CODEC is used to convert an analog voice signal (waveforms) to digitally encoded signal. In addition to performing the analog to digital conversion, CODECs compress the data stream and also provide echo cancellation. The CODECs for VoIP are also termed “vocoders,” meaning voice encoders. CODECs typically perform encoding-decoding, compression-decompression, and least often, encryption-decryption. CODECs vary in the sound quality, the bandwidth required, the computational requirements, etc.
The process of converting analog waveforms to digital information is done with a voice coder-decoder by fallowing below tasks. Most of the CODECs will do first two tasks.
- Encoding and Decoding
- Compression and Decompression
- Encryption and Decryption
Encoding and Decoding:
The voice is first converted to analog electrical pulses, which is then given to analog to digital converter whose output is quantized voice. This process of converting analog signal to digital data is termed as encoding. At the receiver end the digital data is converted back to analog format. This process of converting digital information to analog signal is termed as Decoding.
Compression and Decompression:
Bandwidth is very limited so it is very important to use the available bandwidth very efficiently. The compression reduces the size of the file, while retaining the original data but in a compressed format. This compressed data is transmitted over the network. This helps to reduce the network traffic. The compressed data is decompressed at the receiver before performing the decoding operation.
Types of Compression:
There are two types of compression, one is lossless and second is lossy. In lossless compression, you lose nothing, but you can’t compress that much. In lossy compression, you achieve great downsizing, but you lose in quality. You normally can’t get the compressed data back to its original state with lossy compression, since the quality had been sacrificed for size. But this is most of the time not necessary.
Encryption and Decryption:
Encryption is one of the best ways to achieving security. In voice over IP, voice data packets are transmitted across insecure public networks. In encryption, original data is converted into other form that no one can understand. These encrypted packets are transmitted over the public network. Even if any other individual accesses the packet, still the information is safe and confidential. At the receiving end the encrypted data is decrypted back to its original form.
Filed Under: IP Telephony
About the Author: