AX is that these devices do not support simultaneous voice and data transmis- sions. For example, when a user receives a voice call, her data connection is dropped. The Streamlined Infrastructure of Long-Term Evolution Architecture The same device can be used for voice and Internet access, just not simultaneously. Handsets with 4G capability also have second- or third-generation air interfaces for voice. The 3GPP organization is working toward agreement with manufacturers and carriers on a VoIP variation called Voice over LTE (VoLTE). Agreement on how to transmit VoIP is critical for roaming capabilities. The VoLTE protocol will be tightly specified SO that roaming and interoperability with earlier-generation networks will be possible. VoLTE will be implemented over Internet Protocol Multimedia Subsystems (IMSs). IMS enables applications for voice, video, and online games to be stored, billed for, and accessed on a common IP platform that is available from mobile as well as wired networks. When VoLTE is adopted, users will be able to use their mobile devices simulta- neously for voice and for surfing the Internet. Carriers, including Verizon Wireless, started trialing VoLTE in 2011 and it is anticipated that it will be implemented widely in 2013. Because it will take many years for LTE and WiMAX to become ubiquitous, there are various schemes for roaming between networks with VoLTE and 2G and 3G networks. THE STREAMLINED INFRASTRUCTURE OF LONG- TERM EVOLUTION ARCHITECTURE Long-Term Evolution (LTE) uses fewer protocols and requires less equipment in its core network than second-generation (2G) and third-generation (3G) architectures. It also distributes some functions found in 3G core networks to equipment in the cell site. LTE Cell Sites Offer Additional Functionality An LTE cell site consists of antennas, amplifiers to adjust power levels, and a single piece of equipment, the evolved NodeB (eNodeB). The eNodeB allocates radio fre- quency (wireless spectrum) to users' devices and passes calls off to other cell si