Let's start with simple definitions for these two type of architectures
Reference Point architecture consist of a set of Network Elements (NE) which use point to point interfaces to inter-connect those Network Elements.
Service Based architecture replaces the set of Network Elements with a set of Network Functions (NF). Each Network Function is a service provider to other Network Function(s).
5G Reference Point System Architecture
5G System Reference point architecture is shown in Figure below. It lists a set of Network elements and set of point to point interfaces which interconnect those Network Elements (functionality of these network elements is not listed in this article)
5G System Service Based System Architecture
5G System service based architecture is shown below. It specifies a set of Network Function (NF) and a common bus which connects these Network Functions.
Service based architecture is applicable to the control plane section of 5G Core Network only.
Network Function Repository Function (NRF) plays a central role within the Service based architecture. Network functions register the services they offer with the NRF. They use NRFas a database to discover the services offered by other Network Functions. Following three mechanisms are used.
Services Offered by a Network Function
Example of services offered by a Network Function is presented in the Table below. This table represents the services offered by Access and Mobility Management Function (AMF).
The list of Network Functions which are described in 3GPP standards are listed in the table below.