ineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Mobile Switching Center (MSC) Planning Mobile Switching Center (MSC) Planning 34.6.5 Voice-mail planning The size of the voice-mail database is the size of the voice-mail subscriber list. Like the HLR and SMSC, there should be no surprises in the number of subscribers who are paying for voice-mail service. The number of voice links to the voice-mail system should be traffic engineered based on two sources of demand. There are callers leaving messages, and there are voice-mail subscribers receiving their messages. Both these groups require voice connections from the MSC to the voice-mail system, and neither of these likes being blocked. We recom- mend a very low blocking rate for voice mail because subscribers remember for a long time when they cannot get through. Another dimension of voice-mail planning is how long voice messages are stored. Both subscribers and voice-mail planners have a say in the average message storage time. The subscribers may get their messages quickly, or they may let messages sit for several days. And the voice-mail system can have a maximum storage time limit after which voice messages are deleted automatically. The size of the voice-message database depends on how many messages need to be stored, how long the messages are, and how long they need to be stored. There is marketing experience in voice mail for different groups of subscribers, and the voice-mail planners for a new wireless system should use their forecasts of subscriber demographics to design a voice-mail system with adequate message storage space. When things go wrong, there is a surge in voice-mail activity. Late flights and traffic accidents generate more calls, and some of those calls roll over to voice mail. Also, when the sudden increase in call traffic uses up all the air-interface capacity, calls will roll over to voice mail