两个公司希望通过Internet 进行安全通信保证从信息源到目的地之间的数据传输以密文形式出现，而且公司不希望由于在传输节点使用特殊的安全单元而增加开支，最合适的加密方式是(1)，使用的会话密钥算法应该是(2)。

(75)

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(77)

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

 To a router, a flow is a(71)of packets that share the same characterstics, such as traveling the same(72), using the same(73), having the same kind of security, and so on. A router that supports the handling of flow labels has a(74)table. The table has an entry for each Active flow label; each entry defines the(75)required by the corresponding flow label.

(74)

(70)

(71)

(72)

(69)

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

 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(66)between sending the notification and notification arriving at the source, thousands of additional(67)may arrive. In ATM network, a major tool for preventing(68)is(69)control. When a host wants a new virtual(70), it must describe the traffic to be offered and the service expected.