for each span and, if that age exceeds the span's configured aggregation time limit, gives the "buffer full" semaphore for that span to initiate block segmentation and transmission by ltpmeter.

In so doing, it also infers link state changes ("link cues") from data rate changes as noted in the RFX database by rfxclock:

If the rate of transmission to a neighbor was zero but is now non-zero, then transmission to that neighbor is unblocked. The applicable "buffer empty" semaphore is given if no outbound block is being constructed (enabling start of a new transmission session) and the "segments ready" semaphore is given if the outbound segment queue is non-empty (enabling transmission of segments by the link service output task).

If the rate of transmission to a neighbor was non-zero but is now zero, then transmission to that neighbor is blocked -- i.e., the semaphores triggering transmission will no longer be given.

If the imputed rate of transmission from a neighbor was non-zero but is now zero, then all timers affecting segment retransmission to that neighbor are suspended. This has the effect of extending the interval of each affected timer by the length of time that the timers remain suspended.

If the imputed rate of transmission from a neighbor was zero but is now non-zero, then all timers affecting segment retransmission to that neighbor are resumed.

Then ltpclock retransmits all unacknowledged checkpoint segments, report segments, and cancellation segments whose computed timeout intervals have expired.

EXIT STATUS

  • "0"

    ltpclock terminated, for reasons noted in the ion.log file. If this termination was not commanded, investigate and solve the problem identified in the log file and use ltpadmin to restart ltpclock.

  • "1"

    ltpclock was unable to attach to LTP protocol operations, probably because ltpadmin has not yet been run.

FILES

No configuration files are needed.

ENVIRONMENT

No environment variables apply.

DIAGNOSTICS

The following diagnostics may be issued to the ion.log log file:

  • ltpclock can't initialize LTP.

    ltpadmin has not yet initialized LTP protocol operations.

  • Can't dispatch events.

    An unrecoverable database error was encountered. ltpclock terminates.

  • Can't manage links.

    An unrecoverable database error was encountered. ltpclock terminates.

BUGS

Report bugs to <https://github.com/nasa-jpl/ION-DTN/issues>

SEE ALSO

ltpadmin(1), ltpmeter(1), rfxclock(1)