equiring Quality of Service (QoS). It also generates usage records that it sends to the carrier's billing system, indicating levels of customer voice and data usage. The PGW has links to the roaming database for functions related to roaming and billing roaming traffic. The PGW and SGW transmit mobile traffic to the Internet and other data networks. 3G traffic is handed off to these LTE gateways by earlier-generation controllers and signaling gateways. Note that Voice over LTE is outside of the evolved packet core. www.TechnicalPDF.com Databases in the LTE Evolved Packet Core Gateways in core networks connect to a variety of databases that support roaming, billing functions, voice messaging, and text messaging services. The following is a listing of key Evolved Packet Core databases in core 4G networks: Home Subscriber Services (HSSs)-Keep - track of roamers' locations and temporary records of roaming subscribers' devices. Store telephone identities and authentication codes for digital phones. Perform security functions including authenticating that users are subscribers. Messaging center databases and processors-Handle text messages. Also store multimedia messages including voicemail, facsimile, and e- mail. Policy and Charging Rule Function (PCRF)-Contains QoS parameters and details of each subscriber's plan. A Traffic Detection Function enforces these Policy and Charging policies. The PCRF sends information to the Packet Data Network Gateway, which then forwards traffic to the Internet and broadband networks. Billing databases-Contain specific information on contract terms for each subscriber. The Packet Data Network (PDN) transmits usage records to the PCRF, which is connected to billing software. In addition to above databases and functions, there are security applications in the evolved packet core. This may include firewalls that screen traffic for malware. The firewall may be located in the cloud. Voice over LTE-Packetized Voice Voice over LTE (VoLTE) is an international standard for transmitting voice ove