Chapter 12
!
0
In even the most basic networks, all messages must arrive at their intended des-
tinations without errors, and each node must respond only to those messages
intended for it.
For example, assume that Node A wants to send a message to Node B, telling
Node B to set a port to a value and to send back a value read from another port.
In a typical serial network, all of the following must take place:
Node A does the following:
Enables its network driver.
Sends the address of the node to transmit to.
Sends the message.
Disables the network driver and waits for a response.
Node B does the following:
Reads incoming data.
Detects the node’s address.
Reads the message associated with the address.
Detects when the message has ended.
Takes the requested action.
Prepares a response.
Enables the network driver.
Sends the response.
Disables the network driver.
Node A then does the following:
Reads the response.
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 communica-
tions. Three types of network protocol are primary/secondary, token passing,
and collision detecting.