通信系统的目的是在通信双方之间交换数据，对于构成通信模型的5大要点分别是信源、发送器、传输系统、接收器、(57)。

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Flow control is a function that prevents network congestion by ensuring that(71)do not overwhelm(72)with data. There are three commonly used methods for handling network congestion.(73)is used by network devices to temporarily store bursts of excess data in memory until they can be processed. (74)are used by receiving devices to help prevent their buffers from overflowing.(75)is a flow -control scheme in which the source device requires an acknowledgment from the destination after a certain number of packets have been transmitted.

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The purpose of the requirements definition phase is to produce a clear, complete, consistent, and testable (66) of the technical requirements for the software product.

 During the requirements definition phase, the requirements definition team uses an iterative process to expand a broad statement of the system requirements into a complete and detailed specification of each function that the software must perform. and each (67) that it must meet. The starting point is usually a set of high-level requirements from the (68) that describe the project or problem.

 In either case, the requirements definition team formulates an overall concept for the system and the defines (69) showing how the system will be operated, publishes the system and operation concept documents,and conducts a system concept review(SCR).

 Following the SCR, the team derives (70) requirements for the system from the highlevel requirements and the system operations concept. Using structured or object-oriented analysis, the team specifies the software functions and algorithms needed to satisfy each detailed requirements.