e use of SMS clearer: To start a relationship - 17 % To break a relationship - 9% While driving a car - 21 % During work hours - 86 % While having sex - 14 % The conclusion was drawn that mobile phones and text messaging are the ubiquitous communication phenomena of our time. 5.4 SERVICE SEGMENTATION FOR PLANNING Service segmentation is based on a pragmatic selection. Since QoS and security are success factors used in this book, the majority of classes come from these two areas. In UMTS four traffic classes have been identified, which can be used as a definition of service requirements: conversational streaming interactive background The services are characterized by the QoS parameter, which is related to different radio access bearer attributes. The main QoS attributes used to define a service are bit rate, transfer delay, transfer delay variations/jitter and bit error rate (BER). The UMTS network designer must fulfil QoS requests from the UMTS application or user. In addition to these four classes the global information infrastructure (GII) presented another two classes according to a taxonomy described in the Telecommunication Journal of Australia, 47(2), 1997. Understanding Changing Telecommunications - Building a Successful Telecom Business GII considers transactional and messaging services as separate from other conventional groups. A particular advantage is that both these service types were represented among the list for mobile Internet. See Sections 5.3.2 (Transactional services) and 5.3.6 (Mes- saging services). Messaging is in addition a very important service type, today it is the biggest non-voice service used over mobile networks. Some analysts expect transactional mobile services to successively become one of the biggest non-voice services. In addition, transactional services represent the important security area. This book thus uses a set of six service classes as an input to service implementation. See Figure 5.7. All the services are covered, but some services need one or more service enablers, 