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What is Congestion Control in Computer Networks and Its Types?

Last Updated on August 24, 2023 by Mayank Dham

Congestion control at the network layer arises when data surpasses the capacity limits of a node or link. This frequently results in packet queuing, and in more severe instances, packet loss, causing a decline in the Quality of Service (QoS) of the network.

Occasionally, abrupt surges in traffic stemming from special occasions can overwhelm otherwise stable and sufficient network links, resulting in an overall decline in network performance. Additionally, network congestion can stem from protocols like TCP (Transmission Control Protocol), which uses re transmissions to prevent packet loss, potentially maintaining congestion even after the load has lessened. This situation, characterized by diminished network throughput despite a decrease in the initial load, is termed Congestive Collapse.

What is congestion control in computer networks?

A network functions as a communal resource utilized by numerous participants who engage in cooperative interactions. Nonetheless, a small number of flawed or unauthenticated users transmitting data across the network can trigger a scenario known as "congestive collapse." This situation is characterized by a significant deterioration in the Quality of Service (QoS), rendering effective communication either hindered or restricted.

Congestion control serves as a mechanism designed to regulate the influx of data packets into the network. Its purpose is to optimize the utilization of a shared network infrastructure and avert the occurrence of congestive collapse. Within the TCP layer, Congestive-Avoidance Algorithms (CAA) are deployed as the means to prevent the onset of congestive collapse within a network.

Types of Congestion Control in Computer network

Various types of congestion control mechanisms are employed in computer networks (CN) to manage and mitigate network congestion. Here are some notable types:

  • Open Loop Congestion Control: This approach employs preset, static methods to control congestion. It doesn’t rely on real-time feedback or dynamic adjustments. Examples include traffic shaping and admission control.
  • Closed Loop Congestion Control: In this type, the network continuously monitors its state and adapts congestion control strategies based on real-time feedback. TCP (Transmission Control Protocol) is a classic example of closed loop congestion control.
  • End-to-End Congestion Control: This approach involves end systems, such as computers and servers, in the congestion control process. They adjust their behavior based on signals from the network. TCP’s congestion control is an example of end-to-end congestion control.
  • Network-Assisted Congestion Control: In this case, network elements (routers, switches, etc.) play an active role in controlling congestion. They provide feedback and assist end systems in managing congestion. Explicit Congestion Notification (ECN) is an example of network-assisted congestion control.
  • Implicit Congestion Signaling: This involves detecting congestion based on observed changes in network performance rather than explicit signals. It might involve monitoring packet loss or delays.
  • Explicit Congestion Signaling: This method uses explicit signals to indicate network congestion. One example is the ECN field in IP packets, which routers can use to signal congestion to endpoints.
  • Active Queue Management (AQM): AQM mechanisms involve actively managing the length of queues in network routers or switches to prevent excessive queuing and buffer overflows. Examples include Random Early Detection (RED) and its variants.
  • Quality of Service (QoS) Congestion Control: This approach prioritizes traffic based on its class or type, ensuring that high-priority traffic is given precedence during times of congestion.

In conclusion, congestion control plays a crucial role in maintaining the stability and optimal performance of computer networks. By preventing congestion or managing it effectively, these mechanisms ensure that data transmission remains reliable, timely, and efficient. A variety of congestion control strategies, from end-to-end protocols like TCP to network-assisted mechanisms and quality of service management, contribute to the seamless functioning of modern computer networks. As networks continue to evolve and handle increasing volumes of data, congestion control remains an essential area of research and implementation to uphold the quality of service and user experience.

Frequently Asked Questions (FAQs) related to Congestion Control in Computer Network

Below are some FAQs related to the Congestion Control in Computer Networks:

1. Why is congestion control important?
Congestion control is vital to prevent network instability, ensure fair resource allocation, maintain data integrity, and provide consistent quality of service to users.

2. What is the role of TCP in congestion control?
TCP (Transmission Control Protocol) employs congestion control mechanisms like slow start, congestion avoidance, and fast retransmit to regulate data flow, respond to network conditions, and prevent congestion.

3. How does AQM (Active Queue Management) work?
AQM mechanisms actively manage router or switch queues by dropping or marking packets before the buffer overflows, thus preventing excessive delays and maintaining smooth data flow.

4. What is the difference between open loop and closed loop congestion control?
Open loop congestion control uses static methods without real-time feedback, while closed loop congestion control adapts strategies based on real-time network feedback.

5. What is ECN (Explicit Congestion Notification)?
ECN is a network-assisted congestion control mechanism where routers mark packets to signal congestion, allowing endpoints to adjust their behavior before congestion worsens.x`

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