From trees to DAGs: Improving the performance of bridged Ethernet networks

Ethernet is widely used in Local Area Networks (LANs) due to its simplicity and cost effectiveness. Today, a great deal of effort is being devoted to extending Ethernet capabilities in order to elevate it from a LAN technology to a ubiquitous networking technology, suitable for deployment in Metropolitan Area Networks (MANs) and even in core, Wide Area Networks (WANs). Current standardized Ethernet networks are based on a spanning tree topology, using the Rapid Spanning Tree Protocol (RSTP) or Multiple Spanning Tree Protocol (MSTP). The spanning tree architecture is useful for avoiding forwarding loops, but may lead to low link utilization and long failure recovery time. In this paper we propose to shift from tree to Directed Acyclic Graph (DAG) topologies and offer a new bridged Ethernet architecture called Orient. Orient is based on assigning an orientation state to each port in the network in order to prevent loops. Thus, the Orient architecture enables a full utilization of all network links and ports, while maintaining simplicity of implementation and compliance with the standardized spanning tree protocols.