As mobile network operators and carriers transition into Long Term Evolution (LTE) technology, they are faced with the challenge of marrying a successful, running network with increased capacity demands. They must also adhere to the core network architecture of 3GPP’s LTE wireless communication standard, known as System Architecture Evolution (SAE). LTE MME lends a hand.
What is LTE MME?
The main component of the SAE architecture is the Evolved Packet Core (EPC). Mobility Management Entity (MME) plays an important role in LTE EPC architecture. In fact, MME is the main signaling node in the EPC. According to LTE University, LTE MME is responsible for initiating paging and authentication of the mobile device. MME retains location information at the tracking area level for each user and then selects the appropriate gateway during the initial registration process. MME connects to the evolved node b (eNB) through the S1-MME interface and connects to S-GW through the S11 interface. Multiple MMEs can be grouped together in a pool to meet increasing signaling load in the network. MME also plays a vital part in handover signaling between LTE and 2G/3G networks.
In whitepaper Mobility Management Entity in LTE EPC Networks, tellabs also highlights MME as the main control node in the LTE access network and breaks down MME’s critical functions and interfaces as follows:
- Network Access Control: MME manages authentication and authorization for the UE. It also facilitates UE access to the network to gain IP connectivity.
- Radio Resource Management: MME works with the HSS and the RAN to decide the appropriate radio resource management strategy (RRM) that can be UE-specific.
- Mobility Management: One of the most complex functions MME performs. Providing seamless inter-working has multiple use cases such as Inter-eNB and Inter-RAT, among others. The use cases become more complex depending on a change in MME, S-GW, P-GW or inter-working across other wireless networks.
- Roaming Management: MME supports outbound and inbound roaming subscribers from other LTE/EPC systems and legacy networks.
- UE Reach-ability: MME manages communication with the UE and HSS to provide UE reach-ability and activity-related information.
- Tracking Area Management: Allocates and reallocates a tracking area identity list to the UE.
- Lawful Intercept: Since MME manages the control plane of the network, MME can provide the whereabouts of a UE to a law enforcement monitoring facility.
- Load Balancing Between S-GWs: Directs UEs entering an S-GW pool area to an appropriate S-GW. This achieves load balancing between S-GWs.
Within the EPC protocol stack are unique, and identifiable MME protocols. This stack consists of the S1-MME stack, which supports S1-MME interface with eNodeB, and the S11 stack, responsible for supporting the S11 interface with Serving Gateway. MME supports the S1 interface with eNodeB. The integrated S1 MME interface stack consists of IP, SCTP, S1AP.
- SCTP (Stream Control Transmission Protocol)is a transport protocol that uses the services of Internet Protocol (IP) to provide a reliable datagram delivery service to the adaptation modules, such as the S1AP. SCTP provides reliable delivery on top of the existing IP framework. SCTP’s main features include:
- Association setup: An association is a connection that is set up between two endpoints for data transfer, much like a TCP connection. A SCTP association can have multiple addresses at each end.
- Reliable Data Delivery: Delivers sequenced data in a stream (Elimination of head-of-line blocking): SCTP ensures the sequenced delivery of data with multiple unidirectional streams, without blocking the chunks of data in other direction.
- S1AP (S1 Application Part) is the signaling service between E-UTRAN and the EPC that fulfills the S1 Interface functions such as SAE Bearer management functions, Initial context transfer function, Mobility functions for UE, Paging, Reset functionality, NAS signaling transport function, Error reporting, UE context release function and Status transfer.