The SGW determines
whether a bearer needs DDN throttling based on the bearer's ARP priority level
and operator policy (operator's configuration in the SGW of the ARP priority
levels to be considered as priority or non- priority traffic). While
throttling, the SGW throttles the DDN Requests for low and normal bearers based
on priority. The MME determines whether a Downlink Data Notification request is
priority or non-priority traffic on the basis of the ARP priority level that
was received from the SGW and operator policy.
Profile supports DDN Throttling. The Congestion Control policy allows the
operator to configure three different action profiles critical, major and minor
based on the congestion level. During Congestion the operator configures the
action to be taken using action profiles. Congestion Action profile allows
configuration of DDN Throttling parameters.
threshold is reached the following actions are taken on DDN requests based on
the operator configuration:
- Reject all DDN requests based
on ARP and LAPI. DDN Ack message is sent with failure cause to the SGW. Paging
is not initiated.
- Reject all DDN requests if
ARP or LAPI values are not configured.
- Enable SGW Throttling. DDN
Ack message is sent to the SGW with throttling factor and throttling delay
The Session Manager
is configured to handle DDN requests based on the DDN's current congestion
status and the operator configuration. Session Manager stores the congestion
status information along with S1-AP or NAS messages received from the MME
manager. This data is used to handle DDN requests.
The Session Manger
handles congestion for incoming DDN requests in the following ways:
- If the congestion status does
not indicate any congestion, session manager initiates paging without any
change in existing behavior.
- If the congestion threshold
is reached, session manager either decides to reject DDN requests or enable
throttling DDN requests towards SGW, based on the action profile corresponding
to the threshold level. A throttling factor and throttling delay is added to
the DDN Ack message and is sent to the SGW. If DDN Rejection is based on
configuration then DDN Ack will not contain any throttling factor and
throttling delay value.
- If the action profile indicates DDN
requests to be rejected, the sessmgr does not initiate paging. A DDN Ack
message is sent with the configured cause value. The default cause value is
"Unable to page UE".
- If the action profile indicates
throttling in SGW is enabled, then the sessmgr includes the throttling factor
and the throttling delay value in the DDN Ack, which is sent to the SGW. If
action profile indicates DDN requests to be rejected, then throttling
parameters are not included in the DDN Ack message.
is configured with arp-watermark, and if the PDN has multiple bearer and ARP
values, the DDN requests are serviced depending on the following scenarios:
- If DDN is
received without bearer ID and ARP value, then the DDN requests are allowed and
all bearers remain active. The DDN requests will not be rejected unless MME
receives the ARP values and all bearers remain active, as part of the paging
- If DDN is
received with a bearer ID but not an ARP value, the DDN requests are still
allowed and all bearers will be active as part of a paging procedure. But, if a
stored ARP value matches with the configured arp-watermark value, DDN requests
The action to
reject DDN requests or enable SGW throttling is independent of each other. The
operator can configure either or both actions for each action profile.
If there is a
configuration change in DDN Throttling parameters, then the action is applied
only upon receiving the next DDN request.
- If configuration
is modified to disable throttling, then it will come into effect immediately
while processing the next DDN. MME shall send throttling IE so that it
de-activates the DDN throttling timer at SGW.
- If configuration
is modified to change throttling values, throttling begins after a delay of few
seconds. The new throttling value is sent to the SGW when the ongoing
throttling time (timer = previously sent timestamp + new throttling delay)
If the Session
Manager crashes, the SGW list with throttling information is lost on recovery.
In this condition, the throttling parameter information is sent to the SGW even
before the ongoing throttling expires. If congestion persists after session
manager recovery, the throttling parameters are sent again for recovery.