在OSI参考模型中，物理层的功能是(1)等。实体在一次交互作用中传送的信息单位称为(2)，它包括(3)两部分。上下邻层实体之间的接口称为服务访问点(SAP)，网络层的服务访问点也称为(4)，通常分为(5)两部分。

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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 preventing(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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To a router, a flow is a(66)of packets that share the same Characterstics, such as traveling the same(67),using the same(68),having the same kind of security, and so on. A router that supports the handling of flow labels has a(69)table. The table has an entry for each active flow label; each entry defines the(70)required by the corresponding flow label.

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