Till when the eNB-S1AP ID is stored in the MME? and till when the MME-S1AP-ID is stored in the eNB?

Question

Is it possible any scenario when sctp communication is up between mme and eNodeB but s1ap wil not be up ?
Is there need to send different alarm for s1ap failure and sctp communication failure as part of fault management . Please, suggest me required spec.

Answer 1

Both the ids are generated when UE makes radio connection with eNodeB. Once the RRC connection setup completes between UE and eNodeB i.e when UE moves from RRC-IDLE to RRC-CONNECTED state, eNodeB prepares and sends the "Initial UE message" to MME. Initial UE message carries the eNodeb UE S1AP ID identifier for an UE at the eNodeB. MME also generates an identifier for the UE named as "mme UE S1AP ID" and informs to eNodeB in Initial context setup request message.

As long as UE has radio connection with eNodeB i.e UE is in RRC-Connected mode, both the identifiers will exist and used to identify an UE over S1-C interface. When UE moves to RR-IDLE state or in other words when radio connection is released between UE and eNodeB, UE context is deleted at eNodeB. Afterwards, both the identifiers become invalid.