What is the OSI model? Network Architecture and Analysis Professor Peter Fall 2009 Kersey Lambert

Physical Layer Information is carried over wires as bits (1’s and 0’s) and converted into electrical pulses. This layer handles the physical connections within the computer and from terminal to terminal and completes no error checking.

OSI Model OSI stands for Open Systems Interconnection. There are seven layers in the OSI Model, as seen in this diagram. http://www.novell.com/info/primer/prim05.html It was widely adopted because it offers a high level of interoperability. OSI stands for Open Systems Interconnection. There are seven layers in the OSI Model, as seen in this diagram. It was widely adopted because it offers a high level of interoperability. OSI stands for Open Systems Interconnection. There are seven layers in the OSI Model, as seen in this diagram. It was widely adopted because it offers a high level of interoperability. OSI stands for Open Systems Interconnection. There are seven layers in the OSI Model, as seen in this diagram. http://www.novell.com/info/primer/prim05.html It was widely adopted because it offers a high level of interoperability. OSI stands for Open Systems Interconnection. There are seven layers in the OSI Model, as seen in this diagram. http://www.novell.com/info/primer/prim05.html

Data Link Layer Headers and trailers are added to create frames which allow the computer to know where frames begin and end. No data is interpreted, only encapsulated for the network layer. Packets are checked for errors at this layer.

Network Layer Receives segmented data, adds logical addressing information, and creates packets. This layer handles virtual connections throughout the network and between other networks. Routes and relays data between nodes. IP-Internet Protocol is the standard used to connect networks.

Transport Layer Maximum transmission units are determined here. If units are too large, they are segmented with sequence identifiers. Ensures that packet arrive complete and in the correct sequence. This layer also contains checksum, flow control and acknowledgement data.

Session Layer PDU’s are received, transmission speed is detected, and a session header is added. TCP-Transmission Control Protocol functions at this layer. This layer “establishes, manages, and terminates sessions between applications” (Novell’s networking primer, 2009). Sessions are dialogues between presentation layers of sending and receiving computers.

Presentation Layer Information is encrypted, as needed, and PDU’s (Protocol Data Units) are sent through. FTAM-File Transfer, Access, and Management and VTP-Virtual Terminal Protocol are part of this layer. Developed by DoD as part of the TCP/IP suite of protocols (Novell’s network primer, 2009). This layer “converts incoming and outgoing data from one presentation format to another” (Novell’s networking primer, 2009).

Application Layer This layer uses FTP-File Transport Protocol, Telnet, HTTP-Hypertext Transfer Protocol, and SMTP-Simple Mail Transfer Protocol. This layer “performs high-level services such as making sure necessary resources are present…and authenticating users when appropriate” (Novell’s networking primer, 2009). Processes requests and transfers them down through the layers and across the network.