Node Level Blacklisting
On identifying an unreachable SGW,
the SGW is blacklisted for a configured amount of time. The show CLI discussed
in the Monitoring and Troubleshooting section displays the expiry timestamp of
this SGW, indicating the blacklisting duration. This feature is based on a per
mme-service configuration, therefore a separate list to store blacklisted SGWs
is created for every mme-service.
During the ATTACH, TAU and Handover procedures, the MME selects an SGW
that is not blacklisted. If all SGWs are blacklisted, then the MME attempts to
use one of the blacklisted SGWs instead of directly rejecting the call. If the
Create Session Response time expires, the call is rejected.
The blacklisted SGWs are completely removed from the MME based on the
following configuration changes/execution:
If the sgw-blacklist
configuration is removed – SGW blacklisting feature is disabled.
If the sgw-blacklist configuration is reconfigured, that is, if
the timeout or the msg-timeouts-per-min values are changed.
If mme-service is stopped; a critical parameter is removed from
If the clear CLI is executed, refer to Monitoring and
The MME does not remove the blacklisted SGWs based on any SGW
initiated request/response message.
The following functionalities are also included for SGW blacklisting:
SGW blacklisting takes place using the following methods in the MME:
When no echo response is received from the SGW, a node-level path
failure indication is sent to all SESSMGRs.
Based on the node-level path failure indication, the MME blacklists
the SGW for the configured time and stores it as a node-level blacklisted type.
Along with node-level blacklisting, MME supports blacklisting of SGW
based on Create Session Response timeout per SESSMGR instance. The Session
Manager Level blacklisting is local to a specific SESSMGR instance and its
particular mme-service where the Create Session Response times out.
To avoid broadcasting among SESSMGRs, session manager level
blacklisting is not shared among SESSMGRs.
Along with “sgw-blacklist timeout” configuration,
"msg-timeouts-per-min” configuration is configured, which is only required for
sgmr-level blacklisting. Instead of blacklisting an SGW in the first Create
Session Response timeout, the MME blacklists an SGW if the number of Create
Session Response timeouts within a minute reaches the configured
msg-timeouts-per-minute value. For more information, refer to Configuring SGW
Blacklisting on the MME section.