Acknowledgment Policy :
The acknowledgment policy obligatory by the receiver can also have an effect on congestion.
If the receiver doesn’t acknowledge each packet it receives, it’s going to impede the sender
and facilitate forestall congestion. many approaches area unit utilized inthis case. A
receiver could send Associate in Nursing acknowledgment provided that it’s a packet to
be sent or a special timer expires. A receiver could conceive to acknowledge solely N packets at a time. we’d like to grasp that the
acknowledgments are a part of the load in an exceedingly network. causation fewer acknowledgments suggests that imposing less load on the network
The type of window at the
sender might also have an effect on congestion. The Selective Repeat window is healthier than the Go-Back-N window for congestion management. within the Go-Back-N
window, once the timer for
a packet times out, many packets could also be resent, though some might have arrived safe and sound at the receiver. This
duplication might create the congestion worse. The Selective Repeat window, on the opposite hand, tries to send the precise packets that are lost or corrupted.
Retransmission is typically inescapable. If the sender
feels that a sent packet is lost or corrupted, the packet has to be retransmitted. Retransmission generally might increase
congestion within the network.
However, a decent retransmission
policy will forestall congestion. The
retransmission policy and therefore the retransmission timers should be designed to optimize potency and at identical time forestall congestion. as an example, the retransmission policy employed by TCP is meant to forestall congestion
Admission Policy :
An admission policy, that could be a quality-of-service
mechanism, also can stop congestion in virtual-circuit networks. Switches in a very flow 1st check the
resource demand of a flow
before admitting it to the network. A router will deny establishing a virtual- circuit association if there’s congestion within the network or if there’s a break of future
Discarding Policy :
A good discarding policy by
the routers could stop congestion and at a similar time might not damage the integrity of the transmission. as an example, in audio transmission, if the policy is to discard less
sensitive packets once congestion is probably going to happen, the standard of sound remains preserved and congestion is prevented or relieved.
Techniques for Closed-Loop
congestion control mechanisms try to alleviate congestion after it happens.
Several mechanisms have been used by different protocols
In implicit signal, there’s no
communication between the full node or nodes and also the supply. The supply guesses that there’s a congestion somewhere within the network from alternative symptoms. as an example, once a supply sends many packets and there’s no acknowledgment for a jiffy, one assumption is that the network is full. The delay in receiving associate degreeacknowledgment is taken as congestion within the network; the supply ought to prevent.
The node that experiences congestion will expressly send a proof to the supply or
destination. the express communicationmethodology, however, is completely different from the choke packet methodology. within the choke packet methodology, a separate packet is employed for this purpose; within the express communication methodology, the signal is enclosed within thepackets that carry knowledge. express communication, as we’ll see in Frame
Relay congestion management, will occur in either the forward or the backward
Signaling A bit can be set in a packet moving in the
direction opposite to the congestion. This bit can warn the source that there
is congestion and that it needs to slow down to avoid the discarding of
Forward Signaling A bit can be set in a packet moving in the direction
of the congestion. This bit can warn the destination that there is congestion.
The receiver in this case can use policies, such as slowing down the
acknowledgments, to alleviate the congestion.
Just like in liquids once a blockage happens during a pipe a backpressure is exerted towards the supply that restricts the
flow of liquid. Similar is that the case in network
, backpressure is by selection applied to logical connections, so the ensue one node to future is merely restricted or
halted on some connections, usually those with the foremost traffic. during this case, the restriction propagates back on the association to the supply
A choke packet could be a management packet
generated at a full node and
transmitted back to a supply node to limit traffic flow. associate degree example of a choke packet is that the ICMP (Internet management Message Protocol) supply Quench packet. Either a router or a destination finish system might send this
message to a supply finish system, requesting that it scale back the speed at that it’s causing traffic to the web destination. On receipt of a supply quench message, the supply host ought to shrink the speed at that it’s causing traffic to the required destination till it not receives supply quench messages