quality in this network. This might be the easiest way to dis- play the solution architecturally, but this is often not the case. A high-quality IP network is an essential underlying component of a SIP trunk solution offered by SPs. If this SIP trunk solution is for PSTN access, the level of quality of the IP network should equal or exceed the level of quality and reliability of the PSTN network that is seen as a 99.999 percent (often called "five nines") network. Because other features Chapter 5: Components of SIP Trunks 63 are often seen as enhancements to "basic" SIP trunks for PSTN access, the "five nines" level of reliability is most often seen as a floor, not a ceiling, and other SIP trunking services are assumed to increase the reliability of the overall solution. Two of the major benefits of SIP trunking rely on that the underlying infrastructure is an IP network. These are Flexibility in services Enhanced reliability First, flexibility in services is the capability to transmit many different types of traffic over the same physical medium. For example, the traffic can be narrow-band traditional audio, wide-band/high-fidelity audio, or video. The packetization of these different types of content over an IP network ensures that a single network can be used for many services. Second, an IP network's inherent capability to route around areas disconnected or con- gested can provide reliability that is beyond what can be accomplished in traditional TDM trunking networks that relied on point-to-point connections. Another important component to note is that not all IP networks are created equal. For a SP to offer a high- quality SIP trunk solution, it must have a high-quality IP network. A high-quality net- work from a SIP trunking perspective optimizes the following important components: Latency Packet loss Jitter These three items, which have a devastating effect in any VoIP environment, are especial- ly problematic in SIP trunking networks. A network with a high level of latency has long delays in speech from 