Filter
Equipment that allows the transmission of a specific frequencies, attenuating or excluding others.

Firewall
Equipment used in computer networks which protects an internal network from the external access by non-authorized users.

Frequency
The number of times a signal oscillates, under a given period of time, normally one second, measured in Hertzs, (Hz), kiloHertzs (kHz) or, MegaHertzs (MHz).

Facsimile
A communication service that allows the reception of texts and graphics identical to the original. The original document is analysed point by point at the sender terminal by a device for scanning. The equipment is usually referred to as Fax.

Fault
Any error related to the equipment or an element of the telephone installation.

Frequency Band
Section of the spectrum of frequencies used for a specific purpose, like radio and television transmission

Frequency Band Amplitude
Extension of a frequency band, that is, the difference between the highest and the lowest frequency of a signal for transmission of voice, data and information, generally expressed in kilohertz (kHz) or megahertz (MHz).

Facilities of Service
Set of facilities of service to be provided regularly and at the request of the subscriber.

Fixed Telecommunication Services
Telecommunication services with access through fixed terminals.