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Chapter 1 - Internetworking Basics Notes

• Switches vs Routers
  • Switches create separate collision domains within a single broadcast domain
    • Might be referred to as a multiport bridge (But actually, have advanced management abilities and features and way more ports)
    • Break up collision domains on a LAN
    • Bridges serve as a way to reduce collisions with broadcast domains and to increase the number of collision domains in your network.
      • This provides more bandwidth for users.
      • Using hubs in an Ethernet network can contribute to congestion.
    • Bridges/switches are used to segment networks, but they will not isolate broadcast or multicast packets.
  • Routers provide a separate broadcast domain for each interface.
    • Routers break up broadcast domains for every LAN interface.
    • They also break up collision domains.
• The OSI Reference Model
  • ISO (International Organization for Standardization) created the OSI (Open Systems Interconnection, model). Cisco created the IOS (Internetworking Operating System) 
  • 7 Layers (Mnemonic for the 7 layers: All People Seem To Need Data Processing)
    • The upper layers
      • Application - provides a user interface
        • File, print, message, database, and application services
      • Presentation - Presents data and handles processing such as encryption
        • Data encryption, compression, and translation services
      • Session - Keeps different application' data separate 
        • Dialog control
    • The lower layers
      • Transport - Provides reliable or unreliable delivery and perform error correction before transit
        • End-to-end connection
      • Network - Provides logical addressing, which routers use for path determination
        • Routing
      • Data Link - Combines packets into bytes and bytes into frames, provides access to media using MAC address, and performs error detection, not correction.
        • Framing
      • Physical - Moves bits between devices and specifies voltage, wire speed, and pinout of cables
        • Physical topology
    • The Application Layer
      • File Transfers, email, enabling remote access, network management activities, client/server processes, information location.
      • The application layer works as the interface between actual application programs. End user programs, like Microsoft Word, don't reside in the application layer, they interface with the Application layer protocols.
    • The Presentation Layer
      • By providing translation services, the Presentation layer ensures that data transferred from the Application layer of one system can be read by the Application layer of another system.
      • OSI (Open Systems Interconnection, model) has protocols that define how standard data should be transferred.
    • The Session Layer
      • Responsible for setting up, managing, and dismantling sessions between Presentation layer entities and keeping user data separate. 
      • Communication between the hosts' various applications at the Session layer, as from a client to a server, is organized via three different modes:
        • Simplex (Only one way)
        • Half- duplex (Radio, one way at a time)
        • Full-duplex (Both ways at the same time)
      • The Transport Layer
        • Layers segments and assembles data into a single data stream. Receives data from the upper layer applications, then combines it into the same, concise data stream.
        • TCP and UDP are found in this layer, TCP is known as reliable and UDP is not.
          • The term reliable networking can be used at the Transport layer. Reliable networking requires that acknowledgment, sequencing, and flow control will all be used.
        • Connection-Oriented Communication
          • Establish a connection-oriented communication session (Call setup or three-way handshake).
            • SYNC (Synchronization)
            • ACK (Acknowledgement)
            • ACK (Acknowledgement)
          • Data transfer
          • Call termination tears down the virtual circuit
          • This type of virtual circuit setup is often referred to as Overhead
        • Flow Control
          • Ensures data integrity at the Transport layer by allowing applications to request reliable data transport between systems.
          • The purpose of flow control is to provide a way for the receiving device to control the amount of data sent by the sender.
          • Stoplight for the receiving device, while it processes the current segments in its memory reservoir.
          • A service is considered connection-oriented if it has the following characteristics
            • A virtual circuit or "Three-way-handshake" is set up
            • It used sequencing
            • It uses acknowledgment 
            • It uses flow control
          • Types of flow control are buffering, windowing, and congestion avoidance.