The main benefits of the OSI model

The main benefits of the OSI model include the following: • Helps users understand the big picture of networking • Helps users understand how hardware and software elements function together • Makes troubleshooting easier by separating networks into manageable pieces • Defines terms that networking professionals can use to compare basic functional relationships on different networks • Helps users understand new technologies as they are developed • Aids in interpreting vendor explanations of product functionality Layer 1 The physical layer of the OSI model defines connector and interface specifications as well as the required cables for the job. Electrical, mechanical, functional, and procedural specifications are provided for sending a bit stream on a computer network. Components of the physical layer include:

• Cabling system components • Adapters that connect media to physical interfaces • Connector design and pin assignments • Hub, repeater, and patch panel specifications • Wireless system components • Parallel SCSI (Small Computer System Interface) • Network Interface Card (NIC) Layer 2 Layer 2 of the OSI model is the Data Link layer. In this layer it provides the function of: • Allowing a device to access the network to send and receive messages • Offers a physical address so a device’s data can be sent on the network • Works with a device’s networking software when sending and receiving messages • Provides error-detection capability Common components of this layer are NIC cards, Ethernet and Token ring switches and bridges. Layer 3 Layer 4 Layer 4 being the transport layer of the OSI model offers end-to-end communication between end devices through a network. Depending on the application, the transport layer either offers reliable, connection-oriented or connectionless, best-effort communications.

Some of the functions offered by the transport layer include: • Application identification • Confirmation that the entire message arrived intact • Control of data flow to prevent memory overruns • Establishment and maintenance of both ends of virtual circuits • Transmission-error detection • Realignment of segmented data in the correct order on the receiving side The most common transport layer protocols are the connection-oriented TCP Transmission Control Protocol (TCP) and the connectionless UDP User Datagram Protocol (UDP). Layer 5 This is the session layer it provides various services that include tracking the number of bytes that each end of the session has acknowledged receiving from the other end of the session. The session layer allows applications to function on devices to establish, manage, and terminate a dialog through a network.

Session layer functionality includes: • Virtual connection between application entities • Synchronization of data flow • Connection parameter negotiations • Acknowledgements of data received during a session • Retransmission of data if it is not received by a device Layer 6 Examples of presentation layer functionality include: • Encryption and decryption of a message for security • Compression and expansion of a message so that it travels efficiently • Graphics formatting • Content translation • System-specific translation Layer 7 The final layer of the OSI is the application layer. It provides an interface for the end user operating a device connected to a network. This layer is what the user sees, in terms of loading an application such as a web browser or email service.The application layer is the data the user views while using these applications. Examples of application layer functionality include: • Support for file transfers • Ability to print on a network • Electronic mail • Electronic messaging • Browsing the World Wide Web