5G Technology: 3GPP New Radio, First Edition. Edited by Harri Holma, Antti Toskala, and Takehiro Nakamura. © 2020 John Wiley & Sons Ltd. Published 2020 by John Wiley & Sons Ltd. 5 5G Architecture Standalone architecture Non-standalone Solution 3x with 5G-core (3GPP Solution 2) with data split in 5G BTS 5G BTS LTE eNodeB 5G BTS Radio Control Plane User Plane Figure 5.1 Main architecture options for initial 5G roll-outs. the work progressed the following two main architecture options emerged, with slight difference in timing as discussed in Chapter 2. First in the finalization schedule was the approach with LTE as the connection anchor and using the existing LTE core, with 5G radio as the secondary cell (Architecture option 3). Next to be completed was the stan- dalone 5G radio with the new 5G core (architecture option 2). The options illustrated in Figure 5.1 can be described as follows (in the order of finalization in 3GPP): Option 3 refers to the architecture option which uses LTE as the anchor for the con- nection as well as connecting for via the existing EPC. 5G is only on the user plane in the radio part, which is then used with dual connectivity with LTE. For routing the user plane data, there exist further alternatives, creating different variants from option 3, as described later. From the service point of view, only enhanced Mobile Broadband (MBB) is available. Option 2 refers to architecture with 5G radio connected to the 5G core network. This enables all new functionality brought by the 5G core, such as Service-Based Architec- ture (SBA) or network slicing as described later in this chapter. The Release 15 services offered include the enhanced MBB as well as Ultra Reliable Low Latency Communi- cation (URLLC), but cover also basic services such as voice over 5G. There is no need to operate with LTE-5G dual connectivity in this architecture, and thus this is similar for roll-out as LTE was originally (though 5G-5G dual connectivity was enabled in a later phase). Option 2 enables interworking with LTE (ha