Congestion control is the process of monitoring and regulating the total amount of data entering into a network so as to keep traffic levels at an acceptable value. This is done in order to avoid congestion in a telecommunication network. A network is considered congested when too many packets try to access the same router's buffer and the load may exceed the network capacity. During congestion, actions need to be taken by both the transmission protocols and the network routers in order to avoid a congestion collapse and furthermore to ensure network stability, throughput efficiency and fair resource allocation to network users.
Congestion control is implemented at both the transport layer protocols, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
Two of the congestion control algorithms used in TCP are:
(a) slow start.
(b) exponential backoff.
Slow chart is one of the algorithms that TCP uses to control
congestion inside the network. It is also known as the " exponential growth phase". Slow-start works by increases the window size by number of segments acknowledged. This happens until either an acknowledgement is not received for some segment or a predetermined threshold value is reached. In case a packet is lost, TCP assumes this it is due to network congestion and takes steps to reduce the offered load on the network.
Exponential backoff algorithm uses feedback to multiplicatively decrease the rate of some process, in order to gradually find an acceptable rate. It is often used in network congestion avoidance to help determine the correct sending rate. When a collision first occurs, it sends a jamming signal all participating nodes to prevent sending of further data. It will then send a frame after either 0 seconds or after n number of seconds chosen at random. If this sending fails, it will resend the frame after either 0s, ns, 2ns, or 3ns. If these also do not work, it will resend the frame after (k x n)s, where k is a random number between 0 and 23 - 1.
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