The MME provides the ability for an operator to enable or disable "offload" mode for the specified Visitor Locations Registers (VLRs). This capability enables operators to preemptively move subscribers away from an SGs interface associated with a VLR which is planned for maintenance mode. When the sgs 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 and those configured within an MME LAC pool area.

The VLR offload functionality and MME offload functionality cannot be activated at the same time.

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 and those configured within an MME LAC pool area.

The VLR offload functionality and MME offload functionality cannot be activated at the same time.

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 and 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.

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 and those configured within an MME LAC pool area.

This enables the UE to return to a combined attached state on a different VLR.

When multiple VLRs in the same pool are configured in the MME, and when one VLR fails, the subscribers on the failed VLR get attached to only one of the surviving VLRs. As a result, the subscribers are not distributed evenly across the surviving VLRs. The round-robin balancing algorithm is used to distribute subscribers across multiple available VLRs. VLR round-robin load balance is configurable through the CLI.

The MME allocates a VLR in the pool using the Round-robin algorithm for VLR offload (Active and Passive) and VLR failure cases. However, the MME does not use any form of load balancing if the default VLR is configured in pool area through hash-value non-configured-value use-vlr vlr_name . The default VLR setting takes precedence over the next available or round-robin load balance setting. By default, Round Robin Load Balancing is disabled.

Note	The MME displays a warning message, if the default VLR is already configured while trying to configure the VLR Round-robin Load Balancing.

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:

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 per session manager. For example, a setting of 5 minutes with 600 subscribers in a session manager (from the given VLR) would detach 10 subscribers per 5-second interval. Node level detach rate should be estimated by taking into account the number of session manager tasks. 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.

Use the following configuration to enable VLR round-robin load balance:

configure 
   context context_name 
      sgs-service sgs_svc_name 
         offload method { round-robin |  next-available } 
          end 

NOTES:

• sgs-service sgs_svc_name : Configures the SGs Service.

• offload method { round-robin | next-available } : Configures the round-robin or next-available load balancing method for affected sessions during VLR offload or failure.

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.

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.

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 
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 

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 per session manager. For example, a setting of 5 minutes with 600 subscribers in a session manager (from a given VLR) would result in the session manager processing 10 subscribers per 5-second interval. Node level detach rate should be estimated by taking into account the number of session manager tasks. 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 ] 

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:

show sgs-service vlr-status full 
Exec Configured VLR Failure Detach : No         Detached Count : 0        Total : 0 

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 

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.

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.

This section provides information regarding show commands and/or their outputs.