Description
The EPS Bearer Identity (EBI) is a fundamental identifier within the Evolved Packet System (EPS) architecture, central to bearer management in LTE and continued into 5GS. It is a unique integer value, typically ranging from 5 to 15, assigned by the MME during the establishment of a dedicated bearer or as part of the default bearer setup. The EBI is not just a local tag; it is a globally significant identifier within a UE's PDN connection context, used across multiple network interfaces including the S1-MME, S11, and S5/S8. Its primary role is to provide an unambiguous reference for network entities—such as the MME, Serving Gateway (S-GW), Packet Data Network Gateway (P-GW), and the UE itself—to identify a specific bearer and its associated QoS profile, traffic flow templates (TFTs), and charging rules.
From an operational perspective, the EBI is carried within key signaling messages. For instance, during a dedicated bearer activation, the P-GW initiates the procedure and includes the proposed EBI in the Create Bearer Request sent to the S-GW and MME. The MME then forwards this to the eNodeB and UE. All subsequent modifications, such as bearer resource modification or deactivation, reference the specific bearer using this EBI. This ensures that commands like updating a QoS parameter or tearing down a specific data flow are executed on the correct logical path. The EBI is also tightly coupled with the EPS bearer context stored in the UE and the network nodes, linking the radio bearer (DRB), S1 bearer, and S5/S8 bearer into a cohesive end-to-end pipe.
In the 5G Core (5GC) architecture, the concept evolves with the QoS Flow, but the EBI remains crucial for interworking scenarios and for UEs connected via E-UTRAN to the 5GC (non-standalone or EPS fallback). The 5GC maps 5G QoS Flows to EPS bearers when interfacing with LTE RAN or EPC, and the EBI is used to identify these mapped bearers. Therefore, understanding EBI is essential for managing mobility and session continuity between 4G and 5G networks, as it serves as a common reference point for bearer-level operations across different generations of core networks.
Purpose & Motivation
The EBI was introduced to solve the critical need for unambiguous bearer identification and management in the all-IP EPS architecture of LTE. Prior 3GPP systems like UMTS used RAB (Radio Access Bearer) IDs, but the flatter, more simplified architecture of EPS required a new, standardized identifier that could be used consistently from the UE through the RAN to the core network gateways. Without a unique identifier like the EBI, network nodes would be unable to coordinate the setup, modification, and teardown of multiple simultaneous bearers for a single UE, leading to potential misrouting of traffic, incorrect QoS application, and charging errors.
The creation of the EBI was motivated by the shift to multiple concurrent dedicated bearers per PDN connection, a feature enabling sophisticated service differentiation (e.g., separate bearers for voice, video, and best-effort data). Each of these bearers requires independent management. The EBI provides the handle for this management, allowing the network to instruct the UE and eNodeB to apply specific packet filters and QoS characteristics to a distinct set of IP flows. It is a cornerstone for enabling the promised QoS capabilities of LTE, such as guaranteed bit rate (GBR) bearers for real-time services.
Historically, its design ensures backward compatibility and forward flexibility. The value range is reserved to avoid conflicts with pre-existing identifiers. Its persistence across the network allows for efficient signaling; instead of sending full bearer contexts in every message, nodes can reference the compact EBI. This reduces signaling overhead and simplifies state management, which is crucial for scaling networks to support millions of devices and their complex service requirements.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (29 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, the EBI function was enhanced with procedures for its allocation and assignment, including the handling of EBI allocation rejections and corrections within the PDU session context. Specific clarifications were made for the Modify Bearer Request procedure during idle mode mobility and RAT type changes. The release also introduced mechanisms for Secondary RAT usage reporting in the Delete Bearer Command and addressed the "Always on" setting for an EBI-allocated PDU Session.
- Always on Setting for the EBI allocated PDU Session TS 23.501CR0721
- Corrections to EBI Assignment TS 29.518CR0004
- Custom Operation Name Correction for EBI Assignment TS 29.518CR0054
- EPS bearer identity TS 29.518CR89
- EBI Allocation Rejection Cause TS 29.518CR98
- Clarify the handling of EBI assignment TS 29.518CR105
+ 8 more changes
In Release 16, clarifications were provided for EPS Bearer Identity (EBI) handling during inter-system mobility and for specific data sessions. This included clarifying the EBI context if the target MME does not support EBI extension during 5GS to EPS mobility and specifying the EBI allocation procedure for MPDU sessions.
- UPF Selection influenced by the indication of the identity/identities of 5G AN N3 User Plane capability TS 23.501CR0862
- Introduction of Dedicated Bearer for Ethernet support in EPC TS 23.501CR1022
- UDR service for mapping IMS Public Identity to HSS Group ID for HSS selection TS 23.501CR1759
- Clarification on the EBI context if target MME does not support EBI extension during 5GS to EPS mobility TS 23.501CR2060
- Clarification on EBI Allocation for MAPDU TS 29.518CR0341
- Clarifications to EBI Assignment procedure TS 29.518CR0386
In Release 17, the key update for the EPS Bearer Identity (EBI) function was the introduction of EBI allocation specifically for Emergency PDU Sessions. This change ensures that emergency sessions can be properly established and managed by defining a dedicated procedure for assigning an EBI. Additionally, the release included updates to the mapping between EBI and ARP (Allocation and Retention Priority).
- Support of the mapping from IP addressing information provided to an AF to the user identity TS 23.501CR2385
- EBI and ARP mapping update TS 29.518CR0424
- MSC Server Identity in Forward Relocation Response during SRVCC handover TS 29.274CR2060
- EBI allocation for Emergency PDU sessions TS 29.518CR0462
- MSC Server Identity in Namf_Location_EventNotify during SRVCC handover TS 29.518CR0764
In Release 18, the EPS Bearer Identity (EBI) function was enhanced to support allocation procedures for PDU sessions utilizing SSC (Session and Service Continuity) mode 1. This update integrated EBI allocation with the restoration procedures for PGW-triggered PDN connections, specifically involving the PGW-C TEID within the Update Bearer Response message. These changes ensured the EBI mechanism remained functional within evolved 5G core network procedures involving specific session continuity modes and restoration scenarios.
In Release 19, a clarification was introduced regarding the setting of the RPPCSI parameter specifically within the Create Session Request and Modify Bearer Request messages. This update provides more precise procedural guidance for handling EPS Bearer Identity-related information during these core session management procedures. The change ensures consistent network behavior when establishing or modifying bearers.
- Clarification on the setting of RPPCSI in Create Session Request and Modify Bearer Request message TS 29.274CR2119
In Release 20, the primary new aspect for the EPS Bearer Identity (EBI) function was the introduction of a procedure for its allocation, which is contingent upon specific UE and network capabilities for user plane integrity protection. The specification stipulates that if a UE does not support user plane integrity protection with EPS or the AMF lacks the associated functionality, the SMF shall not trigger this new EPS bearer ID allocation procedure. This change directly links the activation of the EBI allocation mechanism to the support of User Plane Integrity Protection (UPIP) capabilities between the UE and the network.
- Support for Dynamic Network Identity TS 23.501CR6483
Explore further
Broader topics and technologies where EBI plays a role.
Defining Specifications
3GPP specifications that define or reference EBI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 29.274 vj50 | GTPv2-C Control Plane Protocol Specification | Rel-19 |
| TS 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |