Telephone network

A network is a complex grouping of devices or nodes interconnected for the fulfillment of communication between individuals or firms. The wire-based telephone network is nowadays in practice widely but the future generation is eying more sophisticated wireless mobile phone network. Plain old telephone service (POTS) is almost no more now. The basic unit of telephone network is one user or node. A local exchange is a star network which connects a large number of user nodes. These local exchanges are connected to local access and transport area (LATA). Off-hook signal is sent by the telephone to local exchange. After receiving this signal, exchange sends back a special tone called dial tone. Now the user dials a number that is sent to exchange. Dialing schemes may be either pulse dialing or tone dialing. Pulse dialing uses a rotary mechanism while tone dialing uses a set of standard tones or frequencies to pass the phone number to the exchange. Tone dialing is also called touch-tone dialing or dual tone multi frequency (DTMF) dialing. After establishing connection between the numbers, exchange sends ringing voltage to the phone. Otherwise exchange will send busy tone. For the termination, caller places the handset back on the hook which is termed as on-hook. If a fine delay occurs in dialing the number after off-hook, the exchange sends a howler tone. While talking, if another call comes, exchange sends call waiting tone. Flash signal is nothing but a mixture or combination of on-hook and off-hook signals often used to take a waiting call.