(CPE) unit from the SP. It is best if this CPE device is a full session border controller (SBC) that provides Layer 7 application-level protection and session management features. In some cases these CPE units are merely firewall/network address translation (NAT) devices that offer Layer 3 services or perhaps some application layer gateway (ALG) features. Although this might suffice for small business offerings, it typically is not sufficient for medium or larger enterprises. Also consider redundancy and failover call routing. For a SIP trunk of 500 or more ses- sions (500 sessions is the equivalent of approximately 20 T1s or 16 E1s), it is strongly rec- ommended to have a redundant architecture in the CPE devices and network demarcation equipment. Agree on Monitoring and Troubleshooting Procedures Discuss with the SP what methods and tools you will use to troubleshoot voice-quality complaints from your user community and how you will isolate problems to determine if they are present in your network or the provider's. It is also necessary to determine how you, or the provider, will determine if the SIP trunk is overloaded or down and how alternative routing will take place. You also need to agree to how it will be determined that the condition has cleared and normal routing can resume. Also, determine how you will assess billing information and how you will reconcile the provider's billing records with those from your own network. It might be useful to enable billing at the demarcation point for these purposes. Pilot Trial By the time you reach this stage, you have completed all the planning steps, selected your provider, and you are ready to install a SIP trunk, configure the equipment, and start run- ning test calls to see how it operates in your environment. During the Pilot Trial step, work through the following activities to test the operation of the SIP trunk: Define clear success criteria. Assess organizational responsibility. Chapter 11: Deployment Steps and Best Practices 253 Determine the length of the 