The protocol seems to be using all numbers. Are they really communicated in ASCII representation? That means for example the number "123" is not sent as binary 123, but sent as "&H31", "&H32" and "&H33" since that is the way ASCII are used to represent numbers for human to read easily.
Does the protocol use Carriage return to terminate a command and response string? If so, you can easily use the PRINT #n command to send the command and INPUT$(n) to read the response. Of course for INPUT$(n) you may need to put in a loop until you read a returned string or the loop times out.
You can also use the NETCMD$ command (with "~" termination so that it doesn't append the FCS to the string) and the best way is to look at the I-70xx example where we use the NETCMD$ to talk to I-70xx which have their own custom protocol. You can find the examples in the usr\samples\I-7000\ folder.