Approaches to Congestion Control

Congestion control refers to techniques used to prevent or alleviate network congestion, where too much data overwhelms network resources, leading to degraded performance.

1. Open-Loop Congestion Control

• Definition: Proactive methods that prevent congestion before it occurs.

Key Features:

• Policies are set at the start of the connection.
• Does not rely on feedback from the network.

Examples:

• Traffic Shaping:Controls the rate of data transmission (e.g., Leaky Bucket and Token Bucket algorithms).
• Admission Control:Limits the number of users or data flows entering the network.
• Resource Reservation:Allocates bandwidth and buffers in advance.

2. Closed-Loop Congestion Control

• Definition: Reactive methods that detect and mitigate congestion after it occurs.

Key Features:

• Relies on feedback mechanisms to adjust traffic dynamically.

Examples:

• Backpressure:A congested node signals upstream nodes to reduce data transmission rates.
• Choke Packets:Special packets are sent to the sender to slow down the data rate.
• Explicit Congestion Notification (ECN):A mechanism in IP networks where routers mark packets to indicate congestion.
• Load Shedding:Drops low-priority packets to free up resources for critical traffic.

3. End-to-End Congestion Control

• Definition: The endpoints (sender and receiver) handle congestion control without relying on the intermediate network.

Key Features:

• Common in TCP/IP networks.

Examples:

• TCP Congestion Control:Includes mechanisms like Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery.
• Rate Control:Adjusts the sending rate based on acknowledgment (ACK) feedback.

4. Quality of Service (QoS)-Based Approaches

• Definition: Prioritizes traffic and manages resources to avoid congestion.

Key Features:

• Ensures critical traffic like voice or video is less affected by congestion.

Examples:

• Prioritization:Assigns priority levels to different types of data.
• Bandwidth Allocation:Allocates fixed bandwidth to specific flows or applications.

Summary Table: