Kantronics KPC–3 Plus User Manual page 21

Let's assume that an originating station, WØXI, wants to send the message ―HELLO‖ to
a destination station, KBØNYK. Also, assume that WØXI knows that his signal might not
reach KBØNYK's station directly, but that it can be picked up and repeated by an
intermediate station, NØGRG, and then received by KBØNYK.
The following are the basic steps of a station-to-station packet communication, as seen
from the point of view of the message, ―HELLO,‖ sent from source station WØXI to
destination station KBØNYK, through intermediate station NØGRG. Step 1 is one-time
configuration task, Steps 2-3 establish a connection between stations, and Steps 4-13
follow the ―HELLO‖ message from the time it is created by WØXI to when it is read by
KBØNYK.
Step 1. Before this message can be transmitted from a source station to a destination
station, via an intermediate station, all the stations involved have to have
callsigns, which are used by the TNCs involved to identify and process
information (e.g., source, destination, and routing of information).
So we start by assuming each operator involved in this example has already
performed this one-time configuration task, creating the callsigns given
above. Stations are identified by reference to their callsigns. Note that a
callsign can be for a TNC (e.g., KPC-3 Plus) or for a Personal Bulletin Board
System (PBBS) ―mailbox‖ that resides in RAM inside the TNC.
Step 2. This communication begins when the operator of station WØXI turns on his
computer, TNC (e.g., a KPC-3 Plus), and transceiver of his station and uses a
computer software program to tell the TNC that he wants to establish a line of
communication, called a ―connection,‖ with a ―destination‖ station KBØNYK
using an intermediate station NØGRG as a repeater station to carry the
information beyond the range of the originating station and into the range of
the destination station.
The ―connect‖ command with address given to the TNC causes the TNC to
Step 3.
formulate a ―request to connect‖ message that is sent from WØXI. If this
message is detected by the specified intermediate station (i.e., NØGRG),
repeated, and then detected by the destination station (i.e., KBØNYK), a
connection may be established.
To confirm a connection, the destination station automatically sends a special
message back though the reverse path, to the originating TNC.
When this ―confirmation of connection‖ is processed by WØXI's TNC, the
TNC assumes that the operator wants to begin sending messages. So the
TNC: (1) puts a message on the computer monitor confirming that WØXI is
now connected, through intermediate station NØGRG, to KBØNYK, (2) turns
ON the ―connected‖ indicator on the TNC, which stays ON as long as the
connection is in effect, and (3) switches itself from taking commands from the
computer (i.e., TNC in ―command mode‖) to serving as a message-processor,
sending and receiving messages to and from the connected stations (i.e.,
TNC in ―conversation mode‖).
21