What is the function of S1- flex?

Hello Boy! 

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.

Thanks!

Hello, dear.
With S1-flex, an eNodeB in the LTE/SAE network sets up an S1-MME connection with each MME in an MME pool. When a UE accesses the network through the eNodeB, the eNodeB selects an MME from the pool for the UE and sets up a dedicated S1-MME connection with the MME.