VoIP telephone system
A VoIP telephone system , short for voice-over-IP telephone system (English voice-over-IP , German "language over Internet protocol"), also known as a virtual telephone system or IP telephone system , is a telephone system that uses VoIP- enabled end devices. A VoIP telephone system no longer needs a conventional telephone connection, but rather handles the calls via an Internet connection. Another name for a VoIP telephone system is IP-PBX (short for Private Branch Exchange ).
The IP telephony will increasingly be in Germany, both in the private sector, as well as in business telephony. According to a report by the Federal Network Agency, over 25 million people were already using VoIP technology at the end of 2016.
How a VoIP telephone system works
In IP telephony, voice information is passed on via Voice-over-IP over an Internet data line. The digital information is transmitted via the Session Initiation Protocol (SIP) network protocol . Therefore, users of the VoIP telephone system must first register using their personal SIP address. This registration runs via a SIP server. The connection between the VoIP end devices is now established when they are networked through the same SIP server via the IP address of the other devices. This eliminates the need for cabling, as is known from conventional telephone systems such as ISDN or analog telephony .
If at least two people make calls to each other via a VoIP telephone system, the speaking is converted from analog to digital data on the speaker's side. On the other hand, the listener reassembles the individual data packets to form the original speech information.
Call transmission with the right codec
A codec is an algorithm that first encodes the language of the participants in a virtual telephone conversation and then decodes it again (English en code and de code). There are different codecs, each with special advantages and requirements.
The various codecs differ in terms of:
- Voice quality
- required data transfer rate
- Data compression and required computing power
- Bit rate (variable or fixed)
- distribution
For example, some codecs offer better voice quality than others. However, users cannot choose a general codec, as the functionality of the codec depends on other factors. For example, all end devices and the VoIP telephone system itself must support the codec.
Frequently used codecs are:
- G.711 (approx. 100 kbit / s, uncompressed, quality very good)
- G.722 (approx. 100 kbit / s, uncompressed, quality very good)
- G.729 (approx. 15 kbit / s, compressed, quality very good to good)
Codec G.711 (a-law or u-law)
The G.711 codec is very common and offers very good voice quality in the quality of ISDN. The required data transfer rate is approx. 100 kbit / s, including overhead. The G711 codec is supported by almost all end devices and VoIP telephone systems.
Codec G.722 (IP telephony in HD quality)
The G.722 codec enables VoIP telephone systems to carry out IP telephony in HD quality. A data transmission rate of approx. 100 kbit / s is also required here. However, the transmitted frequency spectrum is higher, which makes speech and music sound better. However, this quality is often only achieved internally within the VoIP telephone system. When telephoning outside into the landline or mobile network, however, the ISDN call quality is still given.
Codec G.729
The G.729 codec is ideal for home offices, remote workstations or soft clients (VoIP software on the PC) because these are often connected to the VoIP telephone system via a poorer Internet connection. With the G.729 codec, you can achieve the ISDN quality of G.711, but with a significantly lower data transmission rate.
Advantages of a VoIP telephone system compared to a conventional telephone system
The VoIP telephone system offers several advantages over conventional telephone systems. For example, the VoIP telephone system can use a wide variety of VoIP-enabled devices to connect, such as VoIP phones, smartphones with the appropriate soft client application or a softphone (VoIP software for the PC).
It is also possible to connect an analog telephone to the VoIP telephone system via an analog telephone adapter (ATA). In this way, the old analog equipment can still be used and calls can still be made via VoIP.
In terms of call quality, there are no differences between VoIP telephones, soft clients and softphones. The only decisive factor is the speed of the internet connection. As a general rule, there is a broadband connection of 100 kbit / s per voice channel (upload and download), otherwise the quality of the call may be reduced. Accordingly, a company that has to make several phone calls at the same time must have a sufficient data transmission rate available.
Differences between VoIP telephony and other telephony services via PC
There is often a confusion between VoIP technology and voice / video telephony via services such as Skype and ooVoo . The main difference is that there is no connection to the public telephone network for telephony services . However, this is the case with a VoIP telephone system. In addition, in connection with a VoIP telephone system, the Federal Network Agency assigns local area codes.
Individual evidence
- ↑ Duden | Voice over IP | Spelling, meaning, definition, origin. Retrieved September 28, 2018 .
- ↑ Telecommunications Activity Report 2016/2017. In: https://www.bundesnetzagentur.de/ . Federal Network Agency, accessed on September 28, 2018 .
- ↑ Codecs - VoIP info . In: VoIP info . September 8, 2005 ( voip-info.org [accessed October 12, 2018]).
- ↑ Codecs for VoIP telephone systems - you should know that. Retrieved October 12, 2018 .
- ↑ Federal Network Agency - Local Networks - Determination of the number of phone numbers to be allocated for direct dial-up VoIP connections. Retrieved October 12, 2018 .