Description: This field gives the active loopback status on the synchronous physical interface. When its value is `line' the data flow recieved from the port side is sent back to the line. When its value is `equipment' the data flow recieved form equipment side is send back. The field can be set to a particular loopback value, even if there no garantee that the loopback is really done. The real loopback status of the interface must be checked in the response. The loopback can be cleared by the equipment when it cannot remain for any reason.