The emerging of open source within 5G networks — Part 2
5G brings new requirements and use cases, for example, requiring an entirely new access (RAN) architecture that has open interfaces, flexible and modular. The Cloud-RAN (C-RAN)/Fronthaul Architecture separated the CUs also known as Baseband Units (BBUs) and the DUs also known as Remote Radio Heads or Units (RRHs or RRUs), with the CUs located at Central Offices (CO) or master cell sites while DUs are located at cell sites.
These separately located components are attached currently via CPRI -Common Public Radio Interface Until now, the main frontal standard was CPRI. The replacement is evolved CPRI (eCPRI), implemented in a proprietary, non-interoperable manner.
As part of the new RAN architecture, various functional splits have been proposed, each offering trade-offs such as reduced fronthaul capacity and higher latency. The key to effectively implementing the new RAN architecture with flexible splits and efficient fronthaul is the openness in its specification and implementation. Such proprietary software and interfaces are often tied to the underlying hardware, which is a significant roadblock for openness. Enabling multi-vendor, best-of-breed flexibility in the RAN requires to move away from proprietary hardware to COT hardware. The adoption of such commodity hardware will require a design with standardized interfaces. There are several industry forums such as Open RAN (ORAN) / Telecom Infra Project (TIP), which are focusing on decoupling the RAN control plane from the user plane witch is essential architecture in 5G unlike previous generations of cellular networks, building a modular RAN software stack that uses commodity hardware and open north- and south-bound interfaces. A RAN architecture with disaggregated software based on open specifications running on commodity hardware could allow operators to reduce complexity, innovate faster and significantly reduce deployment and operational costs. With well-established backing from the telecom industry, a growing community and an open hardware ecosystem in communities, such as the Open Compute Project (OCP) and O-RAN, the open specifications and implementations coming out of these forums are, over time, likely to see higher adoption and thus should be considered as applicable.
The core network is a critical component, needs to be robust, highly resilient and high performance. 3GPP’s with its Service-Based Architecture (SBA), has standardized the Network Functions (NFs), their procedures and the inclusion of NF sub-modules. Also define the APIs to be used by providing data model, protocol and format. The following sections identify some ongoing open source initiatives in the control and user planes of the 5G core network.
Unlike previous generations, the 5G architecture is using open APIs referred to as Services Based Interfaces (SBIs). The communication over the SBI will need a services framework implementing a message communication bus that can support an efficient mechanism for synchronous communication between the NFs. New mechanisms are needed for asynchronous data movements, such as transferring event notification, performance data, service availability, and discovery.
Microservices architecture has been adopted by web-scale companies, there is some open-source software that provides a microservice message communication bus. Some of the open-source implementation of a communication bus for synchronous communication are reverse proxies such as NGINX, High Availability Proxy (HAProxy) and Open Network Automation Platform (ONAP) Micro-services Bus Project (MSB). Apache Kafka streams are also a possible implementation for asynchronous data movement that enables real-time data ingestion. This is important in the areas of analytics-based automation and service assurance, where real-time event monitoring becomes highly critical. The Network Repository Function (NRF) will allow every network function to discover the services offered by other NFs. Open-source implementations provide similar service registry and discovery mechanisms, which have been widely deployed by web-scale companies. SBI and NEF have adopted the Open API Initiative, which defines a standard, language-agnostic interface to RESTful APIs. There are other industry forums, such as the OpenAirInterface Software Alliance (OSA), working on developing some of the 5G core network functions, which should be considered as applicable in 5G.
SDN plays a vital role in customizing the user plane for diverse sets of 5G services. There are various open-source initiatives of SDN controllers, such as OpenDayLight, OpenContrail and Open Network Operating System (ONOS), that contain a collection of “pluggable” modules that can perform different network tasks. Some of the basic tasks include determining what devices are within the network, the capabilities of each, gathering network statistics, configuring routing rules for service chaining and enforcing security policies. Open-source protocols such as OpenFlow, Extensible Messaging and Presence Protocol (XMPP) and Network/Configuration (NetConf) could be used by the infrastructure SDN controller to configure the user plane with L0-L3/L4 routing aspects. With the use of commodity hardware, the user plane no longer needs to rely on proprietary silicon, which is not customizable. P4 is an open-source initiative that has projects such as P4 language and P4 runtime, which enable programmable forwarding plane and dynamic provisioning on open-source software. M-CORD is an open-source reference solution for operators deploying 5G. It is built on the CORD infrastructure platform, which brings COT data center and cloud agility to operator networks.
M-CORD transforms the mobile network by disaggregating and virtualizing cellular network functions, as well as operator-specific services. It lay the foundation for 5G networks and services through support for disaggregated and virtualized EPC, end-to-end slicing from RAN to EPC, mobile edge computing and a programmable radio access network.