Fax switch
A fax switch , also called Fax Soft or fax switch called, is either passive or active device on analog telephone lines . With incoming calls, the fax switch distinguishes between telephone calls and fax transmissions at the beginning of the connection and routes them to the correct terminal . A fax switch is used when several terminals, such as telephone , fax machine and answering machine , are operated on one connection or are integrated in a facility. Fax switches evaluate the calling tone (CNG) of 1100 Hz during the first few seconds of the call, which is fed in by a fax ready to send.
In-band signaling
This type of information transmission is called in-band signaling and in this application has the disadvantage that the detection can only be carried out during the existing telephone connection. To distinguish, the pending call must first be accepted, which means that the caller incurs connection charges from this point in time.
Types of fax switches
Active switch
An “ active fax switch ” initially accepts the incoming phone call silently, without a phone ringing. Either a pseudo ringback tone or an announcement ( "Please wait" ) is transmitted to the line. If the fax switch detects regular CNG tones within the next few seconds, the call is forwarded to the fax machine for reception. If no CNG tones are detected, the call is transferred to the phone, which then starts to ring.
Passive crossover
A “ passive fax switch ” waits for an incoming telephone call for the call to be accepted by another device (telephone, answering machine). Only when this has started the call does the switch monitor the connection to see whether CNG tones can be heard in the first few seconds of the call, in order to disconnect the call from the telephone / answering machine and transfer it to the fax machine for reception in this case.
With today's all-in-one devices consisting of fax, printer, copier and scanner, a passive fax switch is usually built in and can be configured via a PC interface. z. B .:
Answer incoming calls:
- Manually
- If fax tones are recognized (means switch on passive fax switch)
- Always after [1–10] ring signals
Advantages and disadvantages
While the active fax switch enables "silent fax reception", it causes additional costs for every caller, since he has to pay for the "examination time". In particular, if no answering machine is connected, the caller only pays for "ringing". The active switch is therefore suitable for connections that receive a lot of faxes, but hardly any phone calls.
The passive switch means that the phone rings with every call - phone call as well as fax. If it is a call, this fax switch does not affect it. When a fax arrives, the person called (or the answering machine) first hears the CNG tones of the calling fax machine. He has to wait for this. The switch switches after about five to 10 seconds, only then may the telephone receiver be replaced. The passive switch is therefore suitable for connections on which more calls are received than faxes.
Additional extensions
Different extensions of the fax switches are marked by the manufacturers with the attribute "intelligent". This includes, for example, "automatic switching between active and passive switch, depending on the user's call acceptance behavior" (Siemens Telfax), "passive fax switch that intercepts the call for incoming calls of less than 10 seconds and always tries to receive a fax" , "day / Night switching between active and passive turnout " , " passive turnout up to the umpteenth ring tone and then active turnout " and any combination thereof.
Current uses
External fax switches are rarely used; not at all with new connections, as the technology is considered out of date. With current telephone connections, which offer several independent telephone numbers, fax switches are not necessary, since a connected fax machine is assigned its own telephone number.
Web links
- www.simple-fax.de exemplary configuration tips for a device (PDF file; 24 kB)