Roon RAAT and "An audio file is loading slowly"

[daniel.avasilichioaei]

Some more observations:

It looks like the variation in network traffic is all down to the TCP flow carrying audio from Roon to the Devialet (as expected).  There is UDP in both traces but at a similarly low frequency in both - I guess this is probably the Devialet discovery protocol (as used for AIR).

As I said in my previous post, the TCP flow at 100 Mbps looks very clean with no re-transmissions.  After things settle down, Roon is consistently sending super-jumbo frames of about 60 KB each.  The round-trip time is very stable - about 6 ms almost all the time, with very occasional peaks upto about 15 ms.

At 1 Gbps there are lots of bursts of duplicate ACKs from the Devialet and re-transmissions from Roon.  This suggests frames are frequently being lost en route.  The round-trip time is also (consequently) much more variable, with peaks up to 800 ms, and the frame size is much smaller on average (1.5 - 2.5 KB by eye).  The most likely cause is that either the Ethernet hardware on the Devialet is running out of receive buffers or (less likely, I'd say) the application software on the Devialet isn't handling the input fast enough.

It looks as though the Devialet is advertising a larger receive window at 1 Gbps than at 100 Mbps (~1 MB vs ~ 0.4 MB).  Maybe that is significant.

As far as I can see, the variation in network flow from Roon to the Devialet is because the traffic is stopping and starting due to the presumed missing packets.  Because the flow is carried in much smaller frames, there is a higher protocol overhead which will tend to increase the overall network throughput.  Also, the smaller average frame size accounts for the much higher level of "back-traffic" because there are many more ACKs coming back from the Devialet for a given volume of data sent to it.

There must surely be some hints in here about what's causing the problems with Devialet/Roon RAAT at 1 Gbps.  I am suspicious about the higher advertised window size at 1 Gpbs and wonder whether the Devialet is asking for more incoming data than it can actually handle - that is, without dropping frames.

Thanks again for sending the traces, @daniel.avasilichioaei.  If I get chance to do any more analysis I'll add further notes here.

Thank you very much for your work!
I'm not sure I fully understand your investigation, but to me it seems that most probably the issue is on Devialet side (not on Roon side). Am I right?

P.S.: On my configuration, the issue is the same (at least his effect), no matter if connection is Roon Core - Devialet [i]directly or via router.[/i]