Design Issues: Services to Network Layer, Framing. Types of errors: Single bit error & more errors, скачать в хорошем качестве

Design Issues: Services to Network Layer, Framing. Types of errors: Single bit error & more errors,

Design Issues: Services to Network Layer, Framing. Types of errors: Single bit error and burst error, Redundancy, detection versus correction, forward error correction versus retransmission, 1) DATA LINK CONTROL – OVERVIEW Data Link Control is responsible for reliable node-to-node delivery of data over a physical link. It handles framing, error detection, flow control, and medium access. -------------------------------------------------- 2) DESIGN ISSUES IN DATA LINK LAYER -------------------------------------------------- A) SERVICES TO NETWORK LAYER The Data Link Layer provides services to the Network Layer. Types of Services: 1. Unacknowledged Connectionless Service No acknowledgment No connection setup Used in reliable channels Example: Ethernet 2. Acknowledged Connectionless Service Each frame is acknowledged No logical connection Used in wireless networks 3. Acknowledged Connection-Oriented Service Connection setup required Reliable transmission Sequence control and acknowledgments used -------------------------------------------------- B) FRAMING Definition: Framing is the process of dividing the stream of bits into manageable units called frames. Purpose: Synchronization Error detection Addressing Framing Methods: 1. Character Count First field specifies frame length 2. Byte Stuffing Special byte marks start and end Extra byte inserted if same pattern appears in data 3. Bit Stuffing Used in bit-oriented protocols After 5 consecutive 1s, insert 0 4. Physical Layer Coding Violations Use special signal patterns -------------------------------------------------- 3) TYPES OF ERRORS -------------------------------------------------- A) SINGLE BIT ERROR Definition: Only one bit in the data unit changes. Example: Original: 1011001 Received: 1010001 Common in: Parallel transmission -------------------------------------------------- B) BURST ERROR Definition: Two or more consecutive bits are corrupted. Example: Original: 1101011101 Received: 1100010101 Common in: Serial transmission -------------------------------------------------- 4) REDUNDANCY -------------------------------------------------- Definition: Redundancy means adding extra bits to detect or correct errors. Purpose: Improve reliability Enable error detection and correction Example: Parity bit -------------------------------------------------- 5) ERROR DETECTION VS ERROR CORRECTION -------------------------------------------------- Error Detection: Detects presence of error Does not fix error Requires retransmission Example: Parity, CRC Error Correction: Detects and corrects error No retransmission needed Example: Hamming Code -------------------------------------------------- 6) FORWARD ERROR CORRECTION (FEC) VS RETRANSMISSION -------------------------------------------------- Forward Error Correction (FEC): Sender adds extra redundant bits Receiver corrects errors without asking for retransmission Used in satellite and wireless communication Faster but more overhead Retransmission (ARQ – Automatic Repeat Request): Receiver detects error Requests sender to resend data Used in TCP Less overhead but higher delay -------------------------------------------------- 7) SUMMARY TABLE -------------------------------------------------- Single Bit Error: One bit corrupted Burst Error: Multiple consecutive bits corrupted Detection: Finds error only Correction: Finds and fixes error FEC: No retransmission required Retransmission: Requires resend of data