HPunix 10.2 to Linux migrations

A GPU is meant to be used for the console...(local graphics), if you now have 20 XDMCP sessions then you will still need 20 X displays (each their own for XRDP), so you would need 20 Video adapters... i doubt you could even build a system like that.

X11 based software runs on the server, and only all graphics tasks are sent off to a remote display, and the mouse and keyboard are received from the remote display.
If you want to secure it you may need IPSEC tunnels or SSH sessions. There is NX from http://NoMachine.com    that doesn exactly that but also uses compression where needed (and useful) to restrict the data transmitted.

XRDP does nothing more then copy the X display to some remote system over RDP (comparable to VNC, but slightly better.
On a LAN XDMCP might still be best (requires yu to change less)
or replace it with NX.

Thank you for the information,

At the moment we are using a HPUNIX 10.2 system and we have 20 people using xdmcp sessions and the Hpunix system runs really well. In fact so well it is like running directly on the server.
I built a 4 CentOS 7 system and a Fedora 23 system with compression on with ssh and XDMCP using the same software to connect and it ran real slow.  In addition, this is for normal users and so the user should be able to just double click and go to a login screen.  

However, i set-up xrdp and it runs great, and circles around the XDMCP connections.  And if you are remote login from another state or country no problems, but my understanding it takes more load on the server vs XDMCP.  This is hard to calculate.  I was hoping someone else has as linux server and have several users logging into the same system to do some work and have a full GUI environment so that I can get an idea on what system to buy.

I have tried several systems to use xdmcp and the best one for performance and easy of use is MobaXterm, but still very slow with any newer system.

Be sure the Centos system has forward (A, CNAME)  & reverse (PTR) lookup setup in DNS correctly. DNS is working well. Check that interfaces are connected to a switch in FDX mode(and the switch is in FDX). If auto interfaces are involved, experiment with setting everything fixed (Speed, FDX).

Try NX, that optimises X protocol over anything, and if it is network related issues then (even allows reasonable access between remote systems accross classic modem connections (56Kbps).  
NX does a tad more then plain SSH for X over some remote connection. NX solves most of latency by collecting some packets and let them travel together.

X11 accross a long distance isn't a good use case in general due to latency (not bandwidth).

I believe we cannot use NX due to the cost, and Xrdp is free.
But I just installed and started to compare the two.

I am also do not want to get off topic, and the topic is to get new hardware.
10.2 HPUnix running J6000 vs CentOS 7 -64bit ???? not sure yet.

This might help (it is the precursor for NX).
http://www.vigor.nu/dxpc/

Thank you for all the support.

I tried XRDP and it worked really well but I could not find why it was not cleanly closing correctly (i.e still running in the background per a user).
However, MobaXterm did work very well.  We have an issue for Windows 10 it seems it would get stuck if left ideal for about 15 mins.

NOTE: I did migrate the HPUnix Agilent application to Linux 64 bit OS.