- 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
Limiting the Number
of SGWs Tried
This feature enables the operator to configure the number of pooled SGWs to be tried.
Feature Description
Default Behavior
If this feature is not enabled or is disabled, the MME uses or falls back to the default behavior which is in compliance with 3GPP TS 29.274, Section 7.6. The MME sends Create-Session-Request message to one SGW in the pool. If the SGW node is not available, the MME picks the next SGW from the pool and again sends a Create-Session-Request message. The MME repeats this process. For an Attach procedure, the MME tries up to five (1 + 4 retries) different SGWs from the pool. In the case of a HO procedure, the MME will try every SGW in the entire pool of SGWs sent by the DNS. If there are no further SGW nodes available in the DNS pool or if the guard timer expires, then MME stops trying and sends a Reject with cause "Network-Failure" towards the UE and the UE must restart the Attach/Handover procedure.
Benefits
The amount of signaling at Attach or Handover can be reduced.
The amount of time to find an available SGW can be reduced.
How It Works
The operator has access to a feature-specific CLI command sgw-retry-max to enable this feature and override the default behavior. sgw-retry-max configures the maximum number of SGWs to be retried from the DNS pool list during either Attach or Handover procedures. So the limit to the number of tries will be 1 + limit set.
For either Attach or Handover procedures, the MME sends Create-Session-Request message to one SGW in the pool. If the SGW node is not available, the MME picks the next SGW from the pool and retries. It again sends a Create-Session-Request message. At most, the MME retries only as many times as the number of retries configured with the sgw-retry-max command. If no SGW responds or only responds negatively and the MME reaches the configured limit for retries, then MME stops trying and sends the UE a Reject with cause "Network-Failure". At this point, the UE must restart the Attach/Handover procedure.
This feature-specific command is available for provisioning in both the MME service configuration and the Call-Control Profile configuration. To enable the feature, the feature-specific command must be configured under MME service configuration. We recommend provisioning under both modes. If sgw-retry-max sgw-retry-max command is configured under both MME service and Call-Control Profile, then the configuration under Call-Control Profile takes precedence.
The configuration under the Call-Control Profile provides the operator with additional control over "roamers" and "homers". For example, if sgw-retry-max under Call-Control Profile is set to 2 and if sgw-retry-max under MME service is set to 4, then if a "homer" subscriber Attaches, the MME retries 2 times but for all the subscribers other than "homers" the MME retries 4 times.
The feature is disabled with the entry of no sgw-retry-max no sgw-retry-max in the configuration. The MME reverts to the use of the default behavior.
To change the Reject cause code sent by the MME, use the local-cause-code-mapping gw-unreachable command in the Call-Control Profile configuration mode. Refer to the Call-Control Profile Configuration Mode Commands section in the Command Line Interface Reference for details.
Configuring a Limit to the Number of SGWs Tried
Enabling the Feature in the MME Service
Using the following configuration enables this feature in the MME service configuration. This feature sets the maximum number of SGW selection retries to be attempted during Attach/HO/TAU. This means, the total number of tries would be 1 (the initial try) + the sgw-retry-max value (the maximum number of retries).
configure context ctxt_name mme-service service_name sgw-retry-max max_number end
Notes:
-
ctxt_name - Identifies the context in which the MME service configuration resides. Enter a string of 1 through 79 alphanumeric characters
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service_name - Identifies the previously configured MME service. Enter a string of 1 through 79 alphanumeric characters.
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max_number - Sets the maximum number of retries possible. Enter an integer from 0 to 5. If 0 (zero) is configured, then the MME sends Create-Session-Request to the 1st SGW and if that SGW does not reply, the MME does not select any further SGW to retry. The MME then rejects the ongoing procedure (Attach/HO/TAU) and sends a Reject message.
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Entering this command enables the feature which overrides the default behavior.
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To disable this feature, enter no sgw-retry-max . The MME falls back to the default behavior.
Enabling the Feature for Call-Control Profile
Using the following configuration enables this feature in the Call-Control Profile configuration. This feature sets the maximum number of SGW selection retries to be attempted during Attach/HO/TAU. This means, the total number of tries would be 1 (the initial try) + the sgw-retry-max value (the maximum number of retries).
configure call-control-profile profile_name sgw-retry-max max_number end
Notes:
-
profile_name - Identifies the previously configured Call-Control Profile. Enter a string of 1 through 64 alphanumeric characters.
-
max_number - Sets the maximum number of retries possible. Enter an integer from 0 to 5. If 0 (zero) is configured, then the MME sends Create-Session-Request to the 1st SGW and if that SGW does not reply, the MME does not select any further SGW to retry. The MME then rejects the ongoing procedure (Attach/HO/TAU) and sends a Reject message.
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Entering this command provides the operator with greater control over "roamers" and "homers". For example, if sgw-retry-max under Call-Control Profile is set to 2 and if sgw-retry-max under MME service is set to 4, then if a “homer” subscriber Attaches, the MME retries 2 times but for all the subscribers other than “homers” the MME retries 4 times.
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If the sgw-retry-max command is configured under both MME service and Call-Control Profile, then the configuration under Call-Control Profile takes precedence.
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To remove this configuration from the Call-Control Profile, enter no sgw-retry-max .
Verifying the Feature Configuration
Use the show configuration command to generate output that displays the values configured with sgw-retry-max . The following illustrates the sections of the output that will indicate the sgw-retry-max configuration for either or both MME service and Call-Control Profile:
(please note that variables shown are for clarification and are not suggested or real)
[local]hostname# show configuration ... ... mme-service mmesvc ... ... bind s1-mme ipv4-address 192.xx.xx.2 msc default ip-address 192.xx.xx.56 sgw-retry-max 2 exit ... ... ... ... call-control-profile ccp ... ... s1-reset detach-ue sgw-retry-max 3 exit