Module 5: Communication Principles and Network Models

Fundamentals of Communication Protocols

  • Communication in daily life takes various forms and occurs in diverse environments, ranging from internet chats to professional job interviews.
  • Every communication situation has unique expected behaviors and styles that participants must adhere to.
  • Before communication begins, rules or agreements must be established to govern the conversation. These rules include:
    • The method of communication to be used.
    • The language to be used.
    • The necessity of confirming that messages are received.
  • Rules that govern successful human communication include:
    • An identified sender and an identified receiver.
    • An agreed-upon method of communicating, such as face-to-face contact, telephone calls, written letters, or photographs.
    • Use of a common language and grammar.
    • Consistent speed and timing of delivery.
    • Defined requirements for confirmation or acknowledgment.
  • These rules, known as protocols, must be followed explicitly for a message to be successfully delivered and understood. Network communications share these same fundamental techniques used in human conversations.

Why Protocols Matter in Networking

  • Computers requires protocols to communicate correctly across a network, just as humans do.
  • In both wired and wireless environments, a local network is defined as an area where all hosts must "speak the same language," meaning they share a common protocol.
  • If devices in a local network did not utilize the same protocols, they would be unable to communicate, similar to a room full of people where every individual speaks a different language.
  • Networking protocols define the essential aspects of communication over local networks to ensure data is transmitted accurately and reliably.

Characteristics of Network Protocols

  • Message Format: Every sent message uses a specific format or structure. This structure depends heavily on the type of message and the specific channel used to deliver it.
  • Message Size: Stringent rules govern the size of data pieces communicated across a network. These rules vary depending on the communication channel. Long messages sent between hosts must be broken into smaller pieces to ensure reliable delivery.
  • Timing: This is critical for many network communication functions. Timing determines the specific speed at which bits are transmitted, when an individual host is permitted to send data, and the total amount of data sent in any single transmission.
  • Encoding: The sending host converts messages into bits. Each bit is encoded into a specific pattern of light waves, sounds, or electrical impulses, depending on the network media. The destination host receives these signals and decodes them to interpret the original message.
  • Encapsulation: Every message transmitted on a network requires a header containing addressing information that identifies the source and destination hosts. Without this addressing, the message cannot be delivered. Encapsulation is the process of adding this header information to the message data. Headers may also contain information ensuring the message reaches the correct application on the destination host.
  • Message Pattern: A common aspect of many protocols is the request/response pattern, where some messages require an acknowledgment before the next message can be be sent. Conversely, other message types are streamed across the network without concern for whether they reach their destination.

The Role of Internet Standards

  • The reliable delivery of services like email, despite the continuous influx of new devices and technologies, is made possible through internet standards.
  • A standard is defined as a set of rules determining how something must be done.
  • Networking and internet standards ensure that all devices connecting to a network implement the same protocols in an identical manner, allowing different types of devices to send information to each other over the internet.
  • Internet standards result from a cycle of comprehensive discussion, problem-solving, and rigorous testing.

Standard Organizations and the RFC Process

  • Various organizations are responsible for developing, publishing, and maintaining network standards.
  • The Internet Engineering Task Force (IETF) publishes and manages Request for Comments (RFC) documents.
  • An RFC is a numbered document that records the development and approval process of a proposed standard, effectively tracking its evolution.

Overview of Network Communication Models

  • Layered models are used to visualize how various protocols work together to enable network communications.
  • These models depict operations occurring within each layer and show how those layers interact with the ones above and below them.
  • Benefits of Layered Models:
    • They assist in protocol design by defining specific information that protocols must act upon and limiting interfaces between layers.
    • They foster competition because products from different vendors can work together seamlessly.
    • they enable technology changes at one level without requiring changes at other levels.
    • They provide a common language to describe networking capabilities and functions.

The TCP/IP Protocol Model

  • Created in the early 1970s, the TCP/IP model was originally referred to as the internet model.
  • It defines four categories of functions that must occur for successful communication:
    • Application Layer: Represents data to the user and manages encoding and dialog control.
    • Transport Layer: Supports communication between different devices across diverse networks.
    • Internet Layer: Responsible for determining the best path through the network.
    • Network Access Layer: Controls the hardware devices and physical media that constitute the network.
  • The TCP/IP model is considered a "protocol model" because it closely matches the structure of the TCP/IP protocol suite.

The OSI Reference Model

  • The Open Systems Interconnection (OSI) model was created by the International Organization for Standardization (ISO) and is the most widely known internetwork reference model.
  • A reference model describes what functions must be completed at a particular layer but does not specify exactly how those functions should be accomplished.
  • The OSI model is used for data network design, troubleshooting, and establishing operation specifications.
  • The Seven Layers of the OSI Model:
    • 7 - Application: Contains protocols used for process-to-process communications.
    • 6 - Presentation: Provides a common representation of data transferred between application layer services.
    • 5 - Session: Provides services to the presentation layer to organize its dialogue and manage data exchange.
    • 4 - Transport: Defines services to segment, transfer, and reassemble data for individual communications between end devices.
    • 3 - Network: Provides services to exchange individual data over the network between identified end devices.
    • 2 - Data Link: Describes methods for exchanging data frames between devices over shared media.
    • 1 - Physical: Describes the mechanical, electrical, functional, and procedural means to activate, maintain, and deactivate physical connections for bit transmission.

Comparative Analysis: OSI vs. TCP/IP

  • While TCP/IP is the actual suite used for internet communications, the OSI model is used to describe these protocols in a standardized way.
  • The internet layer of the TCP/IP model contains the functions categorized in the network layer (Layer 3) of the OSI model.
  • The transport layer (Layer 4) functionality is identical in both models, providing ordered and reliable data delivery between source and destination.
  • The TCP/IP application layer spans the functions found in the OSI session, presentation, and application layers (Layers 5, 6, and 7). Software developers use these three OSI layers as references for producing network-aware applications.
  • The TCP/IP network access layer corresponds to both the data link layer (Layer 2) and the physical layer (Layer 1) of the OSI model.
  • Protocol stacks, such as the TCP/IP stack, illustrate interactions where each higher-level protocol depends on the services provided by the protocols in the levels below it.