Solution:

Congestion, in the context of networks, refers to a network state where a node or link carries so much data that it may deteriorate network service quality, resulting in queuing delay, frame or data packet loss, and the blocking of new connections.

Congestion occurs when bandwidth is insufficient and network data traffic exceeds capacity.

Choke Packets:

This approach can be used in virtual circuits as well as in the datagram subnets. In this technique, each router associates a real variable with each of its output lines.

This real variable says “u” has a value between 0and1 and it indicates the percentage utilization of that line. If the value of “u” goes above the threshold, then that output line will enter into a “warning” state.

The router will check each newly arriving packet to see if its output line is in the “warning state”. If it is in the warning state, then the router will send back a choke packet signal to the sending host.

The sender host will not generate any more choke packets. Several variations on the congestion control algorithms have been proposed, depending on the value of thresholds.

Hop-by-hop choke packets:

This technique is an advancement over the Choked packet method. At high speed over long distances, sending a packet back to the source doesn’t help much, because by the time the choke packet reaches the source, already a lot of packets destined for the same original the destination would be out from the source.

So, to help this, Hop-by-Hop Choke packets are used. Over long distances or at high speeds choke p y packets are not very effective. A more efficient the method is to send choke packets hop-by-hop.

This requires each hop to reduce its transmission even before the choke packet arrives at the source.

Figure Depicts the functioning of Hop-by-Hop choke packets, (a) Heavy traffic between nodes P and Q, (b) Node Q sends the Choke packet to P, (c) Choke packet reaches R and the the flow between R and Q is curtailed down, the Choke packer reaches P and Produces the flow out.