s and the commuter traffic may be another 20,000 erlangs, but the total can be a lot less than 40,000 erlangs if these communities reach their peak traffic at different times. This peak voice demand should be traffic engineered for a very low blocking rate. does not make sense to invest in all the CDMA air-interface capacity only to be block- ing those calls for lack of a few transport links to the PSTN. With traffic quantities of tens of thousands of erlangs, we can offer very low blocking and still maintain high oc- cupancy on these trunks. The engineering of voice transport from the MSC to the PSTN is done when each MSC has a well-thought-out plan for the amount of transport needed for initial service and for the planning horizon. So far we have discussed the link from MSC to PSTN as if it were a single pipe. How- ever, it is possible to reduce costs by traffic engineering pipes between the MSC and in- dividual destinations on the PSTN. The first priority is always to maintain a low block- ing rate, but in those cases where alternate routing is available, the particular traffic engineering job for the direct link can be optimized for cost savings. For local calls, the traffic engineering is from the MSC to the local LATA. For long-distance calls, we set up alternate routes based on lowest-cost options, and the MSC makes a least-cost- routing determination on a per-call basis. A wireless service provider is likely to make arrangements with multiple long-distance carriers to reduce cost. Regulations also require us to arrange for an appropriate link from the MSC to the local emergency call center for emergency calls (911 in North America). This destina- tion is called a public service answering point (PSAP) and is usually reached through a type 1 connection to the PSTN. In engineering this link, our goal would be to prevent blocking the reporting of multiple simultaneous emergencies within one MSC serving area. A single emergency, such as a traffic accident on the freeway at rush hour, might generate a large num