The emerging of open source within 5G networks — Part 1

“5G” and “open source” are by far two of the hottest topics in the telecom industry over the past few years. Mobile operators have begun deploying the solutions produced by these projects to demonstrate the real-world benefits of 5G and open source. So far any 5G deployment has a presence on the access part of the network and demonstrates large bandwidth the other important and critical as LLURC and mIOT are at the design stage as it required a redesign of the core. 5G system architecture has been defined, but many of these initial deployments are expected to have the interoperability challenges that 3G and 4G faced. However, 5G system architecture gives mobile operators more openness than previous generations.

There are quite a few similarities between the standards and open-source paradigms. Both have the objectives of increasing interoperability, reducing costs and facilitating the establishment of business models. The difference has to do with how to achieve those goals. Previously, standards have been developed using consensus-based collaboration within telecommunication vendors in a process that included written of the specific standard. This is no different from open source projects, with the exception that for open source, contributions are in a form of developing and running code. Open source projects can bring implementation transparency during the standardization process, as well as after the finalization of a standard as a way to establish reference implementations, in other words bringing agile in a word that was based on waterfalls. Therefore, open-source projects should be considered complementary to standards development, as a way to accelerate and improve the process of creating interoperable solutions.

“Softwarization” of telecommunication networks has been a major consideration in the development of 5G Core. The control plane in the 5G NGC, 3GPP decided to move away from traditional monolithic logical functions that used telecom-centric protocols (e.g. GTP) to communicate by adopting an architecture that is defined as “service-based” where the control plane is more modularized than the EPC (4G). These modules are called Network Functions, the NFs comprise of one or more services that can be described as submodules. Interaction between NFs is based on Interfaces that are generally web services conforming to REST, or RESTful in nature. Another aspect of the 5G architecture that brings it closer to “cloudification” and softwarization is the concept of network slicing. With this concept, it is now possible to virtualize the 5G core and run several logical instances as needed based on scale, each instance being optimized by a set of predefined KPI’s. Prior to the start of 5G work the EPC had already separated the User Plane and Control Plane functions of the packet core. This concept of separation, which is also aligned with SDN principles, was carried forward into 5G and used as a basis for the 5G system.

Add alt text

Let’s take a look at the 5G control plane core components:

AMF- Access and Mobility Management Function

AMF is responsible for the termination of the Radio Access Network (RAN) CP interface, carries NonAccess Stratum or NAS signaling (therefore, communication between the User Equipment (UE) and Core) and terminates ciphering and integrity protection for communication over NAS. Some of its key functionalities include access authentication and authorization, mobility, reachability and connection management.

SMF — Session Management Function

The SMF is responsible for session-management-related functionalities including User Plane Function (UPF) tunnel maintenance and UE Internet Protocol (IP) address allocation. It also has roles in UPF functionality selection, in lawful intercept and in charge and policy-related communication between the CP and UP.

PCF — Policy Control Function

The PCF provides a unified policy framework for use by the network operator. Among other inputs, it also makes use of subscriber data stored in the Unified Data Repository (UDR) and develops policy rules for the control plane that help manage network behavior.

NEF — Network Exposure Function

The NEF exposes capabilities and events from one NF to other NFs and to third parties. In the process, it stores and retrieves data in the UDR as needed. When third-party exposure is used, the Common API Framework (CAPIF) is also supported by the NEF to offer common sets of functionalities such as third-party authentication.

NRF — Network Repository Function

The NRF maintains a list of available NF instances and the services that each NF supports. NRF may have such info at a slice level or at Public Land Mobile Network (PLMN) level. It is used by an NF instance for the discovery of other NF instances where the requested service may reside. It can also be used in a roaming case.

UDM — Unified Data Management

The UDM is responsible for functionalities such as the generation of authentication credentials and for access authorization based on subscription. Located in the Home PLMN (HPLMN), the UDM uses UDR for storage and retrieval of information used in its transactions.

AUSF — Authentication Server Function

The AUSF supports functionality associated with the authentication of the UE.

AF — Application Function

An AF is used to interact with the 3GPP Core Network Functions such as PCF for influencing network policies, or NEF for accessing network capabilities and events. An AF can be owned by the operator or a third party.

UDR — Unified Data Repository

An UDR is a common repository for subscription data, policy data, and exposure-related data. A UDR and an NF accessing, it is assumed to be in the same PLMN.

NSSF — Network Slice Selection Function

The NSSF is used primarily for selecting instances of slices that would be used to serve a UE based on the information provided by the UE. The NSSF gets slice-level congestion information from the Network Data Analytics Function (NWDAF0 that can help in load balancing across multiple slice instances.

NWDAF — Network Data Analytics Function

NWDAF is an operator-managed network analytics function. In Release 15, NWDAF provides only slice specific congestion-related information to the NSSF and PCF.

UPF — User Plane Function

The UPF acts as the mobility anchor point for user data and hence is the mobility tunnel’s termination point. It provides user connectivity to external networks. Along with packet routing and forwarding, it also performs operator policy enforcement (for example, Quality of Service (QoS), packet marking) in the user plane, lawful intercept, and collection of charging-related data. Not all functionalities need to be supported in a UPF instance. Multiple UPF instances can be placed in the path of IP flow with different sets of functionalities.

In order to provide massive amounts of bandwidth to a massive number of devices, there is a need to transform the network to be able to scale up and be agile while reducing cost. Network disaggregation with separation of user and control plane, separating out the network operating system from the underlying hardware, and the use of general-purpose processing platforms is the key to creating networks that are massively scalable, agile and inexpensive. Disaggregated hardware provides high performance at lower costs via approaches such as specialization of tasks. Some of the projects representing each approach are:

• Open Compute Project (OCP), whose mission is “to apply the benefits of open source to hardware and rapidly increase the pace of innovation in, near and around the data center and beyond.” 9 OCP’s Telecom Working Group has developed the CG-OpenRack-19 specification. This specification offers telecom data center operators the benefits of open platform standards combined with the needed carrier-grade and environmental enhancements required for edge computing,10 which will be one of the most important building blocks for successful 5G deployments.

• Disaggregated Network Operating System (DANOS) is an open and flexible alternative to traditional networking operating systems. DANOS will support a network operating system framework that leverages existing open-source resources and complementary platforms such as switches and white box routers.

• P4 is an open-source initiative designed primarily to provide a declarative language for interacting with networking forwarding planes. P4 programs specify how a switch processes the packets. P4 controls silicon processor chips in network forwarding devices such as switches, routers and network interface cards.

• O-RAN alliance

• Openness and intelligence for the next generation of wireless networks and beyond. Building a more cost-effective, agile RAN requires openness. Open interfaces are essential to enable smaller vendors and operators to quickly introduce their own service.
• Intelligence Networks will become increasingly complex with the advent of 5G, densification and richer and more demanding applications. To tame this complexity, we cannot use traditional human intensive means of deploying, optimizing and operating a network. Instead, networks must be self-driving, should be able to leverage new learning-based technologies to automate operational network functions and reduce OPEX. Leveraging open source is important for enabling a high-performance, flexible 5G user plane.

There are other various open-source networking initiatives — such as:

• Data Plane Development Kit (DPDK)
• Vector Packet Processing (VPP)
• Fast Data Input/Output Project (FD.io)
• Mobile Central Office Re-architected as a Datacenter (M-CORD)
• National Ground Intelligence Center (NGIC)
• Open Virtualized multilayer Switch (Open vSwitch or OVS)

Those project could provide the necessary optimizations, bringing in the ability of the user plane to scale and handle increased throughput necessary for 5G use cases and services.