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The Invention of the Phase 21 Concept In 1992 SMG had to stop adding new items to the phase 2 work programme. It was nevertheless clear that there would be something after phase 2. Some proposed to call it ‘‘phase 3’’. This would of course have later caused some confusion with third generation. But the actual reason why SMG rejected this expression is that it would have suggested a phase 2/phase 3 transition similar to the phase 1/phase 2 transition, while it was thought that, for this further evolution, one should aim at a full cross phase compatibility | GSM and UMTS The Creation of Global Mobile Communication Edited by Friedhelm Hillebrand Copyright 2001 John Wiley Sons Ltd ISBNs 0-470-84322-5 Hardback 0-470-845546 Electronic Chapter 5 Evolving the Services and System Features to Generation 2.5 by the GSM Phase 21 Program Section 1 The GSM Phase 21 Work in ETSI SMG 1993-1996 Philippe Dupuis1 5.1.1 The Invention of Phase 21 5.1.1.1 The Invention of the Phase 21 Concept In 1992 SMG had to stop adding new items to the phase 2 work programme. It was nevertheless clear that there would be something after phase 2. Some proposed to call it phase 3 . This would of course have later caused some confusion with third generation. But the actual reason why SMG rejected this expression is that it would have suggested a phase 2 phase 3 transition similar to the phase 1 phase 2 transition while it was thought that for this further evolution one should aim at a full cross phase compatibility. It would not have been indeed acceptable to impose a retrofit or upgrading to all networks each time a category of mobile equipment with novel features is introduced to suit a particular market requirement. As explained in Chapter 4 such a full cross phase compatibility required more complexity in the mobile equipment but this was now feasible in most cases. Even in phase 2 a trend in this direction existed with the decision to have mobile equipment with multiple encryption algorithms or multiple speech codecs. The expression phase 3 having been rejected different periphrases were used such as beyond phase 2 or the further work programme . Then at the beginning of 1993 PT12 invented the expression phase 21 which was immediately adopted without debate. It appeared for the first time in the meeting report of SMG 6 Reading March 1993 . Phase 21 was considered to be open ended. Its objective was to allow GSM to adapt to new 1 The views expressed in this section are those of the author and do not necessarily reflect the views of his affiliation .
