Virtual telephone system

from Wikipedia, the free encyclopedia

A virtual telephone system is a telephone system whose hardware is not with the company, but with a provider . VoIP (Voice over IP - in German: Internet telephony) enables telephony as a pure software solution over the Internet .

How a virtual telephone system works compared to analog telephony

The conventional telephone system

The conventional telephone system is a central system to which all connections in different rooms are linked with their respective call numbers and telephones. They are purchased and set up from a supplier and require maintenance. The so-called extensions (one set per user) are usually to be connected by a technician. An analog telephone system is therefore relatively complex to use, especially if there is a defect, as a technician is usually required on site.

The virtual telephone system

In the case of internet-based telephony, cabling or a physical telephone system is no longer required, as the calls are transmitted using an internet protocol in data centers via VoIP. Telephone calls are therefore no longer made over a telephone connection , but over a DSL connection . The voice transmission takes place in real time. With a stable internet connection, the virtual telephone system can be accessed from any device (PC, tablet or smartphone) and from any location. A regular phone can also be used for this, as long as it is IP- based. With the help of an Ethernet cable, it can be hooked into the network and connected to a DSL router .

A smartphone can be integrated into the cloud telephone system using " Fixed Mobile Convergence " . This makes it possible for every user to answer the calls that come in on their extension directly on their mobile phone from anywhere.

The function of the codec in transferring calls

The term codec is an algorithm with which what is spoken in a telephone call is encrypted (encoded) and then decrypted (decoded) again. Since there are different requirements for VoIP telephone calls, the algorithms and thus also the codecs differ, each of which has special advantages and properties.

The greatest differences exist with regard to voice quality, required bandwidth, compression & required computing power, bit rate (variable or fixed) and 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.

The following codecs are particularly common in practice:

  • 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)

The most common codecs are described in more detail below

Codec G.711 (a-law or u-law) The G.711 codec is one of the most common and offers very good voice quality, comparable to ISDN.

The required bandwidth is around 100 kbit / s, including overhead. The G711 codec is supported by almost all end devices and VoIP telephone systems.

Codec G.722 (HD codec) The G.722 codec enables IP telephony to be carried out in HD quality via a VoIP telephone system. The bandwidth required here is also around 100 kbits / s. 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. The call quality of ISDN is still given for external calls.

Codec G.729 The codec G.729 is well suited 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. The G.729 codec achieves the ISDN quality of G.711, but with significantly less bandwidth.

Advantages of a virtual telephone system

Location independence

A stationary phone is no longer absolutely necessary; calls can be made using a softphone . This works via software that is installed on a PC, tablet or smartphone and can therefore be used regardless of location. Calls can thus be accepted at any location. This is particularly advantageous if you have several locations and employees work from home.


With the virtual telephone system, new extensions can be added in the cloud with one click. The user does not have to commit to a certain number of extensions at the beginning. Only the extensions actually used are charged.

In addition, all settings can be made online yourself, such as creating forwards or changing the music on hold.

Cost savings

Most providers charge per extension . This means that only what is actually needed is paid for. In addition, no investment in hardware is necessary (apart from the VoIP telephones).

Another advantage is that the provider of the cloud telephone system is responsible for all updates, maintenance and smooth operation, so there are no ongoing costs for maintenance personnel.

Requirements for a virtual telephone system

Sufficient internet connection

High transmission rates are important to ensure that the call connections remain free of interference. One ADSL or SDSL line is sufficient for a connection of approx. 20 extensions . If there are more than 20 extensions, you should switch to a VDSL line in order to guarantee a good connection.

When it comes to the amount of bandwidth, both the number of employees and the volume of calls are decisive, since the use of a call channel takes around 100 Kbit / s per second (upload and download).

VoIP capability


A corresponding LAN infrastructure (local network) is required to use a virtual telephone system in connection with IP end devices . Usually this is available by default.


The common manufacturers of VoIP -capable devices are mainly Gigaset and Snom, but also Yealink, Grandstream and Mitel (Aastra).

You can also use softphones , i.e. telephony software on your computer, or call apps, i.e. telephony apps on smartphones.

Individual evidence

  1. Definition of Voice over IP. In: Duden. Retrieved April 17, 2019 .
  2. importance Fixed Mobile Covergence. Retrieved April 17, 2019 .
  3. Codecs - VoIP info . In: VoIP info . September 8, 2005 ( [accessed October 12, 2018]).
  4. Codecs for VoIP telephone systems - you should know that. Retrieved October 12, 2018 .
  5. Softphones in virtual telephone systems. Retrieved April 17, 2019 .
  6. Internet bandwidth . Retrieved April 23, 2019 .
  7. VoIP-capable devices. In: Retrieved April 17, 2019 .