Internet of Things (IoT) is a computing concept where everyday objects have internet connectivity and they can collect and exchange data. IoT is a network which can comprise of a wide variety of physical devices, vehicles, buildings, and any other device/object used in our daily lives. They are embedded with sensors, software and network connectivity which help them communicate with other devices in the network and can be controlled remotely thus increasing efficiency, accuracy and economic benefit. Any device/object which has to be a part of the IoT network must have:

• Long battery life

• Low device cost

• Low deployment cost

• Full network coverage

• Support to connect to large number of devices

Power Saving Mode (PSM) was introduced in 3GPP Release 12, to improve device battery life of IOT devices. The most significant benefit of this feature is the UE has more control in terms of power management required for its application. There are a wide range of IoT applications where flexibility of the UE to manage its power is very important and also implementation of PSM can prevent network congestion. The timers of all the devices can be managed using PSM, and the wake-up periods can be adjusted to be offset as much as possible. This way all of the devices will not wake at the same time and attempt to access the network. The PSM mode is similar to power-off but the UE remains registered on the network.

The UE activates PSM by including two timer values in the Attach or Tracking Area Update (TAU). The first timer is the T3324, which defines the time the UE stays active after idle mode following the Attach or TAU procedure. The second timer is an extended T3412 which defines the extended time for an UE to send periodic TAU.

Power Saving Mode Timers

T3324 Active Timer

The UE requests for a T3324 Active Timer value during Attach and TAU procedures. The MME allocates the T3324 value to the UE. The T3324 active timer determines the duration during which the device remains reachable for mobile terminated transaction on transition from connected to idle mode. The device starts the active timer when it moves from connected to idle mode and when the active timer expires, the device moves to Power Saving Mode. The MME takes the UE requested value and MME local configuration into account for determining the Active Timer value. The MME includes the T3324 value IE in the ATTACH ACCEPT/TAU ACCEPT message only if the T3324 value IE was included in the ATTACH REQUEST/TAU REQUEST message. A UE using PSM is available for mobile terminating services only for the period of an Active Time after a mobile originated event like data transfer or signaling for example after a periodic TAU/RAU procedure.

The MME allows a value of '0' for the T3324 timer. In this case the UE enters the Power Saving Mode immediately.

T3412 Extended Timer

The T3412 timer is also referred to as the periodic Tracking Area Update (TAU) timer. Periodic tracking area updating is used to periodically notify the availability of the UE to the network. The procedure is controlled in the UE by the periodic tracking area update timer (timer T3412). The value of timer T3412 is sent by the network to the UE in the ATTACH ACCEPT message and can be sent in the TRACKING AREA UPDATE ACCEPT message. The UE shall apply this value in all tracking areas of the list of tracking areas assigned to the UE, until a new value is received. A longer periodic TAU timer is possible using T3412 extended timer. When the UE includes the T3324 value IE and the UE indicates support for extended periodic timer value in the MS network feature support IE, it may also include the T3412 extended value IE. Apart from the value requested by the UE, the MME verifies the local configuration into account while selecting a value for the T3412 extended timer. When the MME includes the T3412 extended value IE in the ATTACH ACCEPT message or TRACKING AREA UPDATE ACCEPT message , the MME uses timer T3412 extended value IE as the value of timer T3412.

Other Feature Enhancements

The MME allows a value of "0" for timer T3324 (Which implies the UE enters Power Saving Mode immediately).

MME may also include Downlink buffer duration and "Downlink suggested packet count" in DDN ACK if it is configured.

The following new flags are introduced as part of this feature; these flags are supported in GTPCv2 Indication IE:

• Pending Network Initiated PDN Connection Signaling Indication (PNSI): The source MME supports sending of PNSI flag in GTPCv2 Indication IE of Context response.

• UE Available for Signaling Indication (UASI): The MME supports sending of the UASI flag in GTPCv2 Indication IE of Create Session Request and Modify Bearer Request.

• Delay Tolerant Connection Indication (DTCI): The MME supports receiving the DTCI flag in Create Session Response from the SGW. The MME supports receiving of the DTCI flag in Context Response and Forward Relocation Request from peer MME or S4-SGSN.

The MME rejects CBR/UBR when PPF is False. The cause "UE is temporarily not reachable due to power saving" is sent in the response by the MME if the corresponding PDN was marked "Delay tolerant" by PGW.

A subscriber is PSM enabled only when:

• UE sends T3324 timer in ATTACH/TAU.

• Power Saving Mode is enabled in configuration by providing T3324 active and T 3412 extended timers or by configuring "UE requested" timer values.

A CLI-based configuration is provided to configure the T 3324 active and T 3412 extended timers. The CLI provides an option to either accept UE requested values or MME configured values for these timers. The CLI is also used to configure either to send or not send the Downlink Buffer Duration in DDN Ack, the DDN Ack Optional IE "Downlink Suggested Packet Count" can also be configured. When the PSM CLI configuration is enabled, the MME accepts the use of PSM and a UE requested value of T3324 is received in Attach/TAU request. If the CLI is configured to accept UE requested values of timers and if T3412 extended timer is not received from the UE along with T3324 in Attach/TAU request, then MME uses the same value of T3412 timer available in MME service configuration. The values of T3324 and T3412 timers extended are determined based on the configuration. If the MME has allocated an Active Time (T3324) to the UE, then the MME starts the Active timer with the value of T3324 whenever the UE enters IDLE mode. If this timer expires, then MME clears the PPF (Paging Proceed Flag). When the PPF is clear, the MME does not page the UE on receiving a Downlink Data Notification message and sends a Downlink Data Notification Ack message with cause "Unable to page UE" to the Serving GW with DL buffering duration and DL suggested packet count IEs as per the operator configuration. The MME rejects network initiated PDN connections during power saving mode. The MME sends the cause "UE is temporarily not reachable due to power saving" if the corresponding PDN was marked Delay Tolerant (DTCI flag set) by PGW. The source MME sets the PNSI flag in Context Response if there are any pending network initiated PDN connections (For example, Create Bearer Request/Update Bearer Request). The MME sets the UASI flag in the Create Session Request or Modify Bearer Request message when UE is available for end-to-end signaling. The UE is in PSM until a mobile originated event (for example periodic RAU/TAU, mobile originated data or detach) requires the UE to begin any procedure towards the MME.

UE Power Saving Mode is not supported in the CS domain on the network side. A UE that uses mobile terminated IMS or CS services other than SMS should not use PSM as neither IMS nor the CS domain provide support for mobile terminated CS voice or IMS services to UEs that are in PSM.

The Power Saving Mode feature complies with the following standards:

• 3GPP TS 24.301 Release 13.5.0

• 3GPP TS 23.401 Release 13.5.0

• 3GPP TS 29.274 Release 13.5.0

This section describes how to configure the UE Power Saving Mode feature. The following CLI command is introduced in the Call Control Profile to configure the UE Power Saving Mode parameters.

configure
  call-control-profile profile_name
    [remove] psm {ue-requested [dl-buf-duration [packet-count packet_value ]]| t3324-timeout t3324_value t3412-extended-timeout t3412_ext_value [dl-buf-duration [packet-count packet_value ]]}
    exit

Notes:

• The operator can use the keyword ue-requested, when UE requested values for Active and Extended Periodic timers are to be accepted.

• The keyword dl-buf-duration is used to send Downlink Buffer Duration in DDN ACK when unable to page UE. If this keyword is not configured buffer duration will not be sent in DDN-ACK. By default buffer duration is not sent in DDN ACK.

• The keyword packet-count is used to send 'DL Buffering Suggested Packet Count' in DDN ACK when unable to page UE. The packet count value is an integer value from “0” up to “65535”.

• The keyword t3324-timeout is used to configure the T3324 active timer value. The T3324 active timer is an integer value in the range 0 up to 11160 seconds.

• The keyword t3412-timeout is used to configure the T3412 Extended timer value. The T3412 extended timer is an integer value in the range 0 up to 35712000 seconds.

• This command is not enabled by default.

• The keyword remove is used to disable UE power saving mode.

This section provides information on how to monitor the UE Power Saving Mode feature and to determine that it is working correctly.