INTRODUCTION
The ERAB is a bearer connection between eNB and Serving GW. The MME initiates E-RAB setup, modification, and release procedures, and it also can request eNB to modify E-RAB QoS characteristics. The eNB support all those procedures according to 3GPP TS36.413.
Once eNB and MME setup an E-RAB connection, eNB and S- GW can transmit user packets unlink and downlink through GTP tunnel. They distinguish each E-RAB bearer by Tunnel Endpoint Identifier (TEID).
BENEFIT
The operator can provide EPS bearer service to its subscribers and manage E-RAB resources for user data transport.
DEPENDENCY AND LIMITATION
N/A
FEATURE DESCRIPTION
E-RAB Setup
The E-RAB setup procedure is used to add an E-RAB for a new service to a connected UE. The E-RAB for a new service can be added to the connected UE through E-RAB setup procedure. When receiving the E-RAB Setup Request message from MME, the eNB considers the current resource usage status and determines whether a new bearer can be added. If a new E-RAB can be added, eNB performs the RRC Connection Reconfiguration procedure with UE for resource reconfiguration of the new DRB and transmits the E-RAB Setup Response message to MME.
Each E-RAB will have the following information:
E-RAB ID
The Transport Layer IP Address on the eNB
The eNB GTP Tunneling ID (TEID) for the eNB side.
1 The P-GW transmits the Create Bearer request to S-GW to add the new E-RAB.
2 The S-GW transmits the Create Bearer request to add the new E-RAB.
3 The MME transmit the E-RAB Setup request to start the E-RAB setup procedure.
QoS information of the E-RAB(s) to be added, the NAS message to be sent to UE, and ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST are included in the E-RAB Setup request.
4 When receiving the E-RAB Setup request from MME, the eNB determines whether a new E-RAB(s) can be added. If possible, eNB reallocates internal resources and transmits RRC Connection Reconfiguration to UE.
5 The UE adds the new DRB(s) specified by RRC Connection Reconfiguration and replies to eNB with RRC Connection Reconfiguration Complete.
6 The eNB responds to MME with the E-RAB Setup response. Setup success/failure results for each E-RAB are included in the E-RAB Setup response.
7 The UE transmits the NAS message and ACTIVATE DEDICATED EPS BEARER CONTEXT RESPONSE.
8 The eNB transmits the NAS received from UE to MME.
9 The MME transmits the Create Bearer response to S-GW.
10 The S-GW transmits the Create Bearer response to P-GW.
E-RAB Modification
Use the E-RAB modification procedure to change the QoS setting of a bearer (E-RAB) already in service. To use the E-RAB modification procedure, operator can change UE AMBR for non-GBR bearer and E-RAB Level QoS parameters (QCI, ARP and GBR QoS Information) for GBR bearer.
The E-RAB modification procedure is as follows:
1 The P-GW transmits Update Bearer Request to S-GW to change QoS setting.
2 The S-GW transmits Update Bearer Request to MME to change QoS setting.
3 The MME starts the E-RAB modification procedure by transmitting E-RAB Modify Request to eNB. The E-RAB Modify Request has the QoS information of E-RAB(s) to change, NAS message to send to UE, and MODIFY EPS BEARER CONTEXT REQUEST.
4 When eNB receives E-RAB Modify Request from MME, it selects if it is
6 The eNB replies E-RAB Modify Response to MME. The E-RAB Modify Response has the success or failure of QoS setting change per E-RAB.
7 The UE transmits NAS message, MODIFY EPS BEARER CONTEXT RESPONSE.
8 The eNB transmits the NAS message received from UE to MME.
9 The MME transmits Update Bearer Response to S-GW.
10 The S-GW transmits Update Bearer Response to P-GW.
E-RAB Release
The E-RAB release procedure is used to release specific bearer service of a connected UE. This procedure is performed by request from MME. Also, MME requests E-RAB release based on its own decision (MME initiated E-RAB release) or as following action after an indication from eNB (eNB initiated E-RAB release).
When E-RAB RELEASE REQUEST message is received from MME, eNB performs RRC connection reconfiguration procedure with UE to release the corresponding DRB (data radio bearer). When the DRB is released successfully, eNB returns E-RAB RELEASE RESPONSE message to MME.
The E-RAB release procedure is as follows:
If eNB initiated E-RAB release procedure, eNB transmits the E-RAB Release indication to MME to notify the release of a specific E-RAB. The MME transmits the Delete Bearer command to S-GW for E-RAB release.
1 The S-GW transmits the Delete Bearer command for E-RAB release. The P-GW transmits the Delete Bearer request to S-GW for E-RAB release.
2 The S-GW transmits the Delete Bearer request to MME for E-RAB release.
3 The MME initiates the E-RAB release procedure by transmitting the E-RAB Release command. ID(s) of the E-RAB(s) to be released, the NAS message to be sent to UE and DEACTIVATE EPS BEARER CONTEXT REQUEST are included in the E-RAB Release command.
4 When receiving the E-RAB Release command from MME, eNB transmits RRC Connection Reconfiguration to UE.
5 The UE releases the DRB(s) specified by RRC Connection Reconfiguration and then replies to eNB with RRC Connection Reconfiguration Complete.
6 The eNB responds to MME with the E-RAB Release response.
7 The UE transmits the NAS message and DEACTIVATE EPS BEARER CONTEXT RESPONSE.
8 The eNB transmits the NAS received from UE to MME.
9 The MME transmits the Delete Bearer response to S-GW.
10 The S-GW transmits the Delete Bearer response to P-GW.
SYSTEM OPERATION
How to Activate
In case of standard QCI E-RABs, there is no additional activation procedure required but to activate operator specific QCIs, execute the CHG-QCI-VAL command to equip new QCIs to be used.
Key Parameters
QCIs can be configured by executing the CHG-QCI-VAL command with following parameters:
Parameter Description
QCI QoS Class Identifier (QCI) index. The range is from 0 to 255. The QCI defined in the standard is 1 to 9.
The user can use QCI values 0 and 10-255.
Counters and KPI
Family Display Name
Type Name Type Description
ERAB_ESTAB_A DD
EstabAddAttNbr ERAB SETUP REQUEST count EstabAddSuccNbr ERAB SETUP RESPONSE count ErabAddFailNbr_CP_CC_
TO
E-RAB setup fails due to call control timeout in the protocol blocks (MAC, RLC, PDCP, GTP)
ErabAddFailNbr_CP_CC_
FAIL
E-RAB setup fails due to reset notification (eNB failure or block restart) from ECMB or by the ECCB block
ErabAddFailNbr_UP_GTP _FAIL
E-RAB setup fails due to the failure in the GTP block
ErabAddFailNbr_UP_MAC _FAIL
E-RAB setup fails due to the failure in the MAC block
ErabAddFailNbr_UP_PDC P_FAIL
E-RAB setup fails due to the failure in the PDCP block ErabAddFailNbr_UP_RLC
_FAIL
E-RAB setup fails due to the failure in the RLC block
ErabAddFailNbr_RRC_SI G_FAIL
E-RAB setup fails due to receiving RRC signaling
ErabAddFailNbr_RRC_SI G_TO
E-RAB setup fails due to RRC signaling timeout (not received)
ErabAddFailNbr_CP_BH_
CAC_FAIL
E-RAB setup fails due to Backhaul QoS based CAC
ErabAddFailNbr_CP_CAP A_CAC_FAIL
E-RAB setup fails due to Capacity based CAC ErabAddFailNbr_CP_QOS
_CAC_FAIL
E-RAB setup fails due to Air QoS based CAC
ErabAddFailNbr_S1AP_C U_FAIL
E-RAB setup fails due to the S1AP specification cause
ErabAddFailNbr_S1AP_LI NK_FAIL
E-RAB setup fails due to the S1 SCTP link failure
ErabAddFailNbr_S1AP_SI G_FAIL
E-RAB setup fails due to receiving S1AP signaling
ErabAddFailNbr_CP_CC_I NTERACTION
E-RAB setup fails due to ongoing inter-eNB handover ERAB_REL_
ENB
RelAttbyEnbNbr_CP_CC_
TO
eNB initiated E-RAB Release fails due to call control timeout in the protocol blocks (MAC, RLC, PDCP, GTP) RelAttbyEnbNbr_S1AP_C
U_FAIL
eNB initiated E-RAB Release fails due to the S1AP specification cause
ERAB_REL RelAttNbr ERAB RELEASE COMMAND count
RelSuccNbr ERAB RELEASE RESPONSE count
RelFailNbr_CP_CC_FAIL MME initiated E-RAB Release fails due to reset notification (eNB failure or block restart) from ECMB or by the ECCB block
RelFailNbr_S1AP_SIG_FA IL
MME initiated E-RAB Release fails due to receiving S1AP signaling
RelFailNbr_S1AP_CU_FAI L
MME initiated E-RAB Release fails due to the S1AP specification cause
RelActive Number of active E-RABs abnormally released by eNB
Family Display Name
Type Name Type Description
RelFailNbr_CP_CC_INTE RACTION
MME initiated E-RAB Release fails due to ongoing inter-eNB handover
ERAB_NUM UsageNbr Average number of E-RABs during a time period UsageNbrMax Maximum number of E-RABs during a time period
REFERENCE
[1] 3GPP TS36.300 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2
[2] 3GPP TS36.331 Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification
[3] 3GPP TS36. 413 Evolved Universal Terrestrial Access Network (E-UTRAN);
S1 Application Protocol (S1AP)