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Understanding Open RAN xHaul: A Comprehensive Guide to Next-Generation Network Transport

written by Asterfuison

June 26, 2024

In communications, Open RAN has been popular with operators since its emergence due to its open architecture and flexibility, which has reduced network deployment and maintenance costs, facilitated network vendor diversification, better supported edge computing applications, and accelerated technological innovation.What exactly does Open RAN consist of? What does Open RAN consist of and how is it applied to various personalized scenarios?

What is RAN?

Radio Access Network (RAN) is a part of mobile communication system. It is an implementation of radio access technology. It exists between a device (e.g., a cell phone, a computer, or any remotely controlled machine) and the Core Network (CN), providing a communication link between the two. Depending on the standard, cell phones and other devices connected wirelessly have different names, such as User Equipment (UE), Terminal Equipment, Mobile Station (MS) and so on. Mobile Station (abbreviation: MS) and so on.

What is Open RAN?

Open RAN(O-RAN), or Open Radio Access Network, is a concept of interoperability and standardization based on RAN elements, including a unified interconnection standard for white-box hardware and open-source software elements from different vendors, which allows interoperability between cellular network equipment developed by different vendors. O-RAN aims to transform traditional monolithic hardware-centric RAN designs into designs that use independent building blocks (with open standardized interfaces) to integrate modular base station software stacks on off-the-shelf hardware, allowing baseband and radio unit components from discrete vendors to operate together seamlessly.

O-RAN emphasizes the goal of streamlined 5G RAN performance through the shared attributes of efficiency, intelligence, and versatility. Deployed at the network edge, the open RAN will benefit 5G applications such as self-driving vehicles and IoT, effectively support network slicing use cases, and support secure and efficient over-the-air firmware upgrades.

MeaningIt is a general term for open RAN architecture, which includes open interfaces, virtualization and AI intelligence.It is a sub-project initiated by the TIP Telecom Infrastructure Project, aiming to realize open RAN, and the scope of work includes 2/3/4/5G.Usually refers to the O-RAN Alliance and the standards developed by the O-RAN Alliance. The O-RAN Alliance is a community of interests composed of various participants, including operators, equipment suppliers, chip manufacturers, software suppliers, etc., focusing on developing open and intelligent RAN architecture and specifications

Is it ORAN or Open RAN?

There are several key characteristics that determine whether an architecture is an O-RAN (Open RAN) architecture.

  • Interface standardization

The O-RAN architecture emphasizes the standardization of interfaces between network elements, such as F1, E1, eCPRI, etc., enabling interoperability of devices from different vendors, and these standardized interfaces are one of the fundamental differences between O-RAN and traditional RAN architectures.

  • Openness and Programmability

O-RAN uses open hardware and software platforms, such as general-purpose computing hardware and Linux-based software stacks. This openness gives O-RAN greater programmability and flexibility, and supports dynamic scheduling and optimization of network functions.

  • Virtualization and Cloud

O-RAN makes extensive use of Network Function Virtualization (NFV) and cloud computing technologies to transfer traditional hardware functions to software and cloud platforms, which enables O-RAN to have better scalability and resource utilization.

  • Automation and Intelligence

The O-RAN architecture introduces a wealth of automation and intelligence features, such as automated deployment and automated optimization, which help improve network operation and maintenance efficiency and performance.

  • Multi-vendor ecosystem

O-RAN emphasizes on building an open multi-vendor ecosystem and encourages the innovative participation of different vendors, which helps to break the traditional monopoly and promote the innovative development of 5G network technology.

Therefore, summarizing the above characteristics, if a RAN architecture possesses these key features of O-RAN, then it can be judged as belonging to the O-RAN architecture category. On the contrary, if it lacks these features, it is more likely to belong to the traditional closed RAN architecture.

Why do we need O-RAN?

Previously, carrier wireless access networks were equipment provider-specific hardware, and when a vendor’s core network was selected, his hardware equipment had to be used, and pricing power was firmly held by the vendor. In order to reduce expenses, carriers have established O-RAN alliances to share hardware solutions and unlock equipment vendors, so that any equipment vendor’s wireless access network can be seamlessly connected to any equipment vendor’s core network.

What are the benefits of O-RAN?

  • Reducing the CapEX of Network Deployment

The Open RAN architecture and technology reduces the cost of deploying and maintaining mobile networks by encouraging competition among vendors and simplifying network management. In terms of infrastructure costs, O-RAN allows operators to use COTS servers to act as CU/DU devices and install third-party NICs, which dramatically reduces construction costs by allowing operators to source components from multiple vendors and reducing dependence on specific vendors’ hardware products. This diverse vendor ecosystem not only saves investment costs, but also enhances network resiliency.

  • Reduced OpEX of Network Operating

Open RAN promotes the use of an industrialized hardware supply chain that allows different network functions to run on common hardware platforms that can be categorized based on factors such as indoor vs. outdoor deployments and high vs. standard performance. This approach greatly simplifies procurement, spare parts management, and inventory processes, and reduces reliance on vendor knowledge, eliminating the need for network administrators to undergo specialized training on specific vendor products, lowering employment costs for network operators, and enabling them to manage and maintain their networks more efficiently and cost-effectively.

  • Allows elastic scaling of resources to meet changing network demands.

By disaggregating and separating the hardware and software supply chain, Open RAN enables network operators to easily scale up or down their networks. By leveraging cloud and cloud-native operations, operators can deploy flexible, modular network components that can be individually scaled as needed. This approach enables them to meet growing consumer demand without the need to make significant investments in new infrastructure. Cloud technology enables elastic scaling, allowing network resources to be dynamically allocated or de-allocated based on real-time demand.

  • Enabling Multi-Vendor Management of Networks for Increased Interoperability.

Open RAN facilitates interoperability between devices from different vendors, making it easier for network operators to mix and match components without being locked into a single-vendor ecosystem. By integrating devices from different vendors, operators can reduce the risk of dependency on a single vendor, and Open RAN’s open interfaces support a system-level security approach for increased visibility and control of the network. This enables operators to display more data and gain a deeper understanding of what is happening within their networks, making it easier to identify potential vulnerabilities and respond to security incidents in a timely manner, better protecting their networks from potential breaches or service disruptions.

  • Increasing or decreasing workloads with minimal effort.

O-RAN divides the radio access network into modules, such as baseband processing and RF units. The interfaces between these modules are open, allowing the flexibility to add, replace, or upgrade modules without large-scale changes to the entire system. Meanwhile O-RAN adopts the concepts of SDN and NFV, where network functions are virtualized and implemented in software. This makes it easier to adjust workloads, which can be accomplished by updating the software without the need for physical equipment replacement.

What are the components of O-RAN?

RIC(RAN Intelligent Controller)is is a software-defined component of the Open Radio Access Network (Open RAN) architecture responsible for controlling and optimizing RAN functions.

O-RU is responsible for sending and receiving wireless signals, and connects with O-DU through the pre-transmission interface.

O-DU is responsible for wireless protocol stack processing and data forwarding, and connects with O-CU through the medium transmission interface.

O-CU is responsible for the processing of high-level protocol stack and network management, and connects to the core network through the standard interface.

RIC (RAN Intelligent Controller)

RIC (RAN Intelligent Controller) helps mobile operators reduce infrastructure and operational costs, improve network performance and increase business agility; it also helps them build new revenue streams through personalized services, network slicing and indoor location tracking capabilities.

RICs are categorized into non-real-time and near real-time components. Non-real-time RICs use specialized applications called rApps that enable >1 second control of RAN elements and their resources. It also provides AI-based network optimization recommendations and policy guidance to xApps running on the near-real-time RIC, which in turn provides policy feedback to the non-real-time RIC. Near-real-time RICs are located at the telecom edge or in regional clouds and typically enable network optimization operations that take 10 milliseconds to 1 second to complete.

O-RU (Open Radio Unit)

The O-RU is the unit responsible for radio frequency processing and some physical layer functions. Its main responsibilities include:

-RF Signal Processing: Includes transmission and reception of signals, converting digital signals to RF signals and transmitting them, or converting received RF signals to digital signals.

-Partial Physical Layer Processing: Handles a portion of the physical layer functions such as channel coding and decoding, modulation and demodulation.

-Antenna Interface: Connects to the antenna and is responsible for the spatial transmission of the signal.

Typical scenario: O-RUs are usually deployed near antenna towers or base stations to connect directly to the antenna to ensure efficient signal transmission and reception.

O-DU (Open Distributed Unit)

The O-DU is responsible for low and mid-layer protocol stack processing and some physical layer functions. Its main responsibilities include:

-Physical Layer Processing: Handles the rest of the physical layer functions such as channel coding, decoding, modulation, demodulation, etc.

-MAC Layer Processing: Handles the functions of the Media Access Control Layer (MAC Layer), including scheduling, resource allocation, HARQ, etc.

-Real-time processing: Since O-DUs handle tasks with high real-time requirements, they are usually deployed close to O-RUs to minimize latency.

Typical scenarios: O-DUs are usually deployed in local server rooms, edge computing nodes, or in some cases directly near the base station sites in order to maintain low latency and efficient processing.

O-CU (Open Central Unit)

The O-CU is responsible for high-level protocol stack processing and control functions. Its main responsibilities include:

-RLC Layer Processing: Responsible for Radio Link Control Layer (RLC Layer) functions such as segmentation, reorganization, ARQ, etc.

-PDCP layer processing: Responsible for Packet Data Convergence Protocol layer (PDCP layer) functions, such as encryption, integrity protection, compression, and so on.

-Control Plane Functions: Handles control signaling, such as RRC (Radio Resource Control) signaling, connection management, mobility management, and so on.

-User plane functions: Handle user data, such as packet forwarding, QoS management, etc.

Typical Scenario: O-CUs are usually deployed in more centralized locations, such as regional data centers or centralized data centers, to facilitate centralized management and control, and also to handle large amounts of data and signaling.

If the clock source is located at the O-DU, there are strict clock synchronization requirements for the fronthaul. If the clock source is located higher, such as at the O-CU, there are also strict clock synchronization requirements for the midhaul.

What is xHaul Transport?

Current Open RAN Architecture as defined by the O-RAN Alliance The functional separation of RAN components into Open Radio Units (RUs), Open Distributed Units (O-DUs), and Open Centralized Units (O-CUs). xHaul (front-haul, midhaul, and backhaul) transmissions require Ethernet switches to facilitate efficient and flexible communication between different components of the O-RAN.

Among them, front haul has higher requirements for Ethernet switches, which need to support clock synchronization technologies such as IEEE 1588v2 time synchronization and PTP.

The requirements for clock synchronization are less stringent for the middle and backhaul transmissions, which require certain time synchronization mechanisms, and the backhaul transmissions do not need special technical support for time synchronization.

What is the difference between PTP and SyncE?

The Precision Time Protocol (PTP) is a time synchronization protocol used between network nodes with a synchronization accuracy of sub-microseconds. Through time synchronization, the frequency and phase difference between the devices in the whole network can be kept within a reasonable error range.

Synchronous Ethernet (SyncE) is a synchronization technology based on the physical layer stream to carry and recover frequency information, which can achieve high precision frequency synchronization between network devices and meet the requirements of wireless access services for frequency synchronization. SyncE carries and recovers frequency information based on the physical layer stream. Because frequency signals are transmitted at the physical layer, SyncE clock synchronization is not affected by upper-layer protocols, and is not affected by data network congestion, packet loss, and delay.

The 1588v2+SyncE enables time synchronization with nanosecond accuracy.

Synchronization MechanismSyncE uses the physical layer of Ethernet to distribute a precise frequency reference across the network.PTP uses a software-based protocol to synchronize clocks between network nodes, leveraging packet-based timestamping.
Synchronization AccuracySyncE can achieve sub-microsecond frequency synchronization accuracy, making it suitable for applications with stringent timing requirements, such as fronthaul in 5G networks.PTP can achieve nanosecond-level time synchronization accuracy, which is important for time-sensitive applications and network slicing.
Network TopologySyncE is well-suited for point-to-point or ring topologies, as it relies on the physical layer of Ethernet.PTP can operate in a wider range of network topologies, including more complex mesh and hierarchical designs.
ScalabilitySyncE is generally simpler to deploy and maintain, making it more scalable for large-scale networks.PTP can provide more granular synchronization control and allow for better scalability in terms of the number of synchronized nodes.
RobustnessSyncE is more robust to network impairments, such as packet loss or network congestion, as it does not rely on packet-based synchronization.PTP is more vulnerable to network impairments, but it can provide better adaptability and recovery mechanisms.

In the context of 5G and O-RAN, SyncE is typically used for fronthaul synchronization, where precise frequency alignment is critical, while PTP is often employed for midhaul and backhaul synchronization, where time synchronization is more important for applications like network slicing and timing-sensitive services.

How to choose the right switch for xHaul Transport?

Support for clock synchronization protocols is key when selecting a switch for xHaul Transport. In addition, due to the high latency requirements of 5G services and the high reliability requirements of carrier networks, switches also need to have low latency and high reliability.
Asterfusion provides xHaul with a mobile transport solution that supports IEEE1588v2 and PTP, providing high-precision time-synchronized pre-transmission, low-latency mid-transmission, and back-transmission. xHaul’s ultra-low-latency Ethernet switches are available in 400ns, which is far ahead of other vendors in the industry.
Asterfusion also offers an enterprise-grade SONiC NOS, which helps solve the problem that traditional network operating systems are not suitable for 5G and O-RAN requirements, providing better programmability, scalability, and openness to support the dynamic configuration and management needs of 5G networks.
In addition, Asterfusion switches can support technologies such as BGP, EVPN Multi-homing, QoS, and conversion from CPRI to eCPRI, providing higher bandwidth utilization and helping to address the differentiated quality of service needs of different service traffic in 5G and O-RAN networks.

O-RAN Mobile xHaul Transport

Other Questions:

What’s the relationship between 5G and ORAN?

The relationship between 5G and Open Radio Access Network (O-RAN) is an important one in the evolution of mobile network technologies. Here’s a brief overview:

  1. 5G and O-RAN:
    • 5G is the latest generation of cellular network technology, offering faster speeds, lower latency, and greater capacity compared to previous generations like 4G.
    • O-RAN refers to an open, interoperable radio access network architecture that enables multi-vendor interoperability and flexibility in 5G networks.
  2. Driving 5G Innovation:
    • O-RAN is seen as a key enabler for driving innovation in 5G networks.
    • By promoting open interfaces and disaggregating the traditional radio access network, O-RAN allows for more competition, faster development, and customization of 5G network components.
  3. Benefits of O-RAN in 5G:
    • Increased flexibility: O-RAN allows network operators to mix and match components from different vendors, reducing vendor lock-in.
    • Faster innovation: Open architecture enables quicker deployment of new features and services.
    • Cost optimization: O-RAN can potentially lower the overall costs of building and operating 5G networks.
  4. Adoption and Standardization:
    • O-RAN is gaining traction in the industry, with major network operators and vendors collaborating to develop and adopt O-RAN specifications.
    • The O-RAN Alliance, an industry group, is leading the standardization efforts to define the technical specifications for O-RAN.

In summary, 5G and O-RAN are complementary technologies that work together to enable a more flexible, innovative, and cost-effective 5G network ecosystem. O-RAN is seen as a crucial component in realizing the full potential of 5G networks.

How did RAN evolve into ORAN ?

Simply put, a RAN is a base station, or network. Before the advent of the 5G era, a base station (RAN) was composed of three parts: an antenna, an RRU (Radio Frequency Relay Unit), and a BBU (Baseband Processing Unit.) The RRU is used to transmit and receive signals, and the BBU is used to process signaling messages.

In the 1G and 2G era, equipment such as BBUs, RRUs and power supply units were placed in a cabinet, which was very bloated. ……

What are D-RAN, C-RAN, X-RAN ?

By the 3G era, distributed base stations were proposed. That is, the BBU and RRU are separated, and the RRU can even be hung under the antenna, so it does not have to be placed in the same cabinet with the BBU. This is called D-RAN (Distributed Radio Access Network). As the technology evolved (in large part because it was too expensive for carriers to maintain ……), C-RAN was born.

What is C-RAN is Centralized RAN, which can also be referred to as Cloud- RAN. It still adopts the scheme of separating BBUs and RRUs, but the RRUs are infinitely close to the antennas, so as to greatly reduce the attenuation through the feeder lines (the connection between the antennas and RRUs); meanwhile, the BBUs are relocated and centralized in the CO (Central Office) to form a BBU baseband pool; and the CO and RRUs are connected through the pre-transmission network. RRUs are connected through the pre-transmission network. This is very conducive to inter-cell cooperative work, reducing the attenuation caused in transmission and saving costs.

Operators around the world are also constantly exploring more advanced network architectures. in 2016, AT&T led many overseas operators to form the x-RAN Alliance, with the goal of replacing traditional hardware-based RANs with openly substitutable, standardized equipment. the alliance focuses on three areas: coupling the RAN control plane with the user plane, building modular eNodeBs that use COTS hardware software stack, and exposing southbound and northbound interfaces.

X-RAN and C-RAN are often considered to be the predecessors of O-RAN.

How O-RAN was born?

In June 2018, the O-RAN Alliance was officially founded by 12 operators, including China Mobile, AT&T, Deutsche Telekom, NTT DOCOMO, and Orange, etc. The O-RAN Alliance expands on the work and goals of the existing C-RAN Alliance to promote the evolution of wireless access networks in a more open and smarter direction.

Why the O-RAN Alliance?

In the past, operator radio access networks have been equipment provider-specific hardware, meaning that if you choose Ericsson’s core network, you have to use Ericsson’s radio access network. The same goes for Huawei, Nokia and ZTE. For Open RAN, on the other hand, since the hardware solution is shared, any equipment vendor’s radio access network can be seamlessly connected to any equipment vendor’s core network.

At its core, OPEN RAN is designed to reduce operators’ capital expenditure problems. By sharing hardware designs among device vendors, it reduces the cost investment in R&D and achieves approximate uniformity in device selection. The scale effect of the total use of core chips will amortize the design and R&D costs of upstream chips and devices, and ultimately reduce the cost of device procurement by equipment vendors, thus reducing the hardware cost of equipment in the communications industry from the source.

Wireless network construction has always been the most important part of operators’ total cost of ownership (TCO), roughly accounting for 60% to 70%. In China, for example, most operators have just experienced the huge investment in 4G network, and will face the pressure of investment in 5G network construction. 5G network is different from 4G network, 5G network speed, bandwidth, high frequency band, that is to say, 5G network penetration will be far worse than 4G network.

To explain it in layman’s terms, the original 4G network coverage of a certain area only needs 1 base station, while the 5G network coverage requires 5 base stations. In this way, China will need millions or even tens of millions of small 5G base stations in the future. At the same time, 5G network and operators must invest in the network, large-scale network construction is bound to bring a great deal of money, then you need to introduce new technologies, new programs, program innovation to reduce the difficulty of construction, reduce wireless network investment.

Against this backdrop, the operator-led O-RAN industry alliance has emerged, putting forward two core visions: “open” and “intelligent“.

The core of O-RAN: standardization + open source

ORAN alliance is led and initiated by operators, there are three key principles: the first principle, to guide the evolution direction of the industry, one is open interface, which can support the interoperability of heterogeneous manufacturers’ equipment; the second is to build a wireless access network through virtualization, to realize the intelligent wireless network based on big data. The second principle is to actively and fully utilize common platforms and reduce the dependence on private platforms. The third principle is to formulate and promote standardized definitions of interfaces and related APIs, and explore open source solutions.

Explaining these three rules in layman’s terms, O-RAN is promoting the following four directions: network intelligence, interface openness, hardware generalization and software open source. Equivalent to the original black box hardware, now all transformed into a general standardized product, in which the software code also becomes open source.

This may mean that, in the future, a single manufacturer of existing network equipment, no matter how many, is not irreplaceable; sellers do not need to packaged procurement of the same manufacturer’s hardware and software products, but to make full use of the common platform, reduce the dependence on private platforms, development, promotion of interfaces and related API standardized definitions, and to explore open source solutions, which also means that “standardization This also means that “standardization” will become the trend.

With the opening of generalized hardware, network functions, soft and hard decoupled hardware will be generalized, operators will be more independent, and no longer like now is always left by the equipment vendors. Traditional equipment vendors will face major changes, and some Internet companies, software vendors, IT vendors or will become new players in the market.

O-RAN Organization and Ecology

Several different consortium organizations have been formed to achieve OPEN RAN: xRAN Forum, OpenRAN, Open vRAN, and O-RAN. these consortiums all have the same general purpose, which is to make the radio access network more open with common interfaces and white-box network elements.

  • xRAN was formed in 2016, with key members such as AT&T, Verizon, Deutsche Telekom, KDDI, NTTDocomo, SK Telecom, Telstra, AND Verizon as carriers.The three main objectives are: a) decoupling the user-plane and control-plane of the wireless access network; b) building software architectures that can run on shelf hardware; and c) publishing open southbound and northbound interfaces.
  • The OpenRAN Alliance was created in 2017 when Vodafone contributed their software-defined RAN project to the TIP, thus creating the OpenRAN Alliance.The OpenRAN Alliance aims to develop RAN technologies based on common hardware and decoupled software.
  • Open vRAN was proposed by Cisco at last year’s MWC conference with the main aim of building open as well as modular RANs based on common hardware and decoupled software.
  • O-RAN was also jointly established by five telecom operators, including China Mobile, AT&T of the US, Deutsche Telekom, NTT docomo of Japan, and Orange of France, at MWC. The core objectives and contents of the O-RAN alliance include: network intelligence, open interfaces, white-boxed hardware, and open-source software.

O-RAN Ecosystem Overview

Chip vendors: Intel (general-purpose chips), Nvidia (GPUs), Qualcomm (baseband chips), XILINX (FPGAs)

Virtualization platforms: IBM, Redhat, CISCO, NECT, ROBIN, WindRiver, Vmware

Hardware for CU and DU: General purpose server manufacturers: DELL, QCT,

RU hardware with embedded software: Airspan, flex, Fujitsu, LKMW, NEC, SERCOM

VRAN Software: Altiostar, Mavenir, Parallel Wireless, JMA

System Integrators: CISCO, Fujitsu, IBM, NEC, Rakuten, Tech Mahinda

Traditional end-to-end established telecom equipment vendors: Nokia (active), Samsung (active), Ericsson (against openness), ZTE (not active), Huawei (not participating)

ORAN Distribution

vRAN BB: Altiostar, Mavenir, Parallel Wireless, JMA Wireless

Macro RF: KMW, NEC, possibly Fujitsu

Small Cell, Indoor, low power RF: Commscope , Airspan, Casa

Several baseband vendors have emerged in the US: Altiostar, Mavenir, Parallel Wireless, JMA Wireless

This is probably why the North American market is not open though, and Nokia and Ericsson, traditionally on devices, have not gained much additional market share.

Other players

Most of the new players mentioned above, are from the US, only Rakuten Rakuten is from Japan.


Intelligent O-RAN for Beyond 5G and 6G Wireless Networks | IEEE Conference Publication | IEEE Xplore

An RL Approach for Radio Resource Management in the O-RAN Architecture | IEEE Conference Publication | IEEE Xplore

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