LTE - S1-Flex Mechanism Study

LTE - S1-Flex Mechanism Study

The NGMN Backhaul solution MUST allow connecting each e-NB to one or several aGW’s (i.e. S1 interface in 3GPP LTE standard) for multi-homing purpose (e.g. S1-flex in 3GPP LTE standard) or multioperator RAN Sharing reason. S1 transport connection set up (with or without IPSec) potentially with S1-Flex and multi-operator RAN Sharing.

The S1-flex concept provides support for network redundancy and load sharing of traffic across network elements in the CN (the MME and the SGW) by creating pools of MMEs and SGWs and allowing each eNB to be connected to multiple MMEs and SGWs in a pool. In S1-Flex configuration, each eNB is connected to all EPC nodes within a pool area.

S1-flex mechanism by enabling each eNB to be connected to multiple CN entities.

The support of Network Sharing is based on support for multi-to-multi relationship between nodes in E-UTRAN and MME/UPEs (S1-flex). Network Sharing in SAE/LTE based on S1-flex configuration
- allowing each eNB to be connected to multiple MMEs and SGWs in a pool
- multi-operator RAN Sharing










S1-Flex Deployment Scenarios: Redundancy and Flexiblity with no single point of failure

Support for Network Redundancy and Load Sharing of MME / UPEs in SAE / LTE is achieved by making the S1 interface a multi-to-multi interface, where one node in E-UTRAN can be connected to multiple MME / UPEs for different terminals.

The following assumptions are taken regarding the S1-flex configuration:
1. There is a multi-to-multi relationship between the E-UTRAN and MME / UPEs in SAE / LTE, meaning one node in eUTRAN can communicate with different MME / UPEs and vice versa.
2. One terminal can only be assigned to one MME at a time.
3. The MME / UPE will be assigned to the terminal during attach to the network, and it is FFS whether the MME / UPE will be unchanged until the terminal leaves the serving area of that MME / UPE.

- When S1-flex is used, the eNodeB may receive duplicated Warning messages. Duplicated messages on eNB can be detected by checking the message identifier and serial number fields and they shall not be transmitted on the radio interface.
- HeNB shall only connect to a single HeNB GW at one time, namely no S1 Flex function shall be used at the HeNB in case of connection to the HeNB GW

FFS - The problem of S1-flex without administrative scope (as UPE would have to be able to serve every eNB in the PLMN

Detailed refers to https://docs.google.com/fileview?id=F.165f9eaa-5220-4c80-88b9-90c7343a5600&hl=en