This post first appeared on my SAP blog on June 30, 2020.
The 3GPP 5G standards absolutely support SMS!
5G, the next wireless data standard is actively being deployed around the world. 5G will promise greater data speeds, more capacity, and a better wireless experience for all. But will it affect the messaging sector? I’ve read and heard (during presentations, events [back when we could attend trade shows]) that the “messaging standard for 5G is RCS,” and that “SMS won’t exist in 5G.” Well, I’m happy to say that these statements are blatantly untrue.
Of course, the next generation of mobile operator messaging, RCS (or Rich Communications Service) is creating a pathway to a more engaged, rich messaging ecosystem, but it won’t supplant SMS anytime soon and certainly not as a result of 5G. But there are several organizations that pushed the incorrect narrative that RCS is the messaging standard for 5G or that SMS won’t exist in 5G. That’s just not true.
Deep Dive into 5G SMS
Again, SMS is fully supported in the 5G standards. Let’s look at Section 4.4.2 of the 3GPP standard document: TS 23.501: SMS over NAS. Here’s the non-roaming architecture that support SMS in 5G as envisioned in the TS 23.501 document:
The SMSF is the SMS Function. The functionalities of the SMSF are defined in 3GPP TS 23.501. These include management of subscription data (from UDM) as well as SMS delivery, SMS CDR, lawful interception and notification of AMF and
UE is User Equipment – the mobile device.
AMF is Access and Mobility Management Function – this is responsible for managing connection and mobility tasks. There are multiple AMF instances in a 5G network.
UDM – Unified Data Management – manages user data such as customer profile information, customer authentication information and other items. The UDM is similar to the 4G (LTE) HSS or Home Subscriber Service. In some instances, the UDM is associated with the User Data Repository (UDR) which actually stores a variety of user data.
I won’t go into the roaming architecture, but that too, is fully supported in the 5G standards.
The Nsmsf protocol is fully defined in the 3GPP document TS 29.540 (also called the N20 reference point). This is particularly used between the AMF and the SMSF. Services include: authorization and activation of SMS for a user on the SMSF; sending the SMS payload in the uplink direction to the SMSF. The UplinkSMS service is used in both the MO SMS and MT SMS delivery procedures (which are, in turn, detailed in 3GPP TS 23.502.
Here’s how 3GPP TS 23.502 defines the message flow for an MT SMS message in 5G:
This is in Section 22.214.171.124 of TS 23.502. Note the interface to the UE (User Equipment or Mobile Device is over the NAS or the Non-access stratum. This is a layer in the protocol stacks between the core 5G network and the mobile devices (or User Equipment as it’s called in the various standards). The NAS purpose is to manage the setup and management of communications sessions as well as call control management and even identity management. Think of it as a control channel. You can also contrast this to the Access Stratum, which carries information over the network.
The 5G SMS MO message flow is similar:
Long time SMS aficionados will recognize some of the messages flowing amongst the network elements – especially to/from the SC (or essentially, the “classic” SMSC); however, this is definitely not your father’s old SMS flow – especially with the integration of components such as the SMSF, AMF, and of course UDM, to name a few.
The GSMA published an excellent document titled SMS Evolution (or NG.111) that provides an analysis of SMS as it has evolved from 2G all the way through 5G. They also do a good job of showing both hybrid situations – especially as 4G (LTE) has been deployed in most networks around the world, whereby both GSM MAP and Diameter protocols are used.
SMSC vendors of today are supporting both GSM MAP and Diameter protocols on the evolution of their SMSCs. Additionally, many are now providing the SMSF components as well. As 4G/LTE is well underway, mobile operators use both hybrid Diameter/MAP deployments as well as MAP only deployments, depending on whether they have a fully developed IMS core.
With 5G, per the GSMA document, we’ll also likely be able to support either MAP or Diameter between the SMSC and SMSF as well as UDM. Here’s the GSMA variation of the 5G SMS architecture with clear delineation of the protocols possible or required between the network elements:
The GSMA SMS Evolution document also outlines the MTC/MIoT initiatives, although they are out of scope of this post. This is a worthy document to explore if you want to say up to date with how SMS works “under the bonnet.”
With RCS now starting to become established, it is important to realize that both RCS and SMS will share the same in-box in both 4G and of now 5G. SMS will play roles with RCS and even brand-new roles in new 5G networks, and many of their current roles in P2P, A2P/P2A will continue. Consequently, we need to be clear that SMS will remain an important delivery channel – probably throughout this decade, at least.
The 3GGP and GSMA documents clearly provide amble evidence that SMS is worth evolving to these new and exciting networks.