TAI-based Routing for 20-bit and 28-bit eNB ID

This feature enables MME to perform TAI-based routing for both 20-bit and 28-bit eNB IDs.

Feature Description

MME supports TAI-based routing of handover (HO) and configuration transfer messages towards Pico controller/HeNBGW when the target eNB ID is 28 bits, but it could not support TAI-based routing when the target Pico eNB ID is 20 bits.

Pico controller can transfer the target Pico eNB ID to 28 bits from 20 bits if the handover is Pico-to-Pico, but it could not handle Macro-to-Pico handover as there is no Pico Controller for Macro.

In releases 21.1 and beyond, the behavior of MME is modified so that it can perform TAI-based routing even if target home-eNB ID is 20 bits.

This feature provides a configurable option within MME service to configure target HeNB type (home or macro or both) behind HeNBGW. Based on this configuration, MME allows TAI-based lookup of target eNB, if target eNB ID is not found by MME during handover. By default, TAI-based lookup is performed only for home eNB ID (28-bits).

This feature is also introduced to support identification of target eNB using target TAI for target eNB type Macro or Pico nodes or both so that handover to such eNB can be supported if it is connected to MME through Pico controller/HeNBGW. From MME point of view, Pico controller is a Macro eNB which is using 20 bit eNB ID to support multi-cell.

Along with S1 based intra-MME HO, this feature can be applied to inter MME S1 HO procedures (inbound S10, S3 and Gn handovers). Please note that, in Gn case, MME converts target RNC ID to macro eNB ID so target TAI-based lookup for macro eNB works fine.

This feature allows operators to configure the global eNodeB IDs of HeNBGWs in the MME service. The MME uses this information to perform HeNBGW related functions. In case of S1-based handovers to home eNodeBs served by a HeNBGW, the lookup at MME for the target eNodeB based on global eNB ID will fail, as MME is aware of only the HeNBGW. In those cases, additional lookup needs to be done based on TAI to find the HeNBGW serving the home eNodeB.

Since TAI-based lookup for home or macro eNBs is supported for HeNBGWs, all such HeNBGWs should be defined in HeNBGW management database (HeNBGW-mgmt-db). The HeNBGW-mgmt-db should be associated within mme-service.

In this release, the number of HeNBGW entries in the HeNBGW-mgmt-db has been increased from 8 to 512.

Limitations

The following are the limitations of this feature:

  • TAI-based lookup is performed only for home eNB.

  • TAI should be unique and should not be shared across multiple HeNBGWs. If the TAIs are shared, then any one of the target eNBs sharing the TAC under consideration will be chosen during TAI-based target eNB selection and handover to the eNB might fail.

Configuring TAI-based Lookup of eNB

The following section provides the configuration commands to enable the TAI-based lookup of eNB.

Configuring Target eNB Type for TAI-based Lookup

Use the following configuration commands to configure the target eNB type or target henb-type as home or macro. 

configure
   context context_name
      mme-service service_name
         henbgw henb-type { macro-enb | home-enb | all }
         end

Notes:

  • The henbgw henb-type { macro-enb | home-enb | all } is a new CLI command introduced in 21.1 release to support TAI-based lookup functionality.

  • henbgw: Configures Home eNodeB gateway options.

  • henbgw-type: Configures HeNB type. TAI-based lookup depends on HeNB type.

    • home-enb: Configures HeNB type home-enb (28-bits)

    • macro-enb: Configures HeNB type macro-enb (20-bits)

    • all: Configures HeNB type both macro-enb (20-bits) and home-enb (28-bits)

  • By default, when the henbgw henb-type command is not applied explicitly, target eNB type is set as home-enb.

  • Use the no henbgw henb-type command to delete the existing configuration, if previously configured.

  • The target eNB type configuration is effective only when the henbgw henb-type CLI command is configured within mme-service and the HeNBGW-mgmt-db is associated with HeNBGWs inside mme-service.

Verifying the Target eNB Type Configuration

Use the following commands to verify the configuration status of this feature. 

show mme-service all

- or - 

show mme-service name service_name

service_name must be the name of the MME service specified during the configuration.

This command displays all the configurations that are enabled within the specified MME service.

The following is a sample configuration of this feature. 

configure
   lte policy
      mme henbgw mgmt-db db_name
         henbgw-global-enbid mcc 123 mnc 456 enbid 12345
         henbgw-global-enbid mcc 123 mnc 456 enbid 12543
         end
configure
   context context_name
      mme-service service_name
         henbgw henb-type macro-enb
         associate henbgw-mgmt-db henbdb
         end

Notes:

  • By default, when the henbgw henb-type command is not configured, target eNB type is set as home-enb.

Monitoring and Troubleshooting the TAI-based Lookup

This section provides information regarding show commands and/or their outputs in support of this feature.

The following operations can be performed to troubleshoot any failure related to this feature:

  • Verify if the feature is enabled using show mme-service all CLI command. If not enabled, configure the henbgw henb-type CLI command in MME service Configuration mode and check if it works.

  • Collect and analyze the output of show configuration, show support details, show mme-service name service_name and show mme-service statistics handover commands. Also, check the reported logs, if any. For further analysis, contact Cisco account representative.

  • Check and analyze the debug logs for mme-app, s1ap, mmemgr, and mmedemux facilities to determine if TAI-based lookup fails for a particular TAI.

show mme-service all

The following field is added to the output of the show mme-service all command in support of this feature. 

HENBGW HeNodeB Type: macro-enb
Table 1 show mme-service all Command Output Descriptions

Field

Description

HENBGW HeNodeB Type

Displays the configured type for HeNodeB gateway.

HENBGW HeNodeB Type can be one of the following:

  • macro-enb

  • home-enb

  • all

show mme-service name service_name

The following field is added to the output of the show mme-service name service_name command in support of this feature. 

HENBGW HeNodeB Type: macro-enb
Table 2 show mme-service name service_name Command Output Descriptions

Field

Description

HENBGW HeNodeB Type

Displays the configured type for HeNodeB gateway.

HENBGW HeNodeB Type can be one of the following:

  • macro-enb

  • home-enb

  • all

show mme-service statistics handover

The following fields are added to the output of the show mme-service statistics handover command in support of this feature. 

Handover Statistics:
  Intra MME Handover
    .
    .
    Target TAI based S1 handover
      Attempted:       4
      Success:         3
      Failures:        1
.
.
  EUTRAN<-> EUTRAN using S10 Interface:
    .
    .
    Inbound relocation using Target TAI based S1 HO procedure:
      Attempted:       0
      Success:         0
      Failures:        0
Table 3 show mme-service statisticsCommand Output Descriptions

Field

Description

Target TAI based S1 handover

Attempted

Displays the total number of attempted intra MME S1 handovers that used target TAI to identify the target HeNodeB, if target eNB ID is unknown.

Success

Displays the total number of successful intra MME S1 handovers that used target TAI to identify the target HeNodeB.

Failures

Displays the total number of failed intra MME S1 handovers that used target TAI to identify the target HeNodeB.

Inbound relocation using Target TAI based S1 HO procedure

Attempted

Displays the total number of attempted inter MME S10 handovers where target MME used target TAI to identify the target HeNodeB, if target eNB ID is unknown.

Success

Displays the total number of successful inter MME S10 handovers where target MME used target TAI to identify the target HeNodeB.

Failures

Displays the total number of failed inter MME S10 handovers where target MME used target TAI to identify the target HeNodeB.

show mme-service statistics peer-id

The following fields are added to the output of the show mme-service statistics peer-id peer_id handover command in support of this feature. 

Handover Statistics:
  Intra MME Handover
    .
    .
    Target TAI based S1 handover
      Attempted:       4
      Success:         3
      Failures:        1
.
.
  EUTRAN<-> EUTRAN using S10 Interface:
    .
    .
    Inbound relocation using Target TAI based S1 HO procedure:
      Attempted:       0
      Success:         0
      Failures:        0
Table 4 show mme-service statisticsCommand Output Descriptions

Field

Description

Target TAI based S1 handover

Attempted

Displays the total number of attempted intra MME S1 handovers that used target TAI to identify the target HeNodeB, if target eNB ID is unknown.

Success

Displays the total number of successful intra MME S1 handovers that used target TAI to identify the target HeNodeB.

Failures

Displays the total number of failed intra MME S1 handovers that used target TAI to identify the target HeNodeB.

Inbound relocation using Target TAI based S1 HO procedure

Attempted

Displays the total number of attempted inter MME S10 handovers where target MME used target TAI to identify the target HeNodeB, if target eNB ID is unknown.

Success

Displays the total number of successful inter MME S10 handovers where target MME used target TAI to identify the target HeNodeB.

Failures

Displays the total number of failed inter MME S10 handovers where target MME used target TAI to identify the target HeNodeB.

Bulk Statistics

MME Schema

The following bulk statistics have been added to the MME schema to track the TAI-based lookup attempts, successes and failures during intra-MME S1 and inter-MME inbound S10 handovers:

  • emmevent-s1ho-target-tai-attempt

  • emmevent-s1ho-target-tai-success

  • emmevent-s1ho-target-tai-failure

  • in-s1-ho-4gto4g-s10-target-tai-attempted

  • in-s1-ho-4gto4g-s10-target-tai-success

  • in-s1-ho-4gto4g-s10-target-tai-failures

For detailed information on these bulk statistics, refer to the BulkstatStatistics_documentation.xls spreadsheet that is included as part of the software companion package for this release.