Operator policies (proprietary Cisco functionality) empower the carrier/network operators to configure preferred call handling practices. Also, operator policies can be configured to determine the granularity of the implementation: to groups of incoming calls or simply to one single incoming call. The purpose, use, and configuration of operator policies is outlined in the Operator Policy chapter elsewhere in this guide.
Based on the configuration (see Configuring Operator Policy Based on IMEI-TAC), the MME will select / re-select the operator policy whenever the MME retrieves the IMEI or IMEI-SV in one of the following scenario:
- normal 4G Attach when the IMEI/IMEI-SV is retrieved via Identity-Request with IMEI.
- normal 4G Attach when the IMEI/IMEI-SV is retrieved via Security-Mode-Complete (policy attach imei-query-type under MME service must be enabled).
- normal 4G TAU when the IMEI/IMEI-SV is retrieved via Security-Mode-Complete (policy tau imei-query-type under MME service must be enabled).
- inbound handover when IMEI/IMEI-SV is received with IMSI via the Forward-Relocation-Request.
- S10 and S3 Attaches when IMEI/IMEI-SV is retrieved with IMSI via EGTP-Identification-Request.
- Inter-RAT TAU and Intra-RAT TAU with MME change when IMEI/IMEI-SV is received with IMSI in Context-Response.
Selection Based on IMEI-TAC
With Releases 18.5 and higher,"Operator Policy Selection Based on IMEI-TAC" enables the MME to selects / re-select an operator policy for call handling based on the user equipment's (UE's) unique international mobile equipment identity - type allocation code (IMEI-TAC) rather than the normal selection method, which is based on the UE's international mobile subscriber identity (IMSI) and PLMN-ID. The IMEI number is assigned to a mobile device or user equipment (UE) by the manufacturer. The network uses the IMEI to identify if devices are valid.
Including the type allocation code (TAC) in the operator policy selection process supports network access restrictions being applied to UEs based on the type of wireless device identified by the IMEI-TAC. The TAC, the first eight digits of the 15-digit IMEI or 16-digit IMEI-SV, identifies the equipment manufacturer, the wireless device type and the model number (if there is one); for example, TAC of 35201906 identifies an Apple iPhone 5S.
With Release 18.6 and higher, the MME supports configuration of up to 25,000 IMEI-TAC, up from the original number of 1024 IMEI-TAC per MME. As well, these IMEI-TAC can be configured in groups listing individual IMEI-TAC and/or organized in ranges of IMEI-TAC. Up to 50 IMEI-TAC groups can be configured per MME and once an IMEI-TAC group is created, each group can be configured with up to 500 unique IMEI-TAC values and/or up to 20 IMEI-TAC ranges - which can overlap. For command details, refer to the Configuration section below.
Granular Selection Options for IMEI-TAC: MCC/MNC, MSIN, PLMNID
IMEI-TAC + Service PLMNID,
IMEI-TAC + MCC-MNC of UE,
IMEI-TAC + MCC-MNC of UE + Serving PLMNID,
IMEI-TAC + IMSI,
IMEI-TAC + IMSI + Serving PLMNID,
The MME uses this configuration to select the operator policy whenever it retrieves the IMEI/IMEI-SV from either a UE or a peer for all non-emergency calls.