One problem frequently encountered by organizations looking to implement VoIP is the lack of in-house technical expertise. VoIP is a completely different technology from traditional telecommunications and even the most seasoned telecom executive may not be aware of some issues that can affect VoIP calls.
Common problems which befall data networks within enterprises are jitter, latency, packet loss, poor QoS etc. These are fairly well-publicized issues and known to most people who manage VoIP systems. However there are other factors which can cause problems for VoIP calling. Impairments are those conditions which negatively affect audio quality while those factors which prevent calls from being made at all (or if the call fails after setup) are called failures.
Commonly employed enterprise security practices such as port blocking or network filtering may unintentionally interfer with VoIP. Port blocking is generally used to prevent unauthorized access by external users to confidential data. It can intervene with calls if the blocking and forwarding policies are not changed when VoIP was implemented. In some cases, port blocking can lead to calls being heard in one direction only. The same principle applies to network filtering and traffic management. It is not enough to just set policies, they should also be configured and implemented appropriately.
Some companies use Application Level Gateways or ALGs which can detect incoming VoIP traffic and help it pass through NAT firewalls. Even though this is a legitimate method for NAT traversal, other options such as using STUN or SBCs are preferred since ALGs can often interfer with network traffic. Similarly, organizations filter certain DNS resource records for security reasons which adversely affects VoIP. Deep packet inspection – which may occur for international calls – can also introduce delays in VoIP traffic. Some countries may prohibit VoIP and regularly inspect data packets to enforce restrictions. This practice introduces significant latency making it extremely difficult to conduct business conversations.
Enterprises which are implementing VoIP through SIP trunking should ensure that network policies are implemented properly so as not to interfere with phone calls. Some policies such as port blocking are set up on the VoIP equipment itself such as routers and it is up to IT managers to disable such options. Even if an organization's internal network is correctly configured, some ISPs intentionally adopt policies which block or degrade VoIP. Businesses should make sure that their ISP does not follow such practices before signing a contract as it can be too late to change afterwards.