Compare the Layers of the OSI and TCP/IP Models

Compare the layers of the OSI and TCP/IP models OSI model: The Open Systems Interconnection (OSI) Reference Model is a modular framework for developing standards that are based on a division of network operations into seven, sets of network services. At one time, most vendors agreed to support OSI in one form or another, but the OSI was too loosely defined and proprietary standards were too entrenched. Except for the OSI-compliant X.400 and X.500 e-mail and directory standards, which are still widely used, what was once thought to become the universal communications standard now serves as the teaching model for all other protocols. Most of the functionality in the OSI model exists in all communications systems, although two or three OSI layers may be incorporated into one. A look at each of the OSI layers , and the role it plays. APPLICATION layer 7 PRESENTATION layer 6 SESSION Gives user applications access to network. This layer represents the services, that directly support the user applications such as software for file transfers, database access, and E-mail The presentation layer, usually part of an operating system, converts incoming and outgoing data from one presentation format to another. Presentation layer services include data encryption and text compression. Opens manages, and closes conversations between two computers. It performs name recognition and the layer 5 functions such as security, needed to allow two applications to communicate over the network, also provides error handling. TRANSPORT This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer. layer 4 Sequences data packets, and requests retransmission of missing packets. It also repackages messages for more efficient transmission over the network. NETWORK layer 3 DATA LINK layer 2 Establishes, maintains and terminates network connections. Routes data packets across network segments. Translates logical addresses and names into physical addresses. Transmits frames of data from computer to computer on the same network segment. Ensures the reliability of the physical link established at layer 1. Standards define how data frames are recognized and provide the necessary flow control and error handling at the frame set. The data link layer is divided into two sublayers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sublayer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking. PHYSICAL layer 1 The Physical layer defines all the electrical and physical specifications for devices. This includes the layout of pins, voltages, and cable specifications. Hubs, repeaters and network adapters are physical-layer devices. Defines cabling and connections. Transmits data over the physical media. Example of how the OSI Layers work using an e-mail sent from the computer on the left. Data travels from the sending computer down through all the layers to the physical layer where the data is put onto the network cabling, and then sent to the physical layer of the receiving computer where the process reverses and the data travels up through the layers to the application layer of the receiving computer. E-mail sent from John: E-mail received from John: Meet me at Carl's 1:30 Meet me at Carl's 1:30 John John Identify sender and intended receiver; is there an e-mail application available? APPLICATION Encode data with X coding key; use ASCII characters. PRESENTATION layer 7 layer 6 Identified sender and intended receiver; found e-mail application. Decoded data with X decoding key; used ASCII characters Initiate and terminate SESSION the session according to X protocol layer 5 Initiated and terminated the session according to X protocol. Make sure all data is sent intact. TRANSPORT Make sure all data has arrived intact. Keep track of how many hops; NETWORK layer 4 Keep track of how many hops; layer 3 open shortest path First; opened the shortest path First; Go to IP address 255.65.0.123 Went to IP address 255.65.0.123 Is the initial connection set up? Put data into frames according to X standard DATA LINK layer 2 Send as electrical signal PHYSICAL over the network cable at X voltage, and X layer 1 Mbps. The initial connection set up. Decoded data in frame according to X standard. Receive electrical signal over the network cable at X voltage, and X Mbps. TCP/IP model: The TCP/IP model is not same as OSI model. OSI is a seven-layered standard, but TCP/IP is a four layered standard. OSI Layers TCP/IP Layers APPLICATION layer 7 PRESENTATION layer 6 APPLICATION LAYER (Layer 4) SESSION layer 5 TRANSPORT layer 4 NETWORK layer 3 DATA LINK layer 2 TRANSPORT LAYER (Layer 3) INTERNET LAYER (Layer 2) PHYSICAL layer 1 NETWORK INTERFACE LAYER (Layer 1) Network Interface Layer The network interface layer specifies the form in which data must be routed by the type of network is used. Internet Layer The internet layer is between Network Access Layer and Transport Layer.The internet layer has the responsibility of sending packets across potentially multiple networks. Internetworking requires sending data from the source network to the destination network. This process is called routing. Transport Layer The transport layer can be thought of as a transport mechanism, e.g., a vehicle with the responsibility to make sure that its contents (passengers/goods) reach their destination safely and soundly, unless another protocol layer is responsible for safe delivery. The layer simply establishes a basic data channel that an application uses in its task-specific data exchange. Application Layer (Also described as: Link Layer, Internet Layer, Transport Layer, Application Layer) The three top layers in the OSI model the application layer, the presentation layer and the session layer are not distinguished separately in the TCP/IP model where it is just the application layer. The application layer defines TCP/IP application protocols and how host programs interface with transport layer services to use the network.