PORT necessary for each FTP RETR

Question

When downloading data over FTP, is it necessary to issue a PORT command before each RETR, or would it be legal to

PORT 165,82,22,48,133,72
RETR /1.txt
RETR /2.txt

Answer 1

The answer is yes. (example is not legal)

< PORT 165,82,22,48,133,72
> RETR /1.txt
> RETR /2.txt
< 425 Use PORT or PASV first.