Together with the network layer,the transport layer is the heart of the protocol ( ).The network layer provides end-to-end () delivery using datagrams or virtual circuits.The transport layer builds on the network layer to provide data transport from a process on a () machine to a process on a destination machine with a desired level of reliability that is independent of the physical (请作答此空) currently in use.It provides the abstractions that applications nedd to use the network..Without the () layer,the whole concept of layered protocols would make little sense.

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I can‘t forget the years______ I spent with him and the places______we went together.

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Dr．Smith,together with his wife and two sons,__to arrive on the evening flight.

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The phrase “if not possible, advise” may be used together with the clearance or instruction _______ ．

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The author was required to submit an（）of about 200 words together with his research paper.

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Tom,together with his family,to see us tonight．

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