For determining the bandwidth via FTP...there is no specific command to isolate b/w part. But if the rate of b/w ( upload & download) is to be ascertained thru the link, u can host an ftp server at your end (if u r acting as the provider) and ask him to upload & download file to this server from users source end.
This could be used by using ftp commands :: get 'filename" & put 'filename".
get and put r the commands and substitute filename with the actual name of the file intended for transfer.After the transfer is done...you can see speed of upload and download in KBytes.Multiply this figure by 8 and u get the throughput in Kbits/sec.
Pls rate/mark if this helps!!!