What VoIP and its Technology

VoIP is currently the most important developments in the field Telecommunications. Before 1970, the voice was done analogically on dedicated to the telephony networks. The technology used was the electromechanical technology (Crossbar). In the 80s, the first major change was the shift to digital transmission (CT). The transmission of voice over computer networks IP packet is now a new comparable major evolution previous. The aim of this chapter is the study of this technology and its various aspects. We speak in detail of the architecture of VoIP, its elements and its operating principle. We also detail VoIP signaling protocols and transport and their principles operation and their main advantages and disadvantages.

Introduction to VoIP 

Definition 
VoIP stands for Voice over Internet Protocol or VoIP. As the name suggests, VoIP can transmit sounds (particularly voice) in IP packets on Internet. VoIP can use accelerating hardware to achieve this purpose and can also be used in the PC environment.

Architecture
VoIP is a new communication technology, it has not yet single standard. Indeed, each manufacturer provides its standards and features to its solutions. The three main protocols H.323, SIP and MGCP / MEGACO. There is therefore several approaches to provide telephony and video telephony over IP networks.

Some put the intelligence in the network, while others prefer an equal approach equal with distributed intelligence at the edge. Each with its advantages and disadvantages. It always comprises terminals, a communication server and a gateway to the other networks. Then each standard has its own characteristics to ensure a more or lower quality of service. The intelligence of the network is to be deported on terminals or gateways on / switch controller, called Gatekeeper.

Common elements: 

1. The router: You can switch the data and routing of packets between two networks. Some routers allow to simulate a Gatekeeper by adding cards specialized supports VoIP protocols. 
2. The gateway: to interface the switched network and the IP network. 
3. The PABX: Switch is the traditional telephone network. It allows to link between the gateway or router, and the switched telephone network (PSTN). However, if all IP network becomes, the equipment becomes obsolete. 
4. Terminals: are usually software-based (software phone) or hardware (Hardphone), the softphone is installed in the PC of the user. The audio interface can be a microphone and speakers connected to the sound card, even if headphones are recommended. For better clarity, USB or Bluetooth phone can be used. 

The hardphone is an IP phone that uses Voice over IP technology to allow phone calls over an IP network such as the Internet instead of the ordinary PSTN system. Calls can browse the Internet network as a private network. A device uses protocols such as SIP (Session Initiation Protocol) or any of the proprietary protocols such as that used by Skype.

Operating principle 
Since many years, it is possible to transmit a signal to a destination far as digital data. Before transmission, it is necessary to digitize the signal to using a CAN (ADC). The signal is then transmitted to be used, it must be converted back into an analog signal, with the aid of a DAC (Digital to analog converter). VoIP operates by digitizing the voice, and then by conversion of packets Digital voice on arrival. The digital format is easier to control, it can be compressed, routed, and converted into a new better format. The digital signal is more noise tolerant than analogue. TCP / IP networks are IP packet traffic carriers containing a header (To control communication) and a payload to transport data. There are several protocols that can support VoIP such as H.323, SIP and MGCP. The two most currently used protocols in VoIP solutions on the market are H.323 and SIP.