Re: USB (or Serial) vs Ethernet: Which is better or more reliable?

Dale Ghent

Hi, Peter

I'm not quite sure what you mean by "trust" here. The protocol spoken to and by your mount is comprised of very short ASCII character sequences - nothing like bulk binary data like which you'd see from your two cameras (main and guider). If you're already running USB to your pier for your other accessories, the mount isn't going to amount to much else in terms of perceived instability. It, like a focuser or filter wheel, has a very simple protocol with exceedingly low bandwidth requirements. USB will handle it fine.

It will note, however, that 35 feet for a USB run is *double* the maximum length specified by the USB 2.0 spec, as the maximum length in order to maintain USB 2.0 Hi-speed (480Mbits/s) is 5 meters, or a smidge over 16 feet. In this case, I wouldn't be surprised if the run between your computer and the hub you have on your pier has fallen back to USB 1.1 Full-Speed speeds of 12Mbits/s. Obviously, since you're imaging, that would be or is sub-optimal. You low-bandwith devices such as mount and focuser will still be fine, but downloading images off your cameras will be slower than it should.

You have 2 options in that case:

1. Get an Active USB 2.0 extension cable, also known as repeater cables. The throw distance on these are far greater than the 5 meter limit of USB 2.0. Examples can be seen here:

2. Move your PC physically closer to your pier in order to cut down cable length. I reckon that you would have done this already if you were able to, but it bears mentioning that small x86/x64 computer systems in industrial chassis are pretty ubiquitous now and are small enough that that can live *on* the pier itself. Running windows and file share services on it, you can remote desktop into it and use SMB file shares to offload photo data over an existing 802.11 or hardwire ethernet network.


On Sep 15, 2018, at 2:47 PM, [ap-gto] <> wrote:


Now that Ray Gralak has created a Beta version of A-P V2 ASCOM driver to include Ethernet connection, I am wondering whether it's more worthwhile to switch from USB2 to Ethernet?

Currently, I have a powered USB2 hub velcroed to CP4 and use 35 feet USB active extension cable between laptop and USB2 hub and the outputs of USB hub connect to the following:

1) CP4 (1 foot cable)
2) Optec Focus Boss II auto focuser hub (1 foot cable)
3) QSI 660wsg CCD camera (6 feet cable)
4) Ultrastar auto guider (6 foot cable)

This current setup has worked great and so far no issues or disconnection of any kind.

If I use Ethernet to control CP4 and Optec Focus Boss II auto focuser hub, I will have to velcro a 5 port Ethernet switch to USB hub and use another 35 feet Ethernet cable in between laptop and Ethernet switch. I have personally tested latest A-P V2 ASCOM driver with Ethernet and Ethernet switch and works very well.

My question is, do you trust Ethernet more than USB2 for controlling CP4 as well as Optec Focus Boss II auto focuser hub? I am not interested in high speed transmission because the bandwidth is very low. I have read that more people prefer or trust Ethernet than USB2? Does Ethernet have less overhead in protocol than USB2? Do you think Ethernet is more reliable than USB2? I know one advantage of Ethernet is very long cable can be used like at least a 100 feet but that will never happen to me.



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