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
command in the Call-Control Profile configuration mode. Refer to the
Call-Control Profile Configuration Mode Commands section
Command Line Interface Reference for details.