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An overview of the 5G mobile network architecture

Cost Efficiency. Due to virtualization the network functions earlier realized on costly hardware are now implemented as software function over a low-cost hardware. Also 5G eradicates the need of a dedicated network for each service, since different requirements can be satisfied by multiple logical networks (slices) over a single physical network, making the network cost-effective.

VI. Discussion and Challenges

This section describes some of the implementation and research challenges involved in realizing 5G mobile networks.

A modular refactoring of the functionalities of the existing EPC that is carried over into the 5G architecture is needed. In this process, integrating these modular functions with the new 5G EPC functions that are NOT a carry over from the previous generations, is an important problem in deriving the Control Plane or the CP or the C-Plane for 5G. The important aspects such as security, connectivity management and mobility aspects of these control functions of the C-Plane is an important research area. The orchestration aspects as well require a proper and elegant design in this regard. With specific aspects such as Virtual Machine / Container instantiation, assignment and placement in the proper Data Center location whether it be Core, Edge or Site function Data Centers is important. Their consequent movement later on to another location within the DC or across DCs of the said provider depending on traffic load or basic reassignment to cater to different slices also require careful thought of the basic control plane software infrastructure design and implementation.

Migration of some of the important NFs in the C-Plane from one DC to another require careful procedures for moving and consistently maintaining the state required for the Load Balancers and for the NF and their associated Micro-services themselves to be designed and implemented. Clustering a group of NFs, more than one of a variety and instantiating the Service Chain of such related NFs for a Network Slice catering to
a set of UEs thus providing a hybrid Centralised and locally distributed Control Plane of Control Planes (in a sense a hierarchical C-Plane for the CPlaneNFs) is an important requirement to consider to scale the C-Plane controllers.

When building a hierarchy of controllers for the orchestration design points relating to consistency, race condition handling and appropriate connectivity management and security with mobility considerations need to be taken into account. As the envelope is pushed further and further with respect to scalable and flexible design, innovative design points need to be accorded sufficient amount of attention.

Re-use of existing protocols for service chaining such as Segment Routing based MPLS could be accorded attention as well. The reason for that is that each NF instance in the C-Plane would require a label (such as the one used in MPLS) to be assigned to it to be accorded the place and order required by the C-Plane NF in a series of Service Chain events that need to be accorded to a packet going through that service Chain. Segment routing has a natural placeholder for the architecture required to solve this problem. Relevant connectivity of the C-Plane orchestrator with the load-balancers themselves is also important to assign a stack of such labels to a packet entering the Site DC, Edge DC or the Core DC where the direction of the packet is decided when routed through such a service chain. We deal with abstracting the other physical resources such as the Transport and other core items in the physical infrastructure for network slicing in the end of this section.

With regard to the UDM, UDR functionalities providing an appropriate view of the schema that needs to be
exposed to the other related NFs that require services from it, is also to be worked on. The security aspects of such exposure and the required encryption that needs to be done to protect such data flowing is another area of research that needs to be attended to.

Inter-provider agreements between multiple service providers would require a restricted view and appropriate security for the data flowing in and out of the UDR module and appropriate procedures put in place for the request and reply protocols for such subscriber data. Caching of such data in the appropriate DCs involved would also require careful attention and solutions for keeping the caches consistent would have to be tied together in the solution as well.

Service discovery for the NFs in the C-Plane is another important work item to be considered. An array of
cloud solutions are available for this and choosing the appropriate one requires careful attention. A dynamic generation of DNS records based on the refactoring and movement of the individual NF instances as they appear and disappear and reappear elsewhere in the network could be a possible solution for this problem. Slice monitoring and assignment of the individual NFs to the respective slices created and destroyed requires careful design and implementation. The solution should be scalable and more importantly be flexible.

The Management and Orchestration of the C-Plane NFs and the D-Plane resources in consort with each
other taking into account the proximity considerations and the load factor is an important aspect as well.

Another important aspect is online and offline charging and the related policies that need to be applied for QoS and QoE of the individual services offered for a UE is another important aspect. Proper and consistent and errorless accounting of the packets being maneuvered through different slices in the network is primary to the proper operation of the services.

Traffic detection frameworks that need to be deployed need to be given proper consideration. The TDF
functions in the 5G core need to be scalable and appropriately flexible to work in consortium with any network slice in operation. Slice creation orchestration with appropriate attention to the load of the various NFs instantiated should be a distributed solution and appropriately centralized to the extent to make a proper and informed decision as to which NFs to assign to each slice and for appropriate scale up and down decisions.

With concept of network slicing creating a picture where it is NOT only the C-Plane functions that need to be carved out into slices, but also the Core Resources such as the Transport networks that connect Site, Edge and Core Clouds, and the Orchestration layer as well need to be sliced up. This provides for a scenario where the E2E network and other resources are abstracted for slicing into slices that carve up the shared physical infrastructures whose architectures could be multiple instances of varied combinations of what we know to be these resources, into a further varied architectures of logical resources grouped together as slices. This is an important point to understand in order to get a holistic view of a Many to many mapping of logical slices to actual physical infrastructure blocks of varied resources which are physical.

The physical infrastructure should project (and solutions need to be offered here) an abstraction and allocation strategy layer to the Network Slicing layer above this strategy layer to project actual physical resources and APIs to actually carve these physical resources and group them into network slices with their components in place for service delivery.

With regard to security, the strata where the physical components of varied architectures reside, may be
combined to form a logical network slice, hence the security aspects and requirements for each of the physical pieces put together for the logical network slice may be different but need to be managed as one single whole security strategy for the said network slice.

In summary there are many more issues and design roadblocks that may be faced in the future and as
these problems crop up suitable solutions need to be developed and implemented.


VII. Conclusions

This paper presented a survey of the 5G network architecture and its important components. Most of the
discussion was focused on the Next-Generation RAN (NG-RAN) and the Next-Generation Core (NGC) components. A discussion on research and implementation challenges in realizing 5G network systems was also presented.

Acknowledgments: Part of this work was supported by a project funded by the Government of India’s Department of Telecommunications.



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