Description
Network Assisted Cell Change (NACC) is a mobility management enhancement defined for the GERAN (GSM/EDGE Radio Access Network) in 3GPP. Its core function is to reduce the interruption time experienced by a mobile station (MS) when changing cells, particularly during packet-switched data transfers in GPRS or EDGE networks. In a traditional cell change, the MS must first move to the new cell, then listen to the broadcast channel to acquire essential system information (like routing area code, cell options, and access parameters) before it can resume communication. This acquisition process can cause a data flow interruption of several hundred milliseconds.
NACC works by having the serving Base Station Controller (BSC) pre-emptively provide the MS with the critical system information of the neighbor cell(s) before the cell change is executed. The process is typically triggered during packet transfer mode. The network, based on measurement reports from the MS, decides on a target cell for cell change. The serving BSC then communicates with the target BSC (if different) via the Gb or Iu-g interface to request the relevant System Information (SI) for the target cell. This SI includes data from System Information messages 13 (for GPRS) and potentially others, containing parameters essential for immediate access.
The serving BSC then sends this information to the MS within a Packet Cell Change Order or a Packet Neighbor Cell Data message on the PACCH (Packet Associated Control Channel). Armed with this information, the MS can synchronize to the new cell and immediately begin accessing it using the correct parameters, bypassing the need to wait for and decode the slow broadcast channel. This is especially crucial for real-time services like Voice over IP or streaming. NACC can assist both cell reselection (where the MS decides the change) and network-controlled handovers. The feature requires support in both the network (BSC) and the MS, and it is a key component for enhancing the user experience for delay-sensitive applications on 2.5G networks.
Purpose & Motivation
NACC was developed to address a significant performance limitation in GPRS and EDGE networks: the long interruption time during cell changes for packet data sessions. This interruption was detrimental to the quality of service for real-time applications, such as push-to-talk over cellular (PoC), VoIP, and interactive gaming, which were becoming more prevalent. The standard cell change procedure, where the MS had to acquire system information from the broadcast channel after moving, was a legacy design optimized for circuit-switched voice, where brief interruptions were less noticeable.
The creation of NACC was motivated by the need to make GERAN more competitive for packet-switched services and to provide a smoother mobility experience, akin to what was possible in UMTS. It solved the problem by shifting the burden of information gathering from the MS to the network, leveraging the network's knowledge of neighbor cells. This proactive assistance significantly reduced the cell change interruption time—from potentially over 600ms to less than 200ms—making GERAN more suitable for services requiring seamless mobility. It was a key evolutionary step for 2G networks to better support IP-based services before the widespread deployment of 3G/4G.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (49 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-5, normative work from Rel-15.
In Release 15, the NACC function was enhanced with changes for FullConfig during Inter-RAT intra-system handover, primarily within the LTE specifications. These modifications also involved corrections and clarifications for scenarios like EN-DC Secondary Node change and GERAN redirection procedures. Furthermore, support was introduced for Logical Channel Identity (LCID) changes in conjunction with bearer type changes for multi-connectivity configurations like (NG)EN-DC.
- Introducing support for NR, changes relevant for NSA TS 36.331CR3115
- Introducing support for NR, changes only relevant for SA TS 36.331CR3186
- Introducing NR changes for late drop (resulting from ASN1 review) TS 36.331CR4002
- CR on PSCell (SPCell of SN) change (36.331) TS 36.331CR3799
- Correction on the terminology scg-ChangeFailure TS 36.331CR3807
- Clarification for EN-DC SN change scenario TS 36.331CR3825
+ 7 more changes
In Release 16, the enhancements for Network Assisted Cell Change (NACC) primarily involved clarifications and security improvements for procedures during changes in the radio access network. Specifically, the release introduced a clarification on the use of RRC full configuration during a PSCell change and addressed security risks for RLC AM and UM bearers when the termination point changes. These updates provided more robust handling of cell changes within the GERAN and E-UTRAN access contexts.
- Allowing PDCP version change without handover TS 36.331CR4262
- General changes resulting from ASN.1 review for LTE RRC REL-16 TS 36.331CR4315
- Minor changes collected by Rapporteur TS 36.331CR4414
- Minor changes collected by Rapporteur TS 36.331CR4472
- Minor changes collected by Rapporteur for Rel-16 TS 36.331CR4549
- Clarification on SIB change notification in RRC_INACTIVE TS 36.331CR4555
+ 12 more changes
In Release 17, the updates to the Network Assisted Cell Change (NACC) function were primarily administrative, involving the promotion and upgrade of existing specifications to the Release 17 version without introducing new technical changes or procedures. The modifications included miscellaneous editorial updates collected by the specification Rapporteur, such as clarifying the abbreviation for "DN." No new technical capabilities for handover, service continuity, or radio access network procedures like GERAN G-RNTI management were added in this release.
- Change of abbreviation of DN from Destination Network to Data Network and Distinguished Name TS 21.905CR0125
- Promotion to Release 17 without technical change TS 25.423
- Miscellaneous changes collected by Rapporteur TS 36.331CR4862
- Upgrade to Rel-17 version without technical change TS 43.130
- Upgrade to Rel-17 version without technical change TS 43.901
- Upgrade to Rel-17 version without technical change TS 44.901
+ 1 more changes
In Release 18, the enhancements to Network Assisted Cell Change (NACC) primarily focused on improving inter-RAT mobility procedures, specifically for redirection and reselection to legacy systems. The work introduced protections against improper reselection to GERAN and UTRAN and provided corrections for redirection procedures to GERAN. These updates aimed to ensure more reliable service continuity when a UE undergoes a radio access technology change.
- Protection against improper reselection to GERAN/UTRAN [RESELECTION_TO GSM_AND_UTRAN] TS 36.331CR4971
- Correction on redirection to GERAN [Redirect_to_GERAN] TS 36.331CR5000
- Upgrade to Rel-18 version without technical change TS 43.130
- Upgrade to Rel-18 version without technical change TS 43.901
- Upgrade to Rel-18 version without technical change TS 44.901
- Upgrade to Rel-18 version without technical change TS 48.018
In Release 19, there were no substantive technical changes or new features introduced for the Network Assisted Cell Change (NACC) function. All related Change Requests for this release were limited to procedural upgrades of specification documents to the Release 19 version without any technical change. Therefore, the NACC procedures, including its role in handovers and inter-system changes between radio access technologies like GERAN and UTRAN, remain as defined in prior releases.
- Problem with 36.331 v19.2.0 zip-file. No changes to spec contents. TS 36.331
- Upgrade to Rel-19 version without technical change TS 43.130
- Upgrade to Rel-19 version without technical change TS 43.901
- Upgrade to Rel-19 version without technical change TS 44.901
- Upgrade to Rel-19 version without technical change TS 48.018
Explore further
Broader topics and technologies where NACC plays a role.
Defining Specifications
3GPP specifications that define or reference NACC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 23.060 vj00 | GPRS Service Description Stage 2 | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TS 25.401 vj00 | UTRAN Overall Architecture | Rel-19 |
| TS 25.410 vj00 | Iu Interface Introduction for UTRAN | Rel-19 |
| TS 25.413 vj00 | Radio Access Network Application Part (RANAP) | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TS 29.060 vj00 | GPRS Tunnelling Protocol (GTP) version 1 | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 43.130 vj00 | Iur-g Interface Overview | Rel-19 |
| TR 43.901 vj00 | Generic Access to A/Gb Interface Feasibility Study | Rel-19 |
| TR 44.901 vj00 | Extended NACC for External Cell Change | Rel-19 |
| TS 48.018 vj00 | BSS-SGSN Interface for GPRS Control | Rel-19 |