O. To allow this to happen, the defect is not immediately reported in the client layer; instead, the hold-off timer is activated. If at the end of the hold-off time a defect is still present, protection switching will occur the client layer. The hold-off timer is configurable and generally the range is 0 to 10 seconds in steps of 100 ms. Forced and manual switch commands: The network provider is allowed to initiate protection switching manually to allow, for example, planned engineering works. Automatic Protection Switching Protocol (APS): Coordination can take place between both ends and is one of the OAM protocol data units specified in Y.1731. It is worth noting how protection-switching and STPs should be used. Any ports that are within the protection switching architecture cannot take part in a spanning SO as to avoid protection and spanning tree interaction. This can be achieved in two ways: Next Generation Ethernet Transmission Switch the STP off inside the protection domain. Spanning tree protocols can still be used outside of the protection domain. Protection switching can therefore be used internally to a provider's network or as a means of protection between providers, which avoids interprovider spanning tree interactions. Assign the working entity and the protection entity to separate spanning trees, where an STP section is contained within the protected domain. Although the protection schemes previously described are based on VLANs, it is straightforward to employ such schemes in PBB-TE, and they are under consideration as part of 802.1Qay. In addition to the linear protection schemes described in G.8031, there is ongoing activity in the ITU-T to develop Ethernet-based ring protection schemes. Synchronous Ethernet As a transport mechanism, it is anticipated in some quarters that Ethernet might displace SDH/SONET for a number of applications, particularly if Ethernet can provide the capabili- ties required by network providers to manage the network and provide robust and deter- ministic service offerin