📶 Congestion Control in Computer Networks | Explain about congestion control |
📶 Congestion Control in
Computer Networks
✅ What is Congestion?
Congestion in computer networks occurs when too
many data packets are present in the network, especially in certain parts
of the subnet, and the network resources are not sufficient to
handle the traffic. This results in:
- Packet
loss
- Increased
delay
- Reduced
throughput
- Network
performance degradation
🔍 Why Does Congestion
Occur?
Congestion usually occurs when the incoming data rate
(offered load) exceeds the processing and transmission capacity of
network devices (like routers and switches).
Causes of Congestion:
- Sudden
traffic spikes
- Insufficient
bandwidth
- Slow
processors or queues at routers
- Too
many simultaneous users
- Network
failures or rerouting of traffic
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⚠️ Symptoms of Congestion
- Dropped
packets
- Timeouts
or retransmissions
- High
latency
- Buffer
overflows at routers/switches
- Low
throughput
🧠 Congestion vs.
Throughput
When load increases:
- Initially,
throughput increases proportionally
- At a
certain point, if load exceeds capacity, congestion starts
- After
this, throughput drops drastically, and delay/loss increases
This is often visualized in the Load vs. Throughput
curve.
🛠️ Congestion Control
Techniques
Congestion control refers to the methods used to prevent
and recover from congestion in networks.
1. Open Loop Control (Prevention)
These techniques try to prevent congestion before it
happens.
- Traffic
Shaping: Controls the rate at which traffic is sent (e.g., Token
Bucket, Leaky Bucket)
- Admission
Control: Limits the number of connections admitted
- Resource
Reservation: Allocates resources beforehand
2. Closed Loop Control (Detection & Recovery)
These techniques work after congestion is detected.
- Congestion
Detection: Routers monitor queue lengths
- Backpressure:
Routers signal upstream devices to slow down
- Choke
Packets: Special packets sent to inform the source to reduce traffic
- Explicit
Congestion Notification (ECN): Routers mark packets instead of
dropping
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🌐 Congestion Control in
TCP
TCP uses several built-in mechanisms to control
congestion:
a. Slow Start
- TCP
starts with a small congestion window and increases it exponentially
to avoid burst traffic
b. Congestion Avoidance
- Uses additive
increase and multiplicative decrease (AIMD) to grow the window
cautiously
c. Fast Retransmit and Fast Recovery
- Avoids
timeout by quickly retransmitting lost packets when multiple duplicate
ACKs are received
📊 Summary Table
|
Concept |
Description |
|
Congestion |
Overload in network causing performance degradation |
|
Causes |
Traffic spikes, limited bandwidth, queue overflow |
|
Open-loop control |
Preventive methods like traffic shaping and admission |
|
Closed-loop control |
Reactive methods like backpressure, choke packets |
|
TCP Congestion Control |
Slow start, AIMD, fast retransmit/recovery |
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network, TCP congestion control, congestion avoidance, congestion vs
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Understanding congestion control is essential to
ensure efficient and reliable data communication in modern networks.
From preventing congestion to managing it effectively when it occurs, these
techniques form the backbone of traffic management in networking
protocols like TCP/IP.
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