Protocols and standards
TSI
Acronym: TSI
The TSI is the identifier the sending fax machine announces to the recipient during negotiation, normally its fax number, up to twenty characters long.
It is the counterpart of the CSID, which the called machine sends back: each machine introduces itself to the other. The recipient shows it on screen, records it in its reception log and may print it on the pages received. Like the CSID, it is entered by the machine's owner and checked by no one.
Why it matters for fax
The TSI tells you who probably sent a fax you received, and nothing more: it may be blank, wrong or deliberately false. It therefore replaces neither the caller number supplied by the network nor proof of sending kept by the sender.