Pulse dial
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Revision as of 00:53, 1 January 2014
Most analogue telephone adapters are intended for push button tone dial use, as the tones can be generated natively by all new telephones.
Most subscribers use recent-model handsets to get features such as call display.
There are, however, still a few old 'phones in use which generate dial pulses. Many are intended to look as if they belonged to another era for decorative purposes or may even be legitimate antiques - such as three-slot coin 'phones from the 1950s or candlestick 'phones from the 1920s.
A few 1980s phones look like they offer the standard tone keypad, but keypresses are turned into pulses internally. There are also a few old alarm panels which dial using pulses only.
There are a few options to keep this equipment working when switching to VoIP.
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Analogue telephone adapters
A very small number of analogue telephone adapters support pulse dial:
- Grandstream HandyTone 502 - HT502 has been reported by third-party sites to recognise the pulses, although this feature is not officially documented and appears to have been removed from the later HT702 series. [1][2]
- Grandstream GXW4216/GXW4224/GXW4232/GXW4248 also support pulse as of firmware version 1.0.4.15; [3] these are 16-line (or greater) analogue telephone adapters and aimed primarily at the enterprise PBX market
In general, there is no support for pulse dial on standard Cisco (Linksys/Sipura) boxes, which are the most common adapters. There may be a few small manufacturers who support both pulse and tone in some of their devices, but options are limited.
Autodiallers
In the early days of competitive long-distance, access to alternate carriers required that subscribers dial a local number, a lengthy code and then a destination number to use an alternate long distance provider - much in the same manner as one calls using prepaid long distance cards today. For some business customers, the long distance providers placed a box in the line which would accept pulses or tones, translate the number to send trunk calls to the alternate carrier, then dial out using tones.
These devices are rare (and difficult to configure) but a few are still extant as mail-order surplus.
Pocket diallers
These were small, battery-powered devices which could be held to the handset's microphone; they had a power switch and the standard 12-button tone keypad. These were used mostly to access voicemail (remote playback on answering machines) or interactive voice response systems.
In the 1980s and 1990s these were carried by local electronics dealers such as the Radio Shack chain, but they're becoming harder to find as most new 'phones can be switched to generate either pulses or tones natively.
Pulse to tone converters
These are currently manufactured for a niche market of old 'phone collectors who want to keep the telephone instrument itself historically accurate. Rotary dial appeared in the Bell System in 1919 and tones only became an optional extra (at an added monthly charge) in 1967, so nostalgia and tones don't mix. Devices like www.oldphoneworks.com/pulse-to-tone-converters/ are circuit boards with a small microprocessor wired to the analogue line to listen for the pulses and sends the corresponding tones.
PBXes
Private branch exchanges for office telephones vary widely in their support for rotary dial telephones. Many simply don't work at all with any standard 'phone, pulse or tone, as they're designed for whatever handsets came with the system. Others may be tone-only or (if they were manufactured long ago) pulse only.
Some Asterisk PBX installations run on desktop-style computers to which cards have been added to connect to individual telephones. The Zapata TDM400 card is one option to add FXS ports on which pulse dial may be enabled (set pulsedial=yes in zapata.conf) although some of the other settings (such as debounce) may need to be adjusted to get this to work.
Ringdown
If all else fails (perhaps because a telephone is a pre-1920s model with no dial at all, from a manual system where picking up the earpiece caused the local operator to ask "Number, please?") one last resort is to configure the analogue telephone adapter so that picking up the handset automatically reaches one pre-set number. No dial, tones or pulses required. A dial plan like <:123-456-7890>S0| (on Linksys ATAs) will dial out to the one predefined number as soon as the telephone is taken off-hook.
