dard omits details concerning a particular access network implementation and does not require any device to support multiple modes. However, interoperability between terminals and networks is assured with each mode. Air Interface - Wideband Mode The Wideband mode is based on OFDMA for both forward and reverse links. It is designed to operate for both FDD and TDD bandwidths from 5 to 20 MHz. 6.4.1 Architecture Reference Model The Wideband architecture mainly consists of Access Terminals and Access Networks as shown in Figure 6.1. The overall functional units of the architecture are as follows: Access Terminal (AT): AT is a device that provides data connectivity to a user. AT could be a handheld unit, connected to a computer or embedded into a computer. Access Network: Access network is a collection of access nodes. Access Node (AN): AN is a physical device that implements the MAC and PHY of one or more sectors in the network. Sector: One set of physical layer channels transmitted between the access network and the access terminals within a given frequency assignment. Route: Each InUse protocol stack instance is called a route. The 802.20 Wideband mode is defined as a multi-route standard, each route defining a unique path to the network with an independently operating, but identical protocol stack to support it. Only one route can be in use at a given time for the forward link (FL) and the reverse link (RL); however, multiple routes can be configured as required. Systems that implement wideband mode can support a network based, route-tunneling interface to enable rapid and efficient transfer of control and data between access networks [5]. 1 A protocol instance can be either an InUse instance or an InConfiguration instance. A protocol or transport instance is InUse if it is currently being used to communicate between the access terminal and the accessnetwork. Otherwise, a protocol or transport instance is InConfiguration. Next Generation Mobile Communications Ecosystem Sector Access Node Access Network 1 Access Te