Description
The Edge Application Server Discovery Function (EASDF) is a specialized network function introduced in 3GPP Release 17 to enhance edge computing in 5G systems. Its primary role is to facilitate the discovery and selection of Edge Application Servers (EAS) by User Equipment (UE) or other network functions. The EASDF acts as a DNS (Domain Name System) server or proxy that is aware of the network topology, UE location, and EAS deployment locations. When a UE attempts to access an edge application via a domain name, the EASDF intercepts the DNS query and returns the IP address of the most suitable EAS instance, typically the one closest to the UE to minimize latency.
Architecturally, the EASDF is part of the 5G core network's user plane or can be deployed as a separate function interacting with the control plane. It integrates with the Policy Control Function (PCF) and the Network Exposure Function (NEF) to obtain policies and contextual information that influence EAS selection. Key components include the DNS resolution logic, a database or interface to EAS availability and location information, and policy enforcement mechanisms. The EASDF works by receiving a DNS query from the UE (often routed to it via UE Route Selection Policy (URSP) or local breakout configurations). It then applies selection criteria such as UE current location, EAS load, network conditions, and subscriber profiles to choose the optimal EAS. The resolved IP address is returned to the UE, which then establishes a direct connection to the selected EAS for application data transfer.
How it operates involves close coordination with other 5G systems. The EASDF may be provisioned with EAS information via management systems or dynamically through interfaces with the Network Repository Function (NRF). In operation, it enables dynamic and efficient traffic steering to edge resources. For example, for a latency-sensitive gaming application, the EASDF ensures the UE connects to a game server in a nearby edge data center rather than a distant central cloud. Its role is critical in multi-edge environments where multiple EAS instances are deployed across different geographical points of presence, as it provides the intelligence to direct users to the best instance based on real-time network and service conditions.
Purpose & Motivation
The EASDF was created to solve the challenge of efficiently discovering and connecting to the most appropriate Edge Application Server in a distributed edge computing environment. Before its introduction, edge discovery mechanisms were often proprietary, lacked standardization, or relied on basic DNS which is not network-aware. This led to suboptimal routing where a UE might be directed to a distant EAS despite a closer one being available, negating the latency benefits of edge computing. The proliferation of edge deployments in 5G, driven by applications like autonomous vehicles, industrial IoT, and augmented reality, necessitated a standardized, network-integrated discovery solution.
The primary problem EASDF addresses is the intelligent, policy-driven selection of edge resources. It ensures that edge computing delivers on its promise of low latency and high bandwidth by dynamically directing users to the optimal EAS based on current network conditions. This is especially important for mobile users, as their location changes and the best EAS selection may change accordingly. EASDF also solves the issue of scalability and management in large-scale edge deployments, providing a centralized discovery point that can be updated with new EAS instances and their capabilities.
Historically, the motivation stems from 3GPP's work on edge computing architecture (EDGEAPP) in earlier releases, which defined the EAS but lacked a standardized discovery mechanism. EASDF fills this gap, completing the edge computing framework by adding a crucial control element. It enables operators to offer edge computing as a seamless service, where applications can be deployed at the edge without requiring end-users or application providers to manage complex connectivity details. This standardization encourages ecosystem growth, allowing application developers to rely on a consistent method for edge service discovery across different operator networks.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (91 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the EASDF (Edge Application Server Discovery Function) was newly introduced as a functional entity within the 5G Core architecture. Its defined functionalities include registering to the NRF for discovery, providing DNS security information to the SMF, and reporting information related to received DNS messages. The specification also details its deployment, noting it has direct user plane connectivity to a UPF and that its interactions with 5GC Network Functions take place within a PLMN.
- Handling of error case when UE gets URSP from VPLMN TS 24.501CR0256
- Application detection report when the PFDs are removed TS 29.244CR0154
- (Un)solicited Application Reporting TS 29.244CR0211
- Correct the length of redirection server address TS 29.244CR0248
- Update the redirection server address to support dual stack UE TS 29.244CR0245
In Release 16, the EASDF (Edge Application Server Discovery Function) was newly introduced, with its key functionalities including registering to the NRF for discovery, providing DNS security information to the SMF, and reporting information related to received DNS messages. The release also defined the complementary Edge DNS Client (EDC) functionality in the UE, which configures the DNS client with the EASDF's IP address and security information received from the SMF via PCO. Furthermore, procedures were specified to ensure DNS queries are steered to the EASDF, particularly for URSP-based connectivity models like Multiple PDU Sessions.
- Provisioning of DNS server security information to the UE TS 24.501CR2345
- Applicable URSP is not optional for a UE TS 24.501CR2098
- Clarification on S-NSSAI(s) in URSP(NSSP) be added into the request NSSAI TS 24.501CR2333
- URSP evaluation after rejection with the same URSP rule TS 24.501CR2418
- Provisioning of DNS server security information to the UE-25.401 TS 24.501CR2483
- Application report when the PFDs are removed or modified TS 29.244CR0267
In Release 17, the EASDF (Edge Application Server Discovery Function) was enhanced to support a new EAS discovery procedure with a Local DNS Server/Resolver, including the handling of an IP Address and Port number Replacement Information Element. The release also introduced the Edge DNS Client (EDC) as a UE capability for ensuring EAS (re-)discovery and clarified operational aspects such as when an EASDF is not required and the non-support of NAT deployment between the EASDF and the PSA UPF.
- The impact on UE due to the introduction of Authentication and Key Management for Applications (AKMA) TS 24.501CR2794
- SNN verification for SNPN supporting AAA-Server for primary authentication and authorization TS 24.501CR3137
- "List of subscriber data" handling for SNPN supporting AAA-Server for primary authentication and authorization TS 24.501CR3133
- (Re)configuring DNS server addresses TS 24.501CR3385
- UE required to not accept URSP signalled by non-subscribed SNPNs TS 24.501CR4135
- EAS Discovery procedure with Local DNS Server/Resolver TS 29.244CR0565
+ 22 more changes
In Release 18, the EASDF function was enhanced to support more complex roaming and deployment scenarios. Key additions included specific procedures for EAS (re-)discovery in Home Routed roaming with Session Breakout (HR-SBO), utilizing mechanisms like IP replacement and N6 tunneling between the V-UPF and V-EASDF to handle overlapping IP addresses. Furthermore, support was extended for common EAS discovery for a set of UEs and for UL CL/BP insertion to facilitate this common discovery.
- EAS Re-discovery Procedure with EASDF in HR roaming scenario TS 23.548CR0073
- The EAS discovery procedure with V-EASDF using IP replacement mechanism for supporting HR-SBO TS 23.548CR0088
- KI#5 EDI extension for EAS discovery for GSMA OPG scenario TS 23.548CR0094
- EASDF functional description update TS 23.548CR0105
- UL CL/BP insertion for common EAS Discovery TS 23.548CR0109
- KI#1 EAS Discovery: Resolve ENs TS 23.548CR0120
+ 39 more changes
In Release 19, the EASDF was enhanced with the introduction of the N88a reference point between the I-SMF and the EASDF for the Local Offloading Management scenario. The release also added a new procedure for N6 delay measurement based EAS (re-)discovery enhancement and provided clarifications on handling applications not matched with LOM policy and on the start or stop of an application instance.
- Addition of N6 delay measurement based EAS (re-)discovery enhancement TS 23.548CR0248
- Clarification on handling application not matched with LOM policy TS 23.548CR0309
- URSP and ANDSP storage in non-volatile memory TS 24.501CR6463
- Storage of UPSI(s) for stored signalled URSP rules TS 24.501CR6612
- (Un)Solicited Application Reporting and Application Detection Information TS 29.244CR0991
- Clarification on the start or stop of Application and Application instance TS 29.244CR1012
+ 1 more changes
Explore further
Broader topics and technologies where EASDF plays a role.
Defining Specifications
3GPP specifications that define or reference EASDF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.548 vj50 | 5G System Edge Computing Enhancements | Rel-19 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TR 26.803 vh00 | 5G Media Streaming Extensions for Edge Processing | Rel-17 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | Rel-19 |
| TS 29.556 vj40 | EASDF Service Based Interface Protocol | Rel-19 |
| TR 33.739 vi10 | Study on security enhancement of support for | Rel-18 |