 signaling and tracking calls for billing purposes. A key factor in improved functioning is LTE networks' flexibility in handling voice and data is the fact that www.TechnicalPDF.com signaling messages are carried separately from user data and IP voice. Signaling messages are used to keep track of usage, perform security functions (to keep the network free from hackers and malware), authenticate users, setting up a session (voice, data, or video) and enforce policies. Policies include rules on the number of bits included in various data plans. Signaling enables carriers to monitor this volume SO that a message can be sent to the user's device, notifying him that he has used up his planned quota and will be charged extra for additional transmissions. Functions within the LTE evolved core network are divided into three functional elements. The evolved packet core contains servers for managing these elements. Two elements, the Serving Gateway and the Packet Data Network Gateway, are generally located in the same router. The functional elements making up the LTE's IP core are as follows: Mobility Management Entity (MME) This performs the signaling functions in the IP core. It sends and receives signaling information needed to set up, bill, and address calls to the eNodeB and to the Serving Gateway. In addition, the MME contains the security protocols for authentication and authorization. Serving Gateway (SGW) The SGW forwards the data and voice packets on bearer paths between the eNodeB at the cell site and the Packet Data Network Gateway. Bearer paths carry the actual user IP data. The SGW handles the protocol conversions between LTE devices and 3G systems and relays this traffic to and from the Packet Data Network Gateway and earlier- or later-generation gateways. Packet Data Network Gateway (PGW) This interfaces with the public data network (the Internet and carrier private data networks). It additionally allocates IP addresses to user devices and is responsible for policy enforcement. It can classify packets as r