Cloud the bottom of the hierarchy. Clouds in the troposphere assume five physical forms based on structure and process of formation. These forms are commonly used for the purpose of satellite analysis. They are given below in approximate ascending order of instability or convective activity. "Non-convective" stratiform clouds appear in "stable" airmass conditions and, in general, have flat sheet-like structures that can form at any altitude in the troposphere. The stratiform group is divided by altitude range into the genera cirrostratus (high-level), altostratus (mid-level), stratus (low-level), and nimbostratus (multi-level). Fog is commonly considered a surface-based cloud layer. The fog may form
Internet layer packets specific to the link types. Such protocols belong to the link layer. Internet-layer protocols use IP-based packets. A common design aspect in the internet layer is the robustness principle: "Be liberal in what you accept, and conservative in what you send" as a misbehaving host can deny Internet service to many other users. The internet layer has three basic functions: In Version 4 of the Internet Protocol (IPv4), during both transmit and receive operations, IP is capable of automatic or intentional fragmentation or defragmentation of packets, based, for example, on the maximum transmission unit (MTU) of link elements. However,