Digital transmission of analog data involves converting analog signals into digital form for transmission over digital networks.
• This process includes analog-to-digital conversion, data transmission, and digital-to-analog conversion at the receiving end.
Translating from Analog to Digital
Analog-to-Digital Conversion (ADC):
This process involves converting continuous analog signals into discrete digital signals.
The main steps in ADC are:
1.) Sampling:
Definition: Measuring the amplitude of the analog signal at regular intervals.
Nyquist Theorem: To avoid loss of information, the sampling rate must be at least twice the highest frequency present in the analog signal.
Example: If the highest frequency is 4 kHz, the sampling rate should be at least 8 kHz.
2.) Quantization:
Definition: Assigning each sampled amplitude value to the nearest value within a finite set of levels.
Quantization Error: The difference between the actual analog value and the nearest quantized value, resulting in a loss of accuracy.
3.) Encoding:
Definition: Converting quantized values into a binary format (bits) for digital representation.
Pulse Code Modulation (PCM): A common method for encoding audio signals into digital form.
How Telephones Transmit Voice Data
Traditional Analog Telephony:
- Analog Signal Transmission: Voice is transmitted as analog signals over copper wires.
- Public Switched Telephone Network (PSTN): The traditional network used for voice communication, consisting of a vast infrastructure of switches and copper lines.
Digital Telephony:
- Digital Signal Transmission: Modern telephones convert voice into digital signals using ADC before transmission.
- Integrated Services Digital Network (ISDN): An early form of digital telephony allowing simultaneous voice and data transmission.
Process:
- Voice Input: The telephone’s microphone captures the analog voice signal.
- Analog-to-Digital Conversion: The signal is sampled, quantized, and encoded into a digital format.
- Transmission: The digital data is transmitted over digital networks or converted back to analog for transmission over PSTN.
- Reception: The receiving telephone converts the digital signal back into an analog signal using Digital-to-Analog Conversion (DAC).
- Voice Output: The telephone’s speaker plays the analog voice signal.
How Instant Messengers Transmit Voice Data
Voice Transmission in Instant Messengers:
Instant messaging applications use the internet to transmit voice data.
The process involves:
- Voice Input: The microphone captures the analog voice signal.
- Analog-to-Digital Conversion: The signal is sampled, quantized, and encoded into a digital format.
- Compression: The digital voice data is compressed to reduce the bandwidth required for transmission. Codecs: Audio codecs like Opus, G.711, and G.729 are used for compression and decompression of voice data.
- Packetization: The compressed digital data is divided into packets for transmission over the internet. Real-Time Transport Protocol (RTP): Commonly used for delivering audio and video over IP networks.
- Transmission: The data packets are transmitted over the internet using protocols like TCP/IP or UDP.
- Reception: The receiving device reassembles the packets, decompresses the data, and performs Digital-to-Analog Conversion (DAC).
- Voice Output: The speaker plays the analog voice signal.
Voice over Internet Protocol (VoIP)
VoIP is a technology that allows voice communication and multimedia sessions over the Internet or other IP networks. It converts voice signals into digital data packets for transmission.
How VoIP Works:
- Voice Input: The microphone captures the analog voice signal.
- Analog-to-Digital Conversion: The signal is sampled, quantized, and encoded into digital format.
- Compression: The digital voice data is compressed using codecs.
- Packetization: The compressed data is divided into packets.
- Transmission: The data packets are transmitted over IP networks. Session Initiation Protocol (SIP): Commonly used to establish, manage, and terminate VoIP calls.
- Reception: The receiving device reassembles the packets and decompresses the data.
- Digital-to-Analog Conversion: The digital signal is converted back into an analog signal.
- Voice Output: The speaker plays the analog voice signal.
Advantages of VoIP:
- Cost-Effective: Lower cost compared to traditional telephony, especially for long-distance and international calls.
- Flexibility: Allows integration with various applications and services.
- Advanced Features: Supports features like call forwarding, voicemail, and video conferencing.
