SNMPv1是一个不安全的协议，管理站(Manager)与代理(Agent)之间通过(55)进行身份认证，由于认证信息没有加密，所以是不安全的。1998年公布的SNMPv3定义了基于用户的安全模型USM，其中的认证模型块结合(56)算法形成认证协议，产生了一个 6位的报文摘要。SNMPv3还定义了基于视图的访问控制模型VACM。在这个模型中，用户被分成组，属于同一组的用户可以有不同的安全级别，其中(57)是最高安全级别。 RFC1757定义的RMON管理信息库是对MIB-2的扩充，其中的统计组记录(58)的管理信息，而矩阵组则记录(59)的通信情况。

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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(71)between sending the notification and notification arriving at the source, thousands of additional(72)may arrive. In ATM network , a major tool for pre- venting(73)is(74)control. When a host wants a new virtual(75), it must describe the traffic to be offered and the service expected.

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For each blank, choose the best answer from the four choices and write down on the answer sheet.

  (66) is a six bytes OSI layer 2 address which is burned into every networking device that provides its unique identity for point to point communication.

  (67) is a professional organization of individuals in multiple professions which focuses on effort on lower-layer protocols.

  (68) functions with two layers of protocols. It Can connect networks of different speeds and can be adapted to an environment as it expands.

  (69) is the popular LAN developed under the direction of the IEEE 802.5.

  (70) is the popular backbone technology for transmitting information at high speed with a high level of fault tolerance which is developed under the direction of ANSI.