t the alternative paths are only usable under failure conditions and hence no load sharing is possible. This has led to alternative solutions for resiliency being considered. A number of spanning tree solutions have been developed: 802.1d-Spanning Tree Protocol (STP) is the original version of a spanning tree. It has a significant limitation for larger networks in that it is slow to converge onto a new tree (sometimes 1 to 2 minutes). This results in a significant disruption to customer services. Although a common spanning tree for the entire network can be deployed regardless of the number of VLANs, this is not the most efficient use of topology and lowers overall network utilization. The reconfiguration time of STP is simply too slow for modern applications, and as a result 802.1 W as subsequently described was developed. 802.1s (now integrated into 802.1Q)-The standard describes the Multiple Spanning Tree (MST), which provides a means by which a number of paths can be used across an Protection Mechanisms Ethernet network, thereby increasing network utilization and load sharing. This is achieved by running multiple instances of the spanning tree over the same network and configuring different bridges as the root for each instance. Network management configuration gives the provider control over the number of spanning tree instances and the assignment of ranges of VLANs to each instance, and in doing SO allows creation of a number of logical topologies. 802.1 (now integrated into 802.1D)-The Rapid Spanning Tree Protocol (RSTP) can be seen as a refinement of STP that uses many of the original capabilities but makes a number of changes that enhance performance. The limitation of STP where only the root bridge generates BPDUs and processes topology changes is overcome in RSTP by allowing all bridges to generate BPDUs and respond to topology changes. This and other changes mean that RSTP reduces the response time from a minute or SO down to around a second (or less), resulting in an improved customer experience. It 