LTE S1-AP RESET Procedure

Purpose : S1 Reset procedure used is to release the E-UTRAN or Part of E-UTRAN S1AP UE related context during event of failure at MME or eNodeB side . This procedure comes under Class 1 procedures

Types of RESET

1. RESET ALL
2. RESET- Specific UE context

Behavior of eNB and MME while receiving RESET ALL

eNodeB

1. MME Shall send RESET Message with "Cause" and "RESET type = Reset-all"
2. eNB Shall releases all S1 and Uu related UE associated signalling
1. eNB may send RRC connection release message to UEs
2. In-case of Multiple UEs, eNB shall release all UEs
3. eNB does not need to wait for RESET ACK for releasing radio resources
4. eNB response with RESET ACKNOWLEDGMENT to MME.

MME

1. eNB Shall send RESET Message with "Cause" and "RESET type = Reset-all"
2. MME Shall releases all S1 and Uu related UE associated signalling
3. MME response with RESET ACKNOWLEDGMENT to MME.

Behavior of eNB and MME while receiving RESET -Specific UE context

eNodeB

1. MME Shall send RESET Message with "Cause" , "RESET type= Part of S1 interface", "MME UE S1AP ID" and  "eNB UE S1AP ID"
2. eNB Shall releases specific UE based on "MME UE S1AP ID and eNB UES1AP ID"
1. eNB shall send RRC connection release message to UE
2. Maximum no. of UE-associated logical S1-connections allowed to reset in one message. Value is 256.
3. eNB does not need to wait for RESET ACK for releasing radio resources.
4. eNB response with RESET ACKNOWLEDGMENT to MME with "MME UE S1AP ID and eNB UES1AP ID".

MME

eNB send RESET message when event of a failure at the eNB, which has resulted in the loss of some or all transaction

1. eNodeb Shall send RESET Message with "Cause" , "RESET type= Part of S1 interface", "MME UE S1AP ID" and  "eNB UE S1AP ID"
2. Maximum no. of UE-associated logical S1-connections allowed to reset in one message. Value is 256.
3. MME Shall releases S1 and Uu related UE associated signalling for specific UE.
4. MME response with RESET ACKNOWLEDGMENT to eNB with  "MME UE S1AP ID and eNB UES1AP ID" .
5. Released S1 resources and UE S1 AP id es can be used for new UE.

IE

RESET 

IE/Group Name	Presence	Value
Message Type	M	Initiating Message
Cause	M
Choice Reset Type	M
>S1 interface
>> Reset All	M
>Part of S1 interface
>> UE-associated logical S1-connection list	M
>>>UE-associated logical S1-connection Item		Range from 1 to 256
>>>> MME UE S1AP ID	O
>>>> eNB UE S1AP ID	O

RESET ACKNOWLEDGMENT

IE/Group Name	Presence	Value
Message Type	M
UE-associated logical S1-connection list	O
>UE-associated logical S1-connection Item		Range from 1 to 256
>>MME UE S1AP ID	O
>>eNB UE S1AP ID	O
Criticality Diagnostics	O

Reference

1. 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; 

Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP)