Sending fax works - Need however advice

Hi,
I use a call file to send a fax.
Sending the fax works but I get the fax with an unknown sender.
What can I add to the call file so the receiver of the fax will see who is the
sender?

Also: What is the meaning of the string caller?
(I tried to modify it to caller ID but it did not work)

Call file:
Channel: Zap/3/www1815XXXXXXX
MaxRetries: 1
WaitTime: 20
Application: txfax
Data: /var/spool/asterisk/fax/faxdoctest.tif|caller

Thanks

Solution: Set within the call file the LOCALSTATIONID:

Set: LOCALSTATIONID=xxxyyyyyyy