Introduction to Packet Radio - Part 4
Using Digipeaters and Nodes
by Larry Kenney, WB9LOZ
Digipeaters
Digipeater is the term used to describe a packet radio digital
repeater. Unlike the FM voice repeaters, most digipeaters operate on
simplex and do not receive an transmit simultaneously. They receive the
digital information, temporarily store it and the n turn around and
retransmit it Your TNC can be used by others as a digipeater if you have
the command DIGIPEATER turned ON.
You use a digipeater by entering its callsign after a V or VIA in
your connect sequence. Here are some examples of proper connect sequences:
C W6PW-3 V WB9LOZ-2; C N6ZYX V WA6FSP-1, WD6EOB-3; C W6ABY-4 V K6MYX,
N2WLP-2, AB6XO. In the example, the sequence shown means; Connect to
W6PW-3 via the WB9LOZ-2 digipeater.
Your TNC will allow you to enter up to eight digipeaters in your
connect sequence or in your UNPROTO path, but using more than 3 usually
means long waits, lots of repeated packets and frequent disconnects, due
to noise and other signals encountered on the frequency.
When entering the list of digipeaters in your connect sequence,
you must make sure that you enter them in the exact order that your signal
will use them. You must separate the calls by commas, without any spaces,
and the EXACT callsigns must be used, including the SSID, if any. That
means you need to know what digipe aters are out there before you begin
randomly trying ti connect to someone. Turn MONITOR ON and watch for the
paths that other stations are using.
Something to remember when using digipeaters is the difference
between making a connection and sending information packets. If the path
isn’t all that good, you might be able to get a connect request through,
but will have a difficult time with packets after that. The connect
request is short so it has much less of a chance of being destroyed by
noise or collisions than a packet containing information. Keeping
information packets short (PACLEN set to 40 or less) can help keep retries
down when the path is less than ideal.
Nodes
Net/Rom, TheNet, G8BPQ packet switch and KA-Node are names that
refer to a device called a packet node. This is another means of
connecting to other packet stations. Later on in this series you’ll find a
complete review of node operation, but now we’ll c over the basics so that
you can begin to use the node network. The difference between a digipeater
and a node that you should note here is that you connect to a node rather
than using it in a connect path as you do with a digipeater. Some packet
stations are set up so that they can be used as a digipeater and a node.
First, you need to determine what nodes are located close to you.
You can do this by monitoring and watching for an ID, or by watching to
see what other stations in your area are using. It is most common for a
node to have an alias IN in addition to its callsign. Once you determine
the callsign or alias of a local node, you connect to it the same way as
you connect to any other packet station. You may use either the callsign
or the alias to make the connection. For example, the node I operate has
the alias ID of BERKLY and the callsign of WB9LOZ-2, so you could connect
to it using C BERKLY or C WB9LOZ-2. Either one will work.
When you connect to a node, your TNC automatically switches to
converse mode, just like when you connect to any packet, and acknowledges
each packet back to your TNC. For the remainder of your connection your
TNC works only with this one node. To use the node network to connect to
another local station, you simply co nnect to the node and then enter a
connect request to the other station.
Say you wanted to connect to K9AT using WB9LOZ-2 node. You first
connect to WB9LOZ-2 (C WB9LOZ-2) and then, while you ARE STILL CONNECTED
TO THE NODE, you enter the connect request to K9AT (C K9AT). The node will
then retransmit your connect request and you’ll receive one of two
responses: "Connected to K9AT" or "Failure with K9AT". Once you are
connected you hold your QSO just as if you had connected direct or via a
digipeater. When your QSO is finished, go to command mode on your TNC
(Control C) and enter "D" (CR) and you will be disconnected from the node
and the station you are working. (Note: If the node you're using is a
G8BPQ packet switch, it might have several frequency ports.) You'll have
to enter a port number between the C and callsign in your connect request
to indicate the frequency you want to use, such as: C 2 K9AT. (Enter
"PORTS" for a list of the frequency ports).
Node Network
The packet nodes work together to form a packet node network. Once
an hour each node transmits a list of other nodes that it knows about. The
neighborin nodes use this information to keep track of the other nodes in
the network. We will discuss how al l of this works later on in the
series.
When you're connected to a node you can enter: NODES (or N) [cr]
and you'll receive list of other nodes that you can reach on the network
from the nod you're using. You'll note that the node list will vary in
length and in the calls listed as you move from frequency to frequency,
since all frequencies are not linked together. The list gives both an
alias ID and a callsign for each node. The alias ID often gives you a hint
as to where the node is located, but not always. To find out for sure
where a node is located you'll need a copy of the descriptive node listing
that are available on most packet bulletin board systems. These complete
lists give the alias, calling, location, frequency and other information
on each node in the network.
To connect to a station in another area using the node network,
you first must determine which node is closest to the station you want to
work.
For demonstration purposes, let's say we want to connect to N6XYZ.
He's told you he uses the W6ABC-3 node, so you check the node list and see
that GOLD:W6ABC-3 is listed. WHILE YOU ARE STILL CONNECTED TO YOUR LOCAL
NODE you connect to the distant node by sending a normal connect request,
in this case C GOLD or C W6ABC-3. Your TNC will send this as a packet to
your local node and your local node will acknowledge it. The network will
then go to work for you and find the best path between your local node and
the one you're trying to reach. Remember, with digipeaters you needed to
know the exact sequence of stations. With nodes you don't. The network
does that for you.
You might have to be a little patient here, since it sometimes
takes a few minutes for the connection to be completed. Don't type
anything while you're waiting for a response because any new information
received by your local node will override any previously entered
information. When the network has completed its work you'll receive one
of two responses: "Connected to W6ABC-3" OR Failure with W6ABC-3. If it
can't connect for some reason, try again later. It could be that W6ABC-3
is temporarily off the air or the path has decayed and is no longer
available. We're going to be positive here and say we received the first
option.
Once you're connected to W6ABC-3, enter "C N6XYZ". Again, your TNC
will send this as a packet to your local node and the local node will
acknowledge it and send it down the path to W6ABC-3. W6ABC-3 will then
attempt to connect to N6XYZ. Here again you'll get one of the two
responses: :Connected to N6XYZ" OR "Failure with N6XYZ". If you get
connected, you hold your QSO just as you normally would, but there's one
BIG difference, your TNC is receiving acknowledgements from your local
node, and N6XYZ is receiving acknowledgements from W6ABC-3. The
acknowledgements do not have to travel the entire distance between the two
end stations. Each node in the path handles the acknowledgements with the
next node in line. Because of this, retries are greatly reduced, and your
packets get through much faster than using a similar number of
digipeaters.
When you're finished with the QSO, you disconnect in the normal
manner, go to Command Mode on your TNC and enter "D"[cr]. The entire
path will then disconnect automatically for you. Nodes offer a variety of
other features besides allowing you to connect to other stations. We'll
look at those and go into much more detail on the packet networks in parts
10 and 11 in this series
Courtesy of N0KFQ
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Newsletter "SMARCalling" April 1998
