快速原型模型根据原型的不同作用，有三类原型模型：探索型原型、实验型原型、演化型原型。探索型原型。这种类型的原型模型是把原型用于开发的()，目的是要弄清用户的需求，确定所期望的特性，并探索各种方案的可行性。它主要针对开发目标模糊，用户与开发着对项目都缺乏经验的情况，通过对原型的开发来明确用户的需求。

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In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

 To a router, a flow is a(71)of packets that share the same characterstics, such as traveling the same(72), using the same(73), having the same kind of security, and so on. A router that supports the handling of flow labels has a(74)table. The table has an entry for each Active flow label; each entry defines the(75)required by the corresponding flow label.

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In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

 In low - speed network, it is usually adequate to wait for congestion to occur and then react to it by telling the source of packets to slow down. In high - speed networks, this approach often works poorly, because in the(66)between sending the notification and notification arriving at the source, thousands of additional(67)may arrive. In ATM network, a major tool for preventing(68)is(69)control. When a host wants a new virtual(70), it must describe the traffic to be offered and the service expected.