A number of control mechanisms for congestion control in packet-switching networks have been suggested and tried. The following are examples:1. Send a control packet from a congested node to some or all source nodes. Thischoke packet will have the effect of stopping or slowing the rate of transmissionfrom sources and hence limit the total number of packets in the network. Thisapproach requires additional traffic on the network during a period of congestion.2. Rely on routing information. Routing algorithms, such as ARPANET’s, providelink delay information to other nodes, which influences routing decisions. Thisinformation could also be used to influence the rate at which new packets areproduced. Because these delays are being influenced by the routing decision,they may vary too rapidly to be used effectively for congestion control.3. Make use of an end-to-end probe packet. Such a packet could be timestamped tomeasure the delay between two particular endpoints. This has the disadvantageof adding overhead to the network.4. Allow packet-switching nodes to add congestion information to packets asthey go by. There are two possible approaches here. A node could add suchinformation to packets going in the direction opposite of the congestion. Thisinformation quickly reaches the source node, which can reduce the flow ofpackets into the network. Alternatively, a node could add such information topackets going in the same direction as the congestion. The destination either
asks the source to adjust the load or returns the signal back to the source in the
packets (or acknowledgments) going in the reverse direction.
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