DESCRIPTION AND OPERATION
NIS MODULE
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I-E96-607A
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TIME SYNCHRONIZATION
The time synchronization message is a high priority broadcast
type of message. The NIS module services this message type
immediately. Time synchronization provides a common system
time base for sequencing exception reports, and accessing
trend data for display on a system console.
MULTICAST
A message that contains data for multiple destinations is a
multicast message. This message can have one to 64 destina-
tions.
NIS POLL
The NIS poll is a single destination message. The NIS module
uses this message type to poll the operational status of another
node.
Message Format
Messages exist as frames of information. Each frame consists
of a message control field that follows an information field. The
information field contains the message data. It can consist of
multiple messages and vary in size to a maximum of 1,500
bytes. The control field contains time of origination, source
node message sequence number, source node number, size,
circulation count, message type, destinations and checksum.
The NIS module increments the circulation count field of all
incoming messages. When a message count field reaches 256,
the message is discarded. This is useful in keeping retry and
spurious message traffic to a minimum. The NIS module uses
the message type to determine how to process the message.
The checksum and CRC fields verify data integrity.
Message Transmission
Any NIS module can transmit a message at any time regardless
of the activities of other NIS modules on the system. Each NIS
module can transmit and receive messages simultaneously.
NIS module start-up and shutdown is local and requires no
interaction with other NIS modules on the INFI-NET loop. Each
NIS module receives all incoming messages and transmits a
new stream of messages in a store and forward fashion to the
next node. When there are no messages for the NIS module to
transmit, the NIS module transmits flag characters (null pack-
ets) as the loop synchronizing condition to keep the receivers in
lock.