Ozone depletion as the International Day for the Preservation of the Ozone Layer, or "World Ozone Day", to commemorate the signing of the Montreal Protocol on that date in 1987. Ozone depletion Ozone depletion describes two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions. The latter phenomenon is referred to as the ozone hole. There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric events. The main
Physical layer (LAN) or a metropolitan area network (MAN) using Open Systems Interconnection (OSI) architecture, the "physical signaling sublayer" is the portion of the physical layer that The Internet protocol suite, as defined in RFC 1122 and RFC 1123, is a high-level networking description used for the Internet and similar networks. It does not define an equivalent layer that deals exclusively with hardware-level specifications and interfaces, as this model does not concern itself directly with physical interfaces. Several RFCs mention a "physical layer" and "data link layer", but that is in the context of IEEE protocols. RFC 1122 and 1123 do not