Black Box MDS920C-10BT, User Manual

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Fig.1 Correspondence of TCP/IP layers with the OSI model layers
Layer III
The next layer (Layer III) is a layer of internetwork interconnection, which enables packet
transmission using different transmission media, LANs, WANs, xDSL, etc.
The Internet Protocol is used as the primary protocol of this layer (session layer in terms of the
OSI model).
All protocols, connected with data collecting and updating of routing tables, such as Routing
Internet Protocol (RIP) refer to this layer. This protocol is used in Black Box PAM modems.
Layer II
Layer II is sometimes called basic. The Transmission Control Protocol (TCP) and User Datagram
Protocol (UDP) function at this level. TCP provides reliable packet transmission using virtual
links. UDP, as well as IP, enables datagram application packet transmission. It functions as a
connecting link between network protocols and numerous application processes.
Layer I
Layer I is called the application layer. It contains a great number of application layer protocols
and services. Such widely used protocols as File Transfer Protocol (FTP), Telnet terminal
emulation protocol, Simple Network-Management Protocol (SNMP) (used in the e-mail), WWW
protocols and many others belong to this layer.
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