Open RAN  

 

 

 

 

 

E2AP

 

The interface that is designed for communication between DU/CU and Near-Real Time RIC is called E2. The protocol for the communication over E2 interface is called E2AP. This kind of naming conventions is similar to 3GPP naming convention (e.g, NGAP as Protocol for NG interface, X2AP as Protocol for X2 interface, S1AP as Protocol for S1 interface etc). The algorithms happening inside of RIC would be up to each individual implmentation and out of the scope of this note, but E2AP (protocol and message structure) should be same for every RIC and CU/DU.

 

 

The types of Messages (signaling messages) running over E2 interface is defined in O-RAN specification as follows.

 

< O-RAN.WG3.E2SM-KPM - Table 5-1: Relationship between E2SM services and E2AP Information elements >

RAN Function specific E2SM Information Elements

E2AP Information Element reference

Related E2AP Procedures

RIC Event Trigger Definition

E2AP [O-RAN.WG3.E2AP] section 9.2.9

RIC SUBSCRIPTION

RIC Action Definition

E2AP [O-RAN.WG3.E2AP] section 9.2.12

RIC SUBSCRIPTION

RIC Indication Header

E2AP [O-RAN.WG3.E2AP] section 9.2.17

RIC INDICATION

RIC Indication Message

E2AP [O-RAN.WG3.E2AP] section 9.2.16

RIC INDICATION

RIC Call Process ID

E2AP [O-RAN.WG3.E2AP] section 9.2.18

RIC INDICATION

RIC CONTROL

RIC Control Header

E2AP [O-RAN.WG3.E2AP] section 9.2.20

RIC CONTROL

RIC Control Message

E2AP [O-RAN.WG3.E2AP] section 9.2.19

RIC CONTROL

RAN Function Definition IE

E2AP [O-RAN.WG3.E2AP] section 9.2.23

E2 SETUP

RIC SERVICE UPDATE

 

As you notice from the table above, the elemenary E2AP procedure can be grouped into only a few types : SUBSCRIPTION, INDICATION, CONTROL, UPDATE. The overall procedure of these types can be illustrated as follows (NOTE : The diagram on the left column is from The O-RAN SC RIC). As you would notice here, almost all the procedure except CONTROL procedure is initiated by SUBSCRIPTION. Another common thing to be noticed is that most of the procedure (except CONTROL) is initiated (Requested) by RIC and RAN is supposed to do some action (e.g, Report, Perform Policy, Insert) as per requested by RIC.

 

Functional Procedure

Description

 

 

 

 

 

 

 

Reference