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A.2.7 ITS Communication Network Topology Once We communication loads of an ITS system have been defined, these loads must be geographically placed and an interconnecting communication infrastructure topology must be developed based on Me architecture goals. Topology refers to geographic placement of field equipment, communication nodes and hubs, TOCs, and interconnecting communication links (i.e., mediums) to implement Me required communication infrastructure. The steps in this process include: I. Physical location of data sources and sinks on maps, tables, schematics, etc., so that the data loads are geographically defined. ITS data sources and sinks include controllers, VMS, ramp meters, primary and alternate TOCs, etc. 2. Consideration of repeaterIess distances of alternative communication mediums versus the required interconnect distances of He geographic network. 3. Identification of potential cost-effec~ve multiplexing alternatives and backbone communication network and topology altemadves. It should be noted that some systems (usually smaller systems) may be cost-effectively implemented without multiplexing;and backbone links. 4. Consideration of data load capacities of alternative communication mediums versus local and backbone link load requirements. Overhead for network protocol(s), network management, etc., should be considered. 5. Development of possible interconnecting network topologies that can Interconnect sources, sinks, and backbone nodes~ubs as required. Careful consideration should be given to right of-way and site acquisition requirements and costs. 6. Consideration of redundancy and fault tolerant goals, costs, and impact on the above. 7. Evaluation of cost trade-offs of Me reasonable promising altemadves. u\NCH~pr\ NCHRP3-51 Phase2F'nalReport A2-34 i