IPhone : Open the port 2221 in an iOS app

I am developing an iOS app that makes it as a FTP server. So, I want to enable the port 2221 (For the FTP protocol), as following:

[[NSNetService alloc] initWithDomain:@"" type:@"_ftp._tcp" name:@"FTP Server name" port:2221];

But it doesn't work when I try to connect to the app using FileZilla:

<ip_address>:2221

Any ideas?