In 1877, Thomas Edison created a brilliant voice device known as a phonograph, which is shown below in Figure.
This device was able to record sound by pressing a needle into a cylinder and then playback this sound by removing the needle. This form of voice recording is an example of Analog signals. In this Edison’s phonograph, signals used the property of various indentions in tinfoil.
In today’s world, every communication device is connected through some form of cabling for transferring analog signals. When we speak in a phone, the sounds are converted into electricity and then this electric signals is transferred to the other end of communication channel.
Each analogue circuit is composed of two wires. One wire is the positive or ground and the other wire is the negative or battery side of the connection. Commonly these wires are known as the “tip and ring.” These two wires perform the main function of supplying power to analog phone and allow it to work. Figure shown below illustrates the connections of analog phone.
Loop start signaling is the typical signaling type mostly used in home environments. Glare problem occurs with the Loop start signaling. Glare occurs when you pick up the phone to make an outgoing call and at the same time as a call comes in on the phone line before the phone has a chance to ring. To resolve glare problem, modern PBX systems were designed for larger, corporate environments.
The Evolution: Analog to Digital
An analog electrical signal experienced signal fading issue over long distances. Repeaters were used to keep analog signals strong over long distances. Figure shown below describes how repeaters were deployed for signaling.
Repeater was not a perfect solution as it was unable to differentiate between source voice and line noise. Digital signaling solution was proposed to limit the signal weakening issue and to send multiple calls on a single line.
Whenever you make a call from a home telephone, you experience the results of the traditional telephony network known as PSTN. The primary purpose of this network is to establish worldwide path to allow people to easily connect.
In the initial days of the traditional phone system, individual phones were connected together for communication. Multiple phones were required to communicate more than one person. The modern PSTN is now a worldwide network built from the different components, as shown in figure below.
Following are the components of PSTN:
Analog telephone: It is the most common device on the PSTN, used for converting audio into electrical signals.
Local loop: The link between the customer location and the telecommunications service provider.
CO switch: It provides signaling, call routing, setup, digit collection and teardown services to the devices on the local loop.
Trunk: It is the connection between switches.
Unified Voice: VoIP
VoIP is the latest technology for transmitting voice. IP telephony provides communication services over the internet rather than PSTN. VoIP is now available on many smartphones, tablets, personal computers, and on other Internet access devices.
The business advantages of VoIP include the following:
Reduced cost of communication: VoIP allows you to forward calls over WAN connections that reduces your cost of expensive tie lines to communicate between offices.
Reduced cost of cabling: IP phones cut cabling costs up to 50% by running same Ethernet cable for both voice and data.
Seamless voice networks: VoIP connects offices, mobile workers, and telecommuters. IP Telephony also provides centralized control of all voice devices attached to the network and a consistent dial-plan. For example, all users can dial each other using four-digit extensions.
Mobility: IP phones are becoming increasingly plug-and-play, when combined with a VPN configuration, users can take IP phones home with them and retain their work extension.
IP Softphones: IP Softphones are also used for making calls, software of softphone is installed on users PC/Laptop. Users plug a headset into their laptop or desktop and use it as their phone.
Increased productivity: VoIP extensions can forward to ring multiple devices before forwarding to voicemail. This ensures 24/7 availability.