ce management Call data management 3.9 THE CONNECTIVITY LAYER The three basic layering models or stacks are shown in Figure 3.30. From a management point of view a minimum number of networks is optimal. The possibility of handling all services in one network should justify the choice of just one network, shouldn't it? The only possible common transfer mode is IP, which is installed in practically all computers. The demands from voice services and data services are, however, very different and IP was designed for data. IP voice packets become quite different from IP data packets with much overhead (at least before header compression). See Figure 3.31. The answer to the question could be: 'One network eventually, but the convergence from many tailored Understanding Changing Telecommunications - Building a Successful Telecom Business TCP/IP Open systems Interconnection Common protocols Reference model Application Upper Application Presentation layers Session Error Transport Transport Destination Internet Network Error & Host-to- Could be Data link physical network any network Physical Physical Figure 3.30 Models for layered communication The voice packets are short to minimize delay and jitter Voice 64kb/s CS-Time slots Voice 64kb/s AAL1 Voice compressed AAL2 Data AAL5 Data IP Voice over IP Data FR Voice over FR Figure 3.31 Various transfer modes networks into one network will take time'. See the CS (circuit switched or circuit mode) part in Figure 3.18. In any case protection of investments already made is likely to call for a kind of migration path. Examples of paths are included in the book. See Chapters 8, and Appendix 3. The uncompressed IP header (especially IPv6) for a voice packet is in reality larger than the payload (IPv6/UDP/RTP 60 bytes, voice payload 32 bytes). For ATM there is no need for a tail since the length is always the same (53 bytes). With an increasing number of services and fewer networks the adaptation and enabling area becomes a key part from a business point of view. 3.9.1 STRATIFICATION W