New Search
links in congested areas, and could be considered for short haul communication to the traffic <br />signals and cameras. Wireless communications may also be considered for remote, low data <br />devices and possibly for phased implementation. <br />A wireless system would require a one time purchase of equipment with no monthly or annual <br />costs incurred. The system is easily expandable to future traffic signals or field devices, but the <br />additional devices share the bandwidth of the master modem. Typically, multiple masters are <br />installed at a center to increase bandwidth and support communication to devices in all <br />directions. With any wireless option, there may be service interruptions and the communication <br />link will likely be less robust than a hard wire connection. The wireless network should be <br />carefully designed using a path analysis to ensure the desired performance is provided. <br />4.3.4 Leased Services <br />Leased communication links could be provided by a wireless network provider (e.g. Verizon, <br />Cingular, Sprint) or a wireline network provider (e.g. PAN, local Cable TV provider). Leased <br />services could be provided at each field device location. However, considering the City of <br />Eugene already has a significant base of copper twisted pair it would be more likely to <br />aggregate video and data from field devices at a communication hub for transport over the <br />leased service. <br />The leased broadband wireless option requires a cellular router' in the field to connect multiple <br />IP enabled field devices. This option is similar to the analog cellular options used in the past for <br />communications to remote traffic signals; however, cellular providers have been phasing out the <br />analog cellular technology in favor of digital cellular technologies. The ongoing lease cost for <br />this service is based on the amount of data transferred and not necessarily on a fixed monthly <br />fee (pay as you use). For this reason, some central traffic signal systems have modified <br />communications to traffic signals from a second -by- second communications to an exception <br />based communications that only transmits data when the signal state change (green to yellow, <br />yellow to red) or when an upload or download is requested by central. <br />Leased services are flexible and can be installed anywhere access to cellular networks or <br />broadband cable is available. This type of communication could work well for outlying <br />intersections or field devices where periodic communication is adequate. <br />This type of system would not work as interconnect between signals or for providing large <br />bandwidth between field devices and the center. Constant communication via this type of <br />service could be very expensive, since the pay structure is based on the amount of data <br />transferred. Leasing services requires an ongoing monthly fee for services. <br />4.3.5 Hybrid <br />A hybrid of the technologies discussed in this section (twisted pair copper cable, fiber optic <br />cable, wireless, and leased services) may be the most cost effective and beneficial solution for <br />the traffic communications network. A hybrid approach will be explored as one of the <br />deployment alternatives because different portions of the network may be best supported by <br />different technologies. For example, using leased services to support devices on a corridor <br />without any existing communications infrastructure in the near -term may be more beneficial than <br />installing new infrastructure, especially when there may be opportunities in the long -term (e.g. <br />roadway widening or improvements) that would allow Public Works to eventually install their <br />own infrastructure. <br />r An example of a cellular router is htto:// www. diai. com/ oroducts/ cellularaateways /connectoortwanvon iso <br />DKS Associates Eugene Master Traffic Communications Plan March 2008 ' <br />Page 25 <br />