Telecom Dictionary - Definitions of terms

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Fax Switches - Definition and Use

Fax Switches - Fax switches are devices that automatically route fax, modem or voice calls over a single phone line to the correct device. It listens for a signal and if it is present, it routes the call to the fax machine, fax/modem, fax/printer or other device which will receive a fax transmission.

When a fax machine dials a number and the line answers, it emits an 1100Hz signal (CNG tone) to identify itself. These "fax tones" are the most popular and economical way to automatically route calls to the fax machine over a shared line. This type of product is know as a tone detection device.

Tone detection fax switches "listen" for these tones then automatically route the call to the fax if they are present. Some devices handle data modem switching as well. Modem calls are routed by DTMF (touch) tones placed in the dialing string from the connecting modem software. These extra digits are known as the security access codes (SAC)s. Tone detection devices require no additional services from the phone company to operate.

The second type of fax switches is called a "distinctive ring" device. Instead of using tones to detect the calls, this type uses a phone company feature called "distinctive ring." to automatically route the incoming calls to the proper device. In order to use a distinctive ring fax switch, you must subscribe to distinctive ring service from your local phone company. Distinctive Ring is one of the many other services that local phone companies offer such as call waiting, caller id, voice mail, call forwarding, three-way calling or any of the other features. The phone companies charge between $2.50 to $5.00 a month for the distinctive ring service.

Phone companies have different trade names for distinctive ring such as "ring master", "personalized ring", "smart ring", "selective ringing" and similar names but generically it is called Distinctive Ring. When you subscribe to distinctive ring, the phone company issues you another phone number but not another phone line. It is like a party line for your home or business.

Distinctive ring fax switches takes it one stage further. When anyone calls the primary phone number only the phones (and/or answering machine) would ring. When the distinctive ring number is called, only the phones or devices associated with it ring. In a business application, typically one phone number for your voice and another for your fax number. When anyone calls the voice number the calls automatically ring the phones just like without the switch. But when anyone calls the distinctive ring dedicated fax number, those calls always go to the fax or fax/modem. Each device has its own number but you only pay for one phone line.

Since the need for to subscribe to a separate"fax line" from the local telephone company is eliminated, the return on investment (ROI) is very high. The initial cost of the device is returned in savings in a few months. After that you will save the monthly bills associated with fax, data or voice lines. For almost every business, telephone line sharing technology is a smart investment.