Rapid growth of computer networks led to an increase in the popularity of internet telephony in the late 20th century. Today it is widely used by both large companies and individual users. The use of modern IP telephony technologies allows users to significantly reduce the cost of calls and integrate telephone services with internet services, which causes problems with the dimensioning of network resources needed to maintain a decent quality of services.
For such needs a calculator has been implemented. Based on the key parameters of VoIP technology, it is intended to facilitate the calculation of the necessary parameters for the implementation of a given service, such as:
- Bandwidth
- Packet rate
In the calculator you can specify following parameters described below to find needed bandwidth.
The size of the package strongly depends on the selected codec, and it plays important role in network dimensioning as it affects the required bandwidth. The voice codecs used in VoIP are described by ITU-T and IETF recommendations and are listed in the table below.
| Standard | Codec | Bitrate | Frame Size |
|---|---|---|---|
| ITU-T | G.711 | 64kbps | 10ms |
| ITU-T | G.726 | 16kbps | 5ms |
| ITU-T | G.728 | 16kbps | 2.5ms |
| ITU-T | G.729 | 8kbps | 10ms |
| ITU-T | G.723.1 | 5.3kbps | 30ms |
| IETF | iLBC | 15.2kbps | 20ms |
The stack of used protocols matters when calculating the bandwidth needed, because each of them adds a header to the package for network communication. This process also known as encapsulation.
While VoIP requires the use of RTP and UDP in the transport layer(they are the basis for data transmission real-time), other layers may use different protocols, such as IP or Ethernet.
So, for calculating the bandwidth necessary for transmission important is the possibility of adapt and incorporate different protocols from the layers of the TCP / IP model. Table below describes all used protocols with their header sizes you can specify in calculations.
| Protocol | Header |
|---|---|
| RTP | 12 byte |
| UDP | 8 byte |
| IPv4 | 20 byte |
| IPv6 | 40 byte |
| Ethernet 802.3 | 38 byte |
VoIP calculator is a relatively simple application. It consists of one windows
divided into two sections, the first section is for setting parameters and the other one
is used to demonstrate the results.
In a situation where the entered value is not correct, the user gets a message in the form of a window that describes what is wrong. Example windows with messages can be seen below:
Components layout in application sections:
