QoS Optimized Spanning Tree for Layer 2 Multicast Applications

Recently, more and more QoS-sensitive multicast traffic comes into Ethernet, which requires higher quality of service (QoS) than traditional data traffic. As a result, the current spanning tree protocol (STP) can not provide satisfactory QoS for the new type traffic, because multicast traffic has inherent P2MP characteristic where the root bridge of STP is located greatly affecting its QoS in layer 2. However, the current STP just selects the bridge that owns the smallest bridge ID as its root bridge, leaving QoS out of consideration. In this paper, from the point of view of multicast receivers, the L2 multicast QoS optimized spanning tree concept is brought forward and it is proved that if multicast source is mobile, when multicast source is located at the root bridge of optimized spanning tree, multicast traffic gains optimized QoS. Otherwise, the bridge that multicast source is located at is selected as the root bridge of STP in order to get best multicast QoS. In addition, it is shown that unicast traffic, which shuttles through the root bridge of optimized spanning tree, gains optimized QoS too. Finally, an approximating lookup algorithm of the optimized root bridge is proposed as the complement of the spanning tree algorithm and the validity and reliability of this algorithm are verified in the experiment.