Cisco Cisco ASR 5500 Technical Manual
Maximum number of MM signaling requests are associated with the devices with the subscription for
a particular APN
a particular APN
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Network management settings
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Note: The MME should not apply congestion control for high priority access and emergency services. General
NAS−level MM control can be used in order to reject NAS−level MM signaling requests under a general
congestion condition.
NAS−level MM control can be used in order to reject NAS−level MM signaling requests under a general
congestion condition.
APN−Based Session Management Congestion Control
The APN−based session management congestion control can be activated on the MME due to a congestion
situation, by OAM, or by a restart/recovery of a PGW. The MME can reject ESM requests from the UE,
which can be included in the PDN Connectivity, Bearer Resource Allocation, or Bearer Resource
Modification requests. The MME can also deactivate the current PDN connection during congestion
conditions and send a session back−off timer to the UE. When this timer is included, the reactivation request
should not be activated.
situation, by OAM, or by a restart/recovery of a PGW. The MME can reject ESM requests from the UE,
which can be included in the PDN Connectivity, Bearer Resource Allocation, or Bearer Resource
Modification requests. The MME can also deactivate the current PDN connection during congestion
conditions and send a session back−off timer to the UE. When this timer is included, the reactivation request
should not be activated.
The MME can store the Session Management (SM) back−off timer for a particular UE and APN during
congestion and immediately reject any subsequent SM messages from the UE that is targeted to that APN
until the timer runs out. This is required for the UEs that do not support the SM back−off timer (for UE
releases prior to Release 10). The MME first clears this timer if it wants to send a SM message to the UE for
which the timer already runs.
congestion and immediately reject any subsequent SM messages from the UE that is targeted to that APN
until the timer runs out. This is required for the UEs that do not support the SM back−off timer (for UE
releases prior to Release 10). The MME first clears this timer if it wants to send a SM message to the UE for
which the timer already runs.
The UE can complete these actions while the timer runs:
If the APN is provided in the rejected EPS SM request message, or if the SM back−off timer is
received in the NAS deactivate EPS bearer context request message, the UE should not initiate any
SM procedure for the congested APN.
received in the NAS deactivate EPS bearer context request message, the UE should not initiate any
SM procedure for the congested APN.
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If an APN is not provided in the rejected EPS SM request message, then the UE shall not initiate any
SM requests without the APN.
SM requests without the APN.
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These changes do not stop the back−off timer:
Cell
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Tracking Area (TA)
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Public Land Mobile Network (PLAMN)
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Radio Access Technology (RAT)
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The UE is allowed to initiate the SM procedures for high−priority access and emergency services
even when the SM back−off timer runs.
even when the SM back−off timer runs.
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If the UE receives a network−initiated EPS SM request message for the congested APN while the SM
back−off timer runs, then the UE stops the SM back−off timer that is associated with this APN and
responds to the MME.
back−off timer runs, then the UE stops the SM back−off timer that is associated with this APN and
responds to the MME.
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If the UE is configured with permission to override low access priority, and the SM back−off timer
runs due to a rejection message that is received in response to a request with low access priority, the
upper layers in the UE might request the initiation of SM procedures without low access priority.
runs due to a rejection message that is received in response to a request with low access priority, the
upper layers in the UE might request the initiation of SM procedures without low access priority.
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