Takes any required action.
At the same time, all of the other nodes must do the following:
Read incoming data.
Detect the transmitted address and ignore the message associated with the
address.
The nodes in a network must agree on a protocol for managing communications.
Three types of network protocol are primary/secondary, token passing,
and collision detecting.
Network Programming
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A primary/secondary protocol, also called the master/slave protocol, is often the
least complex network protocol a network can implement. One computer is
designated the primary node in charge of controlling all network traffic. The
other computers are secondary nodes that respond to communications from the
primary node. A network might have a PC as the primary node and embedded
systems as secondary nodes.
To give each node a chance to communicate, the primary node can poll, or send
a message to, each of the secondary nodes in sequence. Each poll can request a
response, which might contain an acknowledgment, requested data, an error
message, or other information. A secondary node transmits only when the primary
node has requested a response. Any message from one secondary node to
another must pass through the primary node.
The main limitation of the protocol is the delays that occur as each node waits
to be polled. For a critical alarm system, waiting to be polled could be a problem,
while a data-acquisition system might tolerate long delays.
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