o-called Feature Sets have been defined to store the combination of capa- bilities supported within one band in a band combination: each feature set is reported only once but can be associated with any band. By combining multiple such feature sets, it is then possible to indicate support for multiple alternative feature sets, as shown in Figure 7.22. This allows that a single Feature Set can be reused in multiple band combi- nations, thus avoiding duplication. 7.7.7 Different Versions of Release 15 RRC Specifications Release 15 NR was released in three different waves, as was described in Chapter 2. The "early drop" with non-standalone NR (only supporting E-UTRA - NR Dual Connectivity), the NR standalone drop (supporting NR but not NR DC), and the "late drop" NR standalone (supporting NR DC and additional architecture options). 7.9 Summary FS ID FS ID Feature Set ID combinations (1..M) Band 1 FS1,1 FS 1,3 Band 2 FS2,1 FS DL1 FS UL FS3.1 FS DL2 FS UL2 Band 3 FS DL3 FS UL3 Band Z Feature Set ID combination per band FS DLX FS ULX Feature Sets (DL and UL) Band Combinations (1..M) Figure 7.22 UE capability feature set and feature set combinations. While the traces of the "RRC versioning" are visible in the RRC specifications, they are not obvious without understanding how ASN.1 works. There are several different ways to extend signaling in ASN.1: using the so-called extension markers (denoted with ellip- sis, i.e. three consecutive dots), using encapsulated extensions (via OCTET STRINGs that hide the content from the decoders through which parts of the message might pass), and the so-called "empty SEQUENCES" (which can be added only at the end of a mes- sage and are signified by leaving an undefined container at the end of the message SO that the container contents are defined only in later versions). All of these mechanisms are used in RRC (for various reasons), but each one signifies that a specification has been extended at some point of time. 7.8 Radio Protocols in RAN Architecture The division of the radio protoc