The 2 most common Internetworking Models are OSI Reference Model and TCP/IP Model.
OSI Reference Model
The Open Systems Interconnection reference model (OSI reference model or OSI model for short)is a layered, abstract description for communications and computer network protocol design,developed as part of the Open Systems Interconnection (OSI) initiative.
Physical layer – Concerned with transmission of unstructured bit stream over the physical link. It invokes such parameters as signal voltage swing and bit duration. It deals with the mechanical, electrical, procedural characteristics to establish, maintain and deactivate the physical link
Data Link layer – Provides reliable transfer of data across the physical link. It sends blocks of data (frames) with the necessary synchronization, error control and flow control.
Network layer – Provides upper layers with independence from the data transmission and switching technologies used to connect systems. It is responsible for establishing, maintaining and terminating connections.
Transport layer – Provides reliable, transparent transfer of data between end points. It provides end-to-end error recovery and flow control.
Session layer – Provides the control structure for communication between applications. It establishes, manages and terminates connections (sessions) between cooperating applications.
Presentation layer – Performs transformations on data to provide a standardized application interface and to provide common communications services. It provides services such as encryption, text compression and reformatting.
Application layer – Provides services to the users, FTP, HTTP, TELNET, etc.
TCP/IP Model
TCP/IP originated out of the investigative research into networking protocols that the US Department of Defense (DoD) initiated in 1969. In 1968, the DoD Advanced Research Projects Agency (ARPA) began researching the network technology that is called packet switching.
Network Access Layer – The lowest layer of the TCP/IP protocol hierarchy. It defines how to use the network to transmit an IP datagram. Unlike higher-level protocols, Network Access Layer protocols must know the details of the underlying network (its packet structure, addressing, etc.) to correctly format the data being transmitted to comply with the network constraints. The TCP/IP Network Access Layer can encompass the functions of all three lower layers of the OSI reference Model (Physical, Data Link and Network layers).
As new hardware technologies appear, new Network Access protocols must be developed so that TCP/IP networks can use the new hardware. Consequently, there are many access protocols - one for each physical network standard.
Access protocol is a set of rules that defines how the hosts access the shared medium. Access protocol have to be simple, rational and fair for all the hosts.
Functions performed at this level include encapsulation of IP datagrams into the frames transmitted by the network, and mapping of IP addresses to the physical addresses used by the network. One of TCP/IP's strengths is its universal addressing scheme. The IP address must be converted into an address that is appropriate for the physical network over which the datagram is transmitted.
Internet layer – Provides services that are roughly equivalent to the OSI Network layer. The primary concern of the protocol at this layer is to manage the connections across networks as information is passed from source to destination. The Internet Protocol (IP) is the primary protocol at this layer of the TCP/IP model.
Transport layer – It is designed to allow peer entities on the source and destination hosts to carry on a conversation, just as in the OSI transport layer. Two end-to-end transport protocols have been defined here TCP and UDP Both protocols will be dicussed later.
Application Layer – includes the OSI Session, Presentation and Application layers as shown in the Figure 4. An application is any process that occurs above the Transport Layer. This includes all of the processes that involve user interaction. The application determines the presentation of the data and controls the session. There are numerous application layer protocols in TCP/IP, including Simple Mail Transfer Protocol (SMTP) and Post Office Protocol (POP) used for e-mail, Hyper Text Transfer Protocol (HTTP) used for the World-Wide-Web, and File Transfer Protocol (FTP). Most application layer protocols are associated with one or more port number. Port numbers will be dicussed later.
As new hardware technologies appear, new Network Access protocols must be developed so that TCP/IP networks can use the new hardware. Consequently, there are many access protocols - one for each physical network standard.
Access protocol is a set of rules that defines how the hosts access the shared medium. Access protocol have to be simple, rational and fair for all the hosts.
Functions performed at this level include encapsulation of IP datagrams into the frames transmitted by the network, and mapping of IP addresses to the physical addresses used by the network. One of TCP/IP's strengths is its universal addressing scheme. The IP address must be converted into an address that is appropriate for the physical network over which the datagram is transmitted.
Internet layer – Provides services that are roughly equivalent to the OSI Network layer. The primary concern of the protocol at this layer is to manage the connections across networks as information is passed from source to destination. The Internet Protocol (IP) is the primary protocol at this layer of the TCP/IP model.
Transport layer – It is designed to allow peer entities on the source and destination hosts to carry on a conversation, just as in the OSI transport layer. Two end-to-end transport protocols have been defined here TCP and UDP Both protocols will be dicussed later.
Application Layer – includes the OSI Session, Presentation and Application layers as shown in the Figure 4. An application is any process that occurs above the Transport Layer. This includes all of the processes that involve user interaction. The application determines the presentation of the data and controls the session. There are numerous application layer protocols in TCP/IP, including Simple Mail Transfer Protocol (SMTP) and Post Office Protocol (POP) used for e-mail, Hyper Text Transfer Protocol (HTTP) used for the World-Wide-Web, and File Transfer Protocol (FTP). Most application layer protocols are associated with one or more port number. Port numbers will be dicussed later.
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