 for each MSC and the SS7 transport links must remain below 40 percent occupancy so that the SS7 network remains fully redundant, as required by SS7. We can add STP capacity and SS7 transport to maintain enough capacity to meet this objective. The SMSC will have to expand to meet increased demand for SMS. This may in- crease in proportion to other services, or it may increase more rapidly as SMS becomes more popular in the subscriber community. Voice-mail growth is simply a matter of tracking usage. As subscribers use more voice mail, we need more voice links between the MSC and the voice-mail system, and we need more voice mailbox capacity. An increase in demand may increase the volume dur- ing voice-mail activity surges when things go wrong, as described in Sec. 34.6.5, but we do not expect system growth to increase the number of events that drive up voice-mail activity. We are not going to have more late flights because we sell more cell phones. New services will create new demands on auxiliary equipment. Enhanced message service (EMS) sends longer messages and will use more message center storage than SMS. Multimedia message service (MMS) allows subscribers to send large graphic im- ages from their cell phones, and this could create large demands for intermediate stor- age. Network-based voice commands for cell phone subscribers could increase message activity as well. When we increase the capacity of an auxiliary box, we should keep in mind that these are computers with computer-upgrade choices. We may decide to buy bigger disks, but it may make more sense to get a new computer instead. While we are busy making sure that our base stations and MSCs are keeping up with subscriber demand, let us not forget the less glamorous auxiliary equipment that manages our calls message message. 43.7 Conclusion In planning MSC growth, we have a major effect on the quality of the services we offer, the reliability of our network, and the profitability of our company. Careful work does more than keep the network running well