Osi vs Tcp Ip Model

OSI vs. TCP/IP Model Comparison & Overview
The Open Systems Interconnection (OSI) reference model created in the late seventies and used today consists of seven layers that include Application, Presentation, Session, Transport, Network, Data Link and Physical. The Application layer often dubbed Layer 7 is the most common layer to end users and can consist of applications such as Microsoft's Internet Explorer or other browser software. The Presentation layer provides a translation of application data to network format in order to be processed and is considered bidirectional. The Session layer is responsible for controlling communication between applications by establishing, managing and ending dialogs. The Transport layer is responsible for end to end error recovery and the complete transparent transfer of data between systems. The Network layer is where all switching and routing of data takes place. This layer is responsible for congestion control as presented in this week's discussion question and also provide packet prioritization. Finally we have the Data Link and Physical layers. The Data Link is where data packets are encoded into bits and is divided into two sublayers: Media Access Control (MAC) and Logical Link Control (LLC). The Physical layer is where hardware such as Network Interface Cards (NIC) and other protocols reside. Prior to OSI becoming a standard there was a dual effort in modeling and Institute of Electrical and Electronic Engineers (IEEE) was in its infancy. IEEE 802 resides in what is known as the Data Link and Physical layer of the OSI model.
The universal Transmission Control Protocol/Internet Protocol (TCP/IP) model is not written in stone and can range from three to five layers depending on the model. I plan to use a model that is often used and contains four layers consisting of the Applications, Transport, Internet and Network Access layer. Under the TCP/IP model the application layer represents data using such protocols as Simple Mail Transfer Protocol (SMTP), File Transfer Protocol (FTP) and Telnet. The Transport layer has two dedicated protocols; the Transmission Control Protocol (TCP) in charge of assuring information is received as it was sent and the User Datagram Protocol (UDP) that performs no end-to-end reliability checks. "In the OSI Reference Model the Network Layer isolates the upper layer protocols from the details of the underlying network and manages the connections across the network." The IP Internet Layer corresponds to the Network Layer of the OSI model and includes the Internet Protocol (IP), Internet Control Message Protocol (ICMP), and Internet Group Management Protocol (IGMP) protocols. The Network Access Layer consists of data link protocols such as Ethernet and Token Ring. The NAL mirrors or ties back to the Data Link and Physical Layers of the OSI model. Table 1 shows how the OSI and TCP/IP models are similar and different and the common protocols used in each layer.
Table 1
Layer OSI TCP/IP Protocols
7 Application Application SMTP, FTP, Telnet
6 Presentation Application SMTP, FTP, Telnet
5 Session Application SMTP, FTP, Telnet
4 Transport Transport TCP, UDP
3 Network Internet IP
2 Data Link Network Ethernet, Token Ring
1 Physical Network Ethernet, Token Ring There are many similarities between the OSI and TCP/IP models. From the research and previous learning experiences it seems the OSI model is all ways the standard seven layers but the TCP/IP model from the Department of Defense (DoD) in most cases is presented as four layers but in some teachings may display five layers. Similarities between the two are similar architecture, shared common applications layer, the network and transport layers are fairly similar, and both models assume the packets may take differing paths to reach their final destination. The TCP/IP model can be referred to as the more credible model and is considered to be the blueprint the Internet was created from. There are several differences between the two models and some of which include the presentation and session layer of TCP/IP are combined into the application layer. This accounts for three layers of the OSI model. Other differences are the data link and physical layer are combined into the networks access layer under TCP/IP and the TCP/IP model can be easier to manage due to less layers, in fact only 4 layers compared to the 7 layers of the OSI model. The OSI and TCP/IP models seem to be very common place and are an important part of a network architect and administrators knowledge base. Without a firm grasp of how these models work it is not possible to understand and troubleshoot problems successfully.