What Is an IPRAN?

Why Do We Need an IPRAN?

A radio access network (RAN), also called a base station backhaul network, is a transport network deployed between base stations (BTSs/NodeBs/eNodeBs/gNBs) and base station controllers (BSCs/RNCs/EPC nodes/5GC nodes).

The traditional RANs of mobile carriers are constructed using time division multiplexing (TDM)/synchronous digital hierarchy (SDH). Because SDH — which is based on TDM — provides only rigid pipes (resulting in low bandwidth utilization), it is suited only for the transmission of 2G audio and text information.

To adapt to the development of services such as Asynchronous Transfer Mode (ATM) and Ethernet, SDH-based multi-service transport platform (MSTP) networks are widely applied. An MSTP-based network allows for concurrent access, processing, and transmission of TDM, ATM, Ethernet, and other services, and consists of multi-service nodes that are managed in a unified manner. However, its traffic transmission is still based on rigid TDM pipes. As a result, it is difficult to provide the high bandwidth required by 3G services.

Although an ATM packet switched network (PSN) can enhance bandwidth utilization, the complexity of ATM deployment and O&M hinders the widespread adoption of ATM. In comparison, traditional connection-oriented IP networks are easy to deploy and cost-effective. However, they cannot guarantee the quality and performance of important services, making them unsuitable for carrier-class transport. Against this backdrop, IPRAN emerges as the next-generation transmission technology. It emphasizes the transmission of packet management data and shifts the focus from audio support to data and multimedia support, gradually leading RANs into the IP transport era.

Building upon traditional IP networks, the IPRAN mobile transport solution incorporates OAM and QoS mechanisms to address wireless backhaul needs. And, in addition to providing IP connectivity between base stations and base station controllers, this solution is compatible with various transmission media. IPRAN combines the advantages of SDH and IP networks, offering carriers a flexible, reliable, and cost-effective base station backhaul network solution.

How Is IPRAN Deployed and Applied?

The IPRAN solution is an integrated router/switch solution customized for IP-based base station backhaul scenarios. Currently, mixed VPN (L2VPN + L3VPN) and hierarchy VPN are two widely used derivatives.

In the mixed VPN (L2VPN + L3VPN) solution, L2VPN is deployed on the access side, and L3VPN is deployed on the aggregation side. The mixed VPN solution can isolate faults from each other, improving the robustness of the entire network and therefore enabling large-scale dynamic networking. In the hierarchy VPN solution, hierarchical L3VPN is used to isolate faults from each other. This results in a network that is relatively robust, reliable, secure, and easy to maintain.

What Are the Differences Between IPRAN and PTN?

IPRAN and packet transport network (PTN) are the most widely used packet backhaul solutions. Although both solutions adopt the concept of packet scheduling, their implementation is different.

PTN inherits SDH's excellent OAM features from traditional transport networks, places packet switching at its core, and uses MPLS to forward services. The access and aggregation layers adopt Layer 2 forwarding and the core layer uses L3VPN for data communication between base stations and core routers. In addition, the base stations are divided into multiple LANs. Packets are forwarded freely within each LAN, and Layer 3 routing is used between LANs.

Unlike initial PTN, IPRAN fully supports Layer 3 forwarding and routing, L3VPN, and Layer 3 multicast functions. With the development of LTE services, PTN devices can also be upgraded to support L3VPN functions. Therefore, L2VPN/L3VPN support is not the essential difference between the two.

Actually, the main difference between PTN and IPRAN lies in the implementation of the control plane. PTN implements its control plane on the NMS, whereas IPRAN implements its control plane through routing devices. That is, PTN's management plane integrates the functions of IPRAN's management and control planes. The NMS manages and controls the entire network in a unified manner and performs O&M in a centralized and E2E manner. In IPRAN, devices communicate through various routing protocols and label distribution protocols to implement functions such as path selection and resource reservation. Each device is independently deployed and maintained. In addition, the scale of IPRAN networking is limited by the routing domain scale, whereas that of PTN networking is unlimited.

From the perspective of maintainability, PTN inherits the benefits of SDH's extensive OAM features, convenient NMS-based maintenance, and IP-based forwarding. This means that PTN fulfills the requirement of 3G/4G data service development while also accommodating traditional maintenance habits. IPRAN, in comparison, inherits traditional routing and switching technologies and can carry some data services in addition to base station services. Furthermore, IPRAN adopts dynamic networking, which facilitates service deployment but complicates maintainability and limits networking scale.

How Will IPRAN Evolve?

To meet 5G transport requirements and build next-generation intelligent transport networks, IPRAN introduces Segment Routing over IPv6 (SRv6) and Ethernet Virtual Private Network (EVPN) as basic protocols, FlexE for network slicing, and IFIT for network O&M.

EVPN uses BGP extensions to move MAC address learning and advertisement between Layer 2 networks from the data plane to the control plane, unifying the control planes of L2VPN and L3VPN. This implementation minimizes the need for full-mesh connections and traffic broadcasting, thereby minimizing the waste of device resources.

FlexE adds a FlexE shim layer between the physical and data link layers of the OSI model to decouple the physical layer from the data link layer. An intelligent transport network can use FlexE to obtain intelligent and flexible hard slices, thereby eliminating port congestion and achieving hard bandwidth isolation and differentiated connections.

SRv6 is a basic forwarding protocol for intelligent transport networks and has powerful programmability and flexibility. It translates services carried over a network into a series of forwarding instructions delivered to network devices along the forwarding path, meeting service customization requirements through network programming. SRv6 has many advantages, such as an almost infinite address space, network-wide unique node identification, and reachability to any node.

IFIT adds IFIT packet headers to real service packets in order to measure network performance, and reports measurement data in real time through telemetry, achieving in-band flow measurement in milliseconds. In collaboration with telemetry-based reporting and iMaster NCE-based intelligent analysis, IFIT can measure service SLAs in real time. When a fault occurs, IFIT can demarcate and locate the fault within minutes, enabling quick service recovery. IFIT possesses advantages such as high precision, easy deployment, proactive O&M, and visualization.

Empowered by these new technologies, intelligent transport networks provide higher transport efficiency, better SLA guarantee, and faster service provisioning, thereby meeting the requirements of new services (such as 5G) for transport networks.