VoIP

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An IP PBX is a private branch exchange or switchboard that is designed to provide video and/or voice communication services over IP data networks. That is, using IP telephony technology, a phone service can be provided through, for example, a company’s IP virtual private network (VPN). When the IP network used is the internet, one can also speak of “Internet Telephony”, which is just one example of a Voice over IP (VoIP) service. There are significant differences in performance guarantees and of voice quality between VoIP on a VPN and through Internet.

Today, the vast majority of telephone exchanges installed are IP PBX:

Advantages of IP Telephony

Simplification and optimisation of IT infrastructure. IP telephony uses the same type of equipment as for IT services (servers, cabling, PCs can even be used as terminals).
a. There is no need to invest in a second cable installation, since the same network can be shared between computers and telephone terminals.
b. Lower operating and management costs. Maintenance can be performed remotely and extensions can be relocated simply by moving the terminal to a new network socket.
Unification of Corporate Telephony in multi-site environments. This unification brings several advantages:
a.    Free calls between sites connected on the VPN.
b.    Integrated numbering plan.
c.    Centralisation of lines of access to the public network (RTP) to one or more points, bringing savings of lines for small locations.
d.    Rationalisation of the post of telephone receptionist, centralising this function, thus saving staff, or decentralising it where appropriate: incoming calls can be forwarded to the location which can offer the best response, depending on availability and current workload.

Better quality of telephone communication, given that it transmits the entire spectrum of the human voice (80 Hz to 14 KHz) instead of just the narrow band (300 Hz to 3 kHz) transmitted by traditional TDM telephony.
New functionalities integrated into the business. There are usually two major applications:
a. Improvement in customer care. For example, certain actions can be performed automatically by entering the appropriate codes.
b. Improving employee productivity in many ways. For example, showing their communication status (available, in a meeting, travelling, etc.) avoiding unnecessary communications or permitting the choice of the most appropriate means of communication (email, chat, etc.), or else identifying the user in the same way even if they are travelling, or at a different office from their usual one.

Architecture or elements of IP Telephony

IP Terminal: This replaces the existing traditional phone. It can be implemented both in software — on a PC or a tablet — and in hardware.
IP PBX: This is the central element of VoIP. Consists of software (whether proprietary or not) hosted on a normal server that will provide the control and routing of calls. This replaces the existing PBX.
IP Gateway: This is the link to the traditional telephone network, and operates seamlessly for the user.
SIP: Session Initiation Protocol (SIP) has become the standard among the signalling protocols for VoIP, even overtaking H.323. It offers registration, location and address services.
Codecs: These are the encoding and decoding algorithms for the compression of the audio or video which is to be transmitted. Depending on the codec used, more or less bandwidth will be used; this parameter is directly proportional to the quality of the data transmitted. The most popular codecs are the different versions of G.711 and G.729.
The Data Networks: Both within the office (LAN) and external (WAN). It is essential that they have stable, guaranteed band widths, with constant and not excessive latencies, and, if the networks are shared with other data, as usually occurs, they must be able to prioritise voice packets using “Quality of Service” (QoS) techniques.