s between communicating parties. Each data- gram handshake causes the link to go into an appropriate well defined state. These states are the basis for handling the communi- cation service such as speech, video or data transmissions. In this context, one encounters terminology that is familiar from Figure 61.35 F./acoustic measurements (GSM) analogue cellular radio networks: 1. Registration. 2. Call set up by the mobile subscriber. 3. Call set up by the fixed network subscriber. 61.14 Test set up configurations 4. Call clear down. 5. Channel change over within cell or to another cell. The set up for GSM will be configured SO as to permit both data 6. Power control levels. analysis (protocol checks, error rates etc.) and analogue measure- 7. Queue mode. ments. As the measurements specified by GSM are nearly always Speech Speech Demod Decod. Decod. Acoustic Digital testing testing Figure 61.34 Division of measurements into r.f. (digital) and audio (acoustic) Test set up configurations 61/31 Test set Test set Stimulation Measurements Stimulation Response Conventional interpretation Mobile station Mobile station Figure 61.36 Comparison between conventional mobile and GSM measurements set up for receiver made on closed radio sets, there is a need for test procedures which to the factory control by means of standard interfaces such as can supply information about the behaviour of the set using the Ethernet. signals that are available. 61.14.2 Base stations 61.14.1 Mobile station measurements Because of the widespread use of modular techniques, the distinc- The test set up for mobile station type approval measurements is tion between transmitter and receiver measurements is more marked fundamentally different from conventional (analogue) test set up, as in the base station than in the mobile station. To perform measure- shown in Figures 61.36 and 61.37. Because of the loop back tech- ments on the modules, further interfaces in addition to the r.f. nique used, the test set has to rely exclusively on the r.f. port without