is likely that customers will elect to run a spanning tree on their Ethernet LANs to prevent loops for the same reasons that service providers will choose to implement it. Should the customer's STP interact with the service provider's STP? The simple answer is no. Any changes to a customer's spanning tree could impact the spanning tree of the service provider and consequently impact the performance and availability of the service provider's network. A service provider's network does, however, need to transport customer spanning tree frames because the blocking of spanning tree control frames between customer sites can lead to undesirable effects, such as loops within the customer's network. The introduction of hierarchy in 802.1ah allows, as described earlier, the complete separation of customer and provider concerns. When there are multiple Ethernet links between two switches, they can be aggregated together into a Link Aggregation Group (LAG), which can be logically treated as a single link with a higher speed. A Link Aggregation Control Protocol (LACP) is utilized to control the properties of the link by communicating with the switches at either end of the logical link. Traffic is distributed across the individual links by means of a hashing algorithm in manner that maintains frame ordering for each communication session. A LAG can be used to protect against failure of an individual link in the group by redistributing the traffic between the remaining links. When the failed link has been restored, the LAG distribution function reintroduces it to allow redistribution of traffic. The ITU-T has defined linear protection-switching schemes for point-to-point VLANs in the form of 1+1 and 1:1 protection-switching architectures in G.8031 (ITU-T, 2006b). In these schemes the route and bandwidth of the protected entity is reserved for a chosen working entity, thereby providing a simple survivability mechanism. This makes for an attractive approach for network providers because it is simpler from an operational perspec- 