  The journey towards the deployment of next generation networks has recently
accelerated, driven by the joint effort of research and standards
organisations. Despite this fact, the overall picture is still unclear as
prioritization and understanding on several key concepts are not yet agreed by
major vendors and network providers. Network Slicing is one of the central
topics of the debate, and it is expected to become the key feature of next
generation networks, providing the flexibility required to support the variety
of 5G use cases and business. Network slices are seen as network operator
business, offering the possibility to provide flexible services and even
infrastructures to vertical industries and classical Telco customers alike.
Another key ingredient is the Architecture Modularisation concept, discussed in
this paper and regarded by the authors as the essential design principle to
build a flexible network architecture natively supporting Network Slicing.
According to this concept, conventional monolithic network functions, often
corresponding to physical network elements in the existing systems, are to
split into basic building blocks defined with the proper granularity, allowing
the definition of different logical architectures (i.e. different Network
Slices). In this paper, we further discuss a modularisation methodology as a
criteria to define the right set of basic building blocks. Defined through this
proposed methodology, the set of basic building blocks and the relating
interfacing model are discussed. The paper concludes by proposing a modular 5G
network architecture as candidate for next generation network standards.
