All answers have been held as short as possible and require an understanding and study of the corresponding chapter of the book.
The basic concept of the 5G Non-Standalone architecture is to add a 5G NR cell as a speed booster to an existing LTE radio and core network. It is different from LTE carrier aggregation as the 5G cell acts independently from the LTE part of the connection. Data is transmitted over LTE and 5G NR simultaneously.
TDD = Time Division Duplex, e.g. used in band n78. Uplink and downlink are transmitted over the same channel. FDD = Frequency Division Duplex, typically used in frequency bands in Europe < 3 GHz. Uplink and Downlink are separated in the frequency domain, i.e. they use different channels. Hence, uplink and downlink are transmitted simultaneously.
In 5G NSA, data is transmitted over LTE and 5G NR at the same time. Typically the 5G gNB receives the data, splits a apart of it away and forwards it to the LTE part of the connection while it transfers another part itself.
In the uplink direction LTE and 5G use different frequencies and one transmitter in the UE is required for each channel as data is transferred simultaneously over both legs of the connection in the uplink direction.
In 5G NR, a UE does not necessarily need to support the full channel bandwidth and can be assigned only a part of the channel on the frequency axis. Also, a network might decide to assign different bandwidth parts to a UE to conserve power with a narrow BWP while only small amounts of data are transferred.
The CORESET is the Control Region Set, i.e. the control regions the UE has to monitor on the channel for uplink and downlink assignments.
Dynamic Spectrum Sharing (DSS) can be used to transmit LTE and 5G NR on the same channel. This way, the channel can serve older LTE only mobiles and newer 5G NR mobiles. This is done by transmitting the control channels of LTE and 5G NR in the channel at different times and by using several methods and signaling alignments for 5G NR devices to only notice the 5G transmissions while LTE devices only see the LTE signaling channels and reference signals.
The LTE eNB and 5G NR gNB have independent schedulers and communicate over the X2 interface which each other. This way, handovers can be made independently as only the X2 connection is switched. In practice it often occurs that the LTE and 5G NR parts are served by different sites. The uplink/downlink data is split/combined at one of the two sites.
The idea behind the Service Oriented Architecture is to leverage container technology in combination with microservices and stateless communication to build a highly adaptable, configurable and scalable 5G core network.
5G registration management is performed by the Access Management Function and deals with authentication of subscribers and managing their presence in the network. Session management on the other hand is managed by the Session Management Function and deals with the establishment with user plane bearers between the mobile device and an external network such as the Internet.
In RRC-Idle state, no active connection exists between the mobile device and the gNB over the air interface. Also, the signaling connection and the user data tunnel to the core network have been removed. In RRC-Inactive state, only the air interface connection is removed while the connection between the gNB and the core network remains in place. This significantly reduces signaling when connectivity needs to be restored.
The idea of Network Slicing is to have a single end to end network and serve devices with different requirements in different ways. On the air interface, different parts of the channel can use different configurations. One part of the channel could be used for fast Internet access, while another part, that is configured differently could be used for slow but very reliable communication. Other parts of the network can be sliced in a similar manner.