![]() ![]() ![]() ![]() A minimum span network, one formed with the smallest number of links possible, is chosen as a reference point, and is called "a network of redundancy level one." If two times as many links are used in a gridded network than in a minimum span network, the network is said to have a redundancy level of two. The term "redundancy level" is used as a measure of connectivity, as defined in Fig. Since destruction of a small number of nodes in a decentralized network can destroy communications, the properties, problems, and hopes of building "distributed" communications networks are of paramount interest. Such a network is sometimes called a "decentralized" network, because complete reliance upon a single point is not always required. 1 shows the hierarchical structure of a set of stars connected in the form of a larger star with an additional link forming a loop. In practice, a mixture of star and mesh components is used to form communications networks. The centralized network is obviously vulnerable as destruction of a single central node destroys communication between the end stations. Centralized, Decentralized and Distributed Networks This means that small groups of stations isolated from the single largest group are considered to be ineffective.Īlthough one can draw a wide variety of networks, they all factor into two components: centralized (or star) and distributed (or grid or mesh) (see Fig. This criterion is chosen as a conservative measure of the ability of the surviving stations to operate together as a coherent entity after the attack. As a criterion of survivability we elect to use the percentage of stations both surviving the physical attack and remaining in electrical connection with the largest single group of surviving stations. Let us consider the synthesis of a communication network which will allow several hundred major communications stations to talk with one another after an enemy attack. ![]() The high degree of connectivity afforded allows the use of low-cost links so unreliable as to be unusable in present type networks. Simulation results are shown to indicate that highly efficient routing can be performed by local control without the necessity for any central-and therefore vulnerable-control point.Ī comparison is made between "diversity of assignment" and "perfect switching" in distributed networks. Recent history of measured network traffic is used to modify path selection. This network rapidly responds to changes in the network status. The use of a standard format message block permits building relatively simple switching mechanisms using an adaptive store-and-forward routing policy to handle all forms of digital data including "real-time" voice. The requirements for a future all-digital-data distributed network which provides common user service for a wide range of users having different requirements is considered. The payoff in terms of survivability for a distributed configuration in the cases of enemy attacks directed against nodes, links, or combinations of nodes and links is demonstrated. This Memorandum briefly reviews the distributed communications network concept and compares it to the hierarchical or more centralized systems. ![]()
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