 which increases the speed on the uplink transmission. The combination of HSDPA and HSUPA is also referred to as HSD/UPA (high-speed downlink/uplink packet access). Doubling Voice Capacity with CDMA2000 1X The first phase of 3G CDMA2000, CDMA2000 1X, provided "always-on" data rates anywhere from 60Kbps to 100Kbps plus doubled voice capacity. All that is required Mobile and Wi-Fi Networks for upgrades to 1X are new cards in the Base Transceiver Station (BTS) and software in the mobile switching center. Routers, billing, authentication and authorization sys- items, and connections to IP networks are necessary for the data services. Carriers in South Korea implemented the first release (IS-2000 Rel. 0) of CDMA2000 in October 2000. In the United States, Sprint Nextel, Verizon Wireless, and some smaller cellular operators upgraded to CDMA2000 1X in 2001-2004. Other international carriers such as China Telecom, VIVO (Brazil), and Telstra (Australia) also upgraded. CDMA2000 1xEV-DO (Data Optimized or Data Only) Network providers upgrade to higher data speeds by adding software and channel cards to their base stations for High Data Rate (HDR) service. HDR service is a data- only enhancement with higher downlink speeds. No capacity is gained for voice traf- fic. Download speeds (from the network to their wireless devices) of close to 1Mbps within a single 1.25MHz carrier (like CDMA2000 1X) are significant because they require less spectrum than protocols that require perhaps 5MHz per carrier. The Evolution of CDMA2000: 1xEV-DO Service Revision A The CDMA2000 1xEV-DO service Revision A is also referred to as Rev A. Its air interface supports packet-switched data in the over-the-air channel as well as the core. Because of its real-time capabilities, Rev A supports applications such as multiplayer games, push-to-talk, and videoconferencing in which latency must be minimal. Uplink speeds are increased to a peak of 1.8Mbps and downlink speeds to a peak of .1Mbps. Enhancements to CDMA2000 1xEV-DO include multicasting, which is 