Network congestion
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In data networking and queueing theory, network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates. Typical effects include queueing delay, packet loss or the blocking of new connections. A consequence of these latter two is that incremental increases in offered load lead either only to small increases in network throughput, or to an actual reduction in network throughput.
Network protocols which use aggressive retransmissions to compensate for packet loss tend to keep systems in a state of network congestion even after the initial load has been reduced to a level which would not normally have induced network congestion. Thus, networks using these protocols can exhibit two stable states under the same level of load. The stable state with low throughput is known as congestive collapse.
Modern networks use congestion control and network congestion avoidance techniques to try to avoid congestion collapse. These include: exponential backoff in protocols such as 802.11's CSMA/CA and the original Ethernet, window reduction in TCP, and fair queueing in devices such as routers.
RFC 2914 addresses the subject of congestion control in detail.
[edit] See also
[edit] External links
- Nagle, J. RFC 896: Congestion control in IP/TCP internetworks (1984)
- Floyd, S. RFC 2914: Congestion control principles (2000)
- Floyd, S. and K. Fall, Promoting the Use of End-to-End Congestion Control in the Internet (IEEE/ACM Transactions on Networking, August 1999)
- Sally Floyd, On the Evolution of End-to-end Congestion Control in the Internet: An Idiosyncratic View (IMA Workshop on Scaling Phenomena in Communication Networks, October 1999) (pdf format)
