某种中继设备提供运输层及运输层以上各层之间的协议转换，这种中继设备是(19)，从OSI协议层次来看，用以实现不同网络间的地址翻译、协议转换和数据格式转换等功能的路由器属于(20)范畴，当采用数据报服务时，负责端到端的流量控制的是(21)，路由器的主要功能是(22)。下列接入方式中，(23)不属于ISP的接入方式。

(81)

(79)

(80)

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.

(78)

(76)

(75)

(73)

(74)

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.