Network Fiber Terminal (OLT) Network Terminal (ONT) Outside Plant (((III)) Wireless Example: Smartphone eNodeB Network Spectrum FIGURE 11.1 Access network architecture examples. Network Access However, this type of transport is not available in wide-coverage broadband access networks, because the distances are much greater, requiring specialized and more expensive electronics, optics, and radio transceivers for access links of a given speed. Also, access networks require substantial physical infrastructure, such as buried or aerial cable with splices, cell site infrastructure, and spec- trum. The costs of the electronics and infrastructure means that a fully transparent dumb pipe infra- structure would make broadband services unaffordable. Modern wireless and wireline broadband access networks are cost effective because they use specialized hardware and sophisticated network protocols to enable longer transport distances, automatic range detection with timing adjustments for devices at different distances from the network, and multiple access with statistical multiplexing on shared access media. These techniques make broadband access affordable by allowing the cost of one access fiber, or one cell site's radio frequencies, to be efficiently shared by multiple endpoints. The software-driven functions that enable resource sharing in the access network must be dis- tributed close to the access endpoints. Some functions such as radio interference mitigation require very low latency with distances limited by the speed of light. Other functions such as statistical mul- tiplexing must take place close enough to the customer endpoints to enable effective sharing of the access network infrastructure. In practical terms, the allowable distances for performing a specific function will vary, depending on factors such as propagation limits of the access signals and speed of light latency requirements. Certain software functions of access networks need to be within no more than 10-20 km of the customer endpoints. For high-spee