对于一个大型的软件项目，由于项目的复杂性，需要进行一系列的估算处理。主要按(24)和(25)手段进行。估算的方法分为三类：从项目的整体出发，进行(25)的方法称为(26)估算法。把待开发的软件细分，直到每一个子任务都已经明确所需要的开发工作量，然后把它们加起来，得到软件开发总工作量的方法称为(27)估算法。而把待开发的软件项目与过去已完成的软件项目做类比，区分出类似部分和不同部分分别处理的方法称为(28)估算法。

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Rapid advances in computer and communication technologies have resulted in the(71)merger of these two fields. The lines have bluned among computing, switching, and digital transmission equipment, and the same digital techniques are being used for data, voice, and image transmission. Merging and evolving technologies, coupled with increasing demands for efficient and timely collection, processing, and(72)of information, are leading to the development of(73)that transmit and process all types of datA. The ultimate goal of this evolution is something its proponents-some of the most powerful forces in the computing and telecommunications industries-call the(74). The(74)will be a worldwide public telecommunications network that will deliver a wide variety of services. The(74)will be defined by the standardization of user interfaces, and will be implemented as a set of digital switches and paths supporting a broad range of traffic types and providing(75)processing servicess. Inpractice, there will be multiple networks, implemented within national boundaries, but from the user's point of view there will be a single, uniformly accessible worldwide network.

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Even though current technologies make the ultimate segmented network impractical, new technologies and products hold the promise of making the concept a reality. Most important of all these new technologies are(66). The ultimate switched LAN, which is technically possible, now, exhibits the following characteristics:

 1. High-speed yet cost-effective switching devices can be implemented on a wide scale, providing dedicated connections for individual users and supporting the aggregate(67)of all networked users.

 2. The ability to deploy switching capabilities incrementally into the(68)base. Switching implementations support switching of individual users or groups so that existing users of shared media modules can continue to use the existing equipment until they can justify moving to dedicate switched LAN connections.

 3. Support and enhancement of existing routed environments. Switching(69)routint, but rather can be introduced into the network without making any changes to the existing routing equipment or configuration.(70)play a critical role in the integration of switching into existing networks.

66. A. switch-based LANs

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