UDP writing/reading data?

Hello,

I am currently working on such a system:

• Windows PC with MATLAB/Simulink;
• Real-Time Linux system, where the compiled model of Simulink is uploaded and running every time;
• 5DOF robotic arm.

Between Windows PC and RTL there is an Ethernet cable, which allows communication through UDP protocol.

I am able to read the data from the robot on the Windows PC, using the following settings:

rhost = '10.1.64.97'; %this is RTL IP address
rport = 26000; %this port is on RTL
localPort = 1597; %this port is on WIN
echoudp('on', rport);
u = udp(rhost, rport, 'LocalPort', 'localPort');
fopen(u)
A = fread(u, 19, 'double'); % this is because I have 152 bytes I have to read, so 19 * 8 = 152

But now I would like to write the data, from the Windows PC to the robot (or to the RTL system first), and I don't know which ports to use as remote or local, nor which IP address I should use as rhost. Since I will use the function fwrite, I am guessing it could be something like this:

rhost = '10.1.64.97'; %this is RTL IP address
rport = 4012; %this port is on RTL
localPort = 2103; %this port is on WIN
echoudp('on', rport);
u = udp(rhost, rport, 'LocalPort', 'localPort');
fopen(u)
Data = zeros(25,1); % I need to send 200 bytes; 25 * 8 = 200
fwrite(u, Data, 'double');

However, this doesn't work, because if I close the u object and try to read out the data, it won't match (I added some constants to check if they eventually become zero, as I would expect them to).

Do you have any suggestions, or perhaps maybe just a good explanation WHAT is the remote host/port and what is the local host/port in my case??

Thank you!!