Congestion Control techniques in Computer Networks

Open Loop Congestion Control
Open loop congestion control policies are applied to prevent congestion before it happens.
Retransmission Policy
It is the policy in which retransmission of the packets are taken care of.
If the sender feels that a sent packet is lost or corrupted, the packet needs to be retransmitted.
This transmission may increase the congestion in the network.
To prevent congestion, retransmission timers must be designed to prevent congestion and also able to optimize efficiency.
Window Policy
The type of window maintained at the sender’s side can impact congestion.
In the Go-back-n window, several packets are re-sent, even if some have been successfully received by the receiver.
This duplication can worsen congestion.
To mitigate this, consider adopting the Selective Repeat window, which retransmits specific lost packets.
Discarding Policy
A good discarding policy adopted by the routers is that the routers may prevent congestion and at the same time partially discard the corrupted or less sensitive packages and also be able to maintain the quality of a message.
In case of audio file transmission, routers can discard less sensitive packets to prevent congestion and also maintain the quality of the audio file.
Admission Policy
In admission policy a mechanism should be used to prevent congestion.
Switches in a flow should first check the resource requirement of a network flow before transmitting it further.
If there is a chance of a congestion or there is a congestion in the network, router should deny establishing a virtual network connection to prevent further congestion.
Acknowledgment Policy
Since acknowledgements are also the part of the load in the network, the acknowledgment policy imposed by the receiver may also affect congestion.
Several approaches can be used to prevent congestion related to acknowledgment.
The receiver should send acknowledgement for N packets rather than sending acknowledgement for a single packet.
The receiver should send an acknowledgment only if it has to send a packet or a timer expires.
The congestion control is handled either by the source or the destination.
Backpressure is a technique in which a congested node stops receiving packets from upstream node
A choke packet is a packet sent by a node to the source to inform it of congestion.
In explicit signaling, if a node experiences congestion it explicitly sends a packet to the source or destination to inform about congestion.