31 Days Before Your CCNA Exam

Day 31 9Logical topologies refer to the way a signal travels from one point on the network to another andare largely determined by the access method—deterministic or nondeterministic. Ethernet is a nondeterministicaccess method. Logically, Ethernet operates as a bus topology. However, Ethernetnetworks are almost always physically designed as a star or extended star.Other access methods use a deterministic access method. Token Ring and Fiber Distributed DataInterface (FDDI) both logically operate as ring, passing data from one station to the next. Althoughthese networks can be designed as a physical ring, like Ethernet, they are often designed as a staror extended star. But logically, they operate like a ring.The Hierarchical Network ModelHierarchical network design involves dividing the network into discrete layers. Each layer providesspecific functions that define its role within the overall network. By separating the various functionsthat exist on a network, the network design becomes modular, which facilitates scalabilityand performance. The hierarchical design model is broken up into three layers as follows:■■■Access layer: Provides local and remote user accessDistribution layer: Controls the flow of data between the access and core layersCore layer: High-speed redundant backboneFigure 31-3 shows an example of the hierarchical model.Figure 31-3The Hierarchical ModelCoreDistributionAccessAccessWANInternetTelephoneNetwork