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Networking Models

Updated Jan 16, 2019 ·

Overview​

Various models, architectures, and standards facilitate the interconnection of hardware and software systems for sharing information and coordinating activities.

  1. Provide Reliable Communications

    • Ensure dependable communication between hosts and users.

  2. Isolate Functions in Layers

    • Segment functions into distinct layers for better organization and management.

  3. Packets as Communication Basis

    • Use packets as the fundamental unit of communication.

  4. Standardize Routing, Addressing, and Control

    • Implement standardized protocols for routing, addressing, and control.

  5. Allow Additional Layer Functionality

    • Enable flexibility for layers beyond internetworking to add functionality.

  6. Vendor-Agnostic, Scalable, and Resilient

    • Ensure compatibility across vendors, scalability, and resilience in network design.

In the most basic form, a network model has at least two layers:

  • Upper Layer

    • Also known as the host or application layer
    • Manages connection integrity
    • Controls sessions
    • Handles communication session establishment, maintenance, and termination
    • Transforms data into a universally understandable format
    • Facilitates communication between applications
    • Checks availability and accessibility of remote communication partners

  • Lower Layer

    • Often referred to as the media or transport layer
    • Receives bits from the physical connection medium
    • Converts bits into standardized frames
    • Frames function like buckets holding water (bits)
    • Ensures controlled transportation of data within standardized frames
    • Adds route data to frames to create packets
    • Preparation for further management and processing by the upper layer

OSI Model​

The Open Systems Interconnection (OSI) Model is a conceptual framework for describing the communication structure of interconnected computer systems, comprising seven layers.

  • Application, Presentation, and Session Layers (5-7) - Commonly referred to as data potential for encapsulation.

    • SNMP (Layer 7)

  • Transport Layer (4) - Manages protocols like TCP/UDP

  • Network Layer (3) - Handles routing and packet transmission

    • ICMP
    • IGMP
    • IP

  • Data Link Layer (2) - Manages frames and devices like switche

  • Physical Layer (1) - Converts data into binary for transmissio

Encapsulation and De-encapsulation​

Encapsulation occurs as data descends, and de-encapsulation happens as it ascends. The OSI Model aids in understanding networking terminology and processes.

The encapsulation/de-encapsulation process is best depicted visually below:

TCP/IP​

Transmission Control Protocol/Internet Protocol (TCP/IP) is platform-independent but resource-intensive and designed for ease of use rather than security. It predates the OSI model.

  • Application Layer - Defines transport layer protocol

    • Telnet - Allows terminal emulation over the Interne

    • File Transfer Protocol (FTP) - Facilitates file transfers between device

    • Simple Mail Transport Protocol (SMTP) - Manages email transmissio

    • Domain Name Service (DNS) - Resolves domain names to IP addresse

  • Transport Layer - Facilitates data movemen

    • TCP (Transmission Control Protocol) - Full-duplex, connection-oriented protoco

    • UDP (User Datagram Protocol) - Simplex, connectionless protoco

  • Internet Layer - Handles packet creation and insertio

    • Internet Control Message Protocol (ICMP) - Determines network or link health. Used b tools like ping and traceroute.

    • The ping utility employs ICMP echo packets to assess:

      • Online status of a remote system.

      • Prompt responsiveness of the remote system.

      • Support for communications by intermediary systems.

      • Level of performance efficiency in communication among intermediary systems.

  • Network Interface Layer - Manages data flow in the networ

SYN, SYN-ACK, ACK Handshake​

The SYN, SYN-ACK, and ACK handshake is a process used in the TCP (Transmission Control Protocol) to establish a connection between two devices on a network.

  • SYN (Synchronize)

    • Initiates the connection request.
    • The sender indicates its intention to establish a connection.
    • The sender picks an initial sequence number.

  • SYN-ACK (Synchronize-Acknowledge)

    • Acknowledges the receipt of the SYN packet.
    • Indicates acceptance of the connection request.
    • The receiver also selects an initial sequence number.

  • ACK (Acknowledge)

    • Confirms the acknowledgment of the SYN packet.
    • Establishes the connection.
    • Data transfer can begin after the ACK is received.

This three-step handshake ensures that both the sender and receiver are ready to exchange data and have agreed upon initial sequence numbers for reliable communication.

UDP​

User Datagram Protocol (UDP) is a connectionless protocol that enables fast data transmission without establishing a connection, making it suitable for low-latency applications like gaming and streaming.

  • Connectionless, reducing overhead but less reliable
  • No error checking or data recovery, leaving this to the application
  • Lightweight, fast, and efficient for small data transmissions
  • Supports broadcasting and multicasting, ideal for live broadcasts and conferencing

Distributed Network Protocol (DNP3)​

DNP3 is a communication protocol primarily used in utility and industrial automation systems to enable reliable and efficient data exchange between control equipment.

  • Widely used in SCADA systems for monitoring and controlling remote equipment in real-time
  • Supports robust communication and offers features like time-stamped data and event logging
  • Ensure interoperability between different vendors' equipment in complex networks

How It Works:

  • Remote Terminal Unit (RTU): The RTU gathers data from sensors or field devices and sends it to the SCADA master station.
  • Communication Links: These are the channels (wired or wireless) that facilitate the exchange of data between RTUs and the SCADA master station.
  • SCADA Master Station: This central system receives data from RTUs, processes it, and issues control commands back to the RTUs, enabling real-time monitoring and control of the entire network.

Diagram: