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  • 5G Core Network – a Short Overview

    5G Core Network – a Short Overview

    Date: 05.06.2017

    Category: 5G, Mobile Networks

    5G Core Network

    The 5G System (5GS) will have three main components as defined below:

    1. 5G Access Network (5G-AN)
    2. 5G Core Network (5GC)
    3. Use Equipment (UE)

    This blog is dedicated to describing the main components of the 5G Core Network as defined by the ongoing efforts at 3GPP SA [1].

    The 5G system is being designed to support data connectivity and services which would enable deployment, by the industry, using new techniques such as Network Function Virtualization and Software Defined Networking. The need for these new techniques rises due to the various different profiles of data services that need to be supported by the 5G network. So far mobile networks had been designed keeping the average smartphone user in the center but with 5G this is changing as with the boom of data connectivity various use cases having completely different data requirements have come up and the network operator needs to satisfy all these requirements as efficiently as possible.

    Having such requirements in mind the 3GPP has kept the basic idea of having a flat architecture where the Control Plane (CP) functions are separated from the User Plane (UP) in order to make them scaling independent allowing operators to use this functional split for dimensioning, deploying and adapting the network to their needs easily. Another central idea in the design of 5G has been to minimize dependencies between the Access Network (AN) and the Core Network (CN) with a converged access-agnostic core network with a common AN – CN interface which integrates different 3GPP and non-3GPP access types.

    Network Functions of 5G Core Network

    In order to facilitate the enablement of different data services and requirements the elements of the 5GC, also called Network Functions, have been further simplified with most of them being software based so that they could be adapted according to need. The 5G System architecture consists of the following network functions (NF) majority of which constitute the 5GC:

    • Authentication Server Function (AUSF)
    • Core Access and Mobility Management Function (AMF)
    • Data network (DN), e.g. operator services, Internet access or 3rd party services
    • Structured Data Storage network function (SDSF)
    • Unstructured Data Storage network function (UDSF)
    • Network Exposure Function (NEF)
    • NF Repository Function (NRF)
    • Policy Control function (PCF)
    • Session Management Function (SMF)
    • Unified Data Management (UDM)
    • User plane Function (UPF)
    • Application Function (AF)
    • User Equipment (UE)
    • (Radio) Access Network ((R)AN)


    The modularity of the network functions also opens up the possibility to enable another new and efficient feature i.e. Network Slicing.

    The interaction between network functions in the current form is envisaged in the following two ways as per [1]:

    1. The first method is the service-based representation in which one network function (e.g. AMF) within the Control Plane allows other network functions, which have been authorised, to access its services. This representation also includes point-to-point reference points between the NFs where necessary (see figure 1).


    Figure 1: 5G System Service-based architecture [1]


    1. On the other hand is the reference point representation which focuses on the interactions between pairs of network functions defined by point-to-point reference point (e.g. N7) between any two network functions (e.g. SMF and PCF). This kind of representation is used when some interaction exists between any two network functions (see figure 2).


    5G System Architecture

    Figure 2: Non-Roaming 5G System Architecture in reference point representation [1]



    With the development of 5G speeding up1, we can see a clearer picture of what the future generation wireless network would like to be able to achieve. The 5G core network aims to be flexible enough to adapt and satisfy the needs for Gbps seeking smartphone users as well as low latency seeking critical services along with low speed IoT devices. It is also being designed to be more open and modular than its predecessor allowing the different entities inside the core network to interact with each other without any preconditions and allowing to define procedures for this interaction. And this would be achieved with the help of new techniques like Network Function Virtualization, Network Slicing, and Software Defined Networking2 etc.



    [1] 3GPP TS 23.501 V0.4.0 (2017-04)

    ¹ The evolution to 5G and the progress so far has been discussed in the following post: 3GPP Release-15: Further LTE Enhancements and 5G Normative Work Kick-off

    ² Read about the key technologies creating all the buzz around 5G in our blog post: 5G Trends


    Marcin Dryjanski, Ph.D.

    Marcin Dryjanski received his Ph.D. in telecommunications from the Poznan University of Technology in September 2019. During the past 15 years, Marcin has served as R&D Engineer, Lead Researcher, R&D Consultant, Technical Trainer, Technical Leader and Board Member. He has been providing expert-level courses in the area of 5G/LTE/LTE-Advanced for leading mobile operators and vendors. In addition to that, Marcin was a work-package leader in EU-funded research projects aiming at radio interface design for 5G including FP-7 5GNOW and FP-7 SOLDER. He co-authored a number of research papers targeting 5G radio interface design and a book "From LTE to LTE-Advanced Pro and 5G" published by Artech House. Marcin is co-founder of Grandmetric and co-founder and CEO at Rimedo Labs, currently focusing on Open RAN systems.

    2 November 2017 at 07:09

    Hi Marcin,
    Good Morning, I am a telecom software engineer from Bangalore, India. I work at R&D for IMS, LTE and VoLTE domains.

    I would like to know more about 5G technologies, which is the path forward in telecom.
    Also, I would like to know, what would be the IMS signaling path in 5G.


    Marcin Dryjanski
    2 November 2017 at 10:49

    Hi Manoj,

    thanks for your message.

    To get a knowledge on the 5G aspects, I recommend you to go to an online video course, entitled: “Towards 5G: Research and Standardization” from for which we have contributed with technical insights:

    You can use a promocode: GRANDMETRIC to get a 25% discount.


    11 September 2018 at 13:21

    Could you provide the need for the Service Based architecture and Reference Point architecture

    Marcin Dryjanski
    12 September 2018 at 09:06


    thanks for your question.

    The Reference-Point Based Architecture is a legacy type of how we perceive an build mobile systems, and e.g. in case of interworking with EPC, this type of interfacing is needed, as EPC is build upon this way – see the post on this topic and example here: 5G and EPC interworking

    The Service Based Architecture on the other end, is more towards the future and enabling concepts like: Slicing, where you can easily manipulate how the system is composed of. Secondly, this type of architecture enable easier integration of new features, functions or upgrading of the existing ones.

    Hope this helps,

    17 September 2018 at 13:59

    Thanks for the information.
    I just started understanding the 5G technology. I know little bit about the LTE.
    When I co-relate the LTE Core network elements with Reference point architecture
    I can say,
    MME ———- AMF,
    PGW-C ———- SMF
    PGW-U —– UPF
    HSS — UDM. I might be wrong in some cases.

    May I know the remaining AF, AUSF, DN resemblances.

    one more thing , where is the SGW functionalities in 5G

    If I am wrong correct me.

    Thanks in advance.

    Marcin Dryjanski
    25 September 2018 at 11:14


    The answer for your question is pretty much given in the following post on the same topic:, where I put analogies of the 5GC functions to EPC nodes.

    But in short, for example:
    * MME -> is split onto AMF and partly SMF
    * PGW-C -> is partly SMF
    * PGW-U & SGW -> is combined onto UPF
    * HSS -> is split onto AUSF and UDM
    * AF is the same as AF in EPC
    * DN is PDN – it is simply the data network.

    And there are new functions, like NRF, NEF, NSSF etc – please refer to the post on those aspects.

    Hope this helps,

    Aleksandar Otasevic
    20 September 2019 at 12:35

    Hi Marcin,

    Isn’t AUSF in 5G like AAA in 3G,4G?
    Thank You

    Marcin Dryjanski, Ph.D.
    26 September 2019 at 11:56

    Dear Aleksandar,

    AAA was more for non-3GPP access. AUSF is rather part of “HSS” from 4G together with UDM. For more details about the functions themselves in 5G-Core and how they relate to the previous generations, please go to my other blog:

    Hope this helps,

    2 October 2019 at 04:22

    Why is DNS not used in 5G Core and NRF is being used . Can someone please highlight me the usecases which DNS can’t address and using NRF is the best option to identify the services .
    Thanks in advance .

    Marcin Dryjanski, Ph.D.
    14 October 2019 at 20:47


    DNS is used in 5G Core, you can read about the details in the nice paper here:

    In 5G with regard to different services and delay requirements, DNS service can be placed at the edge or in the core (the paper above describes that in details).

    NRF – is having a different role to DNS, NRF relates to the network functions in the 5GCore, while DNS relates to IP addresses to domain names for the end services.

    Hope this helps.


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