Nodes and Digipeating

First you need to understand how the connected packet 'conversation' takes place between two TNCs. It goes like this (in a much simplified example):

Stn 1 to Stn 2: "Here is packet 1"

Stn2 to Stn 1: "Received your packet 1"

Stn 1 to Stn 2: "Here is packet 2"

Stn2 to Stn 1: "Received your packet 2"

Stn 1 to Stn 2: "Here is packet 3"  <-- Now let's assume some QRM hits.

Stn2 to Stn 1: "Packet not received"

Stn 1 to Stn 2: "Here is packet 3"  <-- This time it gets through

Stn2 to Stn 1: "Received your packet 3"

etc.

Every packet is acknowledged or re-sent until it's acknowledged, or the link 'Times Out'.

Time Out - If a packet is repeated too many times, usually about 10, then the TNC assumes the link is broken and issues a hard disconnect, ending the session.

Digipeating

Now let's assume that Stn 1 can't hear Stn 2, but can hear Stn 3, which hears both. Using the digipeat function built in to most TNC's a intermediate receiving station will automatically sent packets onwards to the final station. That conversation goes much like this:

Stn 1 to Stn3: "Here is packet 1 for Stn 2"

Stn 3 to Stn 2: "Here is packet 1 from Stn 1"

Stn 2 to Stn 3: " Packet 1 received"

Stn 3 to Stn 1: " Packet 1 received"

etc.

This uses 'end to end' acknowledgements. Only the end stations give Acks.

If Stn 1 doesn't get the acknowledgment, it will automatically retry the packet until it gets the ack or times out. Stn 3 will not automatically retry the packet. It does so only upon receipt of another try from Stn 1. It works fine if the paths are fairly good.

Digipeating is excellent for setting up ad-hoc packet networks, so should be understood for ARES purposes. It doesn't require any special gear. Your regular TNC will do it!

The Connect command for digipeating would be:

C VA3PB VIA VE3FOX. - This tells VE3FOX that it is being asked to forward packets from my station to VA3PB. If there were more hops required, they would be added to the list. (e.g. C VA3PB V VE3FOX, VE3WKJ)

The longer the chain, the more chance of packets being missed along the way.

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Nodes

The use of Nodes is a much more elegant way of achieving multiple hop communications. One of the primary differences between linking from a node vs. linking via digipeating is that Nodes use Station to Station acknowledgements. The conversation would look like this:

Stn 1: Connect to Node

Connection made

Stn 1: Now connect to Stn 2

Connection made

...

Stn 1 to Node: "Here is packet 1 for Stn 2"

Node to Stn 1: "Packet received - I will relay it" <-- that is the ack for packet 1

Node to Stn 2: "Here is packet 1 from Stn 1"

Stn 2 to Node: " Packet 1 received"

Although this looks similar to digipeating, having Node send Stn 1 the ack right away improves channel usage. If there is a breakdown in the link somewhere, only those two stations need to repeat the packet, instead of the whole thing starting over as with digipeating.

Nodes often have extended features built in, like Talk functions which allow several station to talk to each other. They maintain node lists showing where they are capable of connection onward. Here is a sample node list from the VA3BAL node.

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Nodes and Frequencies used in the GTA West

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