 as well as some ATM, FR and other transport network standards that describe how to use these services. Thus, to be an expert in GPRS, you must read and understand something in the range of 3000-4000 pages of technical documents; GPRS is just one of many net- work concepts telecom architects and engineers must deal with. This is, of course exactly why it is SO important that a common terminology that is applicable on any network concept is used, and that this vast amount of information can be structured in formalized network models (e.g. in the SM&AML way). The GPRS standard provides information in GSM 03.60 that corresponds to the GPRS physical network model on level 1. There is no level 0 model. Logical net- works are not defined, and consequently, neither are logical network structures. The correspondence to a model on physical network level 1 is described in GSM 03.60, and appears as shown in Fig. 4.11 (with some minor simplification). Interface User-data flows reference point Control flows only and control flows Fig. 4.16 GPRS physical network level 1, according to GSM 03.60 4 Physical Network Modelling The interfaces (Um, Gb, Gn, etc.) are called either reference points or inter- faces, with definitions that are specific for the GPRS standard. An architecture description for GPRS on this level should describe each reference point/interface in the model. The GSM 03.60 also does that by providing a number of protocol architectures. Such a model slices through a physical network and selects rather arbitrarily certain protocols to be shown. Some of these models from GSM 03.60 are shown in Fig. 4.17. Applications IIP/X.25 IP/X.25 SNDCP SNDCP BSSGP BSSGP UDP/TCP UDP/TCP Network Network Service Service GSM RF GSM RF L1bis L1bis BSSGP BSSGP Network Network Service Service GSM RF GSM RF L1bis L1bis Fig. 4.17 Some protocol architectures defined in GSM 03.60 If we compare these models with the SM&AML terminology, the following conclusion can be made: The burden of understanding the complete contents of a reference poi