Dial tone, ringback and busy signals by country
The sounds the telephone network makes before a modem ever speaks: dial tone, ringback and busy, country by country. Frequencies and cadences come from the ITU-T E.180 list of national tones.
United States
| Dial tone | 350 + 440 Hz, continuous |
|---|---|
| Ringback | 440 + 480 Hz; 2 / 4 s |
| Busy | 480 + 620 Hz; 0.5 / 0.5 s |
| G.711 law | μ-law |
Canada
| Dial tone | 350 + 440 Hz, continuous |
|---|---|
| Ringback | 440 + 480 Hz; 2 / 4 s |
| Busy | 480 + 620 Hz; 0.5 / 0.5 s |
| G.711 law | μ-law |
United Kingdom
| Dial tone | 350 + 440 Hz, continuous |
|---|---|
| Ringback | 400 + 450 Hz; 0.4 / 0.2 / 0.4 / 2 s |
| Busy | 400 Hz; 0.375 / 0.375 s |
| G.711 law | A-law |
E.180 lists the UK dial tone as 350+440 Hz (BT literature often quotes 350+450 Hz).
Germany
| Dial tone | 425 Hz, continuous |
|---|---|
| Ringback | 425 Hz; 1 / 4 s |
| Busy | 425 Hz; 0.48 / 0.48 s |
| G.711 law | A-law |
France
| Dial tone | 440 Hz, continuous |
|---|---|
| Ringback | 440 Hz; 1.5 / 3.5 s |
| Busy | 440 Hz; 0.5 / 0.5 s |
| G.711 law | A-law |
Japan
| Dial tone | 400 Hz, continuous |
|---|---|
| Ringback | 400 Hz × 16 Hz; 1 / 2 s |
| Busy | 400 Hz; 0.5 / 0.5 s |
| G.711 law | μ-law |
Japanese ringback is 400 Hz modulated by 15–20 Hz (E.180 "400x(15~20)"); we use 16 Hz at 50 % depth.
Australia
| Dial tone | 425 Hz × 25 Hz, continuous |
|---|---|
| Ringback | 400 + 450 Hz; 0.4 / 0.2 / 0.4 / 2 s |
| Busy | 425 Hz; 0.375 / 0.375 s |
| G.711 law | A-law |
Australian dial tone is 425 Hz modulated by 25 Hz (E.180 "425x25"); 50 % depth is our assumption.
Reading the table
"350 + 440 Hz" means both tones at once; that pair is the North American "precise tone plan" dial tone. "× 25 Hz" means the tone is amplitude-modulated at that rate, which E.180 writes as 425x25. Cadences are on/off times in seconds: the UK's 0.4 / 0.2 / 0.4 / 2.0 is the familiar double ring.
Our source is the ITU's Various tones used in national networks (according to ITU-T Recommendation E.180), position on 1 May 2010. Where it lists alternatives we pick the first modern entry. One disagreement worth knowing: E.180 gives the UK dial tone as 350 + 440 Hz, while BT's own literature quotes 350 + 450 Hz. We follow the ITU list.
The "G.711 law" row matters for 56k modems: North America and Japan use μ-law, most of the rest of the world A-law, and a V.90 server tells the home modem which one in its INFO0d. Every handshake on this site uses the law of the country you pick.
DTMF digits are the same everywhere: one of four row tones (697, 770, 852, 941 Hz) plus one of four column tones (1209, 1336, 1477, 1633 Hz), per ITU-T Q.23.