ABSTRACT

Widespread use of computer networks and the varied technology for the interconnection of computer have made congestion a significance problem. In this project, summary of findings on congestion avoiding is stated while much effort is given to congestion control even though the concepts of the two are compared. Briefly, congestion avoidance is a prevention mechanism while congestion control is a recovery mechanism. A congestion avoidance scheme allows a network to operate in the region of low delay and high throughput with minimal queuing , thereby preventing it from entering the congested state, while congestion control scheme helps the network to recover from the congested state. A number of possible alternatives for congestion control are identified. A simple definition for congestion based on supply and demand is proposed and is then used to classify various congestion schemes. From these alternatives, timeout based control scheme for window flow-control networks was selected and modeled which is termed CUTE (congestion using at the End-to-end layer). During overload, most networks drop packets due to buffer unavailability. The resulting timeout at the source provide an implicit mechanism to convey congestion signal from the network to the source. On a timeout, a source should not only retransmit the lost packet, but it should also reduce its load on the network. Based on this realization, a simple congestion control scheme using the acknowledgment timeouts an indication of packet loss and congestion is developed. This scheme does not require any message format. Therefore, it can be used in any network with window flow control, e.g. ARP net or ISO. The tools used for the modeling of this project were Visual Basic 6.0 programming.