It used to work, but after some HW changes I cannot get an image accross from the DSLR device to the client. I can see it pumping for 10-20 seconds and then the indi server -vv output says:

The last two data bursts and then the shutdown.
Platform is Ubuntu Wily on an RPi2. Client program is latest CCDCiel on a Windows PC.
Does anybody have a suggestion?
Also out of curiosity, is the indi protocol UDP based? In other words, what happens when a packet gets lost?

You need to run INDI server with -m argument and set it to some large value, like 100 (100MB) or 500 so that it doesn't stop if there is a large blob queued to the client

Thanks, that did the trick.
The FITS of 36MB apparently is expanded by converting it to text (?) Normally about a factor 2, which probably just about made it work with the default 64MB queue (sometimes).

The other question is, how are these large binaries actually transferred to the client? It takes over 6 minutes for a single image, so even taking into account the conversion to text that is long on a high speed network. Do you know how to improve on that?

It looks like you're starting indiserver in full verbose mode which spits out the complete BLOB on the terminal, don't do that unless you're debugging something!! Just start indiserver with '-v' or even without one. All binary data are base64 encoded before they are sent to client. You can try to enable image compression under image settings and see if that makes a difference.

Related to that, does compression affect the actual data, or is it decompressed on arrival?

Certainly: the full verbose was to see why the connection was dropped.
I will try image compression as well, thanks for the tip.