The MME supports
Downlink Data Notification (DDN) Throttling. With this feature, the MME is
provisioned to reject non-priority (traffic based on ARP and LAPI) DDN Requests
when the UE is in idle mode. Additionally, the MME dynamically requests the
S-GW to reduce the number of DDN Requests based on a throttling factor and a
throttling delay specified in the DDN Ack message.
MME supports the
following functions for DDN Throttling:
Rejection of DDN requests when
configured congestion threshold is reached.
configuration of cause value to be sent in DDN Ack message when DDN is rejected
rejection based on ARP.
rejection based on LAPI.
configuration of DDN throttling factor and throttling delay values to be sent
in DDN Ack message to SGW during congestion.
A valid license key
is required to enable DDN Throttling. Contact your Cisco Account or Support
representative for information on how to obtain a license.
How It Works
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.
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.
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.
Memory Impact --
There is a negligible impact on memory, which stores the SGW information
created to process the incoming DDN throttling request. A list of SGW entries
are created in this process. The following information is stored in the SGW:
SGW IP address
Congestion Status time at
which throttling status were sent in the DDN Ack
Timestamp Congestion status
for which throttling information was last sent
The above mentioned
information is required to keep the Session Manager in sync with the SGW's
throttling status. However, to keep the memory impact minimal the SGW
information list is created only during congestion and throttling factors are
configured in the action profile. On completion of DDN throttling, congestion
is cleared and the SGW entry in the list is deleted to process the subsequent
The DDN Throttling
feature complies with the following standards:
3gpp TS 29.274, Version
10.4.0, Tunneling Protocol for Control
3gpp TS 23.401, Version
10.4.0, General Packet Radio Service (GPRS) enhancements
for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access.
section documents the configuration procedures for DDN Throttling
and related functionality.
ddn is a newly
added keyword to this command. This keyword allows the operator to reject DDN
requests during congestion. The operator can reject DDN requests based on ARP
or LAPI values or both. An option is provided to reject all DDN requests
without using ARP/LAPI values.
configurelte-policy congestion-action-profile profile_namereject ddn [ arp-watermark arpwatermark_value [ cause cause_value ] | cause cause_value | lapi [ cause cause_value ] ] none ddn [ lapi | arp-watermark ]end
ddn keyword configures action to be taken for all DDN
lapi keyword indicates that DDN reject is applicable
for UEs with LAPI.
arp-watermark keyword indicates that DDN reject is
applicable for ARP values greater than or equal to the ARP specified. The ARP
value ranges from 1 through 15.
cause keyword rejects DDN with the specified cause
value. The valid cause value ranges from 1 through 255. The default value is 90
with the display message “Unable to page ue”.
none disables DDN configuration.
If the value of
arp-watermark does not match with the DDN's ARP value, then the DDN
notifications is not rejected, and all bearers remain active.
delay are new
keywords added to this command in this release. This Command allows the
operator to configure the throttling factor and throttling delay values to be
sent in DDN Ack message.
value will be converted internally to seconds, minutes or hours as defined in
the 3gpp Spec 29.274.
generates a display that provides a concise listing of congestion control
statistics. The command offers four keyword options:
critcal | full | major | minor
In the output example below, the critical keyword has been included
in the command so only Critical information is shown. The displayed fields are
the same when the full, major, or minor options are used with the command.
Critical Congestion Policy Action Congestion Policy Applied : 0 times PS attaches Rejected : 0 times Dropped : 0 times PS attaches Rejected : 0 times Dropped : 0 times Combined attaches Rejected : 0 times Dropped : 0 times S1-Setup Rejected : 0 times Dropped : 0 times Handover Rejected : 0 times Dropped : 0 times Addn-pdn-connect Rejected : 0 times Dropped : 0 times Addn-brr-connect Rejected : 0 times Dropped : 0 times Service-Request Rejected : 0 times Dropped : 0 times TAU-Request Rejected : 0 times Dropped : 0 times S1AP Overload Start Sent : 2 times S1AP Overload Stop Sent : 2 times Excluded Emergency Events : 0 times Excluded Voice Events : 0 times DDN Request Rejected : 0 times ARP-Based : 0 times LAPI-Based : 0 times
The DDN Request field
indicates the number of DDN requests rejected based on the CLI configuration in
the Congestion Action Profile.
The Rejected field provides
information on the total number of DDN rejections based on the CLI
The ARP-based field indicates
the number of DDN rejected based on the ARP value. For example, reject ddn
arp-watermark 10 increments the counter once the ARP value of DDN requests
received is 10 and above.
The LAPI-Based field
indicates the number of DDN rejected based on the LAPI value.
For LAPI based
UEs, both cli are valid, it means if DDN rejection happened due to ARP-based
condition then only ARP-based counter will be incremented.