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Networks use congestion control and congestion avoidance techniques to try to avoid collapse. These include: exponential backoff in protocols such as CSMA/CA in 802.11 and the similar CSMA/CD in the original Ethernet, window reduction in TCP, and fair queueing in devices such as routers and network switches.
In routers and switches, active queue management (AQM) is the policy of dropping packets inside a buffer associated with a network interface controller (NIC) before that buffer becomes full, often with the goal of reducing network congestion or improving end-to-end latency.
In TCP/IP, routers operate within the Internet layer, while the transmission rate is handled by the endpoints at the transport layer. Congestion may be handled only by the transmitter, but since it is known to have happened only after a packet was sent, there must be an echo of the congestion indication by the receiver to the transmitter.
When a router wants to signal congestion to the sender, it adds a bit in the header of packets sent. When a packet arrives at the router, the router calculates the average queue length for the last (busy + idle) period plus the current busy period. (The router is busy when it is transmitting packets, and idle otherwise). When the average queue ...
The TCP congestion-avoidance algorithm is the primary basis for congestion control in the Internet. [ 2 ] [ 3 ] [ 4 ] Per the end-to-end principle , congestion control is largely a function of internet hosts , not the network itself.
AIMD requires a binary congestion signal. Most frequently, packet loss serves as the signal; the multiplicative decrease is triggered when a timeout or an acknowledgement message indicates a packet lost. It is also possible for in-network switches/routers to mark congestion (without discarding packets) as in Explicit Congestion Notification (ECN).
Random early detection (RED), also known as random early discard or random early drop, is a queuing discipline for a network scheduler suited for congestion avoidance. [1]In the conventional tail drop algorithm, a router or other network component buffers as many packets as it can, and simply drops the ones it cannot buffer.
Nagle's algorithm is a means of improving the efficiency of TCP/IP networks by reducing the number of packets that need to be sent over the network. It was defined by John Nagle while working for Ford Aerospace. It was published in 1984 as a Request for Comments (RFC) with title Congestion Control in IP/TCP Internetworks in RFC 896.