HP 3390 Service Manual - Page 122

Fax functions and operation The following sections describe the all-in-one fax capabilities. PSTN operation The public switched telephone network (PSTN) operates through a central office (CO) that generates a constant voltage on the TIP and RING wires (48 V, usually). A device goes on-hook by connecting impedance (such as 600 ohms for the U.S.) across the TIP and RING so that a line current can flow. The CO can detect this current and can send impulses like dial tones. The all-in-one generates more signaling tones, such as dialing digits, to tell the CO how to connect the call. The all-in-one can also detect tones, such as a busy tone from the CO, that tell it how to behave. When the call is finally connected, the CO behaves like a piece of wire connecting the sender and receiver. This is the period during which all of the fax signaling and data transfer occurs. When a call is completed, the circuit opens again and the line-current flow ceases, removing the CO connection from both the sender and the receiver. On most phone systems, the TIP and RING wires appear on pins 3 and 4 of the RJ-11 modular jack (the one on the LIU). These two wires do not have to be polarized because all the equipment works with either TIP or RING on pin 3 and the other wire on pin 4. This means that cables of either polarity can interconnect and will still work. These basic functions of PSTN operation are assumed in the design of the fax subsystem. The all-inone generates and detects the signaling tones, currents, and data signals that are required to transmit and receive faxes on the PSTN. To receive faxes when you hear fax tones In general, incoming faxes to the all-in-one are automatically received. However, if other devices are connected to the same phone line, the all-in-one might not be set to answer automatically. If the all-in-one is connected to a phone line that receives both fax and phone calls, and you hear fax tones when you answer the extension phone, receive the fax in one of two ways: ● If you are near the all-in-one, press Start Fax on the control panel. ● Press 1-2-3 in sequence on the extension phone keypad, listen for fax transmission sounds, and then hang up. NOTE In order for the 1-2-3 sequence to work, the extension phone setting must be set to On in the Fax setup menu. Distinctive ring function Distinctive ring is a service that a telephone company provides. The distinctive ring service allows three phone numbers to be assigned to one phone line. Each phone number has a distinctive ring. The first phone number has a single ring, the second phone number has a double ring, and the third phone number has a triple ring. If the distinctive ring service is used, the fax phone number should be the phone number that uses the double or triple ring. 100 Chapter 4 Theory of operation ENWW