OSI Model - Application Layer

OSI Model and TCP/IP Protocol Suite

• The OSI model provides a clear and standardized framework for understanding network communication processes.
• The TCP/IP protocol suite, also known as the Internet protocol suite, is the set of communications protocols used for the Internet and similar networks.
• The TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and applications.

Application Layer

• Protocols at this layer enable user applications to access network resources and services, such as email, file transfer, and remote login.
• Examples of protocols at this layer include HTTP (Hypertext Transfer Protocol), FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), and DNS (Domain Name System).

TCP/IP Protocol Suite Layers

• Internet Protocol (IP): provides the foundation for addressing and routing packets of data so that they can travel across networks and arrive at the correct destination.
• Key features of IP include:
  • Addressing: IP addresses uniquely identify devices on a network. IPv4 and IPv6 are the two main versions of the IP protocol.
  • Routing: IP routers use routing tables to determine the best path for forwarding packets to their destinations.

Signal Modulation

• Analog Modulation: techniques for embedding analog information into a carrier signal, such as amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM).
• Digital Modulation: techniques for encoding digital information into a carrier signal, such as amplitude-shift keying (ASK), frequency-shift keying (FSK), and phase-shift keying (PSK).

Data Communications

• Periodic analog signals can be classified as simple or composite.
• A sine wave is a mathematical curve that describes a smooth, periodic oscillation.
• Key points about sine waves include:
  • Mathematical representation: the mathematical formula for a sine wave is y(t) = Asin(2πft + ϕ).
  • Characteristics:
    • Amplitude: the maximum displacement of the waveform from its equilibrium position.
    • Frequency: the number of complete cycles of the wave that occur in one second.
    • Period: the time taken for one complete cycle of the wave to occur.

Routing Algorithms

• Distance Vector Routing:
  • Each router maintains a table of distances to all destinations and periodically exchanges routing updates with neighboring routers.
  • Convergence can be slow, and these algorithms are prone to routing loops and counting-to-infinity problems.
• Link State Routing:
  • Routers exchange link state advertisements (LSAs) to construct a detailed map of the network.
  • Shortest path calculations are performed using Dijkstra's algorithm, leading to faster convergence and more efficient routing.
• Hybrid Routing:
  • Combines aspects of both distance vector and link state routing.
  • An example is EIGRP (Enhanced Interior Gateway Routing Protocol), which uses distance vector techniques with additional features like partial updates and faster convergence.

Routing Protocols

• Routing Information Protocol (RIP):
  • One of the oldest distance vector routing protocols.
  • Uses hop count as a metric and supports a maximum of 15 hops.
• Open Shortest Path First (OSPF):
  • A widely used link state routing protocol designed for scalability and fast convergence.
  • Calculates the shortest path to each destination using Dijkstra's algorithm.
• Border Gateway Protocol (BGP):
  • The de facto standard for routing between autonomous systems (ASes) on the internet.
  • Considers policies and attributes when selecting the best route.

Network Protocols

• Definition: network protocols are rules and conventions governing communication between devices in a network.
• Common protocols include:
  • TCP (Transmission Control Protocol): provides reliable, connection-oriented communication between devices.
  • UDP (User Datagram Protocol): offers fast, connectionless communication with minimal overhead.
  • IP (Internet Protocol): fundamental protocol for addressing and routing packets across networks.
  • ICMP (Internet Control Message Protocol): used for diagnostic and error reporting functions in IP networks.
  • ARP (Address Resolution Protocol): maps IP addresses to MAC (Media Access Control) addresses in local network environments.

Ethernet Standards and IEEE 802.3

• Ethernet: a widely used networking technology for local area networks (LANs) and metropolitan area networks (MANs).
• IEEE 802.3: standardized by the Institute of Electrical and Electronics Engineers (IEEE).
• Specifies the characteristics of Ethernet networks, including frame formats, signaling, and media access control (MAC) methods.
• Defines various Ethernet standards based on data transfer rates and media types, such as:
  • 10BASE-T: Ethernet over twisted pair cables with a maximum data rate of 10 Mbps.
  • 100BASE-T (Fast Ethernet): provides data rates up to 100 Mbps over twisted pair cables.
  • 1000BASE-T (Gigabit Ethernet): supports data rates up to 1 Gbps over twisted pair cables.
  • 10GBASE-T (10 Gigabit Ethernet): enables data rates of 10 Gbps over twisted pair cables, typically used in data center environments.

Wireless Networking

• Wi-Fi (IEEE 802.11): a wireless networking standard for local area networks (LANs).
• Provides high-speed internet and network connectivity without the need for physical cables.
• Utilizes radio waves to transmit data between devices within a limited range.
• Bluetooth: a wireless technology for short-range communication between devices.