In order to support time-sensitive applications like VoIP, a network should currently be running at a high performance level, and have the capacity to shoulder the load that will be associated with adding an additional (and time-sensitive) service. As such, a network that already suffers from over-utilization, delay, instability, and latency issues would not be a good candidate to take on packet-switched voice traffic in its current state. In many environments, the proposed implementation of packet-switched voice traffic may necessitate upgrades of hardware or network media (including WAN links), as well as a thorough analysis of network protocols and their configuration. For example, the implementation of IP telephones may require the purchase of new or additional access layer switches. Similarly, voice network modules may need to be added to existing or new routers to support connections to a PBX or the PSTN. The network and routing protocols in use should also be considered, since legacy (and possibly unnecessary) protocols may still be in use on the network, thus negatively impacting performance.
The key to determining network quality is to perform a thorough analysis of the current environment, addressing areas that require attention, and then ensuring that the network is performing in a manner that can support the proposed voice traffic. Many of the software tools looked at in other articles can help a network designer to identify the potential problem areas that may exist. Although these recommendations may seem very generic (they are), any existing data network must be properly designed, stable, and performing at a high level if you intend to implement technologies like VoIP.