First, consider what might be needed to do the job of connecting one LAN to another. We talked about the fact that nodes "Talk" to each other, and that they know that other nodes exist, and what other nodes they can "talk" to. How is this done?
Well, nodes periodically "poll" each other to determine if a node is present, and how good of a communication path exists between them. They exchange a series of packets, and take note of the time that it takes a given node to respond in this exchange. A formula is used to calculate what is known as a "Route Quality" number. The higher the number, the better the "Route Quality".
Different route quality standards are used at different node baud rates. For example, a 1200 baud 2-Meter node may have a route quality of 192, and this is considered good. A UHF Node operating at high speed (9600 baud) may have a good route quality of 225. Nodes linked by wire on the same node stack will usually have the maximum quality possible of 255. Why is this important? Nodes use this information as a means to know how to route your packets through the network. How? Each node sends out a "Broadcast" to other nodes letting them know of other nodes it can reach, and of the route quality. A typical "Nodes Broadcast" may look like this:
KE9LZ-5>NODES UI Pid = CF
Nodes Broadcast de WIGRB:
#446GB N9CFN-4 via N9CFN-4 255
#APL4 KB9BYQ-6 via N9CFN-4 222
#446DC W9AIQ-9 via N9CFN-4 222
#446CR KE9LK-8 via N9CFN-4 222
WIMAR KE9LK-7 via N9CFN-4 200
WIDC W9AIQ-1 via N9CFN-4 200
#GRB4 via KE9PW-5 255
Now a look at the broadcast in a little detail. The top line looks pretty much like most packet "headers" on your monitor screen, with one exception. Notice that it says "PID = CF". This is the "Protocol Identifier". Remember when we talked about nodes speaking to each other in their own language? This is what is known as the "Net/Rom Protocol". This explains why most TNC's cannot interpret these broadcasts, and why you may have never seen them. The above sample came from the Green Bay node with an alias of WIGRB.
Each route that is broadcast consists of a node alias, followed by that node's call-sign, the route it uses to connect to it, and the route quality number. The first entry is a node that is connected by wire to the node, because it's route quality is 255 (the highest it can be). The second, third and fourth entries are nodes that are reachable through a high-speed UHF radio link, of good quality, 222. The fifth and sixth listings are of good quality also, reachable through a UHF link as well, but are wire linked to the high-speed nodes #446DC and #446CR. The last listing is - you guessed it - wire linked to this node.
. By now you may be wondering why we have bothered to learn this information, because you can't normally see the broadcasts. The answer to this is simple: You can see a portion of this broadcast by issuing the ROUTES or R command to a node you have connected to. You will not see all of the routes on the route table, only the ones that can be accessed directly by the node.
This is useful information. It not only tells you that there is a path to a node, but how good it is. Like the rest of radio, not all routes are reliable 100% of the time, and this allows you to determine how to make a long-distance connection. The "Routes" command is one of the more useful that can be givien to a node.
In the next installment, we will explore more of how a node works, and what commands you will find useful when you "Surf the Network".
On to Part 4 - Using the the Route Table on a node
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