【正文】 rs a better method has been devised independently by the authors for generating graphs that reflect the hierarchical domain structure and locality that is present in the Internet [1, 4]. Three levels of hierarchy are modeled, corresponding to transit domains, stub domains, and LANs attached to stub nodes. The method constructs the graph piecewise, where the pieces correspond to domains at the different levels in the hierarchy. The connectivity within a domain (intranet work connectivity) is dealt with separately from that between domains (internetwork connectivity). ParametersTwo sets of parameters control the coarse properties of the networks generated. These parameters are chosen to provide reasonably simple control over the important structural characteristics of the graph. The parameters chosen also have obvious effects on the networks that are produced. The first set of parameters governs the relative sizes of the three levels in the hierarchy: T, the total number of transit domains, and NT, the average number of nodes per transit domain. Note that= 1 and NT=1. S, the average number of stub domains per transit domain, and NS, the average number of nodes per stub domain. Note that S= 1 and NS=1. L, the average number of LANs per stub node, and NL, the average number of hosts per LAN. LANs are modeled as star topologies with a router node at the center of the star and the host nodes each connected to the center router. As pared to using a plete graph connecting all hosts in the LAN, this significantly reduces the number of edges in the graph and reflects the lack of physical redundancy in most LANs. Note that L= 0 and NL=1. The total number of routing nodes, NR, and the total number of hosts, NH are given by: NR =TNT(1 + SNs) NH =TNTSNSLNL Note that the parameter values are taken as the basis for distributions used to obtain the actual value for each run of the algorithm. Extra information can be associated with each parameter to describe the distribution of the parameter. For instance, an upper and lower bound on the number of nodes in a stub domain and the function for distributing the value between the bounds could be described. The second set of parameters governs the connectivity within a domain (intranetwork connectivity) and the connectivity between domains at the same or higher and lower levels (internetwork connectivity).ET, the average number of edges from a transit node to other transit nodes in the same must be large enough so that the graph corresponding to each transit domain can be connected. (ET= 2.) ES, the average number of edges from a stub node to other stub nodes in the same domain. ES must be large enough so that the graph corresponding to each stub domain can be connected. (ES=2.) ETT, the average number of edges from a transit domain to another transit domain. ETT must be large enough so that the transit domains can be connected to one another. . (ETT =2.) EST , the average number of edges from a stub domain to a transit domain. Every stub domain must be connected to at least one transit domain, thus EST =1。 singlehomed stubs connect to only one transit domain. Some stubs domains may have links to other stubs. Transit domains may themselves be organized in hierarchies, . MANs connect mainly to stubs domains and WANs. Existing Topology ModelsOne of the most monly used models for generating random networks algorithmically is due to Waxman [3]. The nodes in the network are placed at random points in a two dimensional grid. Links (represented by edges between nodes) are added to the network by considering all possible pairs of nodes and then deciding whether a link should exist according to a probability function involving how far apart the two nodes are and how many links are expected to be in the whole network. The original intention of this approach was to generate networks for paring Minimum Steiner Tree algorithms. It has several serious drawbacks when used for generating typical internets. First, the networks don39。s Internet can be viewed as a collection of interconnected routing domains. Each routing domain is a group of nodes (routers, switches and hosts), under a single (technical) administration, that share routing information and policy. Each routing domain in the Internet can be classified as either a stub domain or a transit domain. A stub domain carries only traffic that originates or terminates in the domain. Transit domains do not have this restriction. The purpose of transit domains is to interconnect stub domains efficiently。 the typical host will be represented as a leaf connected to a single router node. Additional information about the network can be added to the topological structure by associating information with the nodes and edges. For example, nodes might be assigned numbers representing buffer capacity. An edge might have values of various types, including costs, such as the propagation delay on the link, and constraints, such as the bandwidth capacity of the link. The purpose of this article is to review the basic topological structure of the Internet, then present a modeling method designed to produce graphs that reflect the locality and hierarchy present in the Internet. Two implementations of the method are available。外文原文：MODELING INTERNET TOPOLOGY 1 IntroductionThe explosive growth of networking, and particularly of the Internet, has been acpanied by a wide range of internetworking problems related t