局域网是当前计算机网络研究与应用物一个热点，而符合IEEE 802.3标准的传统Ethemet应用最为广泛。它在MAC层采用方法(8)，物理层采用(9)标准。随着网络技术的发展，以及大型信息系统与多媒体技术的应用，出现了满足人们更高需要的FastEthemet、交换局域网Switching LAN与(10)等高速局域网产品。他们符合(11)标准。(8)方法不适应重负荷与有实时性通信要求。(10)采用Cell作为数据传输基本单元与Ethemet帧结构不一致，但具有高带宽，低延时，可动枋分配带宽等优点。

(85)

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(80)

Rapid advances in computer and communication technologies have resulted in the(71) merger of these two fields. The lines have bluned among computing, switching, and digital transmission equipment, and the same digital techniques are being used for data, voice, and image transmission. Merging and evolving technologies, coupled with increasing demands for efficient and timely collection, processing, and(72) of information, are leading to the development of(73) that transmit and process all types of data. The ultimate goal of this evolution is something its proponents-some of the most powerful forces in the computing and telecommunications industries-call the (74) .The (74) will be a worldwide public telecommunications network that will deliver a wide variety of services. The (74) will be defined by the standardization of user interfaces, and will be implemented as a set of digital switches and paths supporting a broad range of traffic types and providing (75) processing services. Inpractice, there will be multiple networks, implemented within national boundaries, but from the user's point of view there will be a single, uniformly accessible worldwide network.

(78)

(79)

Even though current technologies make the ultimate segmented network impractical, new technologies and products hold the promise of making the concept a reality. Most important of all these new technologies are (66) . The ultimate switched LAN, which is technically possible, now, exhibits the following characteristics:

  1. High-speed yet cost-effective switching devices can be implemented on a wide scale, providing dedicated connections for individual users and supporting the aggregate (67) of all networked users.

  2. The ability to deploy switching capabilities incrementally into the (68) base. Switching implementations support switching of individual users or groups so that existing users of shared media modules can continue to use the existing equipment until they can justify moving to dedicate switched LAN connections.

  3. Support and enhancement of existing routed environments. Switching (69) routint, but rather can be introduced into the network without making any changes to the existing routing equipment or configuration.(70) play a critical role in the integration of switching into existing networks.

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