TSID stands for “transmitting subscriber information.”
When a fax is sent, data from TSID is sent along with the fax. TSID contains both the fax machine’s name as well as the phone number where it is connected.
TSID information is often printed on a header on the fax document along with date and time of the transmission. A fax machine receiving a fax can record TSID information to its logs.
TSID records can be compared with phone call records to authenticate a transmission at a later date.
In today’s terminology, it is a type of metadata that accompanies a fax transmission.
TSID is programmed into a fax machine. If the fax machine moves locations or changes fax numbers, the older TSID information will be sent with faxes until it is updated.
In some models of fax machine, if power is interrupted to the machine, TSID will need to be reprogrammed.
It is not necessary to include TSID in a fax, however, it is considered a “best practice.”