While "TCP transmission policy" isn't a standard, well-defined term, we can interpret it as referring to the mechanisms TCP (Transmission Control Protocol) uses to reliably and efficiently transmit data. It encompasses several key aspects of how TCP manages the flow of data across a network. Therefore, TCP's transmission "policy" is about how it guarantees reliable, ordered, and error-checked delivery.
Key Aspects of TCP Transmission:
1. Reliable Data Transfer:
- Connection-Oriented: TCP establishes a connection between the sender and receiver before transmitting data. This "handshake" ensures both parties are ready.
- Sequence Numbers: Each data segment is assigned a sequence number. This allows the receiver to reassemble the data in the correct order, even if segments arrive out of order.
- Acknowledgements (ACKs): The receiver sends acknowledgements (ACKs) back to the sender to confirm that data segments have been received successfully.
- Retransmission: If the sender doesn't receive an ACK within a certain timeout period, it retransmits the data segment. This ensures no data is lost in transit.
2. Flow Control:
- Sliding Window: TCP uses a sliding window mechanism to prevent the sender from overwhelming the receiver. The receiver advertises a "window size" indicating how much data it can buffer. The sender can only send data within that window.
- Congestion Avoidance: Prevents network collapse by actively monitoring congestion and adjusting transmission rates to avoid overloading the network.
3. Congestion Control:
- Slow Start: When a connection starts or after a period of congestion, TCP starts with a small congestion window and gradually increases it until it detects congestion.
- Congestion Avoidance (AIMD): Additive Increase/Multiplicative Decrease. TCP increases its congestion window linearly until congestion is detected, then reduces it multiplicatively.
- Fast Retransmit/Fast Recovery: If the sender receives multiple duplicate ACKs, it assumes that a segment has been lost and retransmits it immediately, without waiting for a timeout.
4. Segmentation:
- Maximum Segment Size (MSS): TCP divides application data into segments that fit within the Maximum Transmission Unit (MTU) of the network. This avoids fragmentation and improves efficiency. MSS is negotiated during the connection establishment.
5. Connection Management:
- Three-Way Handshake: Used to establish a connection (SYN, SYN-ACK, ACK).
- Four-Way Handshake: Used to terminate a connection (FIN, ACK, FIN, ACK).
Example Scenario:
Imagine sending an email. TCP breaks the email into smaller packets. Each packet is numbered. The receiver acknowledges each packet. If a packet is lost, the sender re-sends it. The receiver assembles the packets in the correct order to reconstruct the original email.
In essence, the TCP transmission "policy" isn't a single setting but rather a collection of robust mechanisms designed to deliver data reliably, efficiently, and without overwhelming the network. It adapts to network conditions, prioritizes data integrity, and provides a foundation for many internet applications.
