VoIP

VoIP – An Introduction

VoIP stands for Voice over Internet Protocol. It provides a means of transmitting voice over Internet Protocol (IP). But for that purpose, voice is to be converted into some packet format so that transmission over IP is possible. VoIP technology helps to make calls between PC and PC, PC and telephone etc. The obvious advantage is the reduction in cost.

How It Works?

First, the speech signals are sampled at or above Nyquist Rate and the samples are quantized into discrete levels. These are then converted into digital format. For the above given process, we can use any of the standard like Pulse Code Modulation (PCM), Adaptive Differential PCM (ADPCM), MP-MLQ LPC-10 etc. At the receiving end you will have to reverse the things. Decompress the encoded data, reassemble packets in order, and convert these digital values into analog using a Digital to Analog Converter (DAC). Once data is converted into digital form, we have to think about transmitting it over IP. Here comes the greatest difficulty in VoIP – the real time nature of voice is very crucial, otherwise the sound would not be so easy to understand. But normal TCP/IP implementations are not real time, just like the nature of internet. You may have to wait until each packet is routed correctly through appropriate machines. But such things should not disturb the normal voice, since we want continuous speech from the other end. Hence VoIP implementations use UDP protocol instead of TCP. VoIP data packets live in RTP (Real-Time Transport Protocol) packets which are inside UDP-IP packets.

VoIP signaling Protocols

VoIP mainly uses two signaling protocols: H.323 and SIP (Session Initiation Protocol).
H.323 is an complex suite of protocols that provides specifications for real-time, interactive videoconferencing, data sharing, and audio applications such as IP telephony. SIP is smaller, more efficient, and takes advantage of existing protocols to handle certain parts of the process. MGCP (Media Gateway Control Protocol), for example, is used by SIP to establish a gateway connecting to the PSTN.

VoIP Advantage

• Reduced Cost.
• Can handle multiple calls at a time, like we browse many sites at a time.

VoIP Limitations

• Unless the delay is overcome and a real time streamlining is obtained voice quality would be just unbearable.
• Insecure lines - meaning anyone can listen to your conversation because of shared servers or open platforms.