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) 

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.

VoLTE Hacking

The 10th Annual HITB Security Conference took place from the 6th till the 10th of May 2019 in The Netherlands. The theme for the conference this year is 'The Hacks of Future Past'. One of the presentations was on the topic 'VoLTE Phreaking' by Ralph Moonen, Technical Director at Secura.

The talk covered variety of topics:

• A little history of telephony hacking (in NL/EU)
• The landscape now
• Intercepting communications in 2019
• Vulnerabilities discovered: some new, some old
• An app to monitor traffic on a phone

The talk provides details on how VoLTE can potentially be hacked. In a lot of instances it is some or the other misconfigurations that makes VoLTE less secure. One of the slides that caught my attention was the differences in VoLTE signaling from different operators (probably due to different vendors) as shown above.

Anyway, I am not going into more details here. The presentation is available here.

Another interesting talk from #HITB2019AMS:
"VoLTE Phreaking"https://t.co/KSMLen6Yb6 [PDF] pic.twitter.com/KakJMGCcVk

— Enno Rey (@Enno_Insinuator) May 9, 2019

The thread in the Tweet above also provided some good references on VoLTE hacking. They are as follows:

• ERNW: Security Analysis of VoLTE, Part 1
• ERNW: Denial of Service attacks on VoLTE
• ERNW: VoLTE Security Analysis, part 2
• ERNW: IMSecure – Attacking VoLTE (and other Stuff)
• ERNW White Paper: Practical Attacks on VoLTE and VoWiFi

Related Posts:

• 3G4G: Voice in 4G: CSFB, VoIP & VoLTE

Summary and Analysis of Ericsson Mobility Report 2018

Ericsson Mobility reports always make a fantastic reading. Its been a while since I wrote anything on this topic so I thought lets summarize it and also provide my personal analysis. Please feel free to disagree as this is just a blog post.

Before we start, the official site for the report is here. You can jump directly to the PDF here. Ericsson will also be holding a webinar on this topic on 19 June, you can register here.

A short summary of some of the highlights are in the table above but lets look at more in detail.

Mobile subscriptions 

• The total number of mobile subscriptions was around 7.9 billion in Q1 2018.
• There are now 5.5 billion mobile broadband subscriptions.
• Global subscription penetration in Q1 2018 was 104 percent.
• The number of LTE subscriptions increased by 210 million during the quarter to reach a total of 2.9 billion.
• Over the same period, GSM/EDGE-only subscriptions declined by 90 million. Other technologies declined by around 32 million.
• Subscriptions associated with smartphones now account for around 60 percent of all mobile phone subscriptions.

Many things to note above. There is still a big part of the world which is unconnected and most of the connectivity being talked about is population based coverage. While GSM/EDGE-only subscriptions are declining, many smartphone users are still camped on to GSM/EDGE for significant time.

While smartphones are growing, feature phones are not far behind. Surprisingly, Reliance Jio has become a leader of 4G feature phones.

My analysis from the developing world shows that many users are getting a GSM feature phone as a backup for when smartphone runs out of power.


Mobile subscriptions worldwide outlook

• 1 billion 5G subscriptions for enhanced mobile broadband by the end of 2023, accounting for 12 percent of all mobile subscriptions.
• LTE subscriptions continues to grow strongly and is forecast to reach 5.5 billion by the end of 2023
• In 2023, there will be 8.9 billion mobile subscriptions, 8.3 billion mobile broadband subscriptions and 6.1 billion unique mobile subscribers.
• The number of smartphone subscriptions is forecast to reach 7.2 billion in 2023.

The report describes "A 5G subscription is counted as such when associated with a device that supports NR as specified in 3GPP Release 15, connected to a 5G-enabled network." which is a good approach but does not talk about 5G availability. My old question (tweet below) on "How many 5G sites does an operator have to deploy so that they can say they have 5G?" is still waiting for an answer.

Question: How many 5G sites does an operator have to deploy so that they can say they have 5G?

— Zahid Ghadialy (@zahidtg) October 18, 2017

5G device outlook

• First 5G data-only devices are expected from the second half of 2018.
• The first 3GPP smartphones supporting 5G are expected in early 2019.
• From 2020, when third-generation chipsets will be introduced, large numbers of 5G devices are forecast.
• By 2023, 1 billion 5G devices for enhanced mobile broadband are expected to be connected worldwide.

Qualcomm has made a good progress (video) on this front and there are already test modems available for 5G. I wont be surprised with the launch. It would remain to be seen what will be the price point and demand for these 5G data-only devices. The Register put it quite bluntly about guinea pigs here. I am also worried about the misleading 5G claims (see here).


Voice over LTE (VoLTE) outlook

• At the end of 2017, VoLTE subscriptions exceeded 610 million.
• The number of VoLTE subscriptions is projected to reach 5.4 billion by the end of 2023.
• VoLTE technology will be the foundation for enabling 5G voice calls.
• New use cases in a 5G context are being explored, such as augmented reality (AR) and virtual reality (VR).

Back in 2011, I suggested the following (tweet below)

Soon = before 2015. Ideally, if its working then never, until forced - RT @Gabeuk: I suspect VoLTE adoption will pick-up briskly in 2013.

— Zahid Ghadialy (@zahidtg) July 13, 2011

Looks like things haven't changed significantly. There are still many low end devices that do not support VoLTE and many operators dont support VoLTE on BYOD. VoLTE has been much harder than everyone imagined it to be.


Mobile subscriptions worldwide by region

• Globally, mobile broadband subscriptions now make up 68 percent of all mobile subscriptions.
• 5G subscriptions will be available in all regions in 2023.
• In 2023, 48 percent of subscriptions in North America and 34 percent in North East Asia are expected to be for 5G.

I think that for some regions these predictions may be a bit optimistic. Many operators are struggling with finance and revenue, especially as the pricing going down due to intense competition. It would be interesting to see how these numbers hold up next year.

While China has been added to North-East Asia, it may be a useful exercise to separate it. Similarly Middle East should be separated from Africa as the speed of change is going to be significantly different.


Mobile data Traffic Growth and Outlook

• In Q1 2018, mobile data traffic grew around 54 percent year-on-year.
• The quarter-on-quarter growth was around 11 percent.
• In 2023, 20 percent of mobile data traffic will be carried by 5G networks.
• North America has the highest monthly usage of mobile data per smartphone at 7.2 gigabytes (GB), anticipated to increase to 49GB in 2023.
• Total mobile data traffic is expected to increase by nearly eight times by the end of 2023.
• In 2023, 95 percent of total mobile data traffic is expected to be generated by smartphones, increasing from 85 percent today.
• North East Asia has the largest share of mobile data traffic – set to reach 25EB per month in 2023.

This is one of the toughest areas of prediction as there are a large number of factors affecting this from pricing to devices and applications.

Quiz question: Do you remember which year did data traffic overtake voice traffic? Answer here (external link to avoid spoilers)


Mobile traffic by application category

• In 2023, video will account for around 73 percent of mobile data traffic.
• Traffic from social networking is also expected to rise – increasing by 31 percent annually over the next 6 years.
• The relative share of social networking traffic will decline over the same period, due to the stronger growth of video.
• Streaming videos in different resolutions can impact data traffic consumption to a high degree. Watching HD video (720p) rather than standard resolution video (480p) typically doubles the data traffic volume, while moving to full HD (1080p) doubles it yet again.
• Increased streaming of immersive video formats would also impact data traffic consumption.

It would have been interesting if games were a separate category. Not sure if it has been lumped with Video/Audio or in Other segments.


IoT connections outlook

• The number of cellular IoT connections is expected to reach 3.5 billion in 2023. This is almost double our last forecast, due to ongoing large-scale deployments in China.
• Of the 3.5 billion cellular IoT connections forecast for 2023, North East Asia is anticipated to account for 2.2 billion.
• New massive cellular IoT technologies, such as NB-IoT and Cat-M1, are taking off and driving growth in the number of cellular IoT connections.
• Mobile operators have commercially launched more than 60 cellular IoT networks worldwide using Cat-M1 and NB-IoT.

It is important to look at the following 2 definitions though.

Short-range IoT: Segment that largely consists of devices connected by unlicensed radio technologies, with a typical range of up to 100 meters, such as Wi-Fi, Bluetooth and Zigbee. This category also includes devices connected over fixed-line local area networks and powerline technologies

Wide-area IoT: Segment consisting of devices using cellular connections, as well as unlicensed low-power technologies, such as Sigfox and LoRa

The Wide-area IoT in the table above includes cellular IoT. If you are a regular reader of this blog, you will know that I think LoRa has a bright future and my belief is that this report ignores some of the reasons behind the popularity of LoRa and its growth story. 


Network coverage

• In 2023, more than 20 percent of the world’s population will be covered by 5G.
• 5G is expected to be deployed first in dense urban areas to support enhanced mobile broadband.
• Another early use case for 5G will be fixed wireless access.
• Today, 3GPP cellular networks cover around 95 percent of the world’s population.

A lot of work needs to be done in this area to improve coverage in rural and remote locations.

I will leave this post at this point. The report also contains details on Network Evolution, Network Performance, Smart Manufacturing, etc. You can read it from the report.

A quick starter on 4G voice (for beginners)

I recently did a 4G voice presentation for beginners after realizing that even though so many years have passed after VoLTE was launched, people are still unsure how it works or how its different from CS Fallback.

There are many other posts that discuss these topics in detail on this blog (follow the label) or on 3G4G website. Anyway, here is the video:

The slides are available on 3G4G Slideshare account here. More similar training videos are available here.

VoLTE Operator Case Study from LTE Voice Summit

Phil Sheppard, Director of Network Strategy & Architecture, Three UK was the keynote speaker of LTE Voice Summit held in London this month. Its been over a year that Three launched its VoLTE service in the 800MHz band. In fact recently, it has started showing adverts with Maisie Williams (Arya Stark from Game of Thrones) fighting black spots (not spots) with 4G Super-Voice.



As I highlighted in the LTEVoice 2015 summary where China Mobile group vice-president Mr.Liu Aili admitted "VoLTE network deployment is the one of the most difficult project ever, the implementation complexity and workload is unparalleled in history", Three UK's experience wasn't very different. Quoting from ThinkSmallCell summary of the event:

It was a huge project, the scope far exceeding original expectations and affecting almost every part of their operations.  They spent 22,245 man days (excluding vendor staff time) – more than 100 man years of effort – mostly involved with running huge numbers of test cases on the network and devices.

There are some other interesting bits from the different summaries that are provided in references below but here are few things I found of interest with regards to Three UK VoLTE deployment:

• 170 million voice calls minutes have used VoLTE since the launch in Sept 2015
• Only devices that can support VoLTE and 800MHz are allowed to camp on 800MHz band. This is to avoid disappointment with CS Fallback
• There are plans to roll out VoLTE in other bands too once all niggles are ironed out in the 800MHz band.

Here is the presentation from 3 UK:

Blog posts summarizing LTEVoice 2016:

• LTE Voice Summit 2016 Event Report - David Chambers, ThinkSmallCell
• The Wi-Fi last operators, Alberto Diez
• LTE Voice Summit 2016: Going beyond VoLTE to advance network performance
• Summary of LTE Voice Summit 2016 - Tweet collection by Zahid Ghadialy

Related posts:

• Quick Summary of LTE Voice Summit 2015
• Whats up with VoLTE Roaming?
• QoS in VoWiFi
• Two VoLTE Deployment Case Studies

Whats up with VoLTE Roaming?

I have been covering the LTE Voice Summit for last couple of years (see here: 2015 & 2014) but this year I wont be around unfortunately. Anyway, I am sure there will be many interesting discussions. From my point of view, the 2 topics that have been widely discussed is roaming and VoWiFi.

One of the criticisms of VoWiFi is that it does not the QoS aspect is missing, which makes VoLTE special. In a recent post, I looked at the QoS in VoWiFi issue. If you haven't seen it, see here.

Coming back to VoLTE roaming, I came across this recent presentation by Orange.

This suggests that S8HR is a bad idea, the focus should be on LBO. For anyone who is not aware of the details of S8HR & LBO, please see my earlier blog post here. What this presentation suggests is to use LBO with no MTR (Mobile Termination Rates) but instead use TAP (Transferred Account Procedures). The presentation is embedded below:

Another approach that is not discussed too much but seems to be the norm at the moment is the use of IP eXchange (IPX). I also came across this other panel discussion on the topic

IPX is already in use for data roaming today and acts as a hub between different operators helping to solve inter-operability issues and mediating between roaming models. It can work out based on the calling and callee party what kind of quality and approach to use.

Here is the summary of the panel discussion:

Hopefully the LTE Voice Summit next week will provide some more insights. I look forward to hearing them.

Blog posts on related topics:

• VoLTE Roaming – Let’s Take Away The Confusion - iBasis
• VoLTE Roaming – Critical enabler or long term ideal? - 5G World
• VoLTE Roaming Confusion and the IPX Provider Opportunity - Ovum
• IPX providers must look internally for class-of-service customers - Ovum

QoS in VoWiFi

Came across this presentation by Eir from last year's LTE Voice Summit.

VoWLAN: Call Quality from 3G4G

As the summary of the above presentation says:

• Turning on WMM (or WME) at access point provides significant protection for voice traffic against competing wireless data traffic
• Turning on WMM at the client makes only a small difference where there are a small number of clients on the wireless LAN. This plus the “TCP Unfairness” problem means that it can be omitted.
• All Home gateways support WMM but their firmware may need to be altered to prioritise on DSCP rather than layer two

As this Wikipedia entry explains:

Wireless Multimedia Extensions (WME), also known as Wi-Fi Multimedia (WMM), is a Wi-Fi Alliance interoperability certification, based on the IEEE 802.11e standard. It provides basic Quality of service (QoS) features to IEEE 802.11 networks. WMM prioritizes traffic according to four Access Categories (AC): voice (AC_VO), video (AC_VI), best effort (AC_BE), and background (AC_BK). However, it does not provide guaranteed throughput. It is suitable for well-defined applications that require QoS, such as Voice over IP (VoIP) on Wi-Fi phones (VoWLAN).

WMM replaces the Wi-Fi DCF distributed coordination function for CSMA/CA wireless frame transmission with Enhanced Distributed Coordination Function (EDCF). EDCF, according to version 1.1 of the WMM specifications by the Wi-Fi Alliance, defines Access Categories labels AC_VO, AC_VI, AC_BE, and AC_BK for the Enhanced Distributed Channel Access (EDCA) parameters that are used by a WMM-enabled station to control how long it sets its Transmission Opportunity (TXOP), according to the information transmitted by the access point to the station. It is implemented for wireless QoS between RF media.

This blog post describes how the QoS works in case of WMM.

Finally, this slide from Cisco shows how it will all fit together.

Further reading:

• CWAP – MAC Header : QoS Control
• Mobile Traffic Engineering with Application Visibility and Control (AVC) - Cisco
• Calling VoWiFi... The Next Mobile Operator Service is here... - Cisco

Two VoLTE Deployment Case Studies

Back in 2011, I was right in predicting that we will not see VoLTE as early as everyone had predicted. Looking through my twitter archive, I would say I was about right.

As I said earlier, CSFB for now and VoLTE around 2014 - RT @mitchellkp: LTE won't find voice anytime soon http://t.co/mn0EwAw

— Zahid Ghadialy (@zahidtg) September 7, 2011

Soon = before 2015. Ideally, if its working then never, until forced - RT @Gabeuk: I suspect VoLTE adoption will pick-up briskly in 2013.

— Zahid Ghadialy (@zahidtg) July 13, 2011

The big issue with VoLTE has always been the complexity. In a post last year I provided a quote from China Mobile group vice-president Mr.Liu Aili, "VoLTE network deployment is the one of the most difficult project ever, the implementation complexity and workload is unparalleled in history".

From a recent information published by IHS, there will only be 310 million subscribers by end of 2016 and 2020 is when 1 billion subscribers can make use of VoLTE. I think the number will probably be much higher as we will have VoLTE by stealth.

Below are couple of case studies, one from SK Telecom, presented by Chloe(Go-Eun) Lee and other from Henry Wong, CTO Mobile Engineering, Hong Kong Telecom (HKT). Hope you find them informative and useful.

ITU Workshop on VoLTE and ViLTE Interoperability

ITU recently held a workshop on "Voice and Video Services Interoperability Over Fixed-Mobile Hybrid Environments,Including IMT-Advanced (LTE)" in Geneva, Switzerland on 1st December 2015.

The following is the summary of that workshop:

I also like this presentation by R&S:

All the presentations from the workshop are available online from ITU website here.

Quick Summary of LTE Voice Summit 2015 (#LTEVoice)

Last year's summary of the LTE voice summit was very much appreciated so I have created one this year too.

The status of VoLTE can be very well summarised as can be seen in the image above.

‘VoLTE network deployment is the one of the most difficult project ever, the implementation complexity and workload is unparalleled in history’ - China Mobile group vice-president Mr.Liu Aili

Surprisingly, not many presentations were shared so I have gone back to the tweets and the pictures I took to compile this report. You may want to download the PDF from slideshare to be able to see the links. Hope you find it useful.

Related links:

• VoLTE Roaming with RAVEL (Roaming Architecture for Voice over IMS with Local Breakout)
• S8HR: Standardization of New VoLTE Roaming Architecture
• VoLTE Roaming: LBO, S8HR or HBO

VoLTE Roaming: LBO, S8HR or HBO

There was an interesting discussion on different roaming scenarios in the LTE Voice Summit on 29th, 30th Sep. in London. The above picture provides a brief summary of these well known options. I have blogged about LBO/RAVEL here and S8HR here. A presentation by NTT Docomo in a GSMA webinar here provides more details on these architectures (slide 29 onwards - though it is more biased towards S8HR).

Ajay Joseph, CTO, iBasis gave an interesting presentation that highlighted the problems present in both these approaches.

In case of LBO, the biggest issue is that the home operator need to do a testing with each roaming partner to make sure VoLTE roaming works smoothly. This will be time consuming and expensive.

In case of S8HR, he provided a very good example. Imagine a VoLTE subscriber from USA is visiting Singapore. He now needs to make a phone call to someone in Indonesia (which is just next to Singapore). The flow of data would be all the way from Singapore to USA to Indonesia and back. This can introduce delays and impact QoE. The obvious advantage of S8HR is that since the call setup and media go to Home PMN (Public Mobile Network), no additional testing with the Visited PMN is required. The testing time is small and rollouts are quicker.

iBasis are proposing a solution called Hub Breakout (HBO) which would offer the best of LBO and S8HR. Each VoLTE operator would need to test their interoperability only with iBasis. Emergency calls and lawful intercept that does not work with S8HR would work with the HBO solution.

While I agree that this is a good solution, I am sure that many operators would not use this solution and there may be other solutions proposed in due course as well. Reminds me of this XKCD cartoon:

Anyway, here is the iBasis presentation:

S8HR: Standardization of New VoLTE Roaming Architecture

VoLTE is a very popular topic on this blog. A basic VoLTE document from Anritsu has over 40K views and my summary from last years LTE Voice summit has over 30K views. I assume this is not just due to the complexity of this feature.

When I attended the LTE Voice summit last year, of the many solutions being proposed for roaming, 'Roaming Architecture for Voice over LTE with Local Breakout (RAVEL)' was being touted as the preferred solution, even though many vendors had reservations.

Since then, GSMA has endorsed a new VoLTE roaming architecture, S8HR, as a candidate for VoLTE roaming. Unlike previous architectures, S8HR does not require the deployment of an IMS platform in VPLMN. This is advantageous because it shortens time-to-market and provides services universally without having to depend on the capability of VPLMN.



Telecom Italia has a nice quick summary, reproduced below:

S8HR simplicity, however, is not only its strength but also its weakness, as it is the source of some serious technical issues that will have to be solved. The analysis of these issues is on the Rel13 3GPP agenda for the next months, but may overflow to Rel14. Let’s see what these issues are, more in detail:

Regulatory requirements - S8HR roaming architecture needs to meet all the current regulatory requirements applicable to voice roaming, specifically:

• Support of emergency calls - The issues in this context are several. For example, authenticated emergency calls rely on the existence if an IMS NNI between VPLMN and HPLMN (which S8HR does not provide); conversely, the unauthenticated emergency calls, although technically feasible in S8HR, are allowed only in some Countries subject to the local regulation of VPLMN. Also, for a non-UE-detectable IMS Emergency call, the P-CSCF in the HPLMN needs to be capable of deciding the subsequent action (e.g. translate the dialed number and progress the call or reject it with the indication to set up an emergency call instead), taking the VPLMN ID into account. A configuration of local emergency numbers per Mobile Country Code on P-CSCF may thus be needed.
• ­Support of Lawful Interception (LI) & data retention for inbound roamers in VPLMN -  S8HR offers no solution to the case where interception is required in the VPLMN for inbound roamers. 3GPP is required to define a solution that fulfill such vital regulatory requirement, as done today in circuit switched networks. Of course VPLMN and HPLMN can agree in their bilateral roaming agreement to disable confidentiality protection to support inbound roamer LI but is this practice really viable from a regulatory point of view?

Voice call continuity – The issue is that when the inbound roamers lose the LTE coverage to enter into  a 2G/3G CS area, the Single Radio Voice Call Continuity (SRVCC) should be performed involving the HPLMN in a totally different way than current specification (i.e. without any IMS NNI being deployed).
Coexistence of LBO and S8HR roaming architectures will have to be studied since an operator may need to support both LBO and S8HR VoLTE roaming architecture options for roaming with different operators, on the basis of bilateral agreement and depending on the capability.
Other issues relate to the capability of the home based S-CSCF and TAS (Telephony Application Server) to be made aware about the VPLMN identity for charging purposes and to enable the TAS to subsequently perform communication barring supplementary services. Also, where the roaming user calls a geo-local number (e.g. short code, or premium numbers), the IMS entities in HPLMN must do number resolution to correctly route the call.
From preliminary discussions held at Working Group level in SA2 (architecture) and SA3 (security) in April, it was felt useful to create a new 3GPP Technical Report to perform comprehensive technical analysis on the subject. Thus it is expected that the discussions will continue in the next months until the end of 2015 and will overheat Release 13 agenda due to their commercial and “political” nature. Stay tuned to monitor the progress of the subject or contact the authors for further information!

NTT Docomo also did some trials back in February and got some brilliant results:

In the trials, DOCOMO and KT achieved the world's first high-definition voice and video call with full end-to-end quality of service. Also, DOCOMO and Verizon achieved the world's first transoceanic high-definition VoLTE roaming calls. DOCOMO has existing commercial 3G and 4G roaming relations with Verizon Wireless and KT.

The calls were made on an IP eXchange (IPX) and network equipment to replicate commercial networks. With only two months of preparation, which also proved the technology's feasibility of speedy commercialization, the quality of VoLTE roaming calls using S8HR architecture over both short and long distances was proven to be better than that of existing 3G voice roaming services.

In fact, NTT Docomo has already said based on the survery from GSMA's Network 2020 programme that 80% of the network operators want this to be supported by the standards and 46% of the operators already have a plan to support this.

The architecture has the following technical characteristics:
(1) Bearers for IMS services are established on the S8 reference point, just as LTE data roaming.
(2) All IMS nodes are located at Home Public Land Mobile Network (HPLMN), and all signaling and media traffic for the VoLTE roaming service go through HPLMN.
(3) IMS transactions are performed directly between the terminal and P-CSCF at HPLMN. Accordingly, Visited Public Land Mobile Network (VPLMN) and interconnect networks (IPX/GRX) are not service-aware at the IMS level. The services can only be differentiated by APN or QoS levels.

These three technical features make it possible to provide all IMS services by HPLMN only and to minimize functional addition to VPLMN. As a result, S8HR shortens the time-to-market for VoLTE roaming services.

Figure 2 shows the attach procedure for S8HR VoLTE roaming. From Steps 1 to 3, there is no significant difference from the LTE data roaming attach procedure. In Step 4, HSS sends an update location answer message to MME. In order for the MME to select the PGW in HPLMN (Step 5), the MME must set the information element VPLMN Dynamic Address “Allowed,” which is included in the subscribed data, to “Not Allowed.” In Step 6, the bearer for SIP signaling is created between SGW and PGW with QCI=5. MME sends an attach accept message to the terminal with an IMS Voice over PS Session Support Indication information element, which indicates that VoLTE is supported. The information element is set on the basis of the MME’s internal configuration specifying whether there is a VoLTE roaming agreement to use S8HR. If no agreement exists between two PLMNs, the information element will not be set.

The complete article from the NTT Docomo technical journal is embedded

Enhancing voice services using VoLTE

VoLTE has been a very popular topic on this blog. My overview of the LTE Voice Summit missed out narrowly from the Top 10 posts of 2014 but there were other posts related to VoLTE that made it.

In this magazine article, NTT Docomo not only talks about its own architecture and transition from 3G to 4G for voice and video, it provides some detailed insights from its own experience.

There is also discussion into technical details of the feature and examples of signalling for VoLTE registration and originating/terminating calls (control, session and user plane establishment), SMS, SRVCC, Video over LTE (ViLTE) and voice to video call switching.

The paper is embedded below and available from slideshare to download.

VoLTE for Enhancing Voice Services from Zahid Ghadialy

Related links:

• DOCOMO VoLTE and Next Steps
• VoLTE Roaming with RAVEL (Roaming Architecture for Voice over IMS with Local Breakout)
• 2015 will finally be the year of Voice over LTE (VoLTE)

2015 will finally be the year of Voice over LTE (VoLTE)

On 4th Nov. 2009, the One Voice initiative was published by 12 companies including AT&T, Orange, Telefonica, TeliaSonera, Verizon, Vodafone, Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Nokia, Samsung and Sony Ericsson. These all agreed that the IMS based solution, as defined by 3GPP, is the most applicable approach to meet their consumers expectations for service quality, reliability and availability when moving from existing CS based voice services to IP based LTE services.

On 15th Feb 2010, GSMA announced that it has adopted the work of the One Voice initiative to drive the global mobile industry towards a standard way of delivering voice and messaging services for LTE. The GSMA’s VoLTE initiative was supported by more than 40 organisations from across the mobile ecosystem, including many of the world’s leading mobile communication service providers, handset manufacturers and equipment vendors, all of whom support the principle of a single, IMS-based voice solution for next-generation mobile broadband networks. This announcement was also supported by 3GPP, Next Generation Mobile Networks alliance (NGMN) and the International Multimedia Teleconferencing Consortium (IMTC).

GSMA has produces various reference documents that map to the 3GPP standards documents as can be seen above.

As per GSA: 71 operators are investing in VoLTE studies, trials or deployments, including 11 that have commercially launched HD voice service. The number of HD voice launches enabled by VoLTE is forecast to reach 19 by end-2014 and then double in 2015. In July 2014 GSA confirmed 92 smartphones (including carrier and frequency variants) support VoLTE, including products by Asus, Huawei, LG, Pantech, Samsung and Sony Mobile. The newly-announced Apple iPhone 6 & 6 Plus models support VoLTE.

Things are also moving quickly with many operators who have announced VoLTE launches and are getting more confident day by day. Du, Dubai recently announced Nokia as VoLTE partner. KDDI, Japan is launching au VoLTE in December. Telstra, Australia has already been doing trials and plans to launch VoLTE network in 2015. Finally, Verizon and AT&T will have interoperable VoLTE calls in 2015.

Below is my summary from the LTE Voice Summit 2014. Let me know if you like it.

Quick Summary of LTE Voice Summit 2014 #LTEVoice from eXplanoTech

Codecs and Quality across VoLTE and OTT Networks

Codecs play an important role in our smartphones. Not only are they necessary and must for encoding/decoding the voice packets but they increase the price of our smartphones too.

A $400 smartphone can have as much as $120 in IPR fees. If you notice in the picture above its $10.60 for the H.264 codec. So its important that the new codecs that will come as part of new generation of mobile technology is free, open source or costs very little.

The new standards require a lot of codecs, some for backward compatibility but this can significantly increase the costs. Its important to make sure the new codecs selected are royalty-free or free license.

The focus of this post is a presentation by Amir Zmora from AudioCodecs in the LTE Voice Summit. The presentation below may not be self-explanatory but I have added couple of links at the bottom of the post where he has shared his thoughts. Its worth a read.

Quality Across VoLTE and non-VoLTE Networks from Amir Zmora

A good explanation of Voice enhancement tools as follows (slide 15):

Adaptive Jitter Buffer (AJB) – Almost all devices today (Smartphones, IP phones, gateways, etc.) have built in jitter buffers. Legacy networks (which were LAN focused when designed) usually have older devices with less sophisticated jitter buffers. When designed they didn’t take into account traffic coming in from networks such as Wi-Fi with its frequent retransmissions and 3G with its limited bandwidth, in which the jitter levels are higher than those in wireline networks. Jitter buffers that may have been planned for, say, dozens of msec may now have to deal with peaks of hundreds of msec. Generally, if the SBC has nothing to mediate (assume the codecs are the same and the Ptime is the same on both ends) it just forwards the packets. But the unexpected jitter coming from the wireless network as described above, requires the AJB to take action. And even if the network is well designed to handle jitter, today’s OTT applications via Smart Phones add yet another variable to the equation. There are hundreds of such devices out there, and the audio interfaces of these devices (especially those of the Android phones) create jitter that is passed into the network. For these situations, too, the AJB is necessary.

To overcome this issue, there is a need for a highly advanced Adaptive Jitter Buffer (AJB) built into the SBC that neutralizes the incoming jitter so that it is handled without problem on the other side. The AJB can handle high and variable jitter rates.

Additionally, the AJB needs to work in what is called Tandem scenarios where the incoming and outgoing codec is the same. This scenario requires an efficient solution that will minimize the added delay. AudioCodes has built and patented solutions supporting this scenario.

Transcoding – While the description above discussed the ability to bypass the need to perform transcoding in the Adaptive Jitter Buffer context, there may very well be a need for transcoding between the incoming and outgoing packet streams. Beyond being able to mediate between different codecs on the different networks on either end of the SBC, the SBC can transcode an incoming codec that is less resilient to packet loss (such as narrowband G.729 or wideband G.722) to a more resilient codec (such as Opus). By transcoding to a more resilient codec, the SBC can lower the effects of packet loss. Transcoding can also lower the bandwidth on the network. Additionally, the SBC can transcode from narrowband (8Khz) to wideband (16Khz) (and vice versa) as well as wideband transcoding, where both endpoints support wideband codecs but are not using the same ones. For example, a wireless network may be using the AMR wideband codec while the wireline network on the other side may be using Opus. Had it not been for the SBC, these two networks would have negotiated a common narrowband codec.

Flexible RTP Redundancy – The SBC can also use RTP redundancy in which voice packets are sent several times to ensure they are received. Redundancy is used to balance networks which are characterized by high packet loss burst. While reducing the effect of packet loss, Redundancy increases the bandwidth (and delay). There are ways to get around this bandwidth issue that are supported by the SBC. One way is by sending only partial packet information (not fully redundant packets). The decoder on the receiving side will know how to handle the partial information. This process is called Forward Error Correction (FEC).

Transrating – Transrating is the process of having more voice payload ‘packed’ into a single RTP packet by increasing the packet intervals, thus changing the Packetization Time or Ptime. Ptime is the time represented by the compression of the voice signals into packets, generally at 20 msec intervals. In combining the payloads of two or more packets into one, the Transrating process causes a reduction in the overhead of the IP headers, lowering the bandwidth and reducing the stress on the CPU resources, however, it increases delay. It thus can be used not only to mediate between two end devices using different Ptimes, but also as a means of balancing the network by reducing bandwidth and reducing CPU pressure during traffic peaks.

Quality-based Routing – Another tool used by the SBC is Quality-based routing. The SBC, which is monitoring all the calls on the network all the time, can decide (based on pre-defined thresholds and parameters) to reroute calls over different links that have better quality.

Further reading:

• 3 Things Required for Managing Cross Network Voice Quality
• The Brain behind Voice Quality
• HD Voice - Next step in the evolution of voice communication
• Patent insanity: Royalty fees could reach $120 on a $400 smartphone