- About this Guide
- Mobility Management Entity Overview
- Mobility Management Entity Configuration
- 128K eNodeB Connections
- A-MSISDN Functionality
- Access Restriction based on Regional Zone Code
- APN Override
- Backup and Recovery of Key KPI Statistics
- Cause Code #66
- Cell Broadcast Center - SBc Interface
- Cell Traffic Trace
- Closed Subscriber Groups
- CSFB and SMS over SGs Interface
- CSFB for 1xRTT
- DDN Throttling
- Default APN for DNS Failure
- eDRX Support on the MME
- Emergency Bearer Services
- Enhanced Congestion Control and Overload Control
- Enhanced Multimedia Priority Service (eMPS)
- Enhanced Event Logging
- Foreign PLMN GUTI Management
- GTP-C Load and Overload Control on MME
- GUTI Re-allocation
- Heuristic and Intelligent Paging
- HSS-based P-CSCF Restoration
- Idle-mode Signaling Reduction
- IMSI Manager Overload Control
- IMSI Manager Scaling on the MME
- Integrity and Confidentiality Algorithms for UE
- IPNE Service
- Limiting the Number of SGWs Tried
- Load Balancing and Rebalancing and VoLTE Offloading
- Local Emergency Numbers List
- Location Services
- MBMS for MME (eMBMS)
- Operator Policy
- Operator Specific QCI
- Operator Policy Selection Based on IMEI-TAC
- Overcharging Protection
- Paging Priority IE Support
- Power Saving Mode (PSM) in UEs
- QoS Profile Support
- S13 Additional IMEI Check
- Selective Authentication
- Session Tracing
- SGW Blacklisting on the MME
- SGSN-MME Combo Optimization
- Single Radio Voice Call Continuity
- SRVCC for 1xRTT
- State-Location Information Retrieval Flag
- TAI-based Routing for 20-bit and 28-bit eNB ID
- Timer-based GBR Bearer Deactivation
- UDPC2 Support for MME/SGSN
- UE Relocation
- VLR Management
- Troubleshooting the MME Service
- Monitor the MME Service
- Engineering Rules
VLR Management
This chapter describes various MME features that provide additional resiliency of the Circuit Switched Fallback (CSFB) service, relating to the management of Visitor Location Registers (VLRs).
- Feature Description
- Enabling VLR Offloading
- Enabling UE Detach on VLR Failure or VLR Recover
- Monitoring and Troubleshooting VLR Offload
Feature Description
These features require a valid license key to be installed. Contact your Cisco Account or Support Representative for information on how to obtain a license.
Passive VLR Offloading
The MME provides the ability for an operator to enable or disable "offload" mode for a specified VLR. This capability enables operators to preemptively move subscribers away from an SGs interface associated with a VLR which is planned for maintenance mode. When this offload command is set on the MME, all sessions matching this VLR are marked with a "VLR offload" flag. During the next UE activity, the MME requires each UE to perform a combined TAU/LAU. This feature is available to all VLRs, both non-pooled VLRs as well as those configured within an MME LAC pool area.
The VLR offload functionality and MME offload functionality cannot be performed at the same time; activation of one prevents activation of the other (and vice versa).
Active VLR Offloading
Active VLR Offloading provides all of the functionality of Passive VLR Offloading, but also actively detaches UEs associated with the VLR during an operator-specified time period. This expedites the process of offloading UEs prior to a planned VLR maintenance event. This feature is available to all VLRs, both non-pooled VLRs as well as those configured within an MME LAC pool area.
The VLR offload functionality and MME offload functionality cannot be performed at the same time; activation of one prevents activation of the other (and vice versa).
UE Detach on VLR Recovery
The MME supports the ability to perform a controlled release of UEs when a failed VLR becomes active again. This feature is available to all VLRs, both non-pooled VLRs as well as those configured within an MME LAC pool area.
This applies to UEs that are currently registered as EPS-Only. This enables the UE to return to a combined attached state to restore SMS services.
UE Detach on VLR Failure
The MME supports the ability to perform a controlled release of UEs when an active VLR connection fails. This applies to CSFB UEs that are currently registered to the VLR that failed. This feature is available to all VLRs, both non-pooled VLRs as well as those configured within an MME LAC pool area.
This enables the UE to return to a combined attached state on a different VLR.
Enabling VLR Offloading
- Enabling Passive VLR Offloading
- Enabling Active VLR Offloading
- Verifying VLR Offload Status and Configuration
Enabling Passive VLR Offloading
The following Exec mode command instructs the MME to mark UEs associated with the specified VLR with a "VLR offload" flag. This enables the MME to preemptively move subscribers away from an VLR which is scheduled to be put in maintenance mode.
sgs offload sgs-service service-name vlr vlr-name start time-duration 0 [ -noconfirm ]
The following command stops the marking of subscribers associated with the specified VLR to an offload state.
sgs offload sgs-service service-name vlr vlr-name stop [ -noconfirm ]
Notes:
Enabling Active VLR Offloading
The following Exec mode command instructs the MME to mark UEs associated with the specified VLR with a "VLR offload" flag, and begin detaching these UEs according to the time-duration specified in the command. Affected UEs are detached and required to reattach to another VLR.
sgs offload sgs-service service-name vlr vlr-name start time-duration duration [ -noconfirm ]
The following command stops active VLR offloading for UEs associated with the specified VLR.
sgs offload sgs-service service-name vlr vlr-name stop [ -noconfirm ]
Notes:
- A start time-duration duration entry must be an integer from 1 through 3000 to enables Active VLR Offloading and Passive VLR Offloading. The MME splits this time duration into n intervals, 5 seconds apart. A maximum of 50 subscribers will be actively detached per interval. For example, a setting of 120 minutes with 60000 subscribers would process all subscribers in 100 minutes. Any subscribers remaining at the expiry of the time-duration will not be detached, but will be marked with the "VLR offload" flag.
- VLR Offloading and MME offloading cannot be performed at the same time.
Verifying VLR Offload Status and Configuration
The following command displays VLR offload statistics for the specified SGs service.
show sgs-service offload-status service-name sgs_svc_name
The following sample output shows VLR Offload related statistics.
[local]asr5x00# show sgs-service offload-status service-name sgssvc VLR Name : vlr1 VLR Offload : Yes Offloaded Count : 31678 Total Count : 43051 VLR Name : vlr2 VLR Offload : No Offloaded Count : 0 Total Count : 45789
To clear the counters displayed by the previous command, issue the following command.
clear sgs-service offload-status service-name sgs_svc_name
When Passive or Active VLR Offload is enabled, the following command displays the "VLR Offload" flag for the specified VLR.
show mme-service session vlr-name vlr_name
The following output shows the VLR Offload flag enabled.
[local]asr5x00# show mme-service session vlr-name vlr1 CSFB Information: SGS Assoc State: SGs-ASSOCIATED SGS Service: sgssvc VLR: vlr1 LAI: 123:456:200 Pool Area: pool1 Non-Pool Area: N/A P-TMSI: 0x1 Flags: VLR Reliable Indicator VLR Offload
The following command shows the offload state of all VLRs on the system.
show sgs-service vlr-status full [local]asr5x00# show sgs-service vlr-status full MMEMGR : Instance 6 MME Reset : Yes Service ID : 2 Peer ID : 100794369 VLR Name : vlr1 SGS Service Name : test SGS Service Address : 192.60.60.25 SGS Service Port : 29118 VLR IP Address : 192.60.60.6 VLR Psgsort : 29118 Assoc State : DOWN Assoc State Up Count : 2 VLR Offload : No
To clear the counters displayed by the previous command, issue either of the following commands. The first command clears statistics for all VLRs, while the second command clears statistics for the specified VLR only.
clear sgs-service vlr-status service-name sgs_svc_name clear sgs-service vlr-status vlr-name vlr_name
Enabling UE Detach on VLR Failure or VLR Recover
- UE Detach on VLR Recovery
- UE Detach on VLR Failure
- Verifying UE Detach on VLR Failure/Recovery Status and Configuration
UE Detach on VLR Recovery
The following Exec mode command instructs the MME to automatically perform active recovery of UEs when a failed VLR becomes responsive again.
sgs vlr-recover sgs-service sgs_svc_name duration duration backoff-timer time [ -noconfirm ]
Notes:
- When this command is issued, the MME monitors the availability of all VLRs. If a failed VLR become available again, the MME attempts to recover UEs that failed while the VLR was unavailable with an EPS Detach.
- When a VLR is down, and a UE needs to associate with the VLR that went down, the UE will be downgraded to EPS-Only-Attach when initially attaching. This command should be issued after the VLR recovers.
- UEs which required CSFB (voice) and were downgraded as a result of the VLR being down will not be affected by this command. This command remains active until it is disabled with the no sgs vlr-recover command.
-
duration duration Specifies the number of minutes during which all qualifying UEs will be recovered.
The MME splits this duration into n intervals, 5 seconds apart. A maximum of 50 subscribers are processed per interval. For example, a setting of 2 minutes with 100 subscribers would result in the MME processing all subscribers in the first 2 intervals (10) seconds. Any subscribers remaining at the expiry of the duration will not be processed.
-
backoff-timer time Specifies the number of seconds that the MME will wait, following the detection of a recovered VLR, before starting the VLR recovery actions.
- Refer to the sgs vlr-recover command in the Exec Mode chapter of the Command Line Interface Reference for more information.
The command listed below disables the sgs vlr-recover functionality.
no sgs vlr-recover sgs-service sgs_svc_name [ -noconfirm ]
UE Detach on VLR Failure
The MME will report a command line interface error (Invalid operation: VLR already set for failure.) if an attempt is made to configure/enable both methods simultaneously.
Configuring Automatic UE Detach on VLR Failure
The following commands configure the MME to automatically detect a VLR failure and initiate the controlled release of CSFB UEs. The configuration of this feature also allows a UE detach rate (UEs per second) to be defined.
configure context context_name sgs-service sgs_svc_name vlr-failure duration minutes backoff-timer seconds detach-rate number [ -noconfirm ] end
The following commands disable this configuration:
configure context context_name sgs-service sgs_svc_name no vlr-failure [ -noconfirm ] end
Refer to the vlr-failure command in the MME SGs Service Configuration Mode Commands chapter of the Command Line Interface Reference for more information.
Manually Enabling UE Detach on VLR Failure
The following Exec mode command instructs the MME to perform controlled release of CSFB UEs connected to a VLR when a VLR becomes unavailable.
sgs vlr-failure sgs-service sgs_svc_name duration duratioin backoff-timer time [ -noconfirm ]
Notes:
- When enabled, the MME monitors the availability of all VLRs. If one or more VLRs become unavailable, the MME performs a controlled release (EPS IMSI detach) for all UEs associated with that VLR. If another VLR is available, the MME sends a combined TA/LA Update with IMSI attach.
-
duration duration Specifies the number of minutes during which all qualifying UEs will be detached. Enter an integer from 1 to 3000.
The MME splits this duration into n intervals, 5 seconds apart. A maximum of 50 subscribers are processed per interval. For example, a setting of 2 minutes with 100 subscribers would result in the MME processing all subscribers in the first 2 intervals (10) seconds. Any subscribers remaining at the expiry of the duration will not be processed.
-
backoff-timer time Specifies the number of seconds the MME will wait following the detection of a VLR condition before starting the controlled release of affected UEs. Enter an integer from 1 through 3000.
-
detach-rate This optional keyword specifies a maximum number of detaches to perform per 5 second cycle. Note: This keyword is available only for the vlr-failure command in the SGs Configuration Mode.
For example, if 12,000 subscribers are to be detached during a 5 minute window (duration = 5 minutes), the MME calculates 60 cycles (5 minutes / 5-second cycles) which results in 200 UEs to detach per cycle.
If the detach-rate is configured to 100, the MME will only detach 100 per 5 second cycle, resulting in a total of 6000 detaches. Any remaining UEs will remain attached until detached by other means (UE/network detach, etc).
The enabling command remains active until it is disabled with the following command:
no sgs vlr-failure sgs-service sgs_svc_name [ -noconfirm ]
Refer to the sgs vlr-failure command in the Exec Mode (D-S) chapter of the Command Line Interface Reference for more information.
Verifying UE Detach on VLR Failure/Recovery Status and Configuration
Use the following command to display the offload status of all VLRs on the system.
show sgs-service vlr-status full
This sample output shows the fields relating to UE Detach on VLR Failure and UE Detach on VLR Recover. Not all fields shown below may be displayed, based on your configuration:
[local]asr5x00# show sgs-service vlr-status full Exec Configured VLR Failure Detach : No Detached Count : 0 Total : 0
SGs Service Configured VLR Failure Detach : Yes Detached Count : 10 Total : 800 VLR Recover Detach : Yes Detached Count : 11 Total : 102
To clear the counters displayed by the previous command, issue either of the following commands. The first command clears statistics for all VLRs for the specified SG, while the second command clears statistics for the specified VLR only.
clear sgs-service vlr-status service-name sgs_svc_name clear sgs-service vlr-status vlr-name vlr_name
Monitoring and Troubleshooting VLR Offload
SNMP Traps
The following traps are generated to track conditions relating to VLR associations:
The VLR down trap is raised only after the VLR goes to the DOWN state after being UP. When all VLR's are down after at least one has been UP, the all VLR's DOWN trap is raised.
- starVLRAssocDown and starVLRAssocUp - indicates a condition when an association of a VLR is down (VLRAssocDown), and when a down association comes back up (VLRAssocUp).
- starVLRDown and starVLRUp - indicates a condition where all SCTP associations to a specific VLR are down (VLRDown), and when a down VLR comes back up (VLRUp).
- starVLRAllAssocDown and starVLRAllAssocDownClear - indicates a condition when all SCTP associations of all VLRs are down (VLRAllAssocDown), and when a down association comes back up (VLRAllAssocDownClear).
Bulk Statistics
This SGs schema provides operational statistics that can be used for monitoring and troubleshooting the SGs connections on a per-VLR basis.
Refer to the SGs Schema Statistics chapter of the Statistics and Counters Reference for detailed explanations of all bulk statistics provided in this schema.
Show Command(s) and/or Outputs
This section provides information regarding show commands and/or their outputs.
VLR Offload Status
The following command shows the status of the VLR offload process for the specified SGs service.
show sgs-service offload-status service-name sgs_svc_name
The following command shows the status and configuration information of all VLRs on the system.
show sgs-service vlr-status full
UE Detach on VLR Recovery and VLR Failure
The following command shows the statistics resulting from the sgs vlr-recover and sgs vlr-failure commands.
show sgs-service vlr-status full
Refer to the show sgs-service chapter of the Statistics and Counters Reference for detailed explanations of all information displayed by this command.