A platform is connected over a synchronous network using a GFP encapsulation scheme to a provider device having a first Ethernet interface with a customer device, said platform being arranged for exchanging tagged frames including a virtual LAN identifier (VID) with a service unit over a second Ethernet interface. If an error condition is detected at a GFP port of the platform, a correspondence is retrieved between said GFP port and a VID and a deregistration message including said VID is forwarded to the service unit. If an error condition is detected at the second Ethernet interface responsive to reception of a deregistration message including a VID from the service unit, a correspondence is retrieved between said VID and a GFP port and said deregistration message is forwarded through said GFP port to the provider device in a GFP error message. When several Ethernet interfaces concentrated by a bridge face the provider device, another VID is taken into account in the correspondence retrieving.