Abap code for Transferring data to a file (presentation server)

REPORT CHAP2603.
* Data declarations for later use
PARAMETERS FILENAME(128) DEFAULT 'c:\users\default\testfile.dat'
LOWER CASE.
TABLES CUSTOMERS.
DATA ALL_CUSTOMERS LIKE CUSTOMERS OCCURS 100
WITH HEADER LINE.
* Get data for file transfer

SELECT * FROM CUSTOMERS INTO TABLE ALL_CUSTOMERS.
SORT ALL_CUSTOMERS BY CITY.
LOOP AT ALL_CUSTOMERS.
WRITE: / ALL_CUSTOMERS-CITY,
ALL_CUSTOMERS-NAME.
ENDLOOP.
* Transferring Data
CALL FUNCTION 'WS_DOWNLOAD'
EXPORTING
FILENAME = FILENAME
TABLES
DATA_TAB = ALL_CUSTOMERS
EXCEPTIONS
FILE_OPEN_ERROR = 1
OTHERS = 2.
CASE SY-SUBRC.
WHEN 1.
WRITE 'Error when file opened'.
EXIT.
WHEN 2.
WRITE 'Error during data transfer'.
EXIT.
ENDCASE.