OSI Model Quiz

Network Models

• Network models divide complex communication processes into smaller, manageable tasks.
• Each layer handles a specific set of tasks.
• This layered approach is fundamental to networking architectures like OSI and TCP/IP.

Layered Tasks

• Layered tasks simplify complex communication processes.
• Each layer is responsible for a dedicated set of tasks.
• An example used is the postal service analogy. The process of sending a letter through the post office is easier because of the specific responsibilities of each stage.

OSI Model

• Established in 1947, the International Standards Organization (ISO) created the OSI model.
• The model covers all aspects of network communications.
• It was introduced in the late 1970s.
• The OSI model is a conceptual framework, not an implementation.

Seven Layers of the OSI Model

• Layer 7 (Application): Implemented by network applications. These applications generate data for transfer. This layer acts as an interface for the application services to communicate with the network and display received information to the user. Some popular protocols include SMTP, FTP, and DNS.

• Layer 6 (Presentation): Also known as the Translation layer. This layer extracts data from the application layer and manipulates it to match the network's required format to transmit over the network. Some examples of protocols used in this layer include JPEG, MPEG, GIF, and TLS/SSL.

• Layer 5 (Session): Responsible for establishing, managing, and terminating connections between devices, which includes authentication and security. Some protocols include NetBIOS and PPTP.

• Layer 4 (Transport): Provides services to the application layer and takes services from the network layer. Data in this layer is referred to as segments. It's responsible for end-to-end delivery, acknowledgment for successful data transmission, and retransmission in case of errors. Protocols used include TCP, UDP, NetBIOS, and PPTP.

• Layer 3 (Network): Responsible for transmitting data from one host to another located on different networks. It handles packet routing, selecting the shortest path, and utilizing available routes. Sender and receiver IP addresses are placed in the header by this layer. Packets in this layer are referred to as packets. This layer uses networking devices such as routers and switches.

• Layer 2 (Data Link): Responsible for node-to-node delivery of messages. It ensures the error-free transfer of data from one node to another over the physical layer. The layer handles packet transmission to the host using the MAC address. This layer divides packets into frames. Common devices are switches and bridges. This layer has two sub-layers: Logical Link Control (LLC) and Media Access Control (MAC).

• Layer 1 (Physical): The lowest layer. It's responsible for the physical connection between devices, and transmits data in the form of bits. It handles the conversion of signals into 0s and 1s and transmits them to the Data Link Layer, which reassembles the frame. Devices in this layer include hubs, repeaters, modems, and cables.

TCP/IP Model

• The layers in the TCP/IP suite do not directly match the OSI layers.
• The TCP/IP protocol suite is characterized by four layers: host-to-network, internet, transport, and application.
• Compared with OSI, the TCP/IP suite has five layers: physical, data link, network, transport, and application.

Addressing

• Addressing is assigning a unique address to each network device to ensure successful communication.
• Four levels of addressing are used in TCP/IP networks: physical, logical, port, and specific.
  • Physical addresses (MAC addresses) are unique hardware identifiers for network interface cards (NICs).
  • Logical addresses (IP addresses) are unique numbers that identify devices on a network.
  • Port addresses are used at the transport layer to differentiate between different applications running on a host.
  • Specific addresses are used to access specific resources or applications on a network (e.g., URLs, email addresses).