🚦 What is Congestion?

Congestion occurs when too much data is sent through the network, overwhelming routers or links, causing:

  • Packet loss
  • Increased delay
  • Throughput degradation

It is similar to traffic jams on roads due to excess vehicles.

🧰 Congestion Control Techniques

  1. Open-Loop Control

    • Prevention-based
    • No feedback from network
    • Techniques: Traffic shaping, admission control

  2. Closed-Loop Control

    • Feedback-based
    • Monitors network to detect congestion
    • Techniques:
      • Retransmission policies
      • Window size adjustment
      • Packet discarding strategies

πŸ“‰ Indicators of Congestion

  • Packet drops
  • Queue build-up in routers
  • Timeout-based retransmissions
  • TCP slow-start triggering

πŸ“Š Algorithms & Mechanisms

  • TCP Congestion Control

    • Slow Start
    • Congestion Avoidance
    • Fast Retransmit
    • Fast Recovery

  • Random Early Detection (RED)

    • Proactively drops packets before the queue is full to signal congestion.

🧠 Deep Insights

  • Congestion control is not just about throughput β€” it’s also about fairness and network health.
  • End-hosts (like TCP) and intermediate routers cooperate for effective control.
  • Designing control algorithms requires balancing utilization vs. delay vs. fairness.

πŸ’‘ QoS Connection

Congestion control is a prerequisite for achieving Quality of Service (QoS) β€” especially in real-time and multimedia communication.

πŸ”— Links