●建筑物综合布线系统中的园区子系统是指(69)。

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• 1●安全电子邮件使用(68)协议。

  A.PGP

  B.HTTPS

  C.MIME

  D.DES

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• 2●IEEE 802.16工作组提出的无线接入系统空中接口标准是(67)。

  A.GPRS

  B.UMB

  C.LTE

  D.WiMAX

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• 3●在无线局域网中，AP的作用是(65)。新标准IEEE802.lln提供的最高数据速率可达到(66)。

  A.无线接入

  B.用户认证

  C.路由选择

  D.业务管理

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• 4●802.11在MAC层采用了(64)协议。

  A.CSMA/CD

  B.CSMA/CA

  C.DQDB

  D.令牌传递

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• 5●在局域网标准中，100BASE-T规定从收发器到集线器的距离不超过(63)米。

  A.100

  B.185

  C.300

  D.1000

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• 6●下面有关RMON的论述中，错误的是(70)。

  A.RMON的管理信息库提供整个子网的管理信息

  B.RMON的管理信息库属于MIB-2的一部分

  C.RMON监视器可以对每个分组进行统计和分析

  D.RMON监视器不包含MIB-2的功能

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• 7●The TCP protocolis a (71) layer protocol. Each connection connects two TCPs that may be just one physical network apart or located on opposite sides ofthe globe. In other words, each connection creates a (72) witha length that may be totally different from another path created by another connection. This means that TCP cannot use the same retransmission time for all connections. Selecting afixed retransnussion time for all connections can result in serious consequences. Ifthe retransmission time does not allow enough time for a (73) to reach the destination and an acknowledgment to reach the source, it can result in retransmission of segments that are still on the way. Conversely, if the retransnussion time is longer than necessary for a short path, it may result in delay for the application programs.Even for one single connection, the retransmission time should not be fixed.A connection may be able to send segments and receive (74)faster during nontraffic period than during congested periods. TCP uses the dynamic retransmission time,a transmission time is different for each connection and which may be changed during the same connection. Retransmission time can be made(75)  by basing it on the round-trip time (RTT). Several formulas are used for this purpose.

  A.physical

  B.network

  C.transport

  D.application

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