Ring-back tone characteristics

Ring-back tone characteristics
The ring-back tone is different in various countries depending on the requirements for the ring-back specification in those countries. The ring-back signal may be generated by the called-party servicing switch(S-MSC) or by the calling-party switch (O-MSC), but it is not generated by the called telephone instrument. It is generally started and stopped at the same rate as the ringing signal itself but perhaps out of phase.

[edit] United Kingdom and the Commonwealth
In the UK and many other Commonwealth countries, it is a signature double beep. For most countries, it consists of a 0.4-second pulse, a 0.2-second pause, a 0.4-second pulse, and a 2-second pause.
In some countries the pulse is made by mixing a 400 Hz and 450 Hz sine wave. This tone has been made famous by being included at the end of Pink Floyd's "Another Brick in the Wall (Part 2)" and "Young Lust".
In others, and until the 1990s in the UK on the now obsolete ETACS analogue mobile phone networks the tone is comprised of a single frequency tone of 425 Hz or 450 Hz, generated at the same cadence. This tone is used on the telephone networks of Malaysia and Singapore.

[edit] Personalized ringback tone