Congestion control approaches which can be used in the datagram subnets. The techniques are:

1. Choke Packets.
2. Load Shedding.
3. Jitter control.

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 say “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 algorithm have been proposed, depending on the value of thresholds.

Load shedding:

Admission control, choke packets, fair queuing are the techniques suitable for light congestion. But if these techniques cannot make the congestion to disappear, then the load shedding technique is to be used. The principle of load shedding states that when the routers are being inaundated by the packets away. A router which is flooding with packets due to congestion can drop any packets at random. The policy for dropping a packet depends on the type of packet. So the policy for file transfer called wine (old is better than new) and that for the multimedia is called milk (new is better than old). To implement such an intelligent discard policy, co-operation from the sender is essential. The applications should mark their packets are to be discarded the routers can first drop packets from lowest class.

Jitter control:

Jitter is defined as the variation in delay for the packets belonging to the same flow. The real time audio and video cannot tolerate jitter on the other hand the jitter does not matter if the packets are carrying an information contained in a file. For the audio and video transmission if the packets take 20 msec to 30msec to reach the destination, it does not matter, provided that the delay remains constant. When a packet arrives at a router, the router will check to see whether the packet is behind or ahead and by what time. This information is stored in the packet and updated every hop. If the packet is ahead of the schedule then the router will hold it for slightly longer time and if the packet is behind the schedule, then the router will try to send it out as quickly as possible.