gen-define-tcp-congestion-control-and-give-one-short-worked-exam-1752

Define TCP congestion control and give one short worked example.

# TCP Congestion Control ## Definition **TCP congestion control** is a mechanism that prevents network congestion by regulating the rate at which data is transmitted. It dynamically adjusts the sender's transmission rate based on network conditions to avoid overwhelming the network while maximizing throughput. The key component is the **congestion window (cwnd)**, which limits how many unacknowledged bytes can be in transit. ## Key Phases 1. **Slow Start** - Exponential growth of cwnd 2. **Congestion Avoidance** - Linear growth of cwnd 3. **Fast Recovery** - Respond to packet loss --- ## Worked Example **Scenario:** A TCP connection starts with initial parameters: - Initial cwnd = 1 MSS (Maximum Segment Size = 1000 bytes) - ssthresh (slow start threshold) = 8 MSS - RTT = 100ms **Transmission sequence:** | Round | Event | cwnd (MSS) | Action | |-------|-------|------------|---------| | 1 | ACK received | 1 → 2 | Slow start: double cwnd | | 2 | ACK received | 2 → 4 | Slow start: double cwnd | | 3 | ACK received | 4 → 8 | Slow start: double cwnd | | 4 | Reached ssthresh | 8 → 9 | **Switch to Congestion Avoidance**: +1 MSS per RTT | | 5 | ACK received | 9 → 10 | Congestion Avoidance: +1 MSS | | 6 | **Packet loss** | 10 → 5 | Set ssthresh = cwnd/2, cwnd = ssthresh | | 7 | Recovery | 5 → 6 | Resume Congestion Avoidance | **Result:** The connection adaptively found the network's capacity and backed off when congestion (packet loss) occurred.