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:

Updates from the 3GPP RAN 5G Workshop - Part 2

I have finally got round to having a look at some more presentations on 5G from the recently concluded 3GPP RAN 5G Workshop. Part 1 of the series is here.

Panasonic introduced this concept of Sub-RAT's and Cradle-RAT's. I think it should be obvious from the picture above what they mean but you can refer to their presentation here for more details.

Ericsson has provided a very detailed presentation (but I assume a lot of slides are backup slides, only for reference). They have introduced what they call as "NX" (No compatibility constraints). This is in line to what other vendors have referred to as well that above 6GHz, for efficiency, new frame structures and waveforms would serve best. Their slides are here.



Nokia's proposal is that in the phase 1 of 5G, the 5G Access point (or 5G NodeB) would connect to the 4G Evolved Packet Core (EPC). In phase 2, both the LTE and the 5G (e)NodeB's would connect to the 5G core. Their presentation is available here.

Before we move on to the next one, I should mention that I am aware of some research that is underway, mostly by universities where they are exploring an architecture without a centralised core. The core network functionality would be distributed and some of the important data would be cached on the edge. There will be challenges to solve regarding handovers and roaming; also privacy and security issues in the latter case.

I quite like the presentation by GM research about 5G in connected cars. They make a very valid point that "Smartphones and Vehicles are similar but not the same. The presentation is embedded below.

Qualcomm presented a very technical presentation as always, highlighting that they are thinking about various future scenarios. The picture above, about phasing is in a way similar to the Ericsson picture. It also highlights what we saw in part 1, that mmW will arrive after WRC-19, in R16. Full presentation here.

The final presentation we are looking is by Mitsubishi. Their focus is on Massive MIMO which may become a necessity at higher frequencies. As the frequency goes higher, the coverage goes down. To increase the coverage area, beamforming can be used. The more the antennas, the more focused the beam could be. They have also proposed the use of SC-FDMA in DL. Their presentation is here and also embedded below.

Updates from the 3GPP RAN 5G Workshop - Part 1

3GPP held a 5G Workshop in Phoenix last week. 550 delegates and over 70 presentations contributed to the discussion, which covered the full range of requirements that will feed TSG RAN work items for the next five years. I will eventually look at all the presentations and highlight the ones that I find interesting as a part of this blog. Due to the vast number of presentations, I will split them into a few blog posts.

Lets start with the chairman summary. The chair highlighted three high level use cases that 5G needs to address (This has been highlighted in many presentations, see here for example):

• Enhanced Mobile Broadbandare 
• Massive Machine Type Communications
• Ultra-reliable and Low Latency Communications

As can be seen in the picture above, 3GPP is planning to split the 5G work into two phases. Phase 1 (Rel-15) will look at a subset of requirements that are important for the commercial needs of the day. Phase 2 (Rel-16) will look at more features, use cases, detailed requirements, etc.

Here is the chair summary of the workshop:

The presentation (RWS-150002) from Motorola/Lenovo highlighted the need to handle different spectrum. For sub-6GHz, the existing air interface could work with slight modifications. For spectrum between 6GHz and 30GHz, again a similar air interface like 4G may be good enough but for above 30GHz, there is a need for new one die to phase noise.

The presentation by CATT or China Academy of Telecommunication Technology (RWS-150003) is quite interesting and is embedded below. They also propose Pattern Division Multiple Access (PDMA).

Orange (RWS-150004) has definitely put a thought into what good 5G would be. Their presentation is embedded below too:

The presentation from Huawei (RWS-150006) introduced the concept of Unified Air Interface, UAI.



They presentation also explains the concept of Adaptive Frame structures and RAN slicing very well. For those who may be wondering, uMTC stands for ultra-reliable MTC and mMTC stands for massive MTC. RAN slicing enables the RAN to be partitioned such that a certain amount of carriers are always dedicated to a certain services independently of other services. This ensures that the service in the slice is always served reliably.

The final presentation is the vision and priorities by 5GPPP as follows:

3GPP Release-13 whitepapers and presentations

With 3GPP Release-13 due early/mid next year, there has been a flurry of presentations and whitepapers on this topic. This post provides some of these. I will try and maintain a list of whitepapers/presentations as part of this post as and when released.

1. June 2015: LTE Release 13 and road to 5G - Presented by Dino Flore, Chairman of 3GPP RAN, (Qualcomm Technologies Inc.)

2. Sep 2015: Executive Summary - Inside 3GPP Release 13 by 4G Americas

3. June 2015: Mobile Broadband Evolution Towards 5G: 3GPP Rel-12 & Rel-13 and Beyond by 4G Americas

4. April 2015: LTE release 13 – expanding the Networked Society by Ericsson

HetNets and Ultra Dense Networks

When I did my 5G presentation back in Feb., I explained about Ultra Dense Networks (UDN) that will be a main feature of future traffic hotspots. I have also blogged about Qualcomm having tested 1000 small cells in a square km. Some operators are already running out of spectrum with traditional deployments in hotspots. They are already making their cells smaller (but not yet using Small cells) thereby having less users in each cell. This may not be enough so the approach likely to be taken is:

• Offload to WiFi
• Aggregate WiFi with LTE (different approaches including LTE-U, LAA and LWA)
• Use Small cells and C-RAN
• Multi technology Carrier Aggregation
• Beamforming (and massive MIMO)

The above picture is from a presentation (embedded below) by ZTE in the LTE World Summit. Its a good attempt to show different technologies, the year they are expected to go mainstream, whether they are TDD or FDD and if they will form part of 5G.

Anyway, here is the presentation. There is some interesting information on C-RAN, D-RAN results and fronthaul too.

MCPTT Off-network and UE to UE/Network Relays

3GPP SA6 recently held a workshop on Mission Critical Push To Talk (MCPTT) stage 3 development in Canada. You can look at the meeting report here and download any presentations from here.

An interesting presentation that caught my attention was one on "MCPTT Off-network Architecture". The presentation is embedded below where it is described technically what is meant by Off-network. From my understanding an off-network from MCPTT point of view is one where the UE does not have network coverage.

In such a situation a UE can connect to another UE that can connect to UE/network (if available) to relay the message. Its similar to another technology that I have talked about, Multihop Cellular Networks and ODMA. Anyway, here is the presentation:

Sometimes the standards can take too long to develop a feature and apps can come and deliver a similar service at a very short notice. One such App that does something similar is called Firechat, which played a big role in many protests worldwide. The video explaining it below is worth watching.


The problem with Apps is that they cannot be used by the emergency services or other governmental organisations, unless a standard feature is available. This is the expectation from this Off-network relays. It would work in combination with D2D/ProSe.


For anyone interested in the latest Public Safety (PS), here is a presentation by SA6 chairman from July

Some interesting presentations from ETSI Security workshop

ETSI held their security week from 22-26 June 2015 at their headquarters. There are lots of interesting presentations (see agenda [PDF]); I am embedding some here.

IETF and IoT Security from Zahid Ghadialy

This is a good presentation providing a summary of the reasons for IoT security issues and some of the vulnerabilities that have been seen as a result of that.

Aircraft cyber-security - no need to panic...just yet! pic.twitter.com/hZABvW539B

— Zahid Ghadialy (@zahidtg) August 18, 2015

The next one is The Threat landscape of connected vehicles and ITS (Intelligent Transportation Systems) integration in general

THE THREAT LANDSCAPE … of connected vehicles and ITS integration in general from Zahid Ghadialy

This presentation provides a good summary of the threats in the connected cars/vehicles which is only going to become more common. Some of these issues will have to be solved now before we move on to the autonomous vehicles in future. Security issues there will be catastrophic and many lives can be lost.

The final presentation is from 3GPP SA3 that provides a quick summary of security related work in 3GPP.

Challenges in the future 'Network of Networks'

Came across this paper from Dec. 2000 recently. Its interesting to see that even back then researchers were thinking about multiple networks that a user can have access to via handovers. Researchers nowadays think about how to access as many networks as possible simultaneously. I call is Multi-stream aggregation (MSA), some others call it Multi-RAT Carrier Aggregation (MCA) and so on.

If we look at the different access technologies, each has its own evolution in the coming years. Some of these are:

• Fixed/Terrestrial broadband: (A)DSL, Cable, Fiber
• Mobile Broadband: 3G, 4G and soon 5G
• Wireless Broadband: WiFi
• Laser communications
• LiFi or LED based communications
• High frequency sound based communications 

Then there could be a combination of multiple technologies working simultaneously. For example:

• Broadband Access via Integrated Terrestrial & Satellite Systems (BATS)
• LTE-U / LTE-LAA

And the handover has to be seamless between different access technologies. For example:

• Seamless handovers between cellular and WiFi and vice versa.

There has been an interest in moving on to higher frequencies. These bands can be used for access as well as backhaul. The same applies for most of the access technologies listed above which can work as a backhaul to enable other access technologies.

While planned networks would be commonplace, other topologies like mesh network will gain ground too. Device to device and direct communications will help create ad-hoc networks.

While the current networks are mostly stationary, mobile networks will also become common. Opportunity Driven Multiple Access (ODMA) or Multihop Cellular Networks (MCN) would help devices use other devices to reach their destination. Non-standardised proprietary solutions (for example Firechat) will become common too. Security, Privacy and Trust will play an important role here.

Satellite networks, the truly global connectivity providers will play an important role too. While backhauling the small cells on planes, trains and ships will be an important part of satellite networks, they may be used for access too. Oneweb plans to launch 900 micro satellites to provide high speed global connectivity. While communications at such high frequencies mean that small form factor devices like mobile cant receive the signals easily, connected cars could use the satellite connectivity very well.

Samsung has an idea to provide connectivity through 4,600 satellites to be able to transmit 200GB monthly to 5 Billion people worldwide. While this is very ambitious, its not the only innovative and challenging idea. I am sure we all now about the Google loon. Facebook on the other hand wants to use a solar powered drone (UAV) to offer free internet access services to users who cannot get online.

As I mentioned, security and privacy will be a big challenge for devices being able to connect to multiple access networks and other devices. An often overlooked challenge is the timing and sync between different networks. In an ideal world all these networks would be phase and time synchronised to each other so as not to cause interference but in reality this will be a challenging task, especially with ad-hoc and moing networks.



I will be giving a keynote at the ITSF 2015 in November at Edinburgh. This is a different type of conference that looks at Time and Synchronisation aspects in Telecoms. While I will be providing a generic overview on where the technologies are moving (continuing from my presentation in Phase ready conference), I am looking forward to hearing about these challenges and their solutions in this conference.

Andy Sutton (Principal Network Architect) and Martin Kingston (Principal Designer) with EE have shared some of their thought on this topic which is as follows and available to download here.

Diameter Security is worse than SS7 Security?

Back in December last year, there was a flurry of news about SS7 security flaw that allowed hackers to snoop on an unsuspecting users calls and SMS. The blog readers will also be aware that SS7 is being replaced by the Diameter protocol. The main reason being to simplify roaming while at the same time being able to manage the signalling storm in the networks.


The bad news is that while is case of SS7, security issues are due to network implementation and configuration (above pic), the security issues in Diameter seem to be due to the protocol and architecture themselves (below pic)

Diameter is very important for LTE network architecture and will possibly continue in the future networks too. It is very important to identify all such issues and iron them before some hackers start exploiting the network vulnerabilities causing issues for everyone.

The presentation by Cédric Bonnet, Roaming Technical Domain Manager, Orange at Signalling Focus Day of LTE World Summit 2015 is embedded below:

From SS7 to Diameter Security from Zahid Ghadialy

Some important information from this post has been removed due to a valid complaint.

The Importance of License Exempt Frequency Bands

Some of you may be aware that I am also a Technical Programme Manager with the UK Spectrum Policy Forum. Recently we published a whitepaper that we had commissioned to Plum consulting on "Future use of Licence Exempt Radio Spectrum". It is an interested read not only for spectrum experts but also for people trying to understand the complex world of spectrum.

The report is very well written. Here are a few extracts in purple:

Licence exempt frequency bands are those that can be used by certain applications without the need for prior authorisation or an individual right of use. This does not mean that they are not subject to regulation – use must still comply with pre-defined technical rules to minimise the risk of interference. Most licence exempt bands are harmonised throughout Europe and are shared with other services or applications, such as radars or industrial, scientific and medical (ISM) equipment. Wi-Fi and Bluetooth are probably the most familiar examples of mass-market licence exempt wireless applications, but the bands support many other consumer devices, such as cordless phones, doorbells, car key fobs, central heating controllers, baby monitors and intruder alarms. Looking to the future, licence exempt bands are likely to be a key enabler of wireless machine to machine (M2M) communication applications.

Key benefits of licence exempt bands include:

• For end-users:
• Greater convenience and flexibility by avoiding the need for lengthy runs of cable in home and work environments
• Ability to connect mobile devices to a fixed broadband network, reducing dependence on the mobile network and potentially saving costs both for the service provider and the end-user
• Enhanced convenience, safety and security, e.g. through installation of low cost wireless alarm systems or ability to unlock vehicles remotely rather than fumbling with keys

• For equipment vendors and operators:
• Facilitating market entry – there is no need to acquire a licence to deploy a service
• Enabling niche applications or services to be addressed quickly and cheaply using existing technology and spectrum – this has been particularly effective in serving new machine to machine (M2M) applications in areas such as health, transport and home automation.
• Providing certainty about spectrum access – there is no need to compete or pay for spectrum access (though the collective nature of spectrum use means quality of service cannot be guaranteed)
• The ability to extend the reach of fixed communication networks, by providing wireless local area connectivity in homes, businesses and at public traffic hotspots.

The two most notable drawbacks are the inability to guarantee quality of service and the more limited geographic range that is typically available (reflecting the lower power limits that apply to these bands). Licence exempt wireless applications cannot claim protection from interference arising from other users or radio services. They operate in shared frequency bands and must not themselves cause harmful interference to other radio services.

From a regulator’s perspective, licence exempt bands can be more problematic than licensed bands in terms of refarming spectrum, since it is difficult to prevent the continued deployment of legacy equipment in the bands or to monitor effectively their utilisation. There is also generally no control over numbers and / or location of devices, which can make sharing difficult and limits the amount of spectrum that can be used in this way.

In Europe, regulation of licence exempt bands is primarily dealt with at an international level by European institutions. Most bands are fully harmonised, whereby free circulation of devices that comply with the relevant standards is effectively mandated throughout the EU. However some bands are subject to “soft” harmonisation, where the frequency limits and technical characteristics are harmonised but adoption of the band is left to national administrations to decide.

A key recommendation, which I think would be very interesting and useful would be: Promote further international harmonisation of licence exempt bands, in particular the recently identified 870 – 876 MHz and 915 – 921 MHz band that are likely to be critical for supporting future M2M demand growth in Europe.

Note that a similar sub-1GHz band has been recommended for 5G for M2M/IoT. The advantage for low frequencies is that the coverage area is very large, suitable for devices with low date rates. Depending on how the final 5G would be positioned, it may well use the license exempt bands, similar to the LAA/LTE-U kind of approach maybe.

The whitepaper is embedded below and is available to download from here: