Network printer trouble

Hello,

I have installed 2 printers on an air****t switch (I plug either one 
since there is only on connection available).

With the Epson printer, it can print (however, I have to disconnect and 
then reconnect the network to print a second document).

With an HP Deskjet, I can't make it working. I have done the same 
process than for the Epson. Is there anything I should be aware of? A 
difference between HP and Epson?

The online help tells me I must use the "IPP protocol using HTTP" and 
the ****t 1631. Also, the printer model is not in the list (I have a F380 
series and the only similar model I found in the list is the 340 
(neither "series" or "F" is in the name)).

I tried without the ****t number (maybe it is the default?) and with the 
"generic HP deskjet" "ppd" file (I don't know from where it comes).

Any advice welcome!