3-2 - s1ap
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eRAN2.2S1AP
Issue01
Date2011-09-30
DOCPROPERTY Confidential
HUAWEI TECHNOLOGIES CO., LTD.
Copyright Huawei Technologies Co., Ltd. 2011. All rights reserved.
No part of this document may be reproduced or transmitted in any form or by any means without prior written consent of Huawei Technologies Co., Ltd.
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Huawei Technologies Co., Ltd.
Address:Huawei Industrial Base
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About This Document
Change HistoryThe change history describes the changes in each release, and the latest document contains all change histories in earlier documents.
Issue 01 (2011-09-30)
First official release. Contents
iiiAbout This Document
11 Overview
11.1 S1 User Plane
21.2 S1 Control Plane
62 E-RAB Management
62.1 E-RAB Setup
62.2 E-RAB Modify
72.3 E-RAB Release
83 Context Management
83.1 Initial Context Setup
93.2 UE Context Release
103.3 UE Context Modification
114 Handover Signaling
114.1 Handover Preparation
124.2 Handover Resource Allocation
134.3 Handover Notification
134.4 Path Switch Request
144.5 Handover Cancelation
144.6 eNodeB Status Transfer
154.7 MME Status Transfer
165 Paging
176 NAS Transport
176.1 Initial UE Message
186.2 Downlink NAS Transport
186.3 Uplink NAS Transport
196.4 NAS Non Delivery Indication
207 Management Procedures
207.1 Reset
217.2 Error Indication
227.3 S1 Setup
227.4 eNodeB Configuration Update
237.5 MME Configuration Update
247.6 Overload Start
247.7 Overload Stop
258 UE Capability Information Indication
269 eNodeB Direct Information Transfer
2710 MME Direct Information Transfer
2811 eNodeB Configuration Transfer
2912 MME Configuration Transfer
1 Overview
The S1 interface connects the eNodeB and the mobility management entity (MME) or serving gateway (S-GW) and has two planes: user plane and control plane.
1.1 S1 User Plane
The S1 interface transmits data between the eNodeB and the S-GW. The S1 user plane transmits data at the transport network layer based on the Internet Protocol (IP).
Figure 1-1 S1 user plane
1.2 S1 Control Plane
Figure 1-2 S1 control plane
The S1 control plane transmits data based on the IP and Stream Control Transmission Protocol (SCTP) to provide reliable data transmission for radio networks.
The S1 Application Protocol (S1AP) transmits signaling between the evolved packet core (EPC) and the evolved universal terrestrial radio access network (E-UTRAN) to provide S1AP services. The S1AP has the following functions:
E-UTRAN radio access bearer (E-RAB) management. This function is used to establish, modify, and release an E-RAB.
Initial context transfer. This function is used to establish S1 user equipment (UE) contexts on an eNodeB, to establish one or more E-RABs if requested by an MME, and to transfer information about non-access stratum (NAS) signaling to the eNodeB.
UE capability information indication.
UE mobility management in LTE_ACTIVE mode, including intra-LTE handovers and inter-RAT handovers.
Paging. This function enables the EPC to page UEs.
S1 interface management. For example, error indication and S1 setup.
NAS signaling transfer between the UE and the MME.
S1 UE context release.
UE context modification.
Status transfer.
Tracing
Location reporting.
LPPa signaling transfer.
S1AP has two classes of basic procedures, as shown in Table 1-1 and Table 1-2.
Table 1-1 Class 1 procedures
Elementary ProcedureInitiating MessageSuccessful OutcomeUnsuccessful Outcome
Response MessageResponse Message
Handover PreparationHANDOVER REQUIREDHANDOVER COMMANDHANDOVER PREPARATION FAILURE
Handover Resource AllocationHANDOVER REQUESTHANDOVER REQUEST ACKNOWLEDGEHANDOVER FAILURE
Path Switch RequestPATH SWITCH REQUESTPATH SWITCH REQUEST ACKNOWLEDGEPATH SWITCH REQUEST FAILURE
Handover CancelationHANDOVER CANCELHANDOVER CANCEL ACKNOWLEDGE
E-RAB SetupE-RAB SETUP REQUESTE-RAB SETUP RESPONSE
E-RAB ModifyE-RAB MODIFY REQUESTE-RAB MODIFY RESPONSE
E-RAB ReleaseE-RAB RELEASE COMMANDE-RAB RELEASE RESPONSE
Initial Context SetupINITIAL CONTEXT SETUP REQUESTINITIAL CONTEXT SETUP RESPONSEINITIAL CONTEXT SETUP FAILURE
ResetRESETRESET ACKNOWLEDGE
S1 SetupS1 SETUP REQUESTS1 SETUP RESPONSES1 SETUP FAILURE
UE Context ReleaseUE CONTEXT RELEASE COMMANDUE CONTEXT RELEASE COMPLETE
UE Context ModificationUE CONTEXT MODIFICATION REQUESTUE CONTEXT MODIFICATION RESPONSEUE CONTEXT MODIFICATION FAILURE
eNB Configuration UpdateENB CONFIGURATION UPDATEENB CONFIGURATION UPDATE ACKNOWLEDGEENB CONFIGURATION UPDATE FAILURE
MME Configuration UpdateMME CONFIGURATION UPDATEMME CONFIGURAION UPDATE ACKNOWLEDGEMME CONFIGURATION UPDATE FAILURE
Write-Replace Warning WRITE-REPLACE WARNING REQUESTWRITE-REPLACE WARNING RESPONSE
KillKILL REQUESTKILL RESPONSE
Table 1-2 Class 2 procedures
Elementary ProcedureMessage
Handover NotificationHANDOVER NOTIFY
E-RAB Release IndicationE-RAB RELEASE INDICATION
PagingPAGING
Initial UE MessageINITIAL UE MESSAGE
Downlink NAS TransportDOWNLINK NAS TRANSPORT
Uplink NAS TransportUPLINK NAS TRANSPORT
NAS non delivery indicationNAS NON DELIVERY INDICATION
Error IndicationERROR INDICATION
UE Context Release RequestUE CONTEXT RELEASE REQUEST
DownlinkS1 CDMA2000 TunnelingDOWNLINK S1 CDMA2000 TUNNELING
Uplink S1 CDMA2000 TunnelingUPLINK S1 CDMA2000 TUNNELING
UE Capability Info IndicationUE CAPABILITY INFO INDICATION
eNB Status TransfereNB STATUS TRANSFER
MME Status TransferMME STATUS TRANSFER
Deactivate TraceDEACTIVATE TRACE
Trace StartTRACE START
Trace Failure IndicationTRACE FAILURE INDICATION
Location Reporting ControlLOCATION REPORTING CONTROL
Location Reporting Failure IndicationLOCATION REPORTING FAILURE INDICATION
Location ReportLOCATION REPORT
Overload StartOVERLOAD START
Overload StopOVERLOAD STOP
eNodeB Direct Information TransfereNB DIRECT INFORMATION TRANSFER
MME Direct Information TransferMME DIRECT INFORMATION TRANSFER
eNodeB Configuration TransfereNB CONFIGURATION TRANSFER
MME Configuration TransferMME CONFIGURATION TRANSFER
Cell Traffic TraceCELL TRAFFIC TRACE
Downlink UE Associated LPPa TransportDOWNLINK UE ASSOCIATED LPPA TRANSPORT
Uplink UE Associated LPPa TransportUPLINK UE ASSOCIATED LPPA TRANSPORT
Downlink Non UE Associated LPPa TransportDOWNLINK NON UE ASSOCIATED LPPA TRANSPORT
Uplink Non UE Associated LPPa TransportUPLINK NON UE ASSOCIATED LPPA TRANSPORT
2 E-RAB Management
2.1 E-RAB Setup
The purpose of this procedure is to allocate resources to the Uu and the S1 interfaces for one or more E-RABs and to set up data radio bearers (DRBs) for a specific UE.
Figure 2-3 E-RAB Setup procedure (successful operation)
The MME sends an E-RAB SETUP REQUEST message to initiate the procedure. After receiving the message, the eNodeB sends the MME an E-RAB SETUP REQUEST message if the required resources are available.
If the E-RAB SETUP REQUEST message contains the UE Aggregate Maximum Bit Rate information element (IE), the eNodeB replaces the UE Aggregate Maximum Bit Rate IE with the UE Aggregate Maximum Bit Rate IE. If the E-RAB SETUP REQUEST message does not contain the UE Aggregate Maximum Bit Rate IE, the eNodeB uses the UE Aggregate Maximum Bit Rate IE in the UE context. Resources are set up or modified on an eNodeB based on the Allocation and Retention Priority IE.
2.2 E-RAB Modify
The purpose of this procedure is to modify an E-RAB configured for UEs.
Figure 2-4 E-RAB Modify procedure (successful operation)
The MME sends an E-RAB SETUP REQUEST message to initiate the procedure. An E-RAB MODIFY REQUEST message contains information about one or more configured E-RABs.
2.3 E-RAB Release
The purpose of this procedure is to release a configured E-RAB in either of the following modes:
MME-initiated E-RAB release
Figure 2-5 MME-initiated E-RAB Release procedure (successful operation)
eNodeB-initiated E-RAB release
Figure 2-6 eNodeB-initiated E-RAB Release procedure (successful operation)
3 Context Management
3.1 Initial Context Setup
The purpose of this procedure is to set up mandatory UE contexts, including the E-RAB context, security key, and handover restriction list.
Figure 3-7 Initial Context Setup procedure (successful operation)
The EPC must get ready for receiving user-plane data on an E-RAB before the MME receives a CONTEXT SETUP RESPONSE message from an eNodeB.
The eNodeB must perform the following operations after receiving an INITIAL CONTEXT SETUP REQUEST message:
2. Attempts to execute the requested E-RAB configuration.
3. Saves the UE Aggregate Maximum Bit Rate IE in the UE context and uses the received UE Aggregate Maximum Bit Rate IE.
4. Saves the handover restriction list in the UE context.
5. Saves the UE capability in the UE context.
If the eNodeB cannot set up the UE context, it sends an INITIAL CONTEXT SETUP FAILURE message to the MME.
Figure 3-8 Initial Context Setup procedure (unsuccessful operation)
3.2 UE Context Release
The UE context can be released in either of the following modes:
eNodeB-initiated UE context release
A UE CONTEXT RELEASE REQUEST message contains the reasons why UEs are not in the active state and why UEs exit the wireless network.
MME-initiated UE Context Release procedure
The MME sends the eNodeB a UE CONTEXT RELEASE COMMAND message to initiate the procedure. The UE CONTEXT RELEASE COMMAND message contains the UE S1AP ID pair IE. If the message does not contain the IE, it must contain the MME UE S1AP ID IE. After receiving the UE CONTEXT RELEASE COMMAND message, the eNodeB releases all related resources for the IEs and user-plane data transmission and responds to the MME with a UE CONTEXT RELEASE COMPLETE message.
3.3 UE Context Modification
This purpose of this procedure is to modify the configured UE context.
Figure 3-9 UE Context Modification procedure (successful operation)
A UE CONTEXT MODIFICATION REQUEST message contains the following IEs:
Security Key
Subscriber Profile ID for RAT/Frequency Priority
UE Aggregate Maximum Bit Rate
CS Fallback Indicator
UE Security Capabilities
CSG Membership Status
Registered LAI
Figure 3-10 UE Context Modification procedure (unsuccessful operation)
If UE context modification fails, the eNodeB responds to the MME with a UE CONTEXT MODIFICATION FAILURE message that contains the Cause IE.
4 Handover Signaling
4.1 Handover Preparation
The purpose of this procedure is to enable the EPC to instruct a target eNodeB to prepare all resources before a handover is performed. Each UE has only one handover preparation process at the same time.
Figure 4-11 Handover Preparation procedure (successful operation)
The source eNodeB sends the MME a HANDOVER REQUIRED message to initiate the procedure. When the source eNodeB sends the message, it starts the TS1RELOCprep timer. After the handover preparation, including resource subscription on the target eNodeB, the MME responds to the source eNodeB a HANDOVER COMMAND message. After receiving the HANDOVER COMMAND message, the source eNodeB stops the TS1RELOCprep timer and starts the TS1RELOCOverall timer.
If the EPC or the target eNodeB cannot accept any bearers or the handover fails, the MME sends the source eNodeB a HANDOVER PREPARATION FAILURE message that contains the reason why the failure occurs.
Figure 4-12 Handover Preparation procedure (unsuccessful operation)
4.2 Handover Resource Allocation
The purpose of this procedure is to reserve resources at the target eNodeB for a UE to be handed over.
Figure 4-13 Hanover Resource Allocation procedure (successful operation)
The MME sends the target eNodeB a HANDOVER REQUEST message to initiate the procedure. After receiving the HANDOVER REQUEST message, the target eNodeB saves the UE Security Capabilities IE and uses the configuration of the IE and related UE access stratum (AS) to encrypt data.
Figure 4-14 Hanover Resource Allocation procedure (unsuccessful operation)
4.3 Handover Notification
The purpose of this procedure is to inform the MME, UE, and target cell of a successful S1 handover.
Figure 4-15 Handover Notification procedure
4.4 Path Switch Request
The purpose of this procedure is to request the switch of a downlink GPRS tunneling protocol (GTP) tunnel towards a new GTP tunnel. GPRS is short for general packet radio service. Figure 4-16 Path Switch Request procedure (successful operation)
An eNodeB sends to the MME a PATH SWITCH REQUEST message to initiate the procedure.
Figure 4-17 Path Switch Request procedure (unsuccessful operation)
If the handover fails on the EPC, the MME responds to the eNodeB with a PATH SWITCH REQUEST FAILURE message that contains the reason why the failure occurs.
4.5 Handover Cancelation
The purpose of this procedure is to enable a source eNodeB to cancel ongoing handover preparations or a prepared handover.
Figure 4-18 Handover Cancelation procedure (successful operation)
The source eNodeB sends the MME a HANDOVER CANCEL message to initiate the procedure. A HANDOVER CANCEL message contains the Cause IE. After receiving the HANDOVER CANCEL message, the EPC stops the ongoing process, releases resources for a handover, and sends the source eNodeB a HANDOVER CANCEL ACKNOWLEDGE message.
4.6 eNodeB Status Transfer
In this procedure, two types of status are transmitted: the receiving status of uplink Packet Data Convergence Protocol-sequence number (PDCP-SN) and hyper frame number (HFN) and the transmitting status of downlink PDCP-SN and HFN.
Figure 4-19 eNodeB Status Transfer procedure
4.7 MME Status Transfer
Figure 4-20 MME Status Transfer procedure
5 Paging
The purpose of this procedure is to enable the MME to page UEs.
Figure 5-21 Paging procedure
6 NAS Transport
The purpose of this procedure is to carry UEMME signaling over the S1 interface. The NAS messages are transported in an IE of the INITIAL UE MESSAGE, DOWNLINK NAS TRANSPORT, or UPLINK NAS TRANSPORT message.
6.1 Initial UE Message
Figure 6-22 Initial UE Message procedure
After receiving the first UL NAS message transmitted on a radio resource control (RRC) connection to be forwarded to an MME, the eNodeB must activate the NAS transport procedure and send the MME an INITIAL UE MESSAGE message.
6.2 Downlink NAS Transport
Figure 6-23 Downlink NAS Transport procedure
The MME sends a UE an NAS message through the eNodeB.
6.3 Uplink NAS Transport
Figure 6-24 Uplink NAS Transport procedure
6.4 NAS Non Delivery Indication
Figure 6-25 NAs Non Delivery Indication procedure
If an eNodeB decides not to start the delivery of a NAS message or the eNodeB cannot ensure that a UE receives the message, the eNodeB reports the non-delivery of this NAS message by sending the MME an NAS NON DELIVERY INDICATION message.
7 Management Procedures
7.1 Reset
The reset procedure can be initiated by either the MME or the E-UTRAN.
MME-initiated reset procedure:
Figure 7-26 MME-initiated Reset procedure (successful operation)
If the MME loses some or all transaction reference information, it sends the eNodeB a RESET message. After receiving the RESET message, the eNodeB releases all allocated resources over the S1 interface and Uu interface related to UEs. Then, the eNodeB responds to the MME with a RESET ACKNOWLEDGE message.
E-UTRAN-initiated reset procedure:
Figure 7-27 E-UTRAN-initiated Reset procedure (successful operation)
If the eNodeB loses some or all transaction reference information, it sends the MME a RESET message. After receiving the RESET message, the MME releases all allocated resources over the S1 interface related to UEs. Then, the MME responds to the eNodeB with a RESET ACKNOWLEDGE message.
7.2 Error Indication
The purpose of this procedure is to report detected errors in one incoming message at one node. This procedure can be initiated either by the MME or by an eNodeB.
Figure 7-28 MME-initiated Error Indication procedure (successful operation)
Figure 7-29 eNodeB-initiated Error Indication procedure (successful operation)
An ERROR INDICATION message must contain a minimum of one Cause IE or Criticality Diagnostics IE.
7.3 S1 Setup
Figure 7-30 S1 Setup procedure (successful operation)
The eNodeB sends the MME an S1 SETUP REQUEST message to initiate the procedure. Then, the MME responds to the eNodeB with an S1 SETUP RESPONSE message. When this procedure is finished, the S1 interface is operational and other S1 messages can be exchanged.
Figure 7-31 S1 Setup procedure (unsuccessful operation)
If the MME cannot accept the setup, it responds to the eNodeB with an S1 SETUP FAILURE message.
7.4 eNodeB Configuration Update
The purpose of this procedure is to update configuration data at the application layer over the S1 interface.
Figure 7-32 eNodeB Configuration Update procedure (successful operation)
An eNodeB sends the MME an ENB CONFIGURATION UPDATE message including a set of updated configuration data. If the MME successfully updates the configuration data, it sends the eNodeB an ENB CONFIGURATION UPDATE ACKNOWLEDGE message. If the MME cannot update the configuration data, it responds to the eNodeB with an ENB CONFIGURATION UPDATE FAILURE message.
Figure 7-33 eNodeB Configuration Update procedure (unsuccessful operation)
7.5 MME Configuration Update
The purpose of this procedure is to update configuration data at the application layer over the S1 interface.Figure 7-34 MME Configuration Update procedure (successful operation)
The MME sends an eNodeB an MME CONFIGURATION UPDATE message including a set of updated configuration data. If the eNodeB successfully updates the configuration data, it sends the MME an MME CONFIGURATION UPDATE ACKNOWLEDGE message. If the eNodeB cannot update the configuration data, it responds to the MME with an MME CONFIGURATION UPDATE FAILURE message.
7.6 Overload Start
The purpose of this procedure is to inform an eNodeB to reduce the signaling load towards the connected MME.
Figure 7-35 Overload Start procedure
7.7 Overload Stop
The purpose of this procedure is to inform an eNodeB that the overload status at the MME has ended and normal operation resumes.
Figure 7-36 Overload Stop procedure
8 UE Capability Information Indication
The purpose of this procedure is to enable an eNodeB to provide UE capability information for the MME.
Figure 8-37 UE Capability Information Indication procedure (successful operation)
An eNodeB sends the MME a UE CAPABILITY INFO INDICATION message to provide UE capability information for the MME. After obtaining UE capability information in the received message, the MME replaces any previously stored UE capability information for UEs.
9 eNodeB Direct Information Transfer
The purpose of this procedure is to transfer RAN information from an eNodeB to the MME in unacknowledged mode.
Figure 9-38 eNodeB Direct Information Transfer procedure (successful operation)
10 MME Direct Information Transfer
The MME sends an eNodeB a DIRECT INFORMATION TRANSFER message to initiate the procedure.
Figure 10-39 MME Direct Information Transfer procedure (successful operation)
11 eNodeB Configuration Transfer
The purpose of this procedure is to transfer RAN configuration information from an eNodeB to the MME in unacknowledged mode.
Figure 11-40 eNodeB Configuration Transfer procedure (successful operation)
12 MME Configuration Transfer
The purpose of this procedure is to transfer RAN configuration information from the MME to an eNodeB in unacknowledged mode.
Figure 12-41 MME Configuration Transfer procedure (successful operation)
ivHuawei Proprietary and Confidential Copyright Huawei Technologies Co., LtdIssue 01 (2009-04-10)
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HANDOVER FAILURE
target eNB
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HANDOVER REQUEST
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INITIAL UE MESSAGE
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S1 SETUP RESPONSE
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OVERLOAD STOP
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ENB CONFIGURATION UPDATE ACKNOWLEDGE
eNB
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ENB CONFIGURATION UPDATE
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ENB CONFIGURATION UPDATE
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NAS NON DELIVERY INDICATION
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DOWNLINK NAS TRANSPORT
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HANDOVER CANCELACKNOWLEDGE
HANDOVER CANCEL
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IP
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MME
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UDP
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