In this section, we consider the problem of congestion control in a general context, seeking to understand why congestion is a "bad thing," how network congestion is manifested in the performance received by upper-layer applications, and various approaches that can be taken to avoid, or react to, network congestion. This more general study of congestion control is appropriate since, as with reliable data transfer, it is high on the "top-10" list of fundamentally important problems in networking. The Causes and the "Costs" of Congestion: Congestion control can be studied by examining three increasingly complex scenarios in which congestion occurs. In each case, we'll look at why congestion occurs in the first place, and the "cost" of congestion (in terms of resources not fully utilized and poor performance received by the end systems). Scenario 1: Two senders, a router with infinite buffers We begin by considering perhaps the s...
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