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发布时间：2006-06-28 05:00     点击：

As another disadvantage, connectionless network service does not predetermine the path from the source to the destination system, nor are packet sequencing, data throughput, and other network resources guaranteed. Each packet must be completely addressed because different paths through the network may be selected for different packets, based on a variety of influences. Each packet is transmitted independently by the source system and is handled independently by intermediate network devices.

Connectionless service, however, offers two important advantages over connection-oriented service: dynamic-path selection and dynamic-bandwidth allocation. Dynamic-path selection enables traffic to be routed around network failures because paths are selected on a packet-by-packet basis. With dynamic-bandwidth allocation, bandwidth is used more efficiently because network resources are not allocated a bandwidth that they will not use.

Connectionless services are useful for transmitting data from applications that can tolerate some delay and resequencing. Data-based applications typically are based on connectionless service.

3) Describe data link addresses and network addresses, and identify the key differences between them.

A data-link layer address uniquely identifies each physical network connection of a network device. Data-link addresses sometimes are referred as physical or hardware addresses. Data-link addresses usually exist within a flat address space and have a pre-established and typically fixed relationship to a specific device.

End systems generally have only one physical network connection, and thus have only one data-link address. Routers and other internetworking devices typically have multiple physical network connections and therefore also have multiple data-link addresses.

A network-layer address identifies an entity at the network layer of the OSI layers. Network addresses usually exist within a hierarchical address space and sometimes are called virtual or logical addresses.

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