 fibre. The signal is then either directly modulated to an analogue optical signal or, alternatively, converted to a digital signal before the electrical- to-optical conversion. Uplink and downlink signals can be carried over a single fibre by using wavelength division multiplexing (WDM). The remote unit performs optical-to-electrical, and optionally digital-to-analogue, conversion. In a typical office building installation, the optical part would be installed in the riser while thin coaxial cable would be used in the horizontal runs to the antennas. Active DAS systems can incorporate multiple operators, RATs and frequency bands in the same system. They are typically used for building large neutral host systems in office buildings or public venues. Wi-Fi Integration Where the mobile broadband network is overloaded, WLAN, or Wi-Fi, provides an opportunity for relieving the congestion. Traffic steering between the cellular and Wi-Fi networks is possible through access network discovery and selection function (ANDSF). It is a 3GPP- defined entity in the core network that assists the terminal in discovering Wi-Fi networks and defining when and where to connect to Wi-Fi, as well as in setting priorities between Wi-Fi networks and the cellular network. ANDSF settings are sent over the air to the ANDSF client in the mobile terminal. LTE Small Cell Optimization RUCKUS Figure 6.11 Ruckus ZoneFlex R700 Wi-Fi access point Hotspot 2.0 is a Wi-Fi alliance-defined method for a (Hotspot 2.0 capable) terminal to select the most suitable Wi-Fi access point out of several candidates, based on information derived from the access point prior to attaching to it. Unlike ANDSF, Hotspot 2.0 can provide information of the quality of Wi-Fi networks. 802.11ac is the latest evolution of the 802.11 series of Wi-Fi standards. It enables improved bitrates in the 5 GHz band thanks to, for example, a wider RF bandwidth (up to 160 MHz), more spatial streams (up to 8) and a higher order modulation (up to 256 QAM). An example Wi-Fi access point wit