eneral business calls. SIP trunk provider readiness and cost can vary significantly between countries and continents. Your rollout plan might need geographical phases. Network Design Best practices in the area of network design include the following: Carefully consider the benefits and challenges of the centralized or distributed SIP trunk designs, even if the choice seems obvious. Centralized designs almost always look more attractive because of their cost savings. However, they have network de- sign implications that might increase the overall cost. A distributed design might be viable especially if you already have a distributed multi-protocol label switching (MPLS) network for your data. Most SIP trunk providers enable only two IP addresses with the service, either as primary/secondary or in a load balancing setup. If you need to load balance your calls over more than two devices for either scalability or redundancy reasons, you might need to insert a SIP proxy or load-balancer device to distribute the traffic. Most SIP trunk providers currently do not use domain name system (DNS) but instead use absolute IP addressing. This can influence your redundancy and load- balancing considerations. Load balancing over the two IP addresses the provider provides is generally a more dynamic and flexible call routing configuration than a primary/secondary algorithm. Use a Layer 7 SIP OPTIONS ping to monitor SIP trunk status in addition to one of several Layer 3 mechanisms that might be available, such as Internet Control Message Protocol (ICMP) ping or IP service level agreements (IP SLA). Investigate troubleshooting tools and methods to determine the source of any voice- quality issues. If one is reported, decide how to determine if it is present in your net- work or in the SP's network. Discuss with your provider how such problems will be investigated and resolved. 258 SIP Trunking Turn on CAC features on your SBC regardless of whether the provider offers an SLA-especially if your provider does not offer an SLA. Protoco