RoundTrip & Flood

RoundTrip and Flood are two basic Hello World style Demonstrators.
A simple message is send around toward several (network) nodes. Typically, each node runs on a dedicated Raspberry-Pi. As DDS is network-agnostic; multiple nodes can run on the same computer. By example, on a PC/Laptop, which is great for demonstration and an easy start.

A standard setup is shown below, where 4 nodes are used; a trivial variations is to have more or less nodes
One node is called “master”, as it starts the roundtrip; and executes the measurements. The other nodes are called “hub” and have the same functionality; the “links” are set by configuration.

title “Default setup with 4 nodes” !include ../../_inc/class-as-Node.iuml class Master << (N, Aqua)>> #Aqua/CornflowerBlue class Hub_1 << (N, Aqua)>> class Hub_2 << (N, Aqua)>> class Hub_3 << (N, Aqua)>> Master -right-|> Hub_1 : Topic_0 Hub_1 -down-|> Hub_2 : Topic_1 Hub_2 -left-|> Hub_3 : Topic_2 Hub_3 -up-|> Master : Topic_3 note as N1 Here the <i>functional</i> message-flow is shown, not actual flow! As “DDS-messages” are *not* directed to a node. end note note as N2 This can be implemented by giving each links a (topic)Name; and subscribe to the “incoming” name and publish on the “outgoing” name. Those topic/names are typically specified at start-up, as command-line options. end note N1 .. N2

The difference between ‘RoundTrip’ and ‘Flood’ is how fast and in which order the message are processed.

Demonstrator: RoundTrip RT_001 ../../_images/arrow-right-circle.svg
status: import
tags: RT
links incoming: RT_PY_01c, RT_Cpp_01c, RT_C_01c

In RoundTrip only one message is send around at the same time. The ‘Master’ starts a the sequence by sending one message (by example: “0”). And the receiving hub forwards it; often trivially changing it (in the example: by adding “1” to the incoming message).

Only when the ‘master’ receives the message (let’s say “3”), it send a new message. In the example, that would be “4” (3+1). And the sequence starts again.

After an configured number of roundtrips, the master stops sending/forwarding; and the demo is over.
Demonstrator: Flood F_001 ../../_images/arrow-right-circle.svg
status: import
tags: F
links incoming: F_PY_01c, F_Cpp_01c, F_C_01c

In Flood the ‘hub’ works exactly as in RoundTrip (RT_001): it receives a message and forwards it. Typically, the message is changed by adding a hub-specific postfix (by example the hub-number)

The ‘master’ differs however: it does NOT wait for an incoming message to send the next message. Instead it sends all message as fast as possible.

Still, the ‘Master’ has to read the incoming message; but can dispose them; reading should have a higher priority the sending!