SDN and NFV Evolution Towards 5G
Marie Paule-Odini, HPE
IEEE Softwarization, September 2017
SDN and NFV have now been around for some years with an uptake in telecom network a bit slower than expected but these technologies are definitely shaping 5G as initiated by NGMN .
This article will highlight the relationships between SDN, NFV and 5G networks.
Standards have this reputation of being slow but standards are still the only way the telecom industry knows to guarantee interoperability, free enterprise and sustainable business to guarantee secured, open, reliable and continuously innovative worldwide communications. 3GPP, that has been shaping mobile telecom networks for years now, is no exception with its three stages approach of requirements, architecture and protocols!
Yet, in June 2017 a number of operators eager to experiment 5G new radio technologies have convinced 3GPP RAN to accelerate and ‘simplify’ the roadmap to issue a first phase a bit ahead of schedule. They agreed on a non-standalone option that will connect the new radio to an LTE network. Then, issue the second phase with standalone 5G.
In the meantime, actors in Asia, and KT in particular, has issued its own specifications to be ready for the Olympics in Korea in 2018, bringing live experience, then influence the 3GPP standard specifications and re-align to the common standard.
Below timeline provides an overview of 5G milestones:
Fig 1 – 3GPP 5G timeline and other events
5G initial specifications
If we look into the initial specifications that have been published, and primarily the architecture specifications 3PP TS 23.501 , we discover a clear split between user plane and control plane following the SDN concepts, and consequently a number of new network elements, with new reference points and new interfaces. The requirements such as IoT or ultra low latency for instance are also driving the need for enhanced or new protocols.
Fig 2. 5G non roaming architecture – source 3GPP TS 23.501 
- The UPF (User Plane Function) and SMF (Session Management Function) in the control plane replaces the SGW–PGW that we know in LTE.
- The AMF (Access and Mobility Management) replaces the MME
- The AUSF (Authentication Server Function) replaces the MME/AAA
- The NEF (Network Exposure Function) is a SCEF evolution and API layer
- The NRF (Network Repository Function) plays a role of evolved DNS
- The PCF (Policy Control Function) is a 5G PCRF
- The UDM (Unified Data Management) is an evolution of HSS and UDR
- The AF (Application Function) is the application layer, like gsmSCF or AS
- The SDSF (Structured Data Storage network function) is now UDR
- The UDSF (Unstructured Data Storage network function) would store states and other information – SDSF and UDSF may be collocated and located with UDM
Clearly from the list above, we identify a number of network elements that are a smooth evolution from LTE, ie PCRF becoming PCF, while for others the evolution is a major impact: typically for SP-GW being split in UPF for the user plane and SMF for the control plane. Similarly the AAA-HSS evolution to AUSF-UDM and storage with SDSF and UDR. More generally speaking we are moving to a Service Based Architecture, more and more IT like, and more and more stateless functions with state and other data being stored in separate components and shared data layer. As 3GPP Release 15 progresses into Stage 3, more details will be provided and of course Release 16 will even refine further for 5G Standalone.
5G and NFV
3GPP SA5, the group that is defining the management of 3GPP networks, has been working with ETSI NFV for some years now, actually starting in Release 13 with 3GPP TR 23.842 . Figure 3 below, where 3GPP defines on the left hand side the Network Element (NE) that are not virtualized (PNF – Physical Network Function), the ones that are virtualized (VNF – Virtual Network Function) as defined by ETSI, the traditional vendor Element Manager (EM) which actually tend to disappear with NFV and DevOps but are still there in the picture or embedded in VNF, interfacing with the Network Management (NM) layer sitting in the OSS. On the right hand side, the NFV MANO (Management and Orchestration) as defined by ETSI NFV, that manages the virtualized infrastructure, the virtualized network functions (VNF) and the network services (NS) that span across VNF and PNF. So besides adopting NFV MANO, NFVI and VNF, 3GPP is also adopting the Os-Ma-Nfvo interface with the 3GPP NM-OSS and the Ve-Vnfm-em interface with the 3GPP PNF-EM.
Fig 3 – Network Management mapping between 3GPP and ETSI NFV – source 3GPP TR32.842 
3GPP has expanded on this ETSI NFV adoption in Release 14 with TS28.525, 526, and 527  specifications, with 3GPP TS28.527  being the shortest 3GPP specifications published, basically referencing ETSI NFV IFA008  and IFA013  for Os-Ma-nfvo and Ve-Vnfm-em interfaces and information model in a couple of pages!
In parallel, ETSI NFV is expanding its work in ETSI NFV Release 3 to explore and address some of the 5G new use cases and requirements, as described by the ETSI NFV. This includes work items on Network Slicing that I personally initiated (NFV-EVE012) but also other topics such as Cloud Native addressing containers (NFV-EVE011), Real time management (NFV-IFA025), but also Policy Management (NFV-IFA023), in line with the recent ETSI ISG ENI .
5G and SDN
In line with previous work from IETF or ONF and projects experimenting SDN use cases or SGI-Lan service chaining, 3GPP has introduced EPC Control Plane-User Plane Separation (CUPS) in Release 14. Typically for SGW, PGW and TDF, three new interfaces were defined: Sxa, Sxb and Sxc in TS 23.214  as illustrated in Figure 4.
Fig 4. 3GPP User Plane – Control Plane Split – source 3GPP TS 23.214 
Then in June 2017, 3GPP selected a new protocol between these control plane and user plane layers: PFCP, Packet Forwarding Control Plane, as shown in Figure 5.
While lots of work had been done in the research and industry community using Openflow and SDN controller to configure EPC user plane, 3GPP study compared a few protocols, including Forces, Openflow, GTP and Diameter against the requirements for 5G and concluded that gaps were too important and most effective was to define a new protocol, using UDP and managing Sx node procedure as well as Sx session procedures.
Fig 5. 3GPP PFCP protocol – source TS 29.244
Network Slicing Use Case and 5G
The network slicing concept has been introduced several years ago by NGMN 5G white paper : “A network slice, namely “5G slice”, supports the communication service of a particular connection type with a specific way of handling the C- and U-plane for this service. To this end, a 5G slice is composed of a collection of 5G network functions and specific RAT settings that are combined together for the specific use case or business model”. NGMN then refined in their dedicated paper on network slicing  with a definition that set the stage for further work in the industry: “Network Slice Instance: a set of network functions, and resources to run these network functions, forming a complete instantiated logical network to meet certain network characteristics required by the Service Instance(s)”. At this stage, some of the key principles were set such as end to end network slice and logical instance associated to a service. To be pragmatic this slice could combine a set of virtualized and non-virtualized functions.
Then ONF explained how to define and manage network slices  with SDN as described in Figure 6.
Fig 6. ONF and Network Slicing – source ONF 
Lately 3GPP embraced the concept in TS 23.799  and is now studying the management and orchestration of slices in TR28.801 , with a CSP (Communication Service Provider) invoking a Communication Service that ‘uses’ a NOP (Network Operator) Network Slice. This Network Slice ‘contains’ Network Slice Subnets which contains Network Functions (virtualized or not …). These Network Functions are from Access and Core Network. However 3GPP has not defined yet the mapping between Network Slice or Subnet and ETSI NFV Network Services, but others have suggestions. In the 5G America’s paper on Network Slicing  that I co-authored, we agreed that network slices would invoke ETSI NFV network services via NFV MANO, and several 5G-PPP projects took the same path.
In parallel and fueling the standard work, many projects and initiatives also tackle the 5G topic and study the leverage of SDN and NFV technology to deliver next generation networks. I have picked a few examples in this article that illustrate different scenarios.
The European 5G Public Private Partnership (EU 5G PPP) which is sponsored by the European Commission has a series of projects with currently two running phases: a phase 1 which is nearly completed and a phase 2 that is just started. Among those, the 5G-Ex project  where HPE is participating along with Orange, Telefonica, and other ICT actors, is studying next generation networks and management aspects, including virtualization, SDN, slicing, and multi-domain, multi-operator domains. 5G-Ex is typically defining inter-operator interfaces for slice and resource management for more and more dynamic and automated network environments.
Fig 7. 5G-Ex project architecture 
Another interesting project is 5G Lab Germany  which is exploring network coding for 5G radio and SDN as well as Edge IoT use cases for connected cars and robots, addressing the requirements of 5G ultra low latency and tactile internet. This collaboration of industry players with academic research is the secret sauce to break through on some of these complex topics which involve high performance hardware, very flexible architecture and efficient software.
Fig 8. 5G Lab Germany project overview 
Overall, a lot of things are going on, too many things probably for an industry that is transforming rapidly with challenging revenue models, shrinking resources to contribute, align and implement something that will work! but lots of new opportunities coming with 5G and beyond the pure 3GPP-5G as it is shaping now. BBF (Broadband Forum) is building its own 5G roadmap with lots of SDN and NFV very likely and will align with 3GPP as shown below in Figure 9 to deliver 5G Fixe Mobile Convergence (FMC) by 2020. So more changes to come in an ever innovating world!
Fig 9. 5G Fixe Mobile Convergence Timeline 
 Next Generation Mobile Networks (NGMN) Alliance: 5G white paper
 NGMN Alliance: "Description of Network Slicing Concept", Version 1.0, January 13, 2016
 3GPP TR 32.842: “Study on network management of virtualized networks”; Release 13
 3GPP 23.714 v14.0.0 - Study on control and user plane separation of EPC nodes; Release 14
 3GPP 23.214 v14.3.0 - Architecture enhancements for control and user plane separation of EPC nodes; Stage 2; Release 14
 3GPP TS 28.500: "Telecommunication management; Concept, architecture and requirements for mobile networks that include virtualized network functions".
 3GPP TS 28.527: Life Cycle Management (LCM) for mobile networks that include virtualized network functions; stage 2; release 14
 3GPP TS 22.261 v2.0.0: “Service requirements for the 5G system; Stage 1”.
3GPP TR 23.799 v14.0.0: “Study on Architecture for Next Generation System”. Dec. 2016.
 3GPP TS 23.501: "Technical Specification Group Services and Systems Aspects; System Architecture for the 5G system; Stage 2"
 3GPP TR 28.801 V1.2.0; Study on management and orchestration of network slicing for next generation network; release 15
 ETSI GS NFV-IFA 008 (V2.1.1): "Network Functions Virtualisation (NFV); Management and Orchestration; Ve-Vnfm reference point – Interface and Information Model Specification".
 ETSI GS NFV-IFA 013 (V2.1.1): "Network Functions Virtualisation (NFV); Management and Orchestration; Os-Ma-Nfvo reference point – Interface and Information Model Specification".
 ETSI ISG ENI – Experiential networked intelligence
 ONF paper on Applying SDN architecture to 5G Slicing
 5G-PPP 5GEx - http://www.5gex.eu/
 5G Lab Germany - http://5glab.de/
 BBF – 5G Fixe Mobile Convergence
 5G Americas Network Slicing White Paper
Marie-Paule Odini holds a master's degree in electrical engineering from Utah State University. Her experience in telecom experience including voice and data. After managing the HP worldwide VoIP program, HP wireless LAN program and HP Service Delivery program, she is now HP CMS CTO for EMEA and also a Distinguished Technologist, NFV, SDN at Hewlett-Packard. Since joining HP in 1987, Odini has held positions in technical consulting, sales development and marketing within different HP organizations in France and the U.S. All of her roles have focused on networking or the service provider business, either in solutions for the network infrastructure or for the operation.
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