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Most telephones operate through transmission of electric
signals over a complex telephone network which allows almost any phone user to
communicate with almost anyone.
The Public Switched Telephone Network (PSTN) has gradually evolved towards
digital telephony which has improved the capacity and quality of the network.
End-to-end analog telephone networks were modified by upgrading
transmission networks with T1 carrier systems. and Later on with
technologies such as SONET and fiber optic transmissions . Cordless or portable telephone is a
wireless handset that communicates via radio waves with a base station connected
to a fixed telephone line on the subscriber premises, and
attaches to the telephone network the same way a corded telephone does.
Unlike a corded telephone, a cordless telephone needs mains electricity to power
the base station. The cordless handset is powered by a rechargeable battery,
which is charged when the handset sits in its cradle.
A WiFi-based VoIP phoneInternet Protocol (IP) telephony (also known as Internet
telephony) is a service based on Voice over IP (VoIP), a disruptive technology
that is rapidly gaining ground against traditional telephone network
technologies..
IP telephony uses a broadband Internet connection and IP Phones to transmit
conversations as data packets. In addition to replacing POTS(plain old telephone
service), IP telephony is also competing with mobile phone networks by offering
free or lower cost connections via WiFi hotspots. VoIP is also used on private
wireless networks which may or may not have a connection to the outside
telephone network.
Mobile phone
The mobile phone or mobile, also
called a wireless, cellular phone, cell phone, cell speaker box, or hand phone is a short-range, portable electronic device used for mobile
communication that uses a network of specialized base stations known as cell
sites.
current mobile phones may support many additional services, and
accessories, such as SMS for text messaging, email, packet switching for access
to the Internet, and MMS for sending and receiving photos and video.
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