[Day 3] 5. Transport Layer

Primary Functions:

• Reliability: Ensures data is transmitted accurately.
• Windowing (Sliding Window Protocol): Controls the flow of data by allowing multiple segments to be sent before receiving an acknowledgment.
• Error Correction: Detects and corrects errors in transmitted data.
• Connection-Oriented Communication: Establishes a connection before data transmission (used by TCP).
• Sequencing: Ensures data segments are delivered in the correct order.
• Segment Numbers: Range from 0 to 65535.

Traditional Method:

• PC1 sends a segment to PC2.
• PC2 acknowledges the receipt of the segment before PC1 sends the next one.
• If an acknowledgment is corrupted or lost, communication halts.

New Approach (Sliding Window Protocol):

• PC1 sends multiple segments (e.g., 3) without waiting for individual acknowledgments.
• Each segment has its own timer.
• Acknowledgment (ACK) is sent when all segments are received successfully. If an acknowledgment is dropped, the packets are resent after a timeout.
• Negative Acknowledgment (NACK): If any segment is corrupted or lost, PC2 sends a NACK to request a retransmission of that specific segment.

Flow Control

Why Flow Control Is Important?

• Prevents Data Loss: Without flow control, if Device A sends data faster than Device B can process, data might overflow B’s buffer and result in packet loss.
• Efficient Data Transmission: It allows for efficient use of the network bandwidth by dynamically adjusting the transmission rate based on the receiver’s capacity.

| TCP (Transmission Control Protocol) | UDP (User Datagram Protocol) | | ------------------------------------------ | ------------------------------------ | | Reliable | Non-reliable | | Implements Flow Control | No Flow Control | | Slow | Fast | | Sequencing of segments | No Sequencing | | Large header (due to more functionalities) | Small header (fewer functionalities) |

• TCP: Used when reliability and accuracy are more important than speed (e.g., file transfer, email).
• UDP: Used when speed is the primary concern, and packet loss is tolerable (e.g., live streaming, video calls, Instagram Reels).