MOBILITY MANAGEMENT ENTITY (MME)
The MME is really a signaling-only entity, thus user IP packets usually do not glance at the MME. Its main function would be to manage the UE's mobility. Additionally, the MME also performs authentication and authorization; idle-mode UE tracking and reachability; security negotiations; and NAS signaling. An advantage of any separate network element for signaling is that operators can grow signaling and traffic capacity independently. The same benefit can also be accomplished in HSPA Release 7's direct-tunnel architecture, the spot that the SGSN becomes a signaling-only entity.
EFFICIENT QoS
A significant aspect for any all-packet network can be a mechanism to ensure differentiation of packet flows determined by its QoS requirements. Applications such as video streaming, HTTP, or video telephony have special QoS needs, and should receive differentiated service in the network. With EPS, QoS flows called EPS bearers have established yourself between the UE and the P-GW. Each EPS bearer is associated with a QoS profile, which is composed of a radio bearer and a mobility tunnel. Thus, each QoS IP flow (e.g., VoIP) will be of the different EPS bearer, as well as the network can prioritize packets accordingly. The QoS process of packets arriving from the web is similar to those of HSPA. When receiving an IP packet, the P-GW performs packet classification based on parameters including rules received through the PCRF, and sends it from the proper mobility tunnel. In line with the mobility tunnel, the eNB can map packets to the appropriate radio QoS bearer.
EPS SEAMLESS MOBILITY
Seamless mobility is clearly an essential consideration for wireless systems. Uninterrupted active handoff across eNBs may be the first scenario one typically considers. However, other scenarios for instance handoffs across core networks (i.e., P-GW, MME), transfer of access technologies, and idle mobility are also important scenarios paid by EPS.
SEAMLESS ACTIVE HANDOFFS
EPS enables seamless active handoffs, supporting VoIP and also other real-time IP applications. Since there is no RNC, an interface between eNBs is employed to compliment signaling for handoff preparation. In addition, the S-GW behaves as an anchor, switching mobility tunnels across eNBs. A serving eNB maintains the coupling between mobility tunnels and radio bearers, as well as maintains the UE context1. As preparation for handoff, the original source eNB (eNB 1) sends the coupling information as well as the UE context for the target eNB (eNB 2). This signaling is triggered by a radio measurement from the UE, indicating that eNB 2 has a better signal. Once eNB 2 signals that it's willing to perform the handoff, eNB 1 commands the UE to alter the radio bearer to eNB 2. For the eNB handoff to complete, the S-GW must update its records together with the new eNB that is serving the UE. For this phase, MME coordinates the mobility-tunnel switch from eNB 1 to eNB 2. MME triggers the update at the S-GW, determined by signaling received from eNB 2 indicating how the radio bearer was successfully transferred.
Visit Session Persistence or Seamless connectivity for more.