**What is a networking model**? Networking models categorize and provide a structure for networking protocols and standards. ## OSI (Open Systems Interconnection) Model #### Application Layer * Layer closes to the end user. * Interacts with software applications. * It identifies communication partners. * It synchronizes communication. #### Presentation * Data in the application layer is in 'application format'. It needs to be translated to a different format to be sent over the network. * The presentations layers's job is to translate between application and network formats. * For example, encryption of data as it is sent, and description of data as it is received. * Also translates between different application layer formats. #### Session * Controls sessions between communicating hosts. * Establishes, manages, and terminates connections between the local application and the remote application. #### Transport * Segments and resembles data for communication between end hosts. * Breaks large pieces of data into smaller segments which can be more easily sent over the network and are less likely to cause transmission problems if errors occur. * Provides host-to-host communication. * provides process-to-process communication. #### Network * Provides connectivity between hosts on different networks. * Proves logical addressing (IP addresses). * Provides path selection between source and destination. * Routers operate at layer 3. #### Data Link * Provides node-to-node connectivity and data transfer. * Defines how data is formatted for transmission over a physical medium ( for example, copper UTP cables) * Detects and possibly corrects physical layer errors. * Uses Layer 2 addressing, separate from Layer 3 addressing. * Switches operate at Layer 2. #### Physical * Defines physical characteristics of the medium used to transfer data between devices. * Digital bits are converted into electrical (for wired connections) or radio (for wireless connections) signals. #### OSI Model PDUs  #### OSI vs TCP/IP