S 3.57 Scenarios for the use of VoIP

Initiation responsibility: Head of IT, IT Security Officer

Implementation responsibility: Head of IT, Administrator

There are various application scenarios for VoIP, i.e. for the transmission of voice data using an IP network. The potential threats and the security requirements also differ accordingly. Currently typical application cases are presented in the following.

Use of VoIP on terminal device connections

The first application scenario is when VoIP is used for internal voice communication in a company or government agency network.

In this case, VoIP consists of the use (throughout the system or only component-by-component) of IP telephones, a LAN-based telecommunication system that provides the switching and value-added functions and ensures connection to the outside world, and an IP network for connecting terminal devices and a PBX system. Local gateways or a VoIP provider can be used to connect to the digital telephone network. In "hybrid systems", VoIP modules permitting the connection of IP telephones, usually telephones with a proprietary system, are integrated into conventional PBX systems.

The goal is to integrate the data and telephony networks. However, the possible savings on wires, network components, management, administration, and maintenance must be weighed against the additional basic threats, such as the possibility to listen in on the data connection, which requires little expert knowledge. The necessary security safeguards cancel out part of the potential savings, especially when an existing data network is adapted for use with VoIP, but these safeguards are absolutely necessary for the secure and reliable use of this technology.

Use of VoIP to connect PBX systems

Traditionally, PBX systems are usually connected to each other using separate dial-up lines or dedicated lines.

One application of VoIP that is becoming increasingly widespread is to use it to link local telecommunication systems (trunking) via IP connections. In this case, traditional PBX systems at different locations are connected using a WAN data network. The combination of a telephony and data network in the local network provides a high degree of flexibility, more efficient utilisation of bandwidth, and therefore also potential cost savings.

Use of VoIP for internet telephony

Another scenario is to transmit the voice data using public IP networks, in particular the internet. The increased bandwidths available in the backbone and terminal connections, which result in acceptable voice quality nowadays, have accelerated the trend towards internet telephony for private use.

Softphones can be used in this case, which are usually registered using central directors in a similar way to messaging services. Compact and economical VoIP gateways allowing for the use of internet telephony services on conventional telephones (analogue or ISDN) are becoming increasingly popular. However, economical hardphones for private use are also offered by the manufacturers.

Currently, companies and government agencies hardly ever utilise the possibility of transmitting voice data using public IP networks. The main reason for this is that there are no mechanisms available in public IP networks to guarantee a certain level of voice or transmission quality.