 it might give you a certain guarantee to keep running your mission critical systems. Chapter 4: Cost Analysis 51 Signaling quality: Measures call signaling and setup performance. When users pick up the phone to make a call, they expect that call to be quickly and reliably estab- lished on the first attempt. Signaling quality metrics, such as post-dial delay and reg- istration delay, assist in troubleshooting the call setup infrastructure. Delivery quality: Measures transport performance. Problems such as long latencies, lost packets, and signal strength all contribute to overall call satisfaction. Call quality: Measures a user's overall call experience. Call quality metrics, such as the Mean Opinion Score (MOS), reported on a scale of 1 (bad) to 5 (excellent), make it easy to assess call quality on a call-by-call basis. This is not a complete list of SLAs. You might need to get a detailed service plan and quality assurance from the service provider, which might cost you extra money to achieve that SLA. Cost of Usage Cost of usage is the area that makes the difference. SIP trunking enables you to eliminate PRIs, T1s/E1s, and local charges, replacing them with a single pipe to the service provider, which terminates directly at the IP-PBX on your premise. Different analyses show that you should save from 25 percent to 50 percent on your voice call charges through SIP trunks. Fundamentally, it's the VoIP cost savings of as much as 50 percent over TDM charges. However, some service providers lower their TDM charges for a large volume of calls. There are different offering models. The pricing structures vary widely by providers. Let's check those closely. Pay as You Use Some service providers offer a pay as you use plan. The going rate for regular lines is from 2.2 cents (local) to 3.9 cents (long distance) per minute. SIP providers charge in the range of free (local) to 2.9 cents per minute. The major advantage of this model is that you don't make any volume commitment. If you want to keep multiple service providers 