 provide as reliable a link as is possible in a mobile setting. Fast, low-overhead, make-before-break, inter-cell handover is also supported. Differentiated and tiered services are enabled through a flexible QoS mechanism. The 625k-MC system enables end-to-end IP-over-PPP (Point-to-Point Protocol) connectivity between the service providers and their customers who are the end users. 6.6.1 625k-MC Mode Key Features Some key enhancements of 625k-MC features are as follows: Defines additional modulation schemes, 32QAM and 64QAM, to deliver the higher throughputs with the peak downlink data rates of 1.493 Mbps and peak uplink data rates of 571.2 kbps in a channel bandwidth of 625 kHz. Supports three classes of QoS corresponding to three priority levels. These classes incorporate per-hop forwarding behaviors (PHB) in the descending order of priority: Priority 1, Priority 2, and Priority 3, corresponding to Expedited Forwarding (e.g., VoIP), Assured Forwarding (e.g., video stream) and Best Effort (e.g., web surfing) forwarding, respectively. The 625k-MC mode defines five paging activity levels to offer sleep mode control that enables power conservation for the user terminal in idle mode. Provides privacy and authentication enhancement via AES and stream cipher. Defines the MIB to provide radio network quality monitoring and control functionality. The MIB comprises of the managed objects, attributes, actions, and notifications required to manage a base station. Supports BCMCS and provides extensions to what is specified in ATIS-0700004.2005 It defines additional protocols and primitives to deliver BCMCS. Supports make-before-break handover scheme which is device directed. Supports multi-antenna transmission techniques. 6.7 802.20 Network Architecture Figure 6.12 illustrates an example of IEEE 802.20 based network architecture in combination with WLAN. The architecture assumes that the devices (laptops, PDAs, etc.) do not have embedded 802.20 modules. The WiFi network consists of multiple access points which are connected