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Journal of Information Science and Engineering, Vol. 34 No. 1, pp. 225-242

A Novel Algorithm for Loop Prevention and Fast Recovery (LPFR) in Ethernet Rings

1Department of Information and Communications Engineering
Myongji University
Yongin, 17058 Korea

2Cisco Systems, Inc., USA
E-mail: {saad.allawi1; nxtien}@gmail.com; jmr77@mju.ac.kr

Traditional Ethernet networks use the rapid spanning tree protocol (RSTP) or the enhanced RSTP (eRSTP) to ensure a loop-free topology and provide redundant links as backup paths in case an active link has failed. However, when a failure occurs, the RSTP/eRSTP require a significant amount of reconfiguration time in order to find an alternative path. The RSTP/eRSTP are also limited by the number of nodes in a ring network, and their performance degrade when the number of nodes increases; the media redundancy protocol (MRP), which is used in industrial networks, has the same issues. In this paper, we introduce a new algorithm, called loop prevention and fast recovery (LPFR), which can be applied to Ethernet ring networks to provide a loop-free topology. When a failure occurs, LPFR requires only a very short amount of time to switch to an alternative path. LPFR needs a maximum of 6.1 ms for recovery time, versus < 100 ms for the RSTP/eRSTP in a ring size of 20 nodes and < 200 ms for the MRP in a ring size of 50 nodes. The LPFR offers a reduction in recovery time of up to 93.9 % compared to the RSTP/eRSTP, and 96.9 % compared to the MRP. However, in most cases, LPFR requires zero recovery time for such switching. In addition, in most situations, no frames are lost when a node switches to an alternative path. Unlike the RSTP/eRSTP and MRP, LPFR provides a better way for distributing the sent traffic among network links, which in turn improves network performance, reduces the probability of bottleneck occurrences, and reduces the frame latency between the source and the destination. This is because LPFR always sends the frame through the fastest path. The LPFR algorithm can run on a wide variety of ring sizes, which is not the case for the RSTP/eRSTP and MRP. Finally, the LPFR will use the Ethernet standard frame layout without any modifications or changes. This will allow all of the standard Ethernet devices and networks to be directly integrated into the LPFR networks without any proxies.

Keywords: LPFR, RSTP, eRSTP, path redundancy, loop prevention, fast recovery

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