Network Models Chapter 2

Protocol Layering

• Protocols are essential for effective communication among senders, receivers, and intermediaries.
• Simple communications may only require a single-layer protocol, while complex communications utilize multiple layers.
• Advantages of protocol layering include breaking down complex tasks into simpler ones, promoting modularity, and separating service from implementation.
• Each layer in a protocol stack receives services from the layer below and provides services to the layer above regardless of implementation details.
• Principles of protocol layering dictate that in bidirectional communication, each layer must perform tasks in both directions, and objects at each layer must be identical across systems.

OSI Model

• The OSI model, established by the International Organization for Standardization (ISO), aims to facilitate communication between diverse systems without requiring hardware or software alterations.
• It organizes networking tasks into a layered framework, providing a common language to simplify understanding and implementation.
• Contains seven layers:
  • Layers 1-4 (Physical, Data Link, Network, Transport) focus on data flow and transmission.
  • Layers 5-7 (Session, Presentation, Application) focus on services for applications.
• Data moves down the layers encapsulated with protocol-specific information before network transit.

Benefits of the OSI Model

• Promotes interoperability among network elements regardless of the vendor or protocol origin.
• Enhances comprehension of networking frameworks, hardware-software interactions, and eases troubleshooting.
• Provides a foundation for understanding functional relationships and emerging technologies.
• Facilitates clearer vendor communications regarding product functionalities.

OSI Layers

• Physical Layer:
  • Provides the physical interface for data transmission.
  • Defines mechanical, electrical, and procedural attributes for physical communication, including voltage levels, timing aspects, and transmission distances.
• Data Link Layer: Responsible for ensuring reliable communication over physical links, although details were not included in the text.

Protocol Layering

• A protocol is a set of rules for communication between sender and receiver and any intervening devices.
• Protocol layering is essential for managing complex communication tasks.
• Simple communication may require only a single-layer protocol, while complex interactions necessitate multiple layers.

Advantages of Protocol Layering

• Divides complex networking tasks into simpler, manageable units.
• Promotes modularity, enabling independent functional modules.
• Allows separation of services from implementation specifics.

Principles of Protocol Layering

• Bidirectional communication requires each layer to perform opposite tasks (e.g., encrypt/decrypt).
• Objects at each layer in different systems should be identical.

OSI Model Overview

• Established by the International Organization for Standardization (ISO).
• Facilitates communication between heterogeneous systems without requiring hardware/software changes.
• The OSI model helps structure networking functions into manageable layers for better understanding and implementation.

OSI Model Structure

• Comprises seven layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical.
• Each layer services the one above it and communicates with its counterpart on other systems.
• Lower layers (1-4) focus on data flow; upper layers (5-7) focus on application-level services.

OSI Model Benefits

• Facilitates interoperability across various vendors' protocols and systems.
• Aids in troubleshooting and understanding hardware/software functionality.
• Provides a common vocabulary to describe functional relationships in networking.

Individual OSI Layers

• Physical Layer: Manages the physical connection and defines rules for bit transmission.
• Data Link Layer: Ensures reliable communication, error handling, and flow control.
• Network Layer: Responsible for routing packets and defining logical addressing.
• Transport Layer: Manages data exchange reliability and data unit sequencing.
• Session Layer: Controls dialogues (sessions) between applications, including authentication.
• Presentation Layer: Handles data formatting, compression, and encryption.
• Application Layer: The interface for user applications, supporting functions like file transfer and remote access.

TCP/IP Protocol Suite

• Consists of a set of hierarchical protocols used on the Internet.
• Originally defined with four layers but now considered to have five layers.
• Functions similarly to the OSI model but with a slightly different layering approach.

TCP/IP vs OSI Model

• TCP/IP model emphasizes practical application in the Internet context.
• OSI model provides a conceptual framework for understanding various networking processes.

Encapsulation and Decapsulation

• Data moves down through layers, with each layer adding specific headers.
• At the receiving end, headers are stripped away as the data moves back up the layers.

Addressing in TCP/IP

• Communication requires two addresses: source and destination.
• The physical layer does not require addressing due to its focus on bit transmission.

Summary of Data Representation

• Identical objects at different layers of TCP/IP include messages, segments, packets, frames, and bits, each performing a specific function during communication.