- 2073 Shrawan · 2+2 marks
Network congestion and its parameters
Short answer
Congestion occurs when offered load exceeds capacity, causing queue buildup, delay, and packet drops. Higher arrival rate, low bandwidth, small buffers, slow router processing, long latency, retransmissions, bursty traffic, and short timeouts all worsen congestion.
Discuss network congestion. Explain how different network parameters affect the congestion.
Network congestion
Congestion occurs when the load offered to the network (or a router) is greater than it can handle, so queues grow, delay increases and packets are dropped. Dropped packets are retransmitted, adding more load, which can lead to congestion collapse.
Throughput
| ______ ideal
| / ___ with congestion control
| / /
| / /\____ congestion collapse
+---------------------- Offered load
Parameters affecting congestion
| Parameter | Effect |
|---|---|
| Arrival rate (load) | When the rate exceeds link capacity, queues build up. |
| Link bandwidth | Low-capacity links become bottlenecks. |
| Router buffer size | Small buffers overflow and drop packets; very large buffers cause long delay (bufferbloat). |
| Router processing speed | A slow CPU cannot forward at line rate, so queues grow. |
| Delay (latency) | Long delay makes feedback slow, so senders react late. |
| Packet loss and retransmission | Retransmissions add to the load. |
| Burstiness of traffic | Sudden bursts overload queues even when average load is low. |
| Timeout settings | Too short timeouts cause unnecessary retransmissions. |
Queueing delay grows sharply with utilisation ρ. For a simple M/M/1 queue, delay = service time / (1 − ρ):
| Utilisation ρ | 0.5 | 0.8 | 0.9 | 0.99 |
|---|---|---|---|---|
| Delay (× service time) | 2 | 5 | 10 | 100 |
So congestion is controlled by keeping the load below capacity (admission control, traffic shaping, window-based control).
✓ Answer checked by Claude Opus 5.5 (high effort)
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