Comprehensive Analysis of RPR Technology

Features of RPR Technology

RPR is a new MAC layer protocol that optimizes data service transmission in a ring structure. It can adapt to multiple physical layers (such as SDH, Ethernet, and DWDM ), it can effectively transmit data, voice, images, and other business types. It integrates the economic, flexible, and scalable features of the Ethernet technology, while absorbing the advantages of 50 ms fast protection of SDH ring network, it also has technical advantages such as automatic network topology discovery, loop bandwidth sharing, fair allocation, and strict service classification (COS, the goal is to provide a more cost-effective man solution without reducing network performance and reliability.

The main features of RPR technology can be summarized as follows:

Dual-ring (inner ring and outer ring) structure: each pair of nodes has two paths to ensure high availability. The space reuse mechanism is used for loop bandwidth, unicast data transmission can be performed simultaneously in different parts of the loop, improving the bandwidth utilization of the loop;

Automatic Discovery and updating of network topology: when the network topology changes, each node automatically creates and updates its own topology by receiving the MAC addresses of other nodes on the RPR ring, this makes network Initialization Configuration extremely simple, implements plug-and-play, and avoids manual configuration errors, facilitating network operation and maintenance;

Supports 50 ms of fast protection: the RPR ring network can adopt two protection mechanisms, one is the source routing method (steering), that is, directly switch the source point of the business, this ensures the best path for businesses. One is to perform wrapping on two faulty nodes (similar to SDH's 2-fiber MS-spring ); the RPR standard has standardized the source routing mode as the default protection mode;

Flexible loop bandwidth management: this is an important feature of RPR technology. It supports flexible bandwidth sharing and allocation of bandwidth particles. Each node can maintain its own service load (including local upstream and outbound traffic). The network administrator can collect statistics on the resource usage of each cross-segment of the RPR loop based on this information, flexible and dynamic management of loop bandwidth;

Strict cos classification: RPR standardizes the business levels of A, B, and C, and provides a reliable mechanism to ensure high-priority businesses. Class A businesses have the highest priority and can ensure the lowest e2e latency and latency jitter. Class A businesses can be allocated a CIR rate, which can be subdivided into A0 (reserved bandwidth) and A1 (recoverable bandwidth); Class B businesses are allocated a CIR rate, and traffic exceeding CIR is marked as EIR traffic, EIR traffic should join the bandwidth fairness algorithm with Class C businesses. Class C businesses provide best-effort businesses with the lowest priority;

Support fair distribution of loop bandwidth: RPR standardizes a Distributed Fair control algorithm to achieve dynamic and fair distribution of bandwidth of each node, you can also assign different weights to nodes on the ring as needed. When the ring bandwidth is congested, the transmission of high-priority services of each node is guaranteed, and implement fair access and bandwidth allocation for low-priority businesses. EIR and C businesses of Class B businesses participate in fair algorithms. Achieving a sound fairness mechanism is very helpful for the RPR loop to quickly respond to sudden changes in data traffic;

Supports unicast, multicast, and broadcast: You can map unicast, multicast, and broadcast data packets based on IEEE 802.3mac addresses to the node's rpr mac address, the RPR loop transmits unicast, multicast, and broadcast data services based on the node's rpr mac address.

Application of RPR in Metro Transmission Network

As the competition of communication network operators has shifted from backbone networks to man, the establishment of efficient and economical Metro transmission networks that support multiple businesses has become the common goal of all major operators. In view of the many advantages of RPR technology, many domestic and foreign transmission equipment manufacturers have developed the embedded RPR function on their MSTP devices in recent years. Therefore, RPR technology has gradually entered the Metro Transmission Network field and has become one of the hot topics.

At present, the application of RPR Technology in Metro transmission networks can be divided into two types: SDH-based RPR-embedded MSTP devices and RPR devices based on grouping transmission technology, in the industry, it is also often referred to as MSTP devices and pure RPR devices embedded in RPR. From the perspective of network application scope, the MSTP embedded with RPR is suitable for the construction of traditional carrier networks that are supplemented by TDM services, and provides network upgrading and transformation of data service transmission capabilities while being compatible with existing SDH networks. The pure RPR equipment is applicable to the construction of carrier networks that provide data Grouping services, in particular, the network is dominated by emerging data services from the very beginning.

Embedded rpr mstp to repeat new highlights

The implementation of the RPR technology is generally to integrate the RPR processing function into a single board, and configure the board to the corresponding slot of the SDH device, multiple Fe or Ge interfaces can be provided on the user side. This board will directly transparently transmit data packets entering the Ethernet interface or adapt to the rpr mac layer after L2 switching and VLAN processing, that is, the core chip of RPR is used to process the MAC layer of RPR, including service classification (COS), topology discovery and environmental protection, fair algorithms, operation and maintenance management, etc, then, the rpr mac packet is mapped to one or more VC channels on the SDH system side through the green code encapsulation protocol. In the SDH ring network, the SDH channel bandwidth occupied by the RPR ring should be flexibly configured based on application needs, that is, with the increasing data services in the future, you can gradually increase the bandwidth allocated to RPR in the SDH network to reduce the bandwidth of TDM services such as Narrowband Speech, so that network applications can be continuously expanded without updating devices.

The SDH-based MSTP is embedded with the RPR function, which enhances the Ethernet bandwidth sharing and fair competition of the Next Generation MSTP devices. The important highlight of this feature is the dynamic and fair sharing of Ethernet ring network applications. Previously, the Ethernet network of MSTP was generally implemented through layer-2 switching. For example, a VLAN-Based Multi-spanning tree (that is, each VLAN in the ring network has a spanning tree, you can use the cross-segment forbidden by the single spanning tree to reuse the bandwidth of the Ring Network. The business priority is generally implemented by VLAN priority. Protection Switching Based on STP/RSTP is supported, the time ranges from several seconds to dozens of seconds.

In comparison, the Ethernet network implemented by RPR has strong advantages in terms of service processing speed, scalability, cos, protection of switching time, bandwidth utilization, suppression of broadcast storms, and Automatic Topology discovery, in particular, it has a fair distribution mechanism of loop bandwidth and overcomes the inherent defects of Spanning Tree (STP.

Limitations of RPR

However, RPR technology also has limitations in its application. Because IEEE 802.17 is designed for a single physical ring or logical ring (consisting of VC channels that span multiple SDH physical rings) the rpr mac layer technology is designed. Therefore, the application of RPR is only limited to a single ring and must be terminated during cross-ring, achieve end-to-end bandwidth sharing, fairness, QoS, and protection for cross-ring services. Therefore, sdh mstp embedded with RPR alone has certain topology limitations in building complex networks. It is necessary to integrate other technologies to provide end-to-end Ethernet services, therefore, when constructing complex network topologies such as tangent ring, intersection ring, ring belt chain, and mesh network, other technologies need to be integrated, such as Multi-Protocol Label Switching (MPLS) IEEE is developing the 802.1ad "provider bridge", and the IEEE 02.17 working group has just begun drafting the IEEE "Supplement IEEE 802.1d rpr mac bridge, this guarantees end-to-end VPN services and QoS.

Analysis of RPR market space

The embedded RPR technology has developed rapidly in recent years. Many domestic and foreign manufacturers can now provide MSTP products with embedded RPR, however, it is still a question that requires in-depth research and discussion on how to apply it in the Metro Transmission Network.

In the core layer of the Metro Transmission Network, Data Services converge and merge through the aggregation/access layer, resulting in a high filling rate. Therefore, the data service needs to provide high-speed connections between core routers, generally, MSTP Ethernet passthrough mode is used, which is not urgent for bandwidth sharing and fair access. Therefore, the application of RPR embedded in the Metro core layer is not mainstream.

On the contrary, in the convergence and access layer of the metro transmission network, the network structure is mainly the Ring Network, and the MSTP node is mainly responsible for directing and gathering the uploaded data services, the layer-1 passthrough and layer-2 exchange sharing methods are difficult to meet the transmission efficiency and quality requirements of data services. The embedded RPR technology can provide high-quality bandwidth sharing and fair access capabilities for data services, efficiently transfer services to the core layer. Therefore, the MSTP Ethernet network implemented by RPR technology is suitable for the application of the Convergence layer and access layer of the Metro Transmission Network. It is of great significance to improve the data service transmission quality and bandwidth utilization of the MSTP network, however, you should also pay attention to solving RPR cross-ring networking capabilities, flexible configuration of loop bandwidth particles, and cost issues.

We believe that, with the official release of RPR international standards and the gradual improvement of Metro Ethernet business application models, MSTP products embedded with RPR will certainly have a great space for application and development in Metro transmission networks.