The present document is an introduction to the 3GPP TS 37.48x series of technical specifications that define the E1 interface. The E1 interface provides means for interconnecting a gNB-CU-CP and a gNB-CU-UP of a gNB-CU within an NG-RAN, or for interconnecting a gNB-CU-CP and a gNB-CU-UP of an en-gNB within an E-UTRAN, or for interconnecting an eNB-CP and an eNB-UP of an eNB within an E-UTRAN, or for interconnecting an ng-eNB-CU-CP and an ng-eNB-CU-UP of an ng-eNB-CU within an NG-RAN.
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For the purposes of the present document, the terms and definitions given in TR 21.905 and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905.
For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905.
The error indication function is used by the gNB-CU-UP or gNB-CU-CP to indicate to the gNB-CU-CP or gNB-CU-UP that an error has occurred.
The reset function is used to initialize the peer entity after node setup and after a failure event occurred. This procedure can be used by both the gNB-CU-UP and the gNB-CU-CP.
The E1 setup function allows to exchange application level data needed for the gNB-CU-UP and gNB-CU-CP to interoperate correctly on the E1 interface. The E1 setup is initiated by both the gNB-CU-UP and gNB-CU-CP.
The gNB-CU-UP Configuration Update and gNB-CU-CP Configuration Update functions allow to update application level configuration data needed between the gNB-CU-CP and the gNB-CU-UP to interoperate correctly over the E1 interface.
The E1 setup and gNB-CU-UP Configuration Update functions allow to inform NR CGI(s), ECGI(s), S-NSSAI(s), PLMN-ID(s), QoS information and NID(s) supported by the gNB-CU-UP.
The E1 setup and gNB-CU-UP Configuration Update functions allow the gNB-CU-UP to signal its capacity information to the gNB-CU-CP.
The E1 gNB-CU-UP Status Indication function allows to inform the overloaded or non-overloaded status over the E1 interface.
The establishment of the E1 bearer context is initiated by the gNB-CU-CP and accepted or rejected by the gNB-CU-UP based on admission control criteria (e.g., resource not available).
The modification of the E1 bearer context can be initiated by either gNB-CU-CP or gNB-CU-UP. The receiving node can accept or indicate failure to carry out the modification request. The E1 bearer context management function also supports the release of the bearer context previously established in the gNB-CU-UP. The release of the bearer context is triggered by the gNB-CU-CP either directly or following a request received from the gNB-CU-UP.
This function is used to setup and modify the QoS-flow to DRB mapping configuration. The gNB-CU-CP decides flow-to-DRB mapping and provides the generated SDAP and PDCP configuration to the gNB-CU-UP. The gNB-CU-CP also decides the Reflective QoS flow to DRB mapping. The function is also used to send to the gNB-CU-UP the alternative QoS Parameters Sets when available for a QoS flow. For each PDU Session Resource to be setup or modified, the S-NSSAI, shall be provided in the E1 bearer context setup procedure and may be provided in the E1 bearer context modification procedure by gNB-CU-CP to the gNB-CU-UP.
This function is also used to setup and modify the EPS bearer/E-RAB to DRB mapping configuration for the case of eNB-CP and eNB-UP separation. The eNB-CP decides EPS bearer/E-RAB-to-DRB mapping and provides the E-UTRAN/NR PDCP configuration to the eNB-UP.
This function is used for the gNB-CU-CP to send the security information to the gNB-CU-UP.
This function is used for the gNB-CU-CP to send to the gNB-CU-UP transport layer information to be used for data forwarding e.g., during handovers.
This function is used for the gNB-CU-CP to send the parameters for header compression for certain traffic types e.g., IP, Ethernet to the gNB-CU-UP.
This function is used for the gNB-CU-CP to send the uplink data compression parameters to the gNB-CU-UP for certain data radio bearer(s).
This function is used for the gNB-CU-UP to notify the event of DL data arrival detection to the gNB-CU-CP. With this function, the gNB-CU-UP requests gNB-CU-CP to trigger paging procedure over F1 or Xn to support RRC Inactive state. RRC Inactive state is not supported when this function is used between an eNB-CP and an eNB-UP.
This function is used for the gNB-CU-UP to notify the gNB-CU-CP that a DL packet including a QFI value not configured by the gNB-CU-CP or an UL packet including a QFI value in the SDAP header of the default DRB not configured by the gNB-CU-CP is received for the first time. The gNB-CU-CP can take further action if needed.
This function is used for the gNB-CU-UP to notify the event of user inactivity to the gNB-CU-CP. With this function, the gNB-CU-UP indicates that the inactivity timer associated with a bearer, a PDU session or a UE expires, or that user data is received for the bearer, the PDU session or the UE whose inactivity timer has expired. The gNB-CU-CP consolidates all the serving gNB-CU-UPs for the UE and takes further action.
This function is used for the gNB-CU-UP to report data volume to the gNB-CU-CP.
This function is used for the gNB-CU-CP to notify the suspension and resumption of bearer contexts to the gNB-CU-UP. Suspension and resumption of bearer contexts are not applicable to eNB-CP/eNB-UP and ng-eNB-CU-CP/ng-eNB-CU-UP.
This function also allows to support CA based packet duplication as described in TS 38.300, i.e. one data radio bearer should be configured with at least two GTP-U tunnels between gNB-CU-UP and a gNB-DU.
This function is used to support the enhanced mobility operations as described in TS 38.300 in the gNB-CU-UP.
This function is used to update the DL/UL F1-U GTP-U tunnels for an IAB network, and allow the gNB-CU-CP to send the security key info to the gNB-CU-UP for the protection of the F1-U interface with IAB-DU.
The E1 bearer context management function for NR MBS consists of two sub-sets for functions, one for NR MBS broadcast, one for NR MBS multicast.
Both sets follow the principles of the E1 bearer context management functions, with the following differences:
E1 NR MBS procedure concerns a single MBS Session Resource only.
E1 NR MBS procedures concern the control of MRB resources in gNB-CU-UP.
E1 NR MBS procedures do not control security information, as for NR MBS, PDCP does not apply security as specified in TS 38.300.
QoS flow to MRB mapping is determined by the gNB-CU-CP or, in case of shared NR-U terminations, the gNB-CU-UP may be notified about the QoS flow to MRB mapping already determined in the bearer context for the shared NR-U termination. The gNB-CU-CP may inform the gNB-CU-UP whether it is contended with the already determined mapping decision.
DL data arrival detection is not applicable for NR MBS.
Data volume reporting is not applicable for NR MBS.
Suspension and resumption of bearer contexts is not applicable for NR MBS.
CA based packet duplication is not applicable for NR MBS.
The gNB-CU-UP is responsible for the allocation of the F1-U UL GTP TEID for each data radio bearer.
The gNB-CU-UP is responsible for the allocation of the S1-U DL GTP TEID for each E-RAB and the NG-U DL GTP TEID for each PDU Session.
The gNB-CU-UP is responsible for the allocation of the X2-U DL/UL GTP TEID or the Xn-U DL/UL GTP TEID for each data radio bearer.
Figure 7.1-1 shows the protocol structure for E1. The TNL is based on IP transport, comprising the SCTP on top of IP. The application layer signalling protocol is referred to as E1AP (E1 Application Protocol).