Within the context of VPLS services, a loop-free topology within a fully meshed VPLS core is achieved by applying a split horizon forwarding concept that packets received from a mesh SDP are never forwarded to other mesh SDPs within the same service. The advantage of this approach is that no protocol is required to detect loops within the VPLS core network.
In applications such as DSL aggregation, it is useful to extend this split horizon concept also to groups of SAPs and, or spoke-SDPs. This extension is referred to as a split horizon SAP group or residential bridging.
Traffic arriving on an SAP or a spoke-SDP within a split horizon group is not copied to other SAPs and spoke-SDPs in the same split horizon group (but is copied to SAPs/spoke-SDPs in other split horizon groups if these exist within the same VPLS).