Cisco Cisco ASR 5000
MTC Congestion Control
How It Works ▀
SGSN Administration Guide, StarOS Release 18 ▄
How It Works
SGSN Congestion Control
The deciding parameter for triggering congestion control in the SGSN will be the overall system CPU utilization,
service CPU utilization, and system memory utilization. This information will be periodically monitored by the resource
manager (ResMgr) which will informed the SGSN’s IMSIMgr.
service CPU utilization, and system memory utilization. This information will be periodically monitored by the resource
manager (ResMgr) which will informed the SGSN’s IMSIMgr.
Mobility Management (MM) Congestion Control - For congestion control of MM messages, system-detected
congestion is based on
congestion is based on
system CPU utilization,
service CPU utilization
system memory utilization
Session Management (SM) Congestion Control - For congestion control of session management messages, system-
detected congestion is based only on system CPU utilization.
detected congestion is based only on system CPU utilization.
The MTC Congestion Control functionality enables the operator to configure different congestion-action-profiles, which
applies at different threshold levels.
applies at different threshold levels.
APN-level Congestion Control for MM
APN-level congestion control for mobility management (MM) is applied to those UEs that have subscribed for APNs
configured for congestion control.
configured for congestion control.
During system-level congestion, if the chosen congestion-action-profile has the "apn-based" parameter configured as
enabled, then APN-based congestion control is applied.
enabled, then APN-based congestion control is applied.
Once the SGSN receives the subscription for a subscriber, if any of the subscribed APNs are configured for congestion
control, then the call is rejected with a backoff timer value sent to the UE in the Reject message according to the
following scenario:
control, then the call is rejected with a backoff timer value sent to the UE in the Reject message according to the
following scenario:
A random MM backoff timer (T3346) value, derived from the selected min-max range configured for that APN,
is sent to the UE in Reject messages.
1. The minimum and maximum range for the MM backoff timer value is selected from the APN Profile
configuration.
2. If the timer is not configured at the APN Profile level, then the SGSN takes the MM backoff timer as
configured at either the GPRS or SGSN service level.
3. If timer is not configured at the service level, then the default values (min-15 max-4320) are applied.
If the subscriber retries Attach when the backoff timer is running, then the SGSN rejects the Attach, sending the
remaining time for backoff in the Reject message.
If the subscriber retries Attach with a change in signaling priority when the backoff timer is running, then the
SGSN accepts the Attach, based on configuration; for example,
1. if Reject is associated with LAPI and APN-based parameters,
2. then subscriber sends a message without LAPI
3. then the Attach is accepted.
2. then subscriber sends a message without LAPI
3. then the Attach is accepted.