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Ethernet Networks: Design, Implementation, Operation, Management 4th phần 6

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bằng cách sử dụng IBM thiết bị: các máy tính IBM mạng Chương trình, PC DOS 3,1, và các IBM PC Network Adapter. Chương trình Mạng máy tính IBM đã thực sự là một phiên bản thiết kế của phần mềm Microsoft của Tập đoàn Microsoft (MS-NET) Networks, | bridging and switching methods and performance issues 287 Figure 6.5 A weighted network graph. Kruskal s algorithm can be expressed as follows 1. Sort the edges of the graph G in their increasing order by weight or length. 2. Construct a subgraph S of G and initially set it to the empty state. 3. For each edge e in sorted order If the endpoints of the edges e are disconnected in S add them to S. Using the graph shown in Figure 6.5 let s apply Kruskal s algorithm as follows 1. The sorted edges of the graph in their increasing order by weight or length produces the following table Edge Weight Length A-C 1 B-D 3 C-B 4 C-D 6 A-B 8 2. Set the subgraph of G to the empty state. Thus S null. 3. For each edge add to S as long as the endpoints are disconnected. Thus the first operation produces A o S A C or o C 288 chapter six The next operation produces A B o o S A C B D or o o CD The third operation produces AB Q o S A B B D C B or o o CD Note that we cannot continue as the endpoints in S are now all connected. Thus the minimum spanning tree consists of the edges or links A B B D C B and has the weight 1 4 3 or 7. Now that we have an appreciation for the methodby which a minimum spanning tree is formed let s turn our attention to its applicability in transparent bridge-based networks. Similar to the root of a tree one bridge in a spanning tree network will be assigned to a unique position in the network. Known as the root bridge this bridge is assigned as the top of the spanning tree and because of this position it has the potential to carry the largest amount of intranet traffic due to its position. Because bridges and bridge ports can be active or inactive a mechanism is required to identify bridges and bridge ports. Each bridge in a spanning tree network is assigned a unique bridge identifier. This identifier is the MAC address on the bridge s lowest port number and a two-byte bridge priority level. The priority level is defined when a bridge is installed and functions