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Nsmf Service-Based Interface

SMF Testing with dsTest

In the 5G Core (5GC) network, the Session Management Function (SMF) interacts with the Access and Mobility Function (AMF) to establish, modify, and release PDU sessions through the Nsmf Service-Based Interface. When a UE initiates a PDU session request, the serving AMF selects an SMF that will establish and manage that session. This decision is informed in part by subscription data that the AMF receives through the Nudm service.

The SMF, in turn, determines whether the requested PDU session is compliant with the mobile subscriber’s subscription and, if the request is valid, selects the UPF that will host the PDU session. An SMF interacts with UPFs over the N4 interface to direct a UPF to establish or release a PDU session and to push the policies applicable to specific PDU sessions to the UPF when indicated.

A UE may have multiple PDU sessions and they may be managed by different SMFs and may also be hosted on different UPFs.

The dsTest Nsmf application supports the services briefly described below.


An AMF uses the operations provided by this service, specified in TS 29.502, to trigger PDU session establishment, modification, and release in the SMF. The SMF retains Session Management (SM) contexts for all of the active PDU sessions that it is managing. It may also retain SM contexts for inactive PDU sessions if it determines that the session may soon be re-activated. An SM context, in addition to creating an association between a PDU session and the serving AMF, contains the parameters that govern the PDU session.

Interested network functions may subscribe for SM context status notifications from an SMF. The SMF will in turn notify them when the subject SM context has been released either due to a UE-initiated or network-initiated release or due to a PDU session failure after establishment.


The SMF’s Event Exposure service, specified in TS 29.508, enables other network functions — PCF, AMF, NEF, or AF — to subscribe and unsubscribe to event notifications for a specific PDU session, for PDU sessions associated with one UE, for PDU sessions associated with a group of UEs, or for PDU sessions associated with any UE.

An SMF exposes the following events:

  • AC_TY_CH — access type change
  • UP_PATH_CH — UP path change
  • PDU_SES_REL — PDU session release
  • PLMN_CH — PLMN change
  • UE_IP_CH — UE IP address change


Use our SMF emulator in your 5G testing to provide Nsmf services to the consumers in your test network while also verifying their compliance with service specifications.

Nsmf Testing with dsTestTest your Nsmf service producer by surrounding it with our node emulators:

  • Drive Nsmf_PDU_Session operations with our AMF node to test the SMF’s performance and capacity
  • Provide Nudm services with our UDM node
  • Fully test PDU session management over the N4 interface with our UPF node

read moreRead more about dsTest capacity and performance.

As with all dsTest products, the node configurations and test scenarios are easily defined and configured with XML files that are validated against a published XML Schema to avoid invalid definitions. With our dsClient Desktop application you can create, run, and archive tests; capture, graph and archive operational measurements; capture real-time data flows and subscriber events; and manage your dsTest platforms and testing scenarios with a standalone application that runs on your PC.

read moreRead more about the dsClient Desktop application.

Advanced Testing Features

SmartEvents — Alter application behavior or coordinate multiple interface applications with SmartEvents — our programmable, subscriber-level state machine. All dsTest applications are event-driven, enabling you to easily alter subscribers’ activities. Use our visual composer to draw your state machine and to trace a single subscriber’s path through the state machine while the test is running. Define event handlers that affect a subscriber’s behavior in an application, or that trigger an event in another application. You can also configure event handlers to modify subscriber information during run-time, introduce timers, or randomize subscriber behavior based on configurable probabilities to name just a few of the many options in one of dsTest’s most powerful features.

SmartMessageElement — Insert, delete, or replace elements in Diameter, RADIUS, MAP, LDAP, GTP, REST, or SOAP messages with our SmartMessageElement feature. Define proprietary signaling or corrupt elements to facilitate negative testing. You can specify when your elements are used with SmartEvents.

Traffic Profile — Draw the shape of your test actions across time with Traffic Profile. You can define the rate for any action as a static rate or reference a Traffic Profile configuration, which also means that multiple Traffic Profiles can be running concurrently. Use Traffic Profile in conjunction with the randomizing features in SmartEvents to design a test that more truly simulates real-world network activity.

REST Dictionary — Add conformance testing to your performance or functional test with our REST Dictionary. You can validate message types and JSON structures by simply including our base dictionary. You can also build custom dictionaries to explicitly define required parameter and property values and selectively include the dictionary to be used for a particular test.

Operational Measurements

dsTest provides rich sets of measurements for Nsmf services:

  • Transaction and transport layer attempts, successes, and failures
  • Transaction duration, transactions-per-second, and round-trip delay
  • Message and byte counters
  • Errors encountered and error indications received in messages

See our Online Help for 5G SM Transaction measurements, PDU Session Service measurements, and socket measurements.

read moreRead more about dsTest and dsClient reporting features.

Reference Standards