Where did the NEF in 5G come from?

Signalling in the 2G, 3G and 4G systems fell basically into one of two categories: it was either an exchange of information between two network nodes/functions, or an exchange of information between the UE and, well, whichever mobile network entity the UE needed to communicate with — be it in the radio, or in the core of the network that serviced it.


Commercial 5G deployments will be on their way in a not too far away future… And that no longer is the one-size-fits-all transport network the earlier 3GPP technologies were. It cannot afford to be, with the big variety of service types it will need to support — an issue that has already become very clear with the swarms of IoT devices utilizing the LTE access. The need to optimize the 4G networks for the IoT traffic, and protect them from the IoT-generated challenges, has resulted in a rather rushed effort to define enhancements for the Machine Type Communication, MTC. Most of these enhancements provide tools for radio network optimization, but there is a visible standardization effort to define features for the Evolved Packet Core, EPC, too. One of the MTC enhancement for the EPC was the definition of an SCEF – Service Capability Exposure Function, which enables, for example, small amounts of data to be transported within the signalling messages of the Control Plane (“Control Plane Cellular IoT EPS Optimization”). That way small, infrequent bursts of traffic generated by the IoT devices (those with such a specific application behaviour) does not require the establishment of a costly User Plane connection.


One of the major challenges of the all-connected world of 5G is that the customer’s server housing the application needs to be allowed to communicate with the network functions of the mobile network. The external AF wants of course to be able to request from the 3GPP transport network resources suitable for the data it needs to exchange with the UE. But it is also that very external AF that has knowledge of the UEs expected traffic patterns and mobility behaviour – and that is of great interest to the 3GPP network itself… There is a rather basic dilemma here for the mobile operators – on the one hand, allowing customers to push their data into the network is plain dangerous, and to be avoided at all costs, on the other hand – information gained from the customer’s AFs, with their knowledge of the expected UE behaviour, is invaluable as input crucial to optimal allocation and utilization of the resources. The proposed solution is quite obvious: a new group of signalling scenarios will appear, in order to enable exchange of information to/from an external AF in a controlled and secure way. Hence: NEF. The Network Exposure Function has appeared in the 5G standards as an intelligent, service-aware “border gateway” that will enable the external AFs to communicate with the 5G Network Functions in a secure manner.


Ok, so what do the SCEF (for transporting small amounts of data in the Control Plane signalling messages) and the NEF (to guarantee security at the network border) have in common? Other than the fact they have the term “Exposure” in their names? Well, a lot in fact. The 4G SCEF not only enables Non-IP Data Delivery (NIDD), it also has functions for border security, while the 5G NEF will enable so-called Small Data Delivery on top of its security border functionalities. Conclusion? Even though SCEF descriptions in the 4G standards and those of the NEF in 5G documents do not seem extremely alike, the NEF in effect is a newer and better SCEF.

Telecommunication equipment vendors have played to that fact, and when presenting the operators with the 5G purchasing options offer a combined SCEF/NEF solution, creating a natural grouping of service- and customer-aware functionalities at the 3GPP network border.

Learn more about SCEF and NEF

If you’d like to get more knowledge on the SCEF and NEF have a look at our IoT and 5G course portfolio:

Until next time,

The Apis TeamLY

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