2014 network administrator-exam exercise Questions and answers (1)

51cto college specially sorted out "2014 network administrator-exam exercise Questions and Answers" in the soft exam preparation season to help schools pass smoothly! For more software proficiency test counseling and questions, please pay attention to the 51cto college-soft exam classification!

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1. _______ service is a reliable data transmission method provided by the network layer to the transport layer that enables groups to arrive at the destination system in sequence. In the _______ service, each group cannot arrive in order, and some groups may even be lost on the way.

2. in the X.25 group-level (layer) protocol, the group header in the group format is used for network control. The logical channel ID of the group header consists of four lower bits (B4, B3, the Logical Channel group number expressed by B2, B1 and the logical channel number represented by _______-bytes are used to identify the logical channel.

1. Analysis and Solutions

[Related knowledge]

(1) virtual circuit Service

(2) datagram Service

[Question analysis] This question involves the concepts of virtual circuit service and datagram service. The network layer is the highest level in the Communication Subnet. One of its main functions is to provide services to the transport layer. In a Packet Exchange Network, the Communication Subnet provides two services to the terminal system (Transport Layer): virtual circuit service and datagram service. virtual circuit service is a connection-oriented service. In the virtual circuit mode, there is a virtual circuit between two end systems of data exchange to serve them, all data <Groups> are transmitted along the virtual circuit, so all groups are in order. The datagram service is a meta-connection-oriented service. When the end system sends data, the network layer attaches the address, serial number, and other information to the data and sends it as a datagram to the network node, the data packets received by the target system may not arrive in order or may be lost.

[Reference answer and score point] virtual circuit Datagram

2. Analysis and Solutions

[Related knowledge]

(1) X.25 Protocol

(2) formats and meanings of X.25 groups

[Question analysis] the general format and meaning of the X.25 group of candidates for this question. the X.25 protocol consists of three layers: the physical layer, the data link layer, and the group layer. The group level of X.25 is equivalent to the network layer of the OSI reference model. Its main function is to provide multi-channel virtual circuit services to hosts. at the group level, all information is transmitted and processed based on groups.

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