T 2.113 Inadequate planning of network capacity for the use of VoIP

A data network is needed to use the Voice over Internet Protocol (VoIP). Existing data networks, to which the workstation computers and servers are connected, or independent data networks can be used for VoIP. The main reason, though, for migrating from circuit-switching telephone solutions to VoIP is the lower cost of maintaining a single communication infrastructure when an existing data network is used.

Not much experience with VoIP is available to date, since this technology is relatively new. If you want to replace a circuit-switching PBX system with VoIP, you generally cannot use the PBX experience gained in the past. This applies in particular to the response of the VoIP PBX system when the group of users is large.

The providers of VoIP PBX systems try to provide statements regarding the number of users their product can handle. However, these statements are not very accurate when an existing data network is used. When the workstation computers require large amounts of data, the network can quickly become overloaded when it is simultaneously used for VoIP. On circuit-switching PBX systems, the maximum number of ports to which telephones can be connected determines the maximum number of users.

Depending on the configuration of the active network components, certain IP packets can be assigned a higher transmission priority when an overload occurs. If VoIP packets are transmitted according to their priority when the load on the network is high, it might no longer be possible to work efficiently on the workstation computers under certain circumstances. When all IP packets are sent with the same priority, the problem-free use of VoIP cannot be guaranteed any more.

Even if the existing network had enough capacity to use VoIP and transmit regular information in parallel when migrating to VoIP, this capacity might not be sufficient for future constellations. If new employees are hired, then they will need to work on their workstation computers over the data network and be able to make telephone calls using VoIP. This means the load placed on the network will increase and quickly use up the free resources.