uired power enhancing capacity of the network. 6.5.2.3 Seamless Mobility To offer seamless mobility, the access network provides robust handoffs at Layer 1 and Layer 2 at all speeds including speeds in excess of 200 km/hr. At L1/L2, handoff is facilitated through the use of proven, active-set-management techniques based on CDMA cellular methods. The standard also supports disjoint DLs and ULs allows the AT to achieve best cell site selection gains in situations where the best serving sectors for DL and UL differ. 6.5.2.4 Broadcast Multicast Service (BCMCS) The BCMCS is designed to provide TV service to multiple users simultaneously using the MBWA air interface. Figure 6.4 describe the layering architecture for a route of the air interface that carries BCMCS 4 SCW - A MIMO transmission mode where a single code is used to encode the packet being transmitted over the various antennas. MCW - A MIMO transmission mode, where multiple codes are used to encode the packet being transmitted over the various antennas. IEEE 802.20 Mobile-Fi IEEE 802.2 LLC L3-CM IEEE 802.3 Connection Management L3 RM Registration Management L3-MMC L2 RLC L3 RRC Radio Mobility Radio Management Resource 625K-MC MAC/RLC/DLC Control Control Control L2 MAC Media Access Control 625K-MC PHY Figure 6.11 625k-MC PHY/MAC/RLC/DLC Protocol reference. Reproduced with permission from IEEE [4] data. The architecture consists of the physical layer, BCMCS upper layer and MAC and PHY MIB. The functions of PHY and MIB in BCMCS, remains the same as those described in the unicast structure. Each layer or plane consists of one or more protocols that perform the layer's functionality. The BCMCS is provided via Forward Broadcast and Multicast Pilot Channel (F-BMPICH) and Forward Broadcast and Multicast Services Channel (F-BCMCSCH). The BCMCS Upper Layer consists of multiple protocols to carry out the desired services. The broadcast packet data system provides a packet stream that can be used to carry higher-layer packets from the access network to multiple access te