3.2 Important New Concepts of UMTS
As described in the previous paragraphs, UMTS on the one hand introduces a number of new functionalities compared to GSM and GPRS. On the other hand, many properties, procedures and methods of GSM and GPRS, which are described in Chapter 1 and 2, have been kept. Therefore, this chapter first focuses on the new functionalities and changes that the Release 99 version of UMTS has introduced compared to its predecessors. In order not to lose the end-to-end nature of the overview, references are made to Chapter 1 and 2 for methods and procedures that UMTS continues to use. In the second part of this chapter, advancements are discussed that were introduced with later releases of the standard such as HSPA. These enhancements complement the Release 99 functionality but do not replace it.
3.2.1 The Radio Access Bearer (RAB)
An important new concept that is introduced with UMTS is the Radio Access Bearer (RAB), which is a description of the transmission channel between the network and a user. The RAB is divided into the radio bearer on the air interface and the Iu bearer in the radio network (UTRAN). Before data can be exchanged between a user and the network it is necessary to establish a RAB between them. This channel is then used for both user and signaling data. A RAB is always established by request of the MSC or SGSN. In contrast to the establishment of a channel in GSM, the MSC and SGSN do not specify the exact properties of the channel. Instead, ...