Description
The Mobile station Not Reachable Reason (MNRR) is an informational parameter defined in 3GPP TS 23.060, stored alongside the MNRG flag in the SGSN's Mobility Management context for a UE. While MNRG is a simple flag indicating *that* a UE is unreachable for GPRS, the MNRR provides the specific reason *why* the SGSN considers the UE unreachable. This adds granularity to the unreachability state, allowing for more intelligent network behavior and improved diagnostics.
The MNRR can take values such as 'IMPLICIT_DETACH' or 'PURGED.' The most common value is 'IMPLICIT_DETACH,' which indicates that the UE was implicitly detached by the network due to the expiry of the 'mobile reachable timer' without any contact from the UE. This timer starts when the UE moves to an idle state (PMM-IDLE), and its expiry suggests the UE may have left the coverage area or powered off without properly detaching. Another potential value could relate to an administrative purge. The MNRR is set at the same time as the MNRG flag when the triggering condition occurs.
This reason code is used internally by the SGSN and may also be communicated to other network entities in certain scenarios. For instance, when the HLR performs an SGSN restoration procedure or when context is transferred between SGSNs, the MNRR can provide context about the UE's previous state. It aids in network management and troubleshooting by allowing operators to distinguish between a UE that failed to respond to paging (which might set MNRG but not necessarily a detailed MNRR) and one that has been implicitly detached due to prolonged inactivity. The MNRR, combined with MNRG, forms a more complete picture of the UE's mobility management status, enabling optimized procedures for re-attachment and service restoration when the UE becomes reachable again.
Purpose & Motivation
The MNRR was introduced to complement the MNRG flag by providing causal information for a UE's unreachability status. A simple binary flag (MNRG) is sufficient for basic flow control to stop paging, but it offers no insight for network operations, fault management, or advanced procedures. Knowing the reason for unreachability allows the network to handle subsequent events more intelligently.
For example, if a UE marked unreachable due to 'IMPLICIT_DETACH' suddenly performs a Routing Area Update, the SGSN knows this is a re-attachment from a previously lost UE and can handle the procedure accordingly, potentially requiring re-authentication. It also helps in scenarios of network node failure and restoration; if an SGSN restarts and recolds context from a backup, the MNRR indicates whether the UE was actively detached or just temporarily unreachable. This granularity aids in differentiating between a normal, powered-off UE and one that might be experiencing radio problems. It addresses the limitation of a simple flag by adding a diagnostic and procedural layer, which is valuable for network reliability, subscriber experience management, and operational support systems in complex GPRS/UMTS networks.
Key Features
- Reason code stored per UE in the SGSN alongside the MNRG flag
- Provides specific cause for PS domain unreachability (e.g., IMPLICIT_DETACH)
- Enhances network diagnostics and fault management
- Used internally by SGSN for state management and procedure handling
- May be communicated during inter-SGSN context transfer or restoration procedures
- Complements the binary MNRG flag with detailed causal information
Evolution Across Releases
Introduced alongside MNRG in TS 23.060. Defined the MNRR parameter to provide a reason code (such as 'IMPLICIT_DETACH') explaining why a UE was marked as unreachable (MNRG set), adding diagnostic capability and enabling more nuanced handling of UE state recovery and network procedures.
Defining Specifications
| Specification | Title |
|---|---|
| TS 23.060 | 3GPP TS 23.060 |