Volume One, Issue Three, Phile 3 of 10
Signalling Systems Around the World
For those of you who have the desire to make international calls, this info may
be of interest. Thanks to TAP and Nick Haflinger.
- CCITT 1.
- An old international system, now deceased. Used a 500 Hz tone
interrupted at 20 Hz (Ring) for 1-way line signals.
- CCITT 2.
- Proposed "International Standard" that never caught on much.
Used 600 Hz interrupted by 750 Hz. Still used in Australia,
New Zealand and South Africa.
- CCITT 3.
- An early in-band system that uses 2280 for both line and
register (!!). Used in France, Austria, Poland and Hungary.
- CCITT 4
- A variation of 3, but uses 2040 and 2400 for end to end Tx of
line and register. Used for international Traffic in Europe,
but cannot be used with TASI (AKA Multiplex or "that dammed
- CCITT 5
- This is the most popular, and the one used in the US. 2400 and
the infamous 2600 are used for link to link (not merely end to
end line signals. Registers are handled via DTMF (Touchtones).
Anyone know what 2400 does??
- CCITT 5 bis.
- Just like above, but a 1850 Hz tone is used for TASI locking
and transmission of line signals.
- CCITT 6
- The newest and worst for phreaks. It uses digital data sent
out-of-band to control the connection. In other words, the
connection is made and billing started BEFORE you can get
- CCITT 5R1
- A regional system like 5, but doesn't use the mysterious 2400
and can't use the multiplexer.
- CCITT 5R2
- Probably the interface to AUTOVON, as it uses 120 Hz spaced
tones for DTMF instead of 200. Also 3825 Hz is the blow-off
tone instead of 2600.
The "Extra" tones
1700 + 700 = Inward Operator
1700 + 900 = Delay operator, also, in TSPS,STP (a "Zero Plus"-
call from a coin phone)
1700 + 1100 = KP1 (Start recognition of special tones)
1300 + 1700 = KP2 (End recognition of special tones)
12-85 Data Line. CIS 72767,3207: TWX 650-240-6356