Description
The XML Configuration Access Protocol (XCAP) is a client-server protocol that allows a client to manipulate application-specific configuration data stored on a server as XML documents. In the 3GPP ecosystem, XCAP is primarily used within the IP Multimedia Subsystem (IMS) as the standard mechanism for users to manage their service settings. The protocol is built on top of HTTP/1.1, using standard HTTP methods (GET, PUT, DELETE) to perform operations on XML document nodes, which are identified through a hierarchical URI structure. This design makes it inherently web-friendly and easily integrated with existing internet infrastructure.
An XCAP server hosts one or more "XCAP Application Usages." Each usage defines a specific XML schema (the data model) and a set of conventions for how the XML documents are structured, named, and accessed. For example, the `org.openmobilealliance.pres-rules` usage defines the XML schema for presence authorization rules (also known as the 'ruleset document'). A client, such as a UE or a web portal, can fetch this document via an HTTP GET request to a specific URI, modify the XML content locally, and then upload the changes back to the server using an HTTP PUT. The server validates the changes against the XML schema and the application usage semantics before committing them.
The protocol's power lies in its ability to target specific elements or attributes within an XML document using XPath expressions embedded in the HTTP URI. This allows for fine-grained modifications without needing to transfer and parse the entire document for every change. For instance, a user could modify a single call forwarding rule without affecting the rest of their call handling configuration. In IMS networks, the XCAP server is often co-located with or integrated into the Home Subscriber Server (HSS) or a dedicated service configuration server. The client accesses it via the Ut reference point. Authentication is typically handled using IMS Authentication and Key Agreement (AKA), ensuring that users can only modify their own data. The server also handles concurrency control through HTTP entity tags (ETags) to prevent conflicting updates from different clients.
Purpose & Motivation
XCAP was developed to solve the problem of standardized, remote management of user-specific service data in next-generation telecom services, particularly those based on SIP and IMS. Prior to XCAP, service configuration was often handled through proprietary protocols, interactive voice response (IVR) systems, or carrier-specific web portals with no unified data model. This fragmentation made it difficult to create interoperable handsets and third-party service management applications. The driving force behind its adoption in 3GPP was the need for a flexible, extensible, and internet-standard way for subscribers to manage complex IMS services like Presence, Message Waiting Indication, and Call Barring.
The protocol addresses the limitation of SIP itself, which is a signaling protocol not designed for manipulating persistent configuration data. XCAP provides the missing piece: a standardized data store and manipulation interface. It allows users to configure services from any device with an XCAP client, enabling a consistent experience across mobile phones, PCs, and web browsers. Its use of XML and HTTP was a strategic choice to leverage widely understood technologies, reducing implementation complexity and fostering a rich ecosystem of tools and developers. By decoupling service logic (in SIP Application Servers) from service configuration data (in the XCAP server), it created a clean architecture that simplified network management and enabled user empowerment through self-care portals, which became a standard feature of IMS deployments.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (119 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-6, normative work from Rel-15.
In Release 15, the XCAP function was extended to support the configuration of new Mission Critical Services, including specific configurations for MCVideo ambient viewing, off-network MCVideo, and MCPTT UE initial configuration documents. The protocol continued to be used at the Ut reference point with HTTP methods like PUT, GET, and DELETE for manipulating service configuration data. These enhancements introduced new managed objects and flows, such as for MCPTT Servers subscribing to service configuration documents and for configuring 3GPP data off in roaming scenarios.
- MCVideo ambient viewing MCS configuration TS 24.484CR0072
- 3GPP data off in roaming and Ut/XCAP services configuration MO TS 24.424CR0003
- MCPTT Server subscribing to and downloading the service configuration document Flow TS 24.484CR0054
- File availability configurations TS 24.484CR0059
- Service configurations TS 24.484CR0061
- Off-network MCVideo configurations TS 24.484CR0064
+ 3 more changes
In Release 16, the XCAP function was updated to provide specific support for 5G access, including correcting and enforcing access-specific policies when the access type involves 5G or 5Gx. The enhancements also focused on service configurations for Mission Critical services, such as supporting communication priority for functional aliases and configuring resource priority for MCData emergency scenarios. Furthermore, updates were made to user profile configuration to enable restricting incoming private communications and to support limiting the number of authorized clients per MCPTT or MCData user.
- Update user profile configuration to enable restricting of incoming private communications TS 24.484CR0124
- Update service configuration to support communication priority for functional aliases TS 24.484CR0133
- Configuration of resource priority for MCData emergency TS 24.484CR0137
- Update service configuration to support limiting the number of authorized clients per MCPTT/MCData user TS 24.484CR0142
- Correction on MCx UE configuration document TS 24.484CR0105
- Corrections on configurations documents TS 24.484CR0153
+ 6 more changes
In Release 17, the XCAP function was enhanced with new Management Object (MO) configurations to support Standalone Non-Public Networks (SNPN) and to refine 5GS QoS aspects. It also introduced configurations for Mission Critical services, including functional alias associations for groups and updates for MCData and MCVideo service parameters like notification server hostnames and communication limits. Furthermore, updates were made to the HTTP Digest Access Authentication and references to the HTTP/1.1 protocol underlying XCAP.
- Update of HTTP Digest Access Authentication and reference update for HTTP/1.1 protocol TS 24.141CR0119
- Reference update for HTTP/1.1 protocol TS 24.259CR0055
- Update of HTTP Digest Access Authentication TS 24.424CR0012
- SNPN configuration in XCAP MO TS 24.424CR0013
- Management object for APN configuration TS 24.483CR0096
- Functional alias association with group – MO configurations TS 24.483CR0136
+ 20 more changes
In Release 18, the XCAP function was enhanced to support new configuration management objects and elements for Mission Critical Services (MCPTT, MCVideo, MCData), specifically for ad-hoc group communication user profiles and service configuration. The updates also introduced new elements for user profile configuration to manage migration to partner MC systems and added configuration support for MC Gateway UEs. Furthermore, the underlying HTTP procedures were updated to reference the current IETF RFC 9110.
- Adhoc group communication related user profile and service configuration for MCPTT TS 24.483CR0160
- Adhoc group communication related user profile and service configuration for MCVideo TS 24.483CR0161
- Adhoc group call participants modify related user profile configuration – mgmt object MCPTT TS 24.483CR0164
- Adhoc group call participants modify related user profile configuration configuration – mgmt object MCVideo TS 24.483CR0165
- Adhoc group data comn participants modify related user profile configuration – mgmt object MCData TS 24.483CR0166
- Adhoc group communication related user profile and service configuration – mgmt object MCData TS 24.483CR0167
+ 25 more changes
In Release 19, the XCAP function was expanded to support new configuration Management Objects (MOs) and procedures over HTTP, including the addition of an LMS URI for MCS UE initial configuration, multi-talker configuration, and emergency remote floor request authorization. It also introduced new SEALDD-enabled procedures for URLLC transmission connection establishment, deletion, and status reporting, alongside support for BAT and periodicity adaptation to guarantee transmission quality. Furthermore, capabilities for transmission quality measurement with Non-3GPP RAT and for supporting XR Application device capability information were added via HTTP.
- Addition of LMS URI in MCS UE initial configuration MO TS 24.483CR0186
- Multi-talker MO configuration TS 24.483CR0187
- Emergency remote floor request authorization MO configuration TS 24.483CR0190
- Addition of LMS URI in MCS UE initial configuration document TS 24.484CR0280
- Location user profile configuration data TS 24.484CR0284
- Multi-talker configuration TS 24.484CR0283
+ 35 more changes
Explore further
Broader topics and technologies where XCAP plays a role.
Defining Specifications
3GPP specifications that define or reference XCAP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 24.141 vj00 | Presence Service Protocol Details | Rel-19 |
| TS 24.259 vj00 | Personal Network Management (PNM) Protocol Details | Rel-19 |
| TS 24.337 vj00 | IMS Inter-UE Transfer Protocol Specification | Rel-19 |
| TS 24.423 v850 | PSTN/ISDN Simulation Services XCAP Protocol | Rel-8 |
| TS 24.424 vj00 | XCAP over Ut for Supplementary Services MO | Rel-19 |
| TS 24.483 vj20 | Mission Critical Services Management Object | Rel-19 |
| TS 24.484 vj30 | MCS Configuration Management | Rel-19 |
| TS 24.504 v8m0 | Communication Diversion Services Stage 3 | Rel-8 |
| TS 24.543 vj50 | SEAL Data Delivery Management Protocol | Rel-19 |
| TS 24.549 vj10 | SEAL Network Slice Capability Enablement Protocol | Rel-19 |
| TS 24.604 vj00 | Communications Diversion (CDIV) Protocol Spec | Rel-19 |
| TS 24.623 vj00 | XCAP Protocol for Supplementary Services | Rel-19 |
| TS 24.841 v1600 | Presence Service IP Multimedia Subsystem | Rel-6 |
| TS 29.199 v1900 | Multimedia Messaging Web Services | Rel-9 |
| TS 32.808 v1800 | Common User Profile Storage Framework | Rel-8 |