Smart Spanning Tree Bridging for Metro Ethernets

Abstract

Metro Ethernet is taking off rapidly as a WAN service and the simplicity, ubiquity, and plug-and-play features of Ethernet are some key success factors. The original bridging methods assumed the use of VLANs and spanning tree protocols within provider bridge (PB) and provider backbone bridge (PBB) networks. Because of the inadequacy of the existing spanning tree protocols to support carrier network requirements, very recently, a new class of shortest path routing solutions have been introduced that avoid the use of spanning tree protocols in the core namely, shortest path bridging (SPB). This paper aims at illustrating that we can still use spanning trees in metro ethernet provided that the tree generation and VLAN-spanning-tree mapping are performed adequately. We call our solution smart spanning tree bridging (SSTB). SSTB can be used to enhance the 802.1s MSTP, without requiring significant changes in the current Ethernet equipment. Using very simple but yet realistic numerical examples, we show that SSTB yields near optimal bandwidth and link usage. We also show that SSTB outperforms SPB in terms of service delivery, frame loss and jitter, while being comparable in terms of bandwidth usage and latency. Further, SSTB requires only a couple of spanning tree instances, significantly reducing processing and complexity of bridged networks.