diff --git a/doc/E1-design.md b/doc/E1AP/E1-design.md similarity index 97% rename from doc/E1-design.md rename to doc/E1AP/E1-design.md index 6939e3867e3d0d722b712ace237f51f24152d530..eb7e373e7b616a2f5df909d4818bc8c25358e9cb 100644 --- a/doc/E1-design.md +++ b/doc/E1AP/E1-design.md @@ -75,11 +75,11 @@ sequenceDiagram Note over u: E1AP_CUUP_task (SCTP Handler) Note over u: ASN1 decoder ``` - +More details about the E1AP procedures in OAI are available in this document: [E1 Procedures](./e1ap_procedures.md). # 2. Running the E1 Split -The setup is assuming that all modules are running on the same machine. The user can refer to the [F1 design document](./F1-design.md) for local deployment of the DU. +The setup is assuming that all modules are running on the same machine. The user can refer to the [F1 design document](./../F1-design.md) for local deployment of the DU. ## 2.1 Configuration File diff --git a/doc/E1AP/e1ap_procedures.md b/doc/E1AP/e1ap_procedures.md new file mode 100644 index 0000000000000000000000000000000000000000..c46c7103338aedcb8204977dda8c1d157f5e3b2d --- /dev/null +++ b/doc/E1AP/e1ap_procedures.md @@ -0,0 +1,74 @@ +<table style="border-collapse: collapse; border: none;"> + <tr style="border-collapse: collapse; border: none;"> + <td style="border-collapse: collapse; border: none;"> + <a href="http://www.openairinterface.org/"> + <img src="./images/oai_final_logo.png" alt="" border=3 height=50 width=150> + </img> + </a> + </td> + <td style="border-collapse: collapse; border: none; vertical-align: center;"> + <b><font size = "5">E1AP Procedures</font></b> + </td> + </tr> +</table> + +[[_TOC_]] + +# Introduction +The E1 interface is between the gNB-CU-CP (Central Unit - Control Plane) and gNB-CU-UP (Central Unit - User Plane) nodes. This interface is governed by the E1 Application Protocol (E1AP) outlined in the 3GPP release 16 specifications, specifically in the documents: +* 3GPP TS 38.463 - E1 Application Protocol (E1AP) +* 3GPP TS 38.460 - E1 general aspects and principles +* 3GPP TS 38.461 - E1 interface: layer 1 +* 3GPP TS 38.462 - E1 interface: signaling transport + +The E1AP protocol consists of the following sets of functions: +* E1 Interface Management functions +* E1 Bearer Context Management functions +* TEID allocation function + +## E1 Bearer Context Management function +This function handles the establishment, modification, and release of E1 bearer contexts. +* E1 Bearer Context Establishment: initiation of E1 bearer context is by gNB-CU-CP and acceptance or rejection is determined by gNB-CU-UP based on admission control criteria (e.g., resource availability). +* E1 Bearer Context Modification: can be initiated by either gNB-CU-CP or gNB-CU-UP, with the receiving node having the authority to accept or reject the modification. +* Release of Bearer Context: can be triggered either directly by gNB-CU-CP or following a request from gNB-CU-UP. +* QoS-Flow to DRB Mapping Configuration: responsible for setting up and modifying the QoS-flow to DRB mapping configuration. gNB-CU-CP decides the flow-to-DRB mapping, generates SDAP and PDCP configurations, and provides them to gNB-CU-UP. + +# OAI implementation + +For the E1AP design in OAI, please refer to the [E1 Design](./E1-design.md) document. + +## E1 re-establishment + +The purpose of this procedure is to follow-up the re-establishment of RRC connection over the E1 interface. For all activated DRBs a Bearer Context Modification from CU-CP to CU-UP is necessary, according to clause 9.2.2.4 of 3GPP TS 38.463. If any modification to the bearer context is required, the CU-CP informs the CU-UP with the relevant IEs (e.g. in case of PDCP re-establishment, PDCP Configuration IE clause 9.3.1.38), Current implementation in OAI: + +```mermaid +sequenceDiagram + participant e as UE + participant d as DU + participant c as CUCP + participant u as CUUP + + Note over e,c: RRCReestablishment Procedure + e->>d: RRCReestablishmentRequest + Note over d: initial_ul_rrc_message_transfer_f1ap + d->>+c: Initial UL RRC Message Transfer (CCCH, new C-RNTI) + Note over c: rrc_gNB_process_initial_ul_rrc_message + Note over c: rrc_handle_RRCReestablishmentRequests + c-->>+d: DL RRC Message Transfer + note right of d: fallback to RRC establishment + d-->>-e: RRCSetup + e-->>d: RRCSetupComplete + Note over c: rrc_gNB_generate_RRCReestablishment + Note over c: cuup_notify_reestablishment + Note over c: e1apCUCP_send_BEARER_CONTEXT_MODIFICATION_REQUEST + c->>u: BEARER CONTEXT MODIFICATION REQUEST + Note over u: e1apCUUP_handle_BEARER_CONTEXT_MODIFICATION_REQUEST + Note over u: e1_bearer_context_modif + Note over u: nr_pdcp_reestablishment + c->>-d: DL RRC Message Transfer (old gNB DU F1AP UE ID) + d->>e: RRCReestablishment + Note over d: Fetch UE Context with old gNB DU F1AP UE ID and update C-RNTI + e->>d: RRCReestablishmentComplete + u->>c: BEARER CONTEXT MODIFICATION RESPONSE + Note over c: e1apCUCP_handle_BEARER_CONTEXT_MODIFICATION_RESPONSE +``` diff --git a/doc/README.md b/doc/README.md index 9ff7079f8bc0f444656ed760b7e97ef3456e36ba..1ceba8f494c0a6f8d09884c57f785d1a8c324ed0 100644 --- a/doc/README.md +++ b/doc/README.md @@ -57,7 +57,7 @@ Legacy unmaintained files: # Designs - General software architecture notes: [SW_archi.md](./SW_archi.md) -- [Information on E1](./E1-design.md) +- [Information on E1](./E1AP/E1-design.md) - [Information on F1](./F1-design.md) - [Information on how NR nFAPI works](./NR_NFAPI_archi.md) - [Flow graph of the L1 in gNB](SW-archi-graph.md)