2G/3G Shutdown may Cost Lives as 4G/5G Voice Roaming is a Mess

You have probably heard me a complaining about the pace of VoLTE rollout, 2G/3G shutdowns, 4G Voice roaming, etc. This post highlights all these issues coming together in a dangerous way. People often ask me why is it that it's always just me highlighting the issues. The answer is that there are other people but their voice may not reach you. In this post, I am highlighting presentations by Rudolf van der Berg, Project and programme manager at Stratix Consulting.

No more voice roaming in USA! French operator Free warns customers that telephony in USA doesn't work. 2G/#3G shutdown and lack of #VoLTE standardisation and roaming are the cause. Its customers can only use Internet and SMS, but not E.164 number based voice telephony and 911! https://t.co/cbBrNZTskq

— Rudolf van der Berg (@internetthought) April 6, 2022

Let's start with Rudolf's post from LinkedIn:

Stop the shutdown of 2G and 3G networks to save lives. This is the urgent call I make today and I hope you can help me spread it! Please call on people you know in politics, regulators and emergency services to demand a stop! Call on anyone you know in the GSMA, 3GPP, handset makers (Apple, Samsung, Qualcomm, MediaTek), network builders (Ericsson, Nokia, Huawei) to re-engineer VoLTE to an interoperable standard.

Emergency calls (112, 911) should work anywhere in the world on any phone. For GSM and 3G voice calling it did. You could fly anywhere and call emergency services and in the EU we have the roaming regulation that demands calling like at home. Voice over 4G and 5G hasn't been properly standardized and isn't interoperable between networks, devices, chipsets and firmware. People need to be able to make and receive telephone calls around the world, to each other and to emergency services. Unfortunately even according to sector itself emergency services are at risk from VoLTE. A consumer today can't know whether a phone they bought will make VoLTE calls at home or abroad, nor whether it can reach emergency services. That can't be right!

So please help EENA 112 and me share this message! Thank you #eena2022 (Slide 4 contains a mistake, T-Mo USA hasn't decided on 2G shutdown yet. that is good for availability of 911, though fundamental point remains. Apologies.)

Dear foreigner, AT&T regrets you die because you can't dial 911. Try whatsapp and ask a friend in the US to call 911 for you. https://t.co/KqliBXv4ik

— Rudolf van der Berg (@internetthought) April 15, 2022

The video and slides are embedded below:

The slides contain many useful references and links, you can download directly from here.

Back in April, iBASIS hosted a VoLTE and 5G Roaming Roundtable. You can watch the video here and download the presentation and whitepaper as well. It contains talks from Kaleido Intelligence, iBASIS, KPN, Bouygues Telecom and Telus. 

The slide from Dutch MNO KPN above highlights the VoLTE Roaming issues they are observing. Other operators will face this issue sooner or later as well. 

So they are the ones who should be asked to make sure that VoLTE and VoNR is interoperable between vendors and MNOs? Because people will die if we don't fix this. See my presentation from last week https://t.co/Ju3GadO9ie

— Rudolf van der Berg (@internetthought) May 5, 2022

The Regulators, GSMA and 3GPP have to come together to fix this important issue for once and all so no lives are lost because of this. Hopefully someone is listening!

Related Posts: 

• The 3G4G Blog: Transitioning from eCall to NG-eCall and the Legacy Problem
• The 3G4G Blog: GSMA Releases Mobile Economy Report 2022
• The 3G4G Blog: When will 2G & 3G be switched off now that 5G is here?
• The 3G4G Blog: VoLTE Hacking
• The 3G4G Blog: A quick starter on 4G voice (for beginners) 

IP Multimedia Subsystem (IMS) Support for Service Based Architecture (SBA)

I looked at IMS briefly in my LTE voice tutorial here. The Nokia Lectures covered IMS in-depth in part 5 of the video. I recently came across a short overview of IMS for SBA. You can see our old tutorial on Service Based Architecture (SBA) for 5G Core (5GC) here.

I came across this short video from Mpirical that nicely explains the IMS support for SBA. It's embedded below. The related posts at the bottom may also be worth checking out.

Related Posts:

• The 3G4G Blog: A quick starter on 4G voice (for beginners)
• The 3G4G Blog: Nokia Lectures in Collaboration with Bangalore University
• The 3G4G Blog - Tutorial: Service Based Architecture (SBA) for 5G Core (5GC)
• The 3G4G Blog: A look at 5G Applications, Application Functions & Application Servers
• The 3G4G Blog: EPS Fallback in 5G Standalone Deployments
• The 3G4G Blog: Voice over New Radio (VoNR) Establishment and Release between NG RAN and 5G Core
• The 3G4G Blog: Two Types of SMS in 5G
• The 3G4G Blog: 5G User Plane Redundancy
• The 3G4G Blog: Network Slicing using User Equipment Route Selection Policy (URSP) 

Voice over New Radio (VoNR) Establishment and Release between NG RAN and 5G Core

In this video I explain how QoS Flows for VoNR are established and released especially on N2 reference point between 5G Core and NG RAN.

The pervious video about generic aspects of "QoS Flow Establishments in 5G Standalone RAN and Core" you will find in the first link of the Related Posts listed below:

Related Posts: 

• The 3G4G Blog: QoS Flow Establishments in 5G Standalone RAN and Core
• The 3G4G Blog: Anomaly Detection and other AI Algorithms in RAN Optimization
• The 3G4G Blog: How to Identify Network Slices in NG RAN
• The 3G4G Blog: Network Slicing in NG RAN
• The 3G4G Blog: Network Slicing Tutorials and Other Resources
• The 3G4G Blog: Artificial Intelligence (AI) / Machine Learning (ML) in 5G Challenge by ITU
• The 3G4G Blog: Conditional Handover (Rel. 16) Explained
• The 3G4G Blog: UE Radio Capability Signaling Optimization (RACS) in Rel. 16 

EPS Fallback in 5G Standalone Deployments

It can be expected that later this year some mobile network operators will launch their initial 5G standalone (5G SA) deployments.

Nevertheless there will remain areas with temporary or permanently weak 5G NR coverage. One possible reason might be that even when 5G and LTE antennas are co-located, which means: mounted at the same remote radio head, the footprint of the 5G NR cell is significantly smaller when it uses a higher frequency band than LTE - see figure 1.

Figure 1: Smaller footprint of co-located 5G NR cell with higher frequency

Especially UEs making Voice over New Radio (VoNR) calls from the 5G cell edge have a high risk of experiencing bad call quality, in worst case a call drop. To prevent this the UE is forced  during the voice call setup towards 5G core network (5GC) to switch to a LTE/EPS connection where the radio conditions are better for the voice service.

The same procedure for which the term "EPS Fallback" was coined by 3GPP also applies when the UE is served by a 5G cell that is not configured/not optimized for VoNR calls or when the UE does not have all needed VoNR capabilities.

Figure 2: Two options for EPS fallback

When looking at the RAN there are two options for executing the EPS Fallback as shown in figure 2.

In option A the 5G radio connection is released after the initial call attempt is successfully finished and with the 5G RRC Release the UE is ordered to reselect to a 4G cell where a new radio connection is started for the VoLTE call. In this case the UE context is transferred from the AMF to the MME over the N26 interface. 3GPP seems to use also the term "RAT fallback" for this option.

Option B is to perform a 5G-4G inter-RAT handover. Here the session management and user plane tunnels in the core network are handed over from SMF/UPF to MME/S-GW in addition. This is realized with the GTPv2 Forward Relocation procedure on N26 interface.

All in all the EPS fallback is expected to cause an additional call setup delay of approximately 2 seconds.

For the inter-RAT handover case it is easy to detect from signaling information that an EPS fallback was triggered. In the source-eNodeB-to-target-eNodeB-transparent-container sent by the gNB to the eNB a boolean "IMS voice EPS fallback from 5G" indicator will be found that is set to "true". This container is named according to the receiving entity and will be carried by the NGAP Handover Preparation, GTPv2 Forward Relocation Request and the S1AP Handover Request messages.

If a redirection for Voice EPS Fallback is possible or not is indicated in the NGAP Initial Context Setup Request, Handover Request (during 5G intra-system handover) and Path Switch Request Acknowledge (after Xn handover) messages, all sent by the AMF to the gNB.

Further the NGAP protocol provides the cause value "IMS voice EPS fallback or RAT fallback triggered" in the PDU Session Resource Modify Response message indicating that a requested VoNR session cannot be established.  

An excellent, very detailed description of N26 interface functionality and testing ia available here.