Atmosphere of Earth and balloons, and too low to permit orbital spacecraft. The mesosphere is mainly accessed by sounding rockets and rocket-powered aircraft. The stratosphere is the second-lowest layer of Earth's atmosphere. It lies above the troposphere and is separated from it by the tropopause. This layer extends from the top of the troposphere at roughly above Earth's surface to the stratopause at an altitude of about . The atmospheric pressure at the top of the stratosphere is roughly 1/1000 the pressure at sea level. It contains the ozone layer, which is the part of Earth's atmosphere that contains relatively high concentrations of
Session layer the person displayed on screen is the current speaker. Another application is in live TV programs, where streams of audio and video need to be seamlessly merged and transitioned from one to the other to avoid silent airtime or excessive overlap. The TCP/IP reference model does not concern itself with the OSI model's details of application or transport protocol semantics and therefore does not consider a session layer. OSI's session management in connection with the typical transport protocols (TCP, SCTP), is contained in the transport-layer protocols, or otherwise considered the realm of the application layer protocols. TCP/IP's layers are "descriptions"