Chapter-3-DATA-LINK-LAYER-GROUP-3.pdf

AI&ROB, INC. DATA-LINK LAYER WWW.ISUFSTAI&ROB.COM WHAT IS DATA LINK LAYER? The Data-Link Layer, the second layer in the OSI model, ensures reliable communication between devices on the same network. It organizes data into frames, handles addres...

AI&ROB, INC. DATA-LINK LAYER WWW.ISUFSTAI&ROB.COM WHAT IS DATA LINK LAYER? The Data-Link Layer, the second layer in the OSI model, ensures reliable communication between devices on the same network. It organizes data into frames, handles addressing with MAC addresses, checks for errors, and manages data flow and access to the network medium. THE TWO SUBLAYER OF DATA-LINK LAYER Logical Link Control Logical Link Control (LLC): Manages communication between the Data-Link Layer and the Network Layer, handling error detection, flow control, and framing. Media Access Control Media Access Control (MAC): Governs how devices on the network uniquely identify themselves and control access to the physical transmission medium. 3.1 Overview of the Data-Link Layer The Data-Link Layer is the second layer in the OSI (Open Systems Interconnection) model and plays a crucial role in data communication. It is responsible for the reliable transmission of data across a physical network link, ensuring that data frames are delivered without errors. This layer sits between the Physical Layer, which deals with the raw transmission of bits over a medium, and the Network Layer, which manages data routing between devices. Data Link Layer is essential for providing a reliable and efficient method for data transmission across a physical network, ensuring that data is correctly framed, addressed, and error-checked as it travels from one device to another. 3.2 Functions of the Data-Link Layer The primary functions of the Data-Link Layer include: Framing: The Data-Link Layer organizes raw bits from the Physical Layer into structured data units called frames. Framing involves adding headers and trailers around the data payload to create a frame that can be transmitted over the network. Addressing: The Data-Link Layer uses MAC addresses (physical addresses) to identify the source and destination devices on the network. Each network interface card (NIC) has a unique MAC address assigned by the manufacturer. Error Detection and Correction: The layer incorporates error detection techniques, such as cyclic redundancy checks (CRC), to ensure that frames are transmitted without errors. If an error is detected, the frame is either corrected at the sender’s side (using error correction codes) or discarded and retransmitted. Flow Control: This function ensures that the sender does not overwhelm the receiver with data. Flow control mechanisms regulate the pace of data transmission between devices to prevent data loss or overflow at the receiving end. Media Access Control: The MAC sublayer manages how devices on the same network segment access the shared transmission medium. This involves determining when a device can send data to avoid collisions on the network. Common MAC protocols include Carrier Sense Multiple Access with Collision Detection (CSMA/CD) used in Ethernet networks and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) used in wireless networks. Physical Addressing: The Data-Link Layer assigns physical addresses to devices on the network, which are used to ensure data frames reach their correct destination within the same network segment. Error Reporting: When an error occurs at the Data-Link Layer, such as a frame not being acknowledged by the receiver, the layer reports the error to higher layers for corrective action. 3.3 Sublayers of the Data-Link Layer As mentioned, the Data-Link Layer is divided into two sublayers: Logical Link Control (LLC) Sublayer: Provides a standard interface between the Network Layer and the MAC sublayer. Responsible for managing error control and flow control. Handles frame synchronization and frame sequence numbers to ensure the correct order of frames. Media Access Control (MAC) Sublayer: Responsible for controlling how devices on a network access the physical transmission medium. Handles addressing through MAC addresses. Manages collision detection and avoidance in networks where multiple devices share the same medium. 3.4 MAC Addressing and Network Topologies MAC addresses are 48-bit identifiers used to distinguish devices on a local network. They are typically represented in hexadecimal format, such as 00:1A:2B:3C:4D:5E. Network topologies refer to the physical or logical arrangement of network devices and how they communicate with each other. Common network topologies include: Bus Topology: All devices share a common communication line (bus). Devices listen to the medium before transmitting to avoid collisions. Star Topology: Devices are connected to a central hub or switch, which manages data transmission. Ring Topology: Devices are connected in a circular manner, with data passing from one device to the next until it reaches its destination. Mesh Topology: Each device is connected to multiple other devices, providing multiple paths for data transmission. 3.5 Error Detection and Correction Mechanisms To ensure data integrity, the Data-Link Layer employs several error detection and correction techniques: Parity Check: A simple error detection method that adds a parity bit to the data to make the total number of 1s either even (even parity) or odd (odd parity). Cyclic Redundancy Check (CRC): A more robust method where a checksum is computed based on the data before transmission. The receiver recomputes the checksum and compares it with the transmitted one to detect errors. Checksum: Similar to CRC, a checksum is calculated based on the data. However, it is simpler and used in less critical applications. Forward Error Correction (FEC): The sender adds redundant data to the transmitted frames, which allows the receiver to detect and correct errors without needing a retransmission. 3.6 Media Access Control Protocols The MAC sublayer uses various protocols to control access to the network medium: CSMA/CD (Carrier Sense Multiple Access with Collision Detection): Used in Ethernet networks, this protocol listens to the network to check if it is free before transmitting. If a collision occurs, the devices stop transmitting, wait for a random period, and then retry. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance): Used in wireless networks, this protocol also listens to the network before transmitting. However, it uses a different strategy to avoid collisions, such as sending a short control message before transmitting the actual data. Token Passing: Used in token ring networks, this protocol allows devices to transmit data only when they possess a token, a special frame that circulates around the network. 3.7 Switching and Bridging Switches and bridges operate at the Data-Link Layer, managing the flow of data within a network: Switching: Switches use MAC addresses to forward frames between devices on the same network. They build a MAC address table by learning the source address of incoming frames and associating them with specific ports. Bridging: Bridges connect multiple network segments, filtering traffic based on MAC addresses to reduce collisions and improve network performance. They operate similarly to switches but typically work with fewer ports and less complexity. 3.8 Data-Link Layer in Modern Networks In modern networks, the Data-Link Layer continues to play a critical role in ensuring reliable communication between devices. Advances in networking technologies, such as Gigabit Ethernet, Wi-Fi 6, and 5G, have enhanced the capabilities of this layer, enabling faster and more efficient data transmission. The rise of software-defined networking (SDN) and network virtualization has also impacted the Data-Link Layer, allowing more flexible and programmable network configurations. These technologies decouple the control plane from the data plane, enabling centralized management of network traffic and improving overall network agility.  Conclusion The Data-Link Layer is fundamental to the functioning of computer networks, providing the necessary protocols and mechanisms to ensure the reliable transmission of data across physical network links. By handling tasks such as framing, addressing, error detection, and media access control, this layer enables smooth communication between devices and sets the stage for the higher layers of the OSI model to perform their functions. Understanding the Data-Link Layer and its components is essential for anyone involved in network design, management, or troubleshooting, as it forms the backbone of network communication in both wired and wireless environments.  GROUP 3 Joshua Juliana Flea Marie Arnie Badilla Angel Pulgaridad Atonducan Bernasol THANK YOU.. AI&ROB, INC Kindly prepare 1 whole sheet of paper:  Identification (5 items) 1. What is the primary role of the Data-Link Layer in the OSI model? 2. What are the two sublayers of the Data-Link Layer? 3.Which protocol is used in Ethernet networks for collision detection? 4.What is the term for the 48-bit address used to uniquely identify devices on a network? 5.Name one error detection technique used by the Data-Link Layer.  True or False (5 items) 6.The Data-Link Layer is the first layer in the OSI model.. 7.The LLC sublayer is responsible for managing communication between the Data-Link Layer and the Physical Layer. 8.MAC addresses are used to address devices on the network within the same network segment. 9.CSMA/CA is used in Ethernet networks for managing access to the network medium. 10. Forward Error Correction (FEC) allows the receiver to correct errors without needing a retransmission.  Multiple Choice (10 items) 11. Which layer of the OSI model is responsible for framing data? A) Physical Layer B) Network Layer C) Data-Link Layer 12.In which topology do devices connect to a central hub or switch? A) Bus Topology B) Star Topology C) Ring Topology  Multiple Choice (10 items) 13.What is the main function of the MAC sublayer? A) Managing error control B) Controlling access to the physical transmission medium C) Handling logical addressing 14.What type of addressing does the Data-Link Layer use? A) IP Addressing B) Logical Addressing C) Physical Addressing  Multiple Choice (10 items) 15.Which protocol is used in wireless networks to avoid collisions? A) CSMA/CD B) Token Passing C) CSMA/CA 16.What mechanism is used to ensure that frames are transmitted without errors? A) Flow Control B) Error Detection and Correction C) Media Access Control  Multiple Choice (10 items) 17.Which error detection technique involves adding a checksum to data? A) Parity Check B) CRC C) Checksum 18.In which topology do devices form a closed loop for data transmission? A) Mesh Topology B) Bus Topology C) Ring Topology  Multiple Choice (10 items) 19.What role do switches play at the Data-Link Layer? A) Connecting multiple networks B) Filtering traffic based on MAC addresses C) Managing IP addresses 20.What does the term "forward error correction" refer to? A) Error detection only B) Adding redundant data to correct errors C) Retransmitting data when errors are detected  Essay(5pts) 150 words.. 20-25. How does the Data-Link Layer make sure that data is sent correctly across a network? Describe the main jobs it does, like framing data, addressing devices, checking for errors, and controlling the flow of data.. Best wishes!