OSI Model and TCP/IP suite

• Networking models categorize and provide a structure for networking protocols and standards
• Networking protocols are a set of rules defining how network devices and software should work together
• OSI Model and TCP/IP suite are two networking models
• OSI Model is not in use today but has had a big impact on how network engineers think about networking
• OSI stands for 'open systems interconnection' model
• OSI Model was created by the international organization for standardization (ISO) in the late 1970s and early 1980s
• OSI Model divides network functions into 7 layers
• Layer 1 of the OSI Model is the physical layer, defining physical characteristics of the medium used to transfer data between devices
• Layer 2 of the OSI Model is the Data Link Layer, providing node-to-node connectivity and data transfer
• Layer 3 of the OSI Model is the Network Layer, providing connectivity between end hosts on different networks and logical addressing with IP addresses
• Layer 4 of the OSI Model is the Transport Layer, segmenting and reassembling data for communications between end hosts
• Layer 5 of the OSI Model is the Session Layer, controlling dialogues between communicating hosts
• Layer 6 of the OSI Model is the Presentation Layer, translating data between application and network formats
• Layer 7 of the OSI Model is the Application Layer, interacting with software applications and identifying communication partners
• When an application wants to send data to another system, it interacts with the application layer of the OSI stack
• The combination of data plus Layer 4 header is called a Segment
• The combination of data plus Layer 3 header, which includes the IP address, is called a Packet
• The complete unit with Layer 2 header and trailer added at the Data Link layer is called a Frame
• All of these combinations are referred to as Protocol Data Units (PDUs)
• At Layer 1, the physical layer, the PDU is called a bit
• The TCP/IP suite is a conceptual model and set of communication protocols used in the Internet and other networks
• The TCP/IP model has a similar structure to the OSI model but with fewer layers
• The OSI model and the TCP/IP model share the transport layer
• The network layer of the OSI model maps to the Internet layer of the TCP/IP model
• The data link and physical layers of the OSI model are equivalent to the Link layer of the TCP/IP model
• The Link layer of the TCP/IP model is equivalent to the OSI Data Link and Physical layers