Concept of IP Telephony

Posted by AJ × 04:30

IP telephony means transmission of voice over IP networks. The basic steps for transmitting voice over IP network are listed below .

1. Audio from microphone or line input is A/D converted at audio input device.

2. The samples are copied into memory buffer in blocks of frame length.

3. The IP telephony application estimates the energy levels of the block of

samples.

4. Silence detector decides whether the block is to be treated as silence or as part

of a talkspurt.

5. If the block is a talkspurt it is coded with the selected algorithm (e.g., GSM ).

6. Some header information is added to the block.

7. The block with headers is written into socket interface (UDP).

8. The packet is transferred over a physical network and received by the peer.

9. The header information is removed, block of audio is decoded using the same

algorithm it was encoded, and samples are written into a buffer.

10. The block of samples is copied from the buffer to the audio output device.

11. The audio output device D/A converts the samples and outputs them.

All Syllabus