# <center>E2AP & E2SM</center>

# E2AP Communication

## Message Functional Definition and Content

Here, I focus on the critical messages.

### 1. RIC SUBSCRIPTION REQUEST

This message is sent by the Near-RT RIC to an E2 Node to create a new RIC Subscription in the E2 Node.
Direction: Near-RT RIC → E2 Node.
| **IE/Group Name** | **Presence** |
| ------------------------------ | ------------ |
| Message Type | M |
| RIC Request ID | M |
| RAN Function ID | M |
| RIC Subscription Details | M |
| \>RIC Event Trigger Definition | M |
| \>Sequence of Actions | |
| \>>RIC Action ID | M |
| \>>RIC Action Type | M |
| \>>RIC Action Definition | O |
| \>>RIC Subsequent Action | O |
| \>>RIC Action Execution Order | O |
| RIC Subscription Start Time | O |
| RIC Subscription End Time | O |

### 2. RIC SUBSCRIPTION RESPONSE
This message is sent by the E2 Node to accept the request from the Near-RT RIC to create a new RIC Subscription in the E2 Node.
Direction: E2 Node → Near-RT RIC.

### 3. RIC INDICATION
This message is sent by an E2 Node to transfer Report and Insert RIC Service Action information to a Near-RT RIC.
Direction: E2 Node → Near-RT RIC.
| **IE/Group Name** | **Presence** |
| ---------------------- | ------------ |
| Message Type | M |
| RIC Request ID | M |
| RAN Function ID | M |
| RIC Action ID | M |
| RIC Indication SN | O |
| RIC Indication Type | M |
| RIC Indication Header | M |
| RIC Indication Message | M |
| RIC Call process ID | O |

### 4. RIC CONTROL REQUEST
This message is sent by a Near-RT RIC to an E2 Node to initiate or resume a control function logic.
Direction: Near-RT RIC → E2 Node.
| **IE/Group Name** | **Presence** |
| ----------------------- | ------------ |
| Message Type | M |
| RIC Request ID | M |
| RAN Function ID | M |
| RIC Call Process ID | O |
| RIC Control Header | M |
| RIC Control Message | M |
| RIC Control Ack Request | O |

## Information Element definitions

### 1. Cause
The purpose of the Cause IE is to indicate the reason for a particular event for the E2AP protocol.

### 2. Criticality Diagnostics
The Criticality Diagnostics IE is sent by the E2 Node or the Near-RT RIC when parts of a received message have not been comprehended, or were missing, or if the message contained logical errors. When applicable, it contains information about which IEs were not comprehended or were missing.

### 3. Message Type
The Message Type IE uniquely identifies the message being sent. It is mandatory for all messages.

### 4. Global RIC ID
This IE is used to globally identify the Near-RT RIC.

### 5. Time to wait
This IE defines the minimum allowed waiting times.

### 6. Global E2 Node ID
This IE is used to globally identify an E2 node.

### 7. RIC Request ID
This information element indicates the RIC Request ID , and shall be unique for a given E2 Node.

### 8. RAN Function ID
This information element indicates the RAN Function ID, and shall be unique within a given E2 Node.

### 9. RIC Event Trigger Definition
This information element indicates the RIC event trigger description used by the RIC Subscription procedure.
Semantics description: Defined in RAN Function specific E2 Service Model

### 10. RIC Action ID
This information element indicates the Action ID number for a RIC Service Action, and shall be unique within the given RIC Request ID.

### 11. RIC Action Type
This IE defines the type of RIC Service Action to be executed.

### 12. RIC Action Definition
This information element provides parameters to used when executed a Report, Insert or Policy RIC Service Actions.
Semantics description: Defined in RAN Function specific E2 Service Model

### 13. RIC Subsequent Action
This IE defines the subsequent action to be taken after completing a particular RIC Service Action and shall be present when RIC Action Type set to Insert.

### 14. RIC Indication Sequence Number (SN)
This information element indicates the Indication Sequence Number (SN).

### 15. RIC Indication Type
This IE defines the Indication Type.

### 16. RIC Indication message
This information element carries the RIC indication message used for Insert and Report RIC Service Actions.
Semantics description: Defined in RAN Function specific E2 Service Model

### 17. RIC Indication header
This information element carries the RIC indication header used for Insert and Report RIC Service Actions .
Semantics description: Defined in RAN Function specific E2 Service Model

### 18. RIC Call Process ID
This information element carries the RIC Call Process ID used for the Insert and Control RIC Service Actions. The RIC Call Process ID shall be unique within a given RAN Function on a given E2 Node.
Semantics description: Defined in RAN Function specific E2 Service Model

### 19. RIC Control message
This information element carries the RIC Control message.
Semantics description: Defined in RAN Function specific E2 Service Model

### 20. RIC Control header
This information element carries the RIC Control Header.
Semantics description: Defined in RAN Function specific E2 Service Model

### 21. RIC Control Ack Request
This IE defines whether and when the RIC CONTROL ACKNOWLEDGE message shall be sent by the E2 Node as described in the below table.

### 22. Void
### 23. RAN Function Definition
This information element carries the RAN Function Definition.
Semantics description: Defined in RAN Function specific E2 Service Model

### 24. RAN Function Revision
This information element carries the RAN Function Revision.

### 25. RIC Control Outcome
This information element carries the RIC Control Outcome.
Semantics description: Defined in RAN Function specific E2 Service Model

### 26. E2 Node Component Interface Type
This IE is used to identify an E2 node component type.

### 27. E2 Node Component Configuration
This IE is used to carry the E2 Node component configuration update information of a specific E2 Node component.

### 28. E2 Node Component Configuration Acknowledge
This IE is used to carry the E2 Node component configuration update acknowledge of a specific E2 Node component.

### 29. Transport Layer Information
This information element provides Near-RT RIC address and optionally port number to be used by an E2 Node.

### 30. TNL Association Usage
This information element provides TNL association usage.
Semantics description:
Indicates whether E2 connection to be used for RIC services only, or E2 support functions only, or both

### 31. RAN Function OID
This information element carries the RAN Function OID and shall uniquely refer to a specific E2 Service Model (E2SM).

### 32. E2 Node Component ID
This IE is used to locally identify an E2 node component.

### 33. Transaction ID
The Transaction ID IE uniquely identifies a procedure among all ongoing parallel procedures of the same type initiated by the same protocol peer. Messages belonging to the same procedure shall use the same Transaction ID. The Transaction ID is determined by the initiating peer of a procedure.

### 34. RIC Subscription Time
The RIC Subscription Time IE is used to set the start and end time of a RIC Subscription.

### 35. RIC Action Execution Order
This IE is used to modify the default RIC service action execution order.

### 36. RIC Query Header
This information element carries the RIC Query Header.
Semantics description: Defined in RAN Function specific E2 Service Model

### 37. RIC Query Definition
This information element carries the RIC Query Definition.
Semantics description: Defined in RAN Function specific E2 Service Model

### 38. RIC Query Outcome
This information element carries the RIC Query Outcome.
Semantics description: Defined in RAN Function specific E2 Service Model

# E2SM Service Models

## E2SM common IEs

### 1. QoS ID
This IE defines a generic "QoS ID" suitable for both EPC and 5GC networks.

### 2. RRC Message ID
This IE defines the identifier for a specific RRC message defined in either TS 36.331 [14] or TS 38.331 [15].

### 3. Serving Cell PCI
This IE is used to identify the serving cell PCI in an E2 Node. The IE is derived from TS 38.473 [8] clause 9.3.1.10 and TS 36.423 [11] clause 9.2.8.

### 4. Serving Cell ARFCN
This IE is used to identify the serving cell ARFCN in an E2 Node. The IE is derived from TS 38.473 [8] clause 9.3.1.17 and TS 36.423 [11] clause 9.2.26.

## 3GPP derived IEs

### 1. PLMN Identity
This IE indicates the PLMN Identity.

### 2. gNB-CU-UP ID
This IE uniquely identifies the gNB-CU-UP at least within a gNB-CU-CP.

### 3. gNB-DU ID
This IE uniquely identifies the gNB-DU at least within a gNB-CU.

### 4. NR CGI
This IE is used to globally identify an NR cell.

### 5. E-UTRA CGI
This IE is used to globally identify an E-UTRA cell.

### 6. S-NSSAI
This IE is used to indicate the S-NSSAI.

### 7. 5QI
This IE is used to indicate 5QI value.

### 8. QCI
This IE is used to indicate QCI value.

### 9. QoS Flow Identifier (QFI)
This IE identifies a QoS flow within a PDU Session.

### 10. AMF UE NGAP ID
This IE uniquely identifies a UE over the NG interface within a NG-RAN node.

### 11. GUAMI
This IE indicates the AMF identity.

### 12. GUMMEI
This IE indicates the globally unique MME identity.

### 13. Index to RAT/Frequency Selection Priority (IRFSP)
This IE is used to define local configuration for RRM strategies such as camp priorities in Idle mode and control of inter-RAT/inter-frequency handover in Active mode.

### 14. Subscriber Profile ID for RAT/Frequency priority (SPID)
This IE is used to define camp priorities in Idle mode and to control inter-RAT/inter-frequency handover in Active mode.

### 15. NR PCI
This IE is used to identify an NR cell PCI.

### 16. NR ARFCN
This IE is used to identify an NR ARFCN.

### 17. 5GS TAC
This IE is used to identify 5GS Tracking Area Code.

### 18. E-UTRA PCI
This IE is used to identify an E-UTRA cell PCI.

### 19. E-UTRA ARFCN
This IE is used to identify an E-UTRA Frequency Info.

### 20. E-UTRA TAC
This IE is used to identify an E-UTRA Tracking Area Code.

### 21. NR Frequency Info
This IE is used to define the carrier frequency and bands used in a cell.

# Metrics Collected by KPIMON

- the number of utilized and available Physical Resource Blocks (PRBs)
- the number of active UE connections
- QoS Class Identifiers (QCI) with active data transmissions
- the downlink and uplink data transferred in bytes in each session for each QCI