单选题For (1) service, we need a virtual-circuit subnet. Let us see how that works. The idea behind virtual circuits is to avoid having to choose a new (2) for every packet sent. Instead,when a connection is established, a route from the(3) machine to the destination machine is chosen as part of the connection setup and stored in tables inside the (4) . That route is used for all traffic flowing over the connection, exactly the same way that the telephone system works.When the connection is released, the virtual circuit is also terminated. With connection-oriented service, each packet carries an (5) telling which virtual circuit it belongs to.空白（1）处应选择（）AconnectionlessBconnection-orientedCdatagramDtelegram
单选题
For (1) service, we need a virtual-circuit subnet. Let us see how that works. The idea behind virtual circuits is to avoid having to choose a new (2) for every packet sent. Instead,when a connection is established, a route from the(3) machine to the destination machine is chosen as part of the connection setup and stored in tables inside the (4) . That route is used for all traffic flowing over the connection, exactly the same way that the telephone system works.When the connection is released, the virtual circuit is also terminated. With connection-oriented service, each packet carries an (5) telling which virtual circuit it belongs to.
空白（1）处应选择（）
A
connectionless
B
connection-oriented
C
datagram
D
telegram
参考解析
解析：
对于面向连接的服务，我们需要一个虚拟电路子网。让我们看看它是如何工作的。虚电路的核心思想是避免在发送每个数据时为它们选择一个新的路由。相反，当建立一个连接，将从源计算机向目标计算机选择一条路由作为连接设置的一部分并且存储到内部的路由器表中。这条路由承载着所有连接带来的流量，就跟电话系统的工作原理一样。当连接被释放时，虚电路也终止。在面向连接的服务中，每个数据包携带一个标识符，该标识符告诉它所属的虚电路。
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