Analysis of RPR Technology

In the past two years, a variety of new generation of metropolitan network technology, including resilient packet data loop (Rpr-resilient Packet ring IEEE 802. 17 technology to the advanced technology, the effectiveness of investment, the advantages of performance, support business diversity for the metropolitan Area Network provides a good solution, by people's favor.

Historically, SONET has become the choice of transmission, because it can not only restore the transmission loss of fiber, but also effectively support the ring topology. Resilient packet Data Ring RPR is a new type of network architecture and technology designed to meet the requirements of packet metropolitan area network; it is a circular network composed of packet switching nodes, adjacent nodes are connected by a pair of optical fibers, and the network topology is a ring based on two opposite directions.

I. The technical characteristics of RPR

1. Efficient multiplexing of transmission bandwidth

The traditional SONET network needs 50% of the loop bandwidth as redundancy, and RPR is not, it still maintains the protection mechanism similar to SONET PS, utilizes two reverse rotation loops to control the data traffic, especially uses the space reuse protocol patial reuse protocol, referred to as SRP. Space reuse means that there is no repetitive business flow in space, and each traffic can utilize the bandwidth of each line without any influence. Simply put, it is normal that the data is transmitted on the shortest arc between the source node and the target node, and multiple nodes can communicate with each other at the same time. In this way, multiple nodes can send and receive packets at the same time, improve the bandwidth utilization, especially in the case of more nodes on the ring, the utilization rate of bandwidth improvement is especially obvious.

In order to greatly improve the bandwidth utilization of data service transmission, RPR uses the following four kinds of bandwidth multiplexing methods:

In the process of statistical multiplexing and load balancing of multiple LAN ports on any node on the  ring, the nodes can make maximum use of the loop bandwidth.

The statistical multiplexing function of bandwidth on the shared ring of each node on the  ring.

The  adopts 2 layer protection switching mechanism, without reserving the protection bandwidth.

 uses the RPR Mac protocol of destination stripping to realize the space reuse of the transmission bandwidth.

2. Fast Ring Protection Switching (50ms) function

RPR transmission can provide 50ms of source routing protection, under normal circumstances, RPR two fiber is working optical fiber. When a fiber interrupt or node failure occurs, the node fiber inlet physical Layer device detects an error and notifies the MAC layer that the data flow in the direction of the fault path is switched to the opposite direction fiber; a control signaling packet is sent to the other node, and the remaining nodes receive the control signaling packet, It also shifts all the business to a valid loop. RPR's protection switching mechanism based on source routing can transform the data to the best path. During the protection switching process, the switching order and bandwidth allocation strategy are determined according to the different service levels of the business flow.

3. Automatic discovery of topology

That is, each node in the ring knows the identification number of other nodes on the ring and the corresponding connection relationship. In the case of a fixed time or when the RPR fiber ring in the initialization process to add or delete nodes, a node failure or fiber interruption to trigger the ring protection switch, the ring on the single ring or double loop to send Topology discovery packet to achieve the automatic topology discovery function. After the other nodes accept the topology Discovery grouping, the node's MAC address and the node state (such as whether it is in a switching state, etc.) are appended to the group, and then forwarded to the downstream node. If the node is in the switching state, then the packet is switched to the reverse ring transmission, the other nodes receive the switch Topology Discovery Group, if the ring tag in the packet and the current ring mark is not the same, not for group AC operation.

Finally, when the nodes of the topology Discovery group receive the returned packets, the topology discovery is stripped off the loop, and the local topology map is updated according to the information in the packet. Each node in the final RPR ring details the topology map of the network and the state of each link. Topology discovery makes the configuration of network initialization extremely simple and avoids the errors caused by manual configuration. The topology automatic discovery function is the foundation of various main functions in RPR, which is very important not only for routing searching and protection switching, but also for the OAM of network.

4. Access control and fairness algorithm

Because of the statistical multiplexing property of RPR ring, the bandwidth management and control are distributed, that is, the control algorithm of each node can be determined collectively. In order to ensure that each node's business has equal access to the bandwidth of the right, fair algorithm should make each node into the ring business in the presence of competition opportunities. At the same time, in order to ensure the QoS of service transmission, the access control can be based on IEEE802. 1p, set up each business level (COS) queue to ensure that the highest level of business priority for the lower level business.

5. Simple Business Offers

One of the goals of RPR is distributed access. Distributed access, fast protection, and automatic reconstruction of the business provide Plug and play mechanisms for fast insertion and deletion of nodes. RPR is also a packet switching technique that uses shared broadband in the ring, and each node knows the usable capacity of the ring. In the traditional circuit switching mode, the full network connection requires a point-to-point connection between the n^2-n2 (n squared minus N's difference divided by 2,n as the number of nodes), while RPR only needs a business connection with the loop, simplifying the work.

Two, the implementation plan of RPR

The specific scheme of RPR can be divided into three categories: The Independent 2-layer RPR implementation scheme, the single RPR implementation scheme based on router, and the RPR implementation scheme based on MSTP.

For the implementation of the three kinds of RPR, manufacturers have introduced the corresponding products. The independent 2-layer RPR implementation scheme is mainly applicable to the access layer and the aggregation layer of IP metropolitan Area Network, and is the most mature solution at present. Some manufacturers combine multiprotocol label Switching (MPLS) technology, clock synchronization technology, CWDM technology and TV video broadcasting technology with this 2-tier implementation to provide IP-oriented optimization and simultaneously support TDM services for broadband multiple-service solutions.

In addition, some manufacturers launched based on the 2-tier RPR products have strong networking capabilities, it can support linear, tangent loop, intersecting ring topology and two-node interconnection (DNI) cross-loop protection, these enhancements based on 2-layer RPR products can be applied to the core layer of IP metropolitan area network in small cities.

Application prospect of RPR

RPR in the transmission of data-oriented business, its bandwidth utilization compared with SONET technology can be increased 2-8 times, while the rapid ring protection switching and the corresponding QoS mechanism to ensure the performance of data service transmission quality, making it a data-oriented metropolitan area network, one of the main solutions. With the continuous improvement of RPR technology, its application will be more and more extensive.