Data Link Layer

🔤 Character Codes in Communication Character codes convert symbols into binary so they can be transmitted or stored. Common Character Encodings: ASCII (7-bit): Standard for English text. Extended ASCII (8-bit): Includes extra symbols. Unicode (UTF-8): Multi-language, variable-length encoding. Character codes are foundational — they are how meaning is encoded into binary. ⚠️ Error Detection Techniques Communication is susceptible to noise. Error detection techniques help identify if data has been corrupted during transmission. ...

📊 Performance of ARQ Protocols ARQ protocols are central to ensuring reliable data transmission, but their performance can vary based on factors like channel quality, window size, and protocol type. Let’s dive into the performance evaluation of Stop-and-Wait, Go-back-N, and Selective Repeat. 📈 Stop-and-Wait ARQ Efficiency: In Stop-and-Wait ARQ, the sender must wait for an acknowledgment after sending a frame, which leads to poor utilization of available bandwidth, especially in high-latency networks. Throughput: [ \text{Throughput} = \frac{\text{Frame Size}}{\text{Transmission Time} + \text{Round-Trip Time (RTT)}} ] Where RTT represents the time for a packet to go to the receiver and back. ...

🖧 HDLC (High-Level Data Link Control) HDLC is a bit-oriented data link layer protocol used for synchronous data communication. Framing: HDLC frames are used to send data between devices. Error Control: It uses both error detection and error correction techniques, specifically CRC. Flow Control: Employs sliding window technique for managing the flow of data. Types of HDLC Frames: Information Frames (I-frames): Carry user data. Supervisory Frames (S-frames): For error control and flow management. Unnumbered Frames (U-frames): Used for link setup and control. HDLC provides a robust framework for managing reliable communication over unreliable channels. ...

📚 What is LLC? The Logical Link Control (LLC) is the upper sublayer of the Data Link Layer. It manages: Framing Error checking Flow control Interface to the Network Layer LLC is defined in IEEE 802.2 and is common across many IEEE LAN standards (like Ethernet, Wi-Fi). 🧱 Framing Framing is the process of encapsulating data with control information so that it can be transmitted over the physical medium. Each frame includes: ...

📡 What are ARQ Protocols? Automatic Repeat Request (ARQ) protocols ensure reliable communication by handling the retransmission of lost or corrupted data. These protocols are widely used in data link and transport layers to ensure integrity and timeliness. 🧩 Types of ARQ Protocols Stop-and-Wait ARQ: Sender sends one frame, waits for acknowledgment (ACK). Limitation: Low efficiency due to waiting for each frame’s acknowledgment. Use Case: Simple applications where low data rate suffices. Go-back-N ARQ: ...

🛠️ What is Error Correction? Unlike detection, error correction not only detects but also fixes the error without retransmission. This is crucial in environments where: Retransmission is costly or impossible (e.g., deep space, streaming media). Timeliness is critical (e.g., real-time voice). 🧮 Hamming Code: The Foundation of FEC Invented by Richard Hamming, this method introduces redundant parity bits into data to detect and correct single-bit errors. 👨‍🔬 How It Works: For k data bits, it adds r parity bits such that: [ 2^r \geq k + r + 1 ] ...