Basic principles of VoIP and common equipment

Source: Internet
Author: User
Tags coding standards

1995 Israel VocalTec Company launched the Internet phone, not only is the beginning of VoIP network telephony, also opened the telecommunications IP prologue. People will not only be able to enjoy the cheaper and even completely free call and multimedia value-added services, the service content and the face of the telecommunications industry has also changed drastically.

The beginning of the network phone is in the form of software, and only limited to the PC to PC calls, in other words, people only on each side of the different PCs, install network telephony software, you can through the IP network dialogue. With the popularization of broadband and the evolution of related network technology, the network phone also from a simple PC to PC call form, the development of IP to PSTN (Public switched telephone network), PSTN to IP, the PSTN to PSTN and IP to IP and other forms, of course, their common point, is to IP network for the transmission of media, so that the telecommunications industry for a long time to PSTN circuit exchange network for the transmission of the medium of practice and exclusivity is also gradually broken.

The principles, architecture and requirements of VoIP

by Voice over IP literal meaning, can be translated into the IP network transmission of voice signals or video signals, so VoIP is a kind of IP network can be transmitted from the analog audio or video messages of a technology. Simply put, it is through a series of transcoding, coding, compression, packaging and other programs, so that the voice data can be transmitted to the destination on the IP network, and then through the opposite program, revert to the original voice signal to receive the listener.

Further, VoIP roughly through 5 of programs to communicate the voice signal, first of all, the voice of the analog speech signal encoding the action, is currently mainly using the ITU-T g.711 Speech coding standards to convert. The second program is the voice packet compression, and add access and control information, so you can in the third phase, that is, the transmission of IP packet stage, in the vast IP network to find the destination of the transmission. To the destination, IP packets will be decoded to restore the operation, and finally converted to the speaker, handset or headphones can play the simulation thereafter.

In a basic VoIP architecture, roughly 4 basic elements are included:

(1) Media Gateway: Mainly play the role of converting voice signals into IP packets.

(2) Media Gateway Controller (Multimedia Gateway Controller): Also known as Gate keeper or call Server. Mainly responsible for the management of signal transmission and conversion work.

(3) Voice server: mainly provide telephone communication, busy or busy line voice response service.

(4) Signal Gateway (signaling Gateway): The main work is in the exchange process to carry out the relevant control to determine whether the call to establish or not, and provide the relevant application of value-added services.

Although VoIP has many advantages, but it is not possible in the short term to completely replace the already long history and the development of a sophisticated PSTN circuit exchange network, so at this stage the two are bound to coexist for some time. In order for the two to communicate with each other, it is bound to establish an interoperability interface and pipeline, and the media Gateway and Gateway Manager Act as the intermediary of the color angle, because they have the media data stream and IP packets into different networks to support the various protocols.

Its operating principle is that the media gateway first converts voice to IP packet, and then to the media Gateway controller to control the management, and determine the IP packet in the network transmission path. The Signal gateway is responsible for converting the SS7 signal format to IP packets.

Network telephony to meet the enterprise-level operating standards, must meet the following basic requirements:

1. Quality of service (QoS) Guarantee: This is the transition from the PSTN to VoIP, IP PBX to replace the most basic requirements of the PBX. The so-called QoS is to ensure that the minimum delay rate of speech transmission (400 milliseconds) and packet loss rate (5-8%), so call quality to achieve the current PSTN basic requirements and standards, or the implementation of VoIP will be problematic.

2.99.9999% high-availability (High Available;ha): Although network telephony has become an inevitable trend in the future, but with the development of the PSTN compared to its maturity, stability, availability, manageability, and even scalability, etc., still need to be strengthened. Especially in the high availability of telecom class, VoIP must be the same as the current PSTN, to achieve 6 9 (99.9999%) of the basic standards. At present VoIP is to load balance, routing backup and other technologies to solve the requirements and problems, in a word, HA is a VoIP must achieve one of the goals.

3. Openness and compatibility: the traditional PSTN is a closed architecture, but the IP network is an open architecture, now one of the biggest issues of VoIP is how to be in the open architecture, and to achieve the various manufacturers VoIP products or building interoperability and compatibility, at the same time to create products in the integration of testing and verification difficulties. The current solution is to achieve compatibility between different products through the standard protocols that are constantly being developed and modified by the International Telecommunication Organization, as well as the interoperability of IP telephony and traditional telephony.

4. Manageability and security issues: a comprehensive range of telecommunications services, including user management, off-site roaming, reliable billing system, certification and so on, so the management is very complex, VoIP operators must have good management tools and equipment to be able to. At the same time, IP network Architecture technology is completely different from the past PSTN circuit network, and has long been an open IP network has been a very serious security problems, so this also forms a network phone in the future development of major obstacles and the primary solution to the goal.

5. Multimedia applications: Compared with the traditional PSTN, network telephony in the future development of the biggest features and differences, I am afraid, in the application of multimedia. In the foreseeable future, VoIP will be able to provide interactive E-commerce, call center, corporate Fax, multimedia video conferencing, intelligent agents and other applications and services. In the past, VoIP has been popular and eye-catching because of low prices, but multimedia applications are the biggest cause of the future development of VoIP, but also the most active participation of the most dynamic.

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