Module 5: Communication Protocol

Understanding Communication Protocols

Protocols are essential for ensuring that computers can effectively communicate across a network. These protocols define various aspects of data transmission, such as the message format, message size, timing, encoding, encapsulation, and message patterns. These rules are necessary for organizing and managing data flow, ensuring data is transmitted accurately, and preventing confusion between devices.

• Message Format: When a message is sent across the network, it must adhere to a specific format or structure. This standardization ensures that both the sending and receiving devices understand the contents and structure of the communication.

• Message Size: The size of messages transmitted over a network is tightly controlled. Depending on the type of network and the transmission medium, different size limits are enforced to maintain efficiency and prevent data fragmentation.

• Timing: Timing governs the speed at which bits are transmitted over the network. This also affects when a host can send data and how much data can be sent in a single transmission. Timing is critical in determining network throughput and latency.

• Encoding: Messages sent across the network are converted into bits by the sending host. These bits are then encoded into signals (such as electrical impulses, sound waves, or light waves) depending on the medium used for transmission.

• Encapsulation: Each message that travels across a network must include a header with addressing information to identify the source and destination hosts. Encapsulation is the process of adding this crucial header information to the data packets before they are sent.

• Message Pattern: Some messages require an acknowledgment before the next message can be sent. This acknowledgment, part of the request/response pattern, is a fundamental feature of many network protocols. On the other hand, certain messages, such as streaming media, may be transmitted continuously without requiring confirmation of delivery.

Communication Standards

Network communication is based on standardized rules, or protocols, which ensure that devices can connect and interact effectively. A network protocol defines the communication rules, and different devices or systems that adhere to these rules can communicate across the same network or the internet.

A standard is a set of rules established to regulate how something is done. In networking, standards ensure all devices implement the same communication protocols in the same way, facilitating interoperability between diverse systems. These standards make it possible for devices from different manufacturers to communicate with each other over the internet.

The development of internet standards follows a rigorous cycle of discussion, problem solving, and testing. Once a standard is proposed, its progress through the development stages is recorded in an RFC (Request For Comments) document, which keeps track of the evolution of that standard. The RFCs for internet standards are managed by the Internet Engineering Task Force (IETF).

Network Communication Models

Network protocols are the foundation of communication between devices. For effective data transfer, various protocols need to work together. Prominent examples of such protocols include HTTP, TCP, IP, and Ethernet. These protocols are implemented in both software and hardware installed on hosts and networking devices.

To understand how these protocols interact, we use a protocol stack. A protocol stack visualizes the layers of protocols on a device. Each higher-level protocol depends on the services provided by the lower-level protocols. This separation allows the layers to operate independently, making the network more manageable and efficient.

The suite of TCP/IP protocols, widely used for internet communication, is structured in a layered hierarchy, similar to the OSI model. The layers of the TCP/IP model include:

1. Application Layer: This top layer represents the data that is presented to the user. It encompasses encoding, formatting, and dialog control, allowing user applications to interact with the network.
2. Transport Layer: This layer supports communication between devices over diverse networks. It ensures the reliable delivery of data and manages the flow of data across the network.
3. Internet Layer: This layer determines the most efficient route through the network for data packets to travel, utilizing protocols like IP (Internet Protocol).
4. Network Access Layer: The lowest layer handles the physical hardware and media used to transport data. It defines how data is physically transmitted between devices over a network.

A reference model outlines the necessary functions at each layer but does not specify how those functions should be carried out. The goal is to create a clearer understanding of the required steps for successful network communication.

The OSI (Open Systems Interconnection) model is a well-known reference model for data network design, operation, and troubleshooting. It is commonly used to define and troubleshoot network communication. The OSI model consists of seven layers, each with its distinct responsibility:

• Layer 7 – Application: This layer contains protocols used for process-to-process communication, such as HTTP and FTP, enabling applications to communicate across a network.
• Layer 6 – Presentation: This layer ensures that data is presented in a common format. It handles data encryption, compression, and translation between different formats.
• Layer 5 – Session: This layer manages communication sessions between applications. It ensures that data exchange remains organized and that communication sessions are established, maintained, and terminated properly.
• Layer 4 – Transport: The transport layer is responsible for segmenting, transferring, and reassembling data for individual communications between end devices. Protocols such as TCP and UDP operate at this layer.
• Layer 3 – Network: This layer is in charge of routing data packets from one device to another. The network layer uses protocols like IP to find the best path through the network.
• Layer 2 – Data Link: This layer governs how data frames are exchanged between devices over a shared medium. It ensures that data is correctly formatted for transmission over the physical network medium.
• Layer 1 – Physical: The physical layer involves the mechanical, electrical, and procedural aspects of activating, maintaining, and deactivating physical connections for data transmission between devices. It defines how bits are represented on the physical medium (e.g., through electrical signals or light pulses).