A datacentre (100, 200) configured for receiving an optical signal comprising groups of wavelength bands, A1, A2, A3,..., AX, and B, X being an integer, the optical signal being associated with a request for a service to be executed by the datacentre, the datacentre being configured for executing the service and outputting the result of the service, the datacentre comprising: - at least one 1:N Multi Directional Wavelength Selective Switch, MD-WSS (110, 150, 210, 240, 260, 290), having one common port (114, 154, 216, 244, 264, 294) and N tributary ports (111-113, 151- 153, 211-215, 241-243, 261-263, 291-293), where N is an integer and N>1, and - a group (160, 220, 230, 250, 270) of at least one server cluster (131, 132, 221-223, 231-233, 251-253, 271-273, 281-287), each server cluster comprising a respective transceiver configured to receive and transmit optical signals on at least some of the wavelength bands, wherein the at least one MD-WSS (110, 210, 240) is configured to receive the optical signal associated with the service on its common port (114, 216, 244) and to output a part of the optical signal that comprises a first A-group of wavelengths, i.e. one of A1, A2, A3, etc., on an output tributary port (111, 211, 241) for wavelengths of the first A-group towards the group (160, 230, 250) of server clusters (131, 132, 231-233, 251-253, 281, 282, 286, 287), wherein the transceiver of one of the server clusters is configured to receive the optical signal from the at least one MD-WSS (110, 210, 240), the server cluster being configured to perform at least a part of the requested service, wherein the transceiver is further configured to output an optical signal towards one of the at least one MD-WSS (110, 150, 210, 240), the optical signal outputted from the transceiver having a wavelength of group B of wavelengths when at least one part of the service remains to be executed before the service is fully executed, and the optical signal outputted from the transceiver having a wavelength of a second A-group of wavelengths, i.e. one of A1, A2, A3, etc., when the service is fully executed, wherein the first and the second A-group of wavelengths are different, and wherein one of the at least one MD-WSS (110, 150, 210, 240) is configured to receive the optical signal from the transceiver on an input tributary port (112, 151, 214, 242) for wavelengths of the second A-group and group B, and to i) when the optical signal has a wavelength of the group B: output the optical signal on an output tributary port (111, 211, 241) for wavelengths of group B towards the server clusters (131, 132, 231-233, 251-253, 281, 282, 286, 287), the output tributary port for wavelengths of group B being the same as the output tributary port (111, 211, 241) for wavelengths of the first A-group and to ii) when the signal has the wavelength of second A-group: output the optical signal on the common port (114, 154, 216, 244). - at least one 1:N Multi Directional Wavelength Selective Switch, MD-WSS (110, 150, 210, 240, 260, 290), having one common port (114, 154, 216, 244, 264, 294) and N tributary ports (111-113, 151- 153, 211-215, 241-243, 261-263, 291-293), where N is an integer and N>1, and - a group (160, 220, 230, 250, 270) of at least one server cluster (131, 132, 221-223, 231-233, 251-253, 271-273, 281-287), each server cluster comprising a respective transceiver configured to receive and transmit optical signals on at least some of the wavelength bands,