MOBILITY MANAGEMENT ENTITY (MME)
The MME is a signaling-only entity, thus user IP packets don't have the MME. Its main function would be to manage the UE's mobility. Also, the MME also performs authentication and authorization; idle-mode UE tracking and reachability; security negotiations; and NAS signaling. A benefit of a separate network element for signaling is that operators can grow signaling and traffic capacity independently. Much the same benefit can even be accomplished in HSPA Release 7's direct-tunnel architecture, the location where the SGSN becomes a signaling-only entity.
EFFICIENT QoS
A vital aspect for virtually any all-packet network is a mechanism to ensure differentiation of packet flows depending on its QoS requirements. Applications such as video streaming, HTTP, or video telephony have special QoS needs, and will receive differentiated service over the network. With EPS, QoS flows called EPS bearers are in place between UE as well as the P-GW. Each EPS bearer is associated with a QoS profile, and is composed of a radio bearer and a mobility tunnel. Thus, each QoS IP flow (e.g., VoIP) will probably be from a different EPS bearer, plus the network can prioritize packets accordingly. The QoS procedure for packets arriving on the internet is related to that surrounding HSPA. When receiving an IP packet, the P-GW performs packet classification dependant on parameters including rules received on the PCRF, and sends it with the proper mobility tunnel. Based on the mobility tunnel, the eNB can map packets for the appropriate radio QoS bearer.
EPS SEAMLESS MOBILITY
Seamless mobility is clearly a vital consideration for wireless systems. Uninterrupted active handoff across eNBs could be the first scenario one typically considers. However, other scenarios for example handoffs across core networks (i.e., P-GW, MME), transfer of access technologies, and idle mobility can also be important scenarios covered by EPS.
SEAMLESS ACTIVE HANDOFFS
EPS enables seamless active handoffs, supporting VoIP and other real-time IP applications. As there is no RNC, an interface between eNBs is used to guide signaling for handoff preparation. In addition, the S-GW behaves being an anchor, switching mobility tunnels across eNBs. A serving eNB maintains the coupling between mobility tunnels and radio bearers, and also maintains the UE context1. As preparation for handoff, the source eNB (eNB 1) sends the coupling information along with the UE context to your target eNB (eNB 2). This signaling is triggered by the radio measurement from your UE, indicating that eNB 2 has a better signal. Once eNB 2 signals that it must be willing to perform the handoff, eNB 1 commands the UE to switch the radio bearer to eNB 2. To the eNB handoff to finish, the S-GW must update its records with the new eNB which is serving the UE. With this phase, MME coordinates the mobility-tunnel switch from eNB 1 to eNB 2. MME triggers the update on the S-GW, determined by signaling received from eNB 2 indicating the radio bearer was successfully transferred.
Visit Session Persistence or Seamless connectivity for more.