rosserial how to link two desktops?

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Hi, I have two desktop machines, separated by physical distance but linked by serial ports (null model connection). I would like to use rosserial to send ROS messages between them. But the rosserial docs are all focussed on linking one embedded device such as Arduino to one desktop. Can anyone advise on whether its possible between two desktops and if so how to set this up?

Edit: Some more background on this.

I was expecting to be able to set up something like two instances of roscore, one running on each machine. The each machine would run a rosserial node that would send and receive specified messages over the serial link. But all I'm seeing in the docs are special cases of running things like Arduinos as single nodes in the ros network, not running their own local ROS computations and networks. I would like to do this as for this application (robot a long radio distance from base) I need some computation happning on the robot itself and other parts of it at base, with only a low bandwidth serial radio link between them.