| 单词 | RPR (Resilient Packet Ring) |
| 释义 | RPR (Resilient Packet Ring) The IEEE 802.17 specifications for a medium access control (MAC) layer protocol that uses Ethernet switching and a dual counter-rotating ring topology to optimize the transport of Ethernet/IP packet data traffic over optical fiber rings. RPR is designed to maintain the resiliency of SONET/SDH, but at a much reduced level of overhead.As RPR is independent of the Physical Layer, it can be implemented over existing SONET/SDH physical rings or can run on a standalone basis. RPR calls for dual counter-rotating local ringlets that interconnect nodes where data traffic is intended to drop. RPR also uses statistical multiplexing, which allows bandwidth to be oversubscribed, while establishing Committed Information Rate (CIR) and peak-rate thresholds per application. The nodes negotiate bandwidth requirements among themselves based on fairness algorithms and in consideration of a classification scheme that recognizes and provides higher priority access to traffic sensitive to latency and jitter while ensuring that best effort traffic, such as Internet traffic, is afforded equal access and a fair share of the remaining bandwidth. RPR supports the following class of service (CoS) levels: • Class A traffic is intolerant of latency and jitter. RPR addresses Class A traffic through a high CIR that ensures the availability of an average level of bandwidth appropriate for high priority traffic such as real-time voice and video. • Class B is more tolerant of latency and jitter. RPR addresses Class B traffic through either a lower CIR that ensures the availability of an average amount of bandwidth appropriate for medium priority applications that have less stringent QoS requirements, or through an Excess Information Rate (EIR) option. In the event of network congestion, Class B traffic is subject to fairness-based flow control. Class B is intended for business-class data traffic such as transaction processing. • Class C traffic is best effort traffic with no latency or jitter requirements and, therefore, is strictly EIR traffic. In the event of network congestion, Class B traffic is subject to fairness-based flow control. Class B traffic includes low priority applications such as consumer-level Internet access. In the event of a node or link failure, the RPR protection scheme can restore the network in 50 ms or less, which is the SONET/SDH benchmark. There are two restoral mechanisms: wrapping and steer-ing. The wrap option calls for data to travel around the ring until it reaches the node nearest the break. That node turns the traffic around and sends it in the reverse direction over the counter-rotating ring.The steer option calls for the originating station to exercise sufficient intelligence to avoid the failed ring and place the traffic on the ring that retains continuity.Traffic continuously travels over both fibers of the dual counter-rotating ringlets. See also 802.17, bandwidth, best effort, CIR, CoS, EIR, Ethernet, flow control, IEEE, IP, jitter, latency, MAC, node, optical fiber, overhead, QoS, real-time, ring topology, SDH, SONET, and STDM. 74570c18.qxd 9/12/07 12:39 AM Page 422 |
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