Understanding SCEF

DSR has been enhanced to support the capabilities of a Service Capability Exposure Function (SCEF). SCEF is a new network element that securely exposes the servers and capabilities provided by 3GPP network interfaces. Some functions included with SCEF include:

• Non-IP data delivery (NIDD) for low power devices

  Functions for NIDD are used to handle mobile originated (MO) and mobile terminated (MT) communication with UE, where the data used for the communication is considered unstructured from the Evolved Packet System (EPS) standpoint (which we refer to also as non-IP). The support of non-IP data is part of the Consumer Internet of Things (CIoT) EPS optimizations.

• Monitoring a device's state

  The Monitoring Events feature monitors specific events in the 3GPP system and makes the monitoring events information available using SCEF. It allows the identification of the 3GPP network element suitable for configuring the event, the event detection, and the event reporting to the authorized users, for example, for use by applications or logging. If an event is detected, the network can be configured to perform special actions like limit the UE access.

• Device triggering performs application-specific action including communication with the Service Capability Server (SCS)

  Device Triggering allows SCS to send information to the UE through the 3GPP network to trigger the UE to perform application-specific actions that include initiating communication with SCS for the indirect model or an AS in the network for the hybrid model. Device Triggering is required when an IP address for the UE is not available or reachable by SCS/AS.

• Enhanced Coverage Restriction Control

  The support for Enhanced Coverage Restriction Control using SCEF enables 3rd party service providers to query status of enhanced coverage restriction, or enable/disable enhanced coverage restriction per individual UE.

The SCEF server interacts with Internet of Things (IoT) networks as a machine type communication inter-working function (MTC-IWF). Figure 1-1 shows how SCEF interacts with other DSR elements and an IoT network.

Figure 1-1 DSR SCEF Interactions

IoT devices have unique identifiers and can transmit data over a network. An IoT network can consist of numerous devices, characterized by simple design, low power consumption, brief and infrequent data transmissions, and infrequent machine transmissions (mostly they are not transmitting). The SCEF server supports IoT devices through non-IP data delivery (NIDD). An SCEF server can relay triggers from an SMS-SC function to IoT devices using Short Message Service (SMS) messages through the Diameter T4 interface. An SCEF server communicates with the home subscriber server (HSS) using the Diameter S6t and S6m interfaces. An SCEF server communicates with mobility management entity (MME) functions using the Diameter T6a and T6b interfaces. An SCEF server generates charging records and communicates with charging servers using the Diameter Ga interface. Table 1-1 provides a summary of these supported reference points.

Table 1-1 Supported Diameter Reference Points

Reference Point Name	Description
T4	Reference point used between SCEF and SMS-SC/GMSC/IWMSC
T6a	Reference point used between SCEF and serving MME
T6b	Reference point used between SCEF and serving SGSN
T8	Reference point used between SCEF and SCS/AS
S6t	Reference point used between SCEF and HSS
S6m	Reference point used between MTC-IWF and HSS

An SCEF network communicates with services capability server/application server (SCS/AS) functions using either the T8 otherwise known as the WebSocket representational state transfer (REST)ful application program interface (API) protocols using the DSR API gateway, which provides a proxy API gateway with trusted identity management, IP multimedia subsystem (IMS) access, quality of service (QoS) control, messaging services, and industry-standard security, authentication, accounting, and authorization. Configurable, extensible mechanisms support applying rate, volume, and other limits on a per-SCS/AS basis.

To support large network environments, an SCEF network can communicate with charging, home subscriber server (HSS), and mobility management entity (MME) servers using DSR.