5G, NFV and Network Slicing

5G networks have multifaceted requirements where the network needs to be optimised for data rate, delay and connection numbers. While some industry analysts suspect that these requirements cannot be met by a single network, vendors suggest that Network Slicing will allow all these requirements to be met by a single network.

Ericsson's whitepaper provides a good definition of what network slicing means:

A logical instantiation of a network is often called a network slice. Network slices are possible to create with both legacy platforms and network functions, but virtualization technologies substantially lower barriers to using the technology, for example through increased flexibility and decreased costs.

...

Another aspect of management and network slicing is setting up separate management domains for different network slices. This may allow for completely separate management of different parts of the network that are used for different purposes. Examples of use cases include mobile virtual network operators (MVNOs) and enterprise solutions. This kind of network slice would, in current Evolved Packet Core (EPC) networks, only cover the PDN gateway (PGW) and the policy control resource function (PCRF). However, for machine type communication (MTC) and machine-tomachine (M2M) solutions, it is likely that it would also cover the Mobile Management Entities (MMEs) and Serving Gateways (SGWs).

NGMN came out with the 5G whitepaper which touched on this subject too: 

Figure above illustrates an example of multiple 5G slices concurrently operated on the same infrastructure. For example, a 5G slice for typical smartphone use can be realized by setting fully-fledged functions distributed across the network. Security, reliability and latency will be critical for a 5G slice supporting automotive use case. For such a slice, all the necessary (and potentially dedicated) functions can be instantiated at the cloud edge node, including the necessary vertical application due to latency constraints. To allow on-boarding of such a vertical application on a cloud node, sufficient open interfaces should be defined. For a 5G slice supporting massive machine type devices (e.g., sensors), some basic C-plane functions can be configured, omitting e.g., any mobility functions, with contentionbased resources for the access. There could be other dedicated slices operating in parallel, as well as a generic slice providing basic best-effort connectivity, to cope with unknown use cases and traffic. Irrespective of the slices to be supported by the network, the 5G network should contain functionality that ensures controlled and secure operation of the network end-to-end and at any circumstance.

Netmanias has a detailed article on this topic which is quite interesting too, its available here.

Recently, South Korean operator SK Telecom and Ericsson concluded a successful trial of this technology, see here. Ericsson is also working with NTT Docomo on 5G including network slicing, see here.

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

Continuing with the updates from 5G RAN workshop, part 1 and part 2 here.

Dish network wants to have a satellite based 5G network. A recent article from Light Reading shows the following:

Dish states that there are misconceptions about what satellite technology can deliver for 5G networks. Essentially Dish says that satellites will be capable of delivering two-way communications to support 5G.

A hybrid ground and space 5G network would use small satellites that each use a "spot beam" to provide a dedicated area of two-way coverage on the ground. This is different than the old model of using one satellite with a single beam to provide a one-way service like a TV broadcast over a landmass.

Dish argues that newer, smaller satellites, equipped with the latest multi-antenna arrays (MIMO) would allow for "ubiquitous connectivity through hybrid satellite and terrestrial networks," the operator writes. In this model, satellites could connect areas that it would be hard to network otherwise like mountains and lakes.

The presentation from Dish is as follows:

Alcatel-Lucent provided a whitepaper along with the presentation. The paper provides an interesting view of 5G from their point of view. Its embedded below:

The presentation from Kyocera focused on TD-LTE which I think will play a prominent role in 5G. In case of wide channels, TD-LTE can help predict the channel accurately, which is a drawback for FDD at high frequencies. Their presentation is available here.

The presentation from NEC focussed on different technologies that will play a role in 5G. Their presentation is available here.

The final presentation we will look at this time is by the South Korean operator, KT. What is interesting to see is that in the part 1 we saw in the chairman's summary that 5G will come in two phases; Rel-15 will be phase 1 and Rel-16 will be phase 2. In the summary slide in KT's presentation, it looks like they are going to consider Rel-14 as 5G. Its not at all surprising considering that Verizon has said that they want to commercialise 5G by 2017, even though 5G will not be fully specified according to 3GPP by then. Anyway, here is the presentation by KT.

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.

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.

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

Voice over WiFi (VoWiFi) technical details

VoWiFi is certainly a hot topic, thanks to the support of VoWiFi on iPhone 6. A presentation from LTE World Summit 2014 by Taqua on this topic has already crossed 13K views. In this post I intend to look at the different approaches for VoWiFi and throw in some technical details. I am by no means an expert so please feel free to add your input in the comments.

Anybody reading this post is not aware of S2a, S2b, Samog, TWAG, ePDG, etc. and what they are, please refer to our whitepaper on cellular and wi-fi integration here (section 3).

There are two approaches to VoWiFi, native client already in your device or an App that could be either downloaded from the app store or pre-installed. The UK operator '3' has an app known as ThreeInTouch. While on WiFi, this app can make and receive calls and texts. The only problem is that it does not handover an ongoing call from WiFi to cellular and and vice versa. Here are a few slides (slides 36-38) from them from a conference last year:

Quick Summary of LTE Voice Summit 2014 #LTEVoice from eXplanoTech

The other operators have a native client that can use Wi-Fi as the access network for voice calls as well as the data when the device is connected on the WLAN.

A simple architecture can be seen from the picture above. As can be seen, the device can connect to the network via a non-3GPP trusted wireless access network via the TWAG or via a non-3GPP untrusted wireless access network via ePDG. In the latter case, an IPSec tunnel would have to be established between the device and the ePDG. The SIM credentials would be used for authentication purposes so that an intruder cannot access ePDG and the core.

Now, I dont want to talk about VoLTE bearers establishment, etc. which I have already done here earlier. In order to establish S2a (trusted) and S2b (untrusted) connection, the AAA server selects an APN among those which are subscribed to in the HLR/HSS. The PDN-GW (generally referred to as PGW) dynamically assigns an IP address out of a pool of addresses which is associated with this APN. This UE IP address is used by the VoWiFi SIP UA (User Agent) as the contact information when registering to the SIP soft switch (which would typically be the operators IMS network).

If for any reason the SIP UA in the device is not able to use the SIM for authentication (needs ISIM?) then a username/password based authentication credentials can be used (SIP digest authentication).

Typically, there would be a seperate UA for VoLTE and VoWiFi. They would both be generally registering to the same IMS APN using different credentials and contact addresses. The IMS network can deal with multiple registrations from the same subscriber but from different IP addresses (see 3GPP TS 23.237 - 'IMS Service Continuity' for details).

Because of multiple UA's, a new element needs to be introduced in order to 'fork' the downstream media streams (RTP/RTCP packets) to different IP addresses over time.

3GPP has defined the Access Transfer Gateway (ATGW) which is controlled by the Access Transfer Control Function (ATCF); the ATCF interfaces to the IMS and Service Centralization and Continuity Application Server (SCC AS). All these are not shown in the picture above but is available in 3GPP TS 23.237. The IMS networks in use today as well as the one being deployed for VoLTE does not have ATGW/ATCF. As a result vendors have to come up with clever non-standardised solutions to solve the problem.

When there is a handover between 3GPP and non-3GPP networks, the UE IP address needs to be preserved. Solutions like MIP and IPSec have been used in the past but they are not flexible. The Release-12 solution of eSAMOG (see 3GPP TS 23.402) can be used but the solution requires changes in the UE. For the time being we will see proprietary solutions only but hopefully in future there would be standardised solutions available.

3GPP TS 23.234 describes more in detail the interworking of 3GPP based system and WLAN. Interested readers can refer to that for further insight.

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)

The SS7 flaws that allows hackers to snoop on your calls and SMS

By now I am aware that most people have heard of the flaws in SS7 networks that allow hackers to snoop, re-route calls and read text messages. For anyone who is not aware of these things, can read some excellent news articles here:

• Hackers Can Read Your Texts Thanks to Huge Security Flaw - Gizmodo
• German researchers discover a flaw that could let anyone listen to your cell calls. - Washington Post
• White hats do an NSA, figure out LIVE PHONE TRACKING via protocol vuln - The Register
• 1980s technology can be used to hack any smartphone - Beta News

Our trusted security expert, Ravi Borgaonkar, informs us that all these flaws have already been discussed back in May, as part of Positive Hack Days (PHDays).

Here are the slides on SS7 hack from PHDays, http://t.co/VwUwtFVqyc mentions all flaws reveals in 3 #31c3 talks on SS7 security.
— Ravishankar Borgaonk (@raviborgaonkar) December 28, 2014

The presentation is embedded below and can be downloaded from Slideshare:

How to Intercept a Conversation Held on the Other Side of the Planet from Positive Hack Days

xoxoxo Added this new information on the 4th Jan 2015 oxoxox

The following is this presentation and video by Tobias Engel from the 31st Chaos Communication Congress

SS7: Locate. Track. Manipulate. from 3G4G

4G Security and EPC Threats for LTE

This one is from the LTE World Summit 2014. Even though I was not there for this, I think this has some useful information about the 4G/LTE Security. Presentation as follows:

4G Security - Fortinet from Zahid Ghadialy

Observed Time Difference Of Arrival (OTDOA) Positioning in LTE

Its been a while I wrote anything on Positioning. The network architecture for the positioning entities can be seen from my old blog post here. 

Qualcomm has recently released a whitepaper on the OTDOA (Observed Time Difference Of Arrival) positioning. Its quite a detailed paper with lots of technical insights.

There is also signalling and example of how reference signals are used for OTDOA calculation. Have a look at the whitepaper for detail, embedded below.

Observed Time Difference Of Arrival (OTDOA) Positioning in 3GPP LTE from Zahid Ghadialy

4.5G: Integration of LTE and Wi-Fi networks

With LTE-A getting ready to meet the IMT-Advanced requirements and fulfilling the role of promised '4G', we believe the next phase of evolution before 5G will be successful interworking of LTE and Wi-Fi networks.

This whitepaper (embedded below) explores this feature, we call 4.5G, in detail.



We are very thankful to Anritsu for kindly sponsoring this whitepaper. They have their own whitepaper on this topic which is also worth a read, available here.

4.5G: Integration of LTE and Wi-Fi networks from eXplanoTech

Let us know what you think about this.

EE: The Implications of RAN Architecture Evolution for Transport Networks

Here is a presentation by Andy Sutton, EE from the recent LTE World Summit 2014. Unfortunately the event was too big to be present in all presentations but in his own words, "As always the bullet points don’t tell the full story as there’s considerable narrative that goes with this, however it does stress some major themes."

Slides embedded below, can be downloaded from Slideshare:

The Implications of RAN Architecture Evolution for Transport Networks from Zahid Ghadialy

Voice over WiFi (VoWiFi)

One of the changes that I have noticed in the last year is that some of the operators who have been opposed to WiFi in the past have not only embraced it but are now trying to monopolise the same WiFi spectrum they billed as interference prone. Personally, I think the future of Wi-Fi is not just offloading but also working together with LTE. We are billing this as 4.5G and have recently produced a whitepaper, available here.

There has been a flurry of activity on Voice over Wi-Fi in the last few months. Recently the UK operators '3' and EE announced that they are both allowing WiFi calling and SMS. While '3' customers will have to use an OTT app for the time being, EE customers will experience this seamlessly.

I heard Taqua in the recent LTE World Summit talking about their solution and have offered to share their slides (embedded below). It was interesting to find out while having a discussion with them that their solution supports 'hand-in' and 'hand-out'. This takes away a major advantage that Small Cells offered, seamless roaming. Anyway, feel free to let me know of you have any opinion on this topic

Cellular Services over WiFi from 3G4G

Diamater: Market Status, Roaming, NFV and Case Studies

Some more interesting presentations from the Signalling Focus Day of LTE World Summit. Good overview of market by Greg Collins of Exact ventures is embedded below.

Diameter Signaling Market Update from Zahid Ghadialy

A good presentation by Tieto where they presented some good case studies for Diameter Interworking. Presentation embedded below:

Diameter routing & interworking in NFV from Zahid Ghadialy

The final presentation by Diametriq is very interesting because they presented interesting way of mining the control plane. Thee case study presented was of a 'silent roamer' who is not going to spend money while roaming because he is not sure how much money is spent. This can be exploited by the operator to offer flat packages, 1 day pass, etc. to get some revenue from these roamers. Their presentation included some animations that cannot be shown while being embedded. Please download the PPT from Slideshare to view them.

Unlocking New Value in the Diameter Signaling Path from Zahid Ghadialy

LTE Roaming using IPX

A very interesting presentation from Raphaël Glatt of Bics in the Signalling Focus Day of LTE World Summit 2014. IPX is probably the most popular solution as its already being used by many operators for roaming agreements. Anyway, his presentation was the most detailed one I have come across and he was happy to share it with me for this blog. His complete presentation is embedded below:

Enabling Effective Roaming Through IPX from Zahid Ghadialy

NFV and SDN - Evolution Themes and Timelines

We recently held our first Virtual Networks SIG event in Cambridge Wireless. There were some great presentations. The one by the UK operator EE summarised everything quite well. For those who are not familiar with what NFV and SDN is, I would recommend watching the video on my earlier post here.

One of the term that keeps being thrown around is 'Orchestration'. While I think I understand what it means, there is no easy way to explain it. Here are some things I found on the web that may explain it:

Orchestration means Automation, Provisioning, Coordination and Management of Physical and Virtual resources.  

Intelligent service orchestration primarily involves the principles of SDN whereby switches, routers and applications at Layer 7 can be programmed from a centralized component called the controller with intelligent decisions regarding individual flow routing in real time.

If you can provide a better definition, please do so.

There are quite a few functions and services that can be virtualised and there are some ambitious timelines.

ETSI has been working on NFV and as I recently found out (see tweet below) there may be some 3GPP standardisation activity starting soon.

@zahidtg They can for virtualised networks. There is ongoing discussion in 3GPP for service chaining, vEPC etc.
— Dimitris Mavrakis (@dmavrakis) May 16, 2014

Anyway, here is the complete presentation by EE:

Revolutionizing mobile networks with SDN and NFV from Zahid Ghadialy

There was another brilliant presentation by Huawei but the substance was more in the talk, rather than the slides. The slides are here in case you want to see and download.

Related post:

• Small Cells as a Service (SCaaS) using NFV - 3G4G Small Cells Blog

International LTE Data and VoLTE Roaming - NTT Docomo

Quick recap of the Bearer Architecture: Remember the interface between S-GW and P-GW is known as S5/S8. S5 in case the S-GW and P-GW are part of the same network (non-roaming case) and S8 in case where P-GW belongs to another network than S-GW (roaming case). The S5/S8 interfaces are generally exactly the same. There is a possibility of different types of S5/S8 interfaces like GTP based and PMIP based but lets not discuss that here.

NTT Docomo published an excellent article in their magazine recently showing the different approaches to International Data roaming.

The different scenarios above are based on the guidelines provided in GSMA PRD IR.88. Each operator has to adopt one of the scenarios above, NTT Docomo has selected scenario 4. The Home PLMN (HPLMN) and the Visited PLMN (VPLMN) connect via IP eXchange (IPX).

As can be seen above, the MME in VPLMN communicates with HSS in HPLMN using Diameter Edge Agent (DEA).

Finally, it is well known that NTT Docomo is not launching VoLTE untill 2015. The above is their proposal on how they handle VoLTE while in Japan and when roaming.

The paper is an interesting read, embedded below:

NTT Docomo: Implementing LTE International Data Roaming from Zahid Ghadialy

Another article worth a read is the VoLTE roaming with RAVEL here.

Securing the backhaul with the help of LTE Security Gateway

An excellent presentation from the LTE World Summit last year, that is embedded below. The slide(s) that caught my attention was the overhead involved when using the different protocols. As can be seen in the picture above, the Ethernet MTU is 1500 bytes but after removing all the overheads, 1320 bytes are left for data. In case you were wondering, MTU stands for 'maximum transmission unit' and is the largest size packet or frame, specified in octets (8-bit bytes), that can be sent in a packet or frame based network such as the Internet.

Anyway, the presentation is embedded below:

Securing the backhaul from 3G4G Blogs

VoLTE Roaming with RAVEL (Roaming Architecture for Voice over IMS with Local Breakout)

Voice over LTE or VoLTE has many problems to solve. One of the issues that did not have a clear solution initially was Roaming. iBasis has a whitepaper on this topic here, from which the above picture is taken. The following is what is said above:

The routing of international calls has always been a problem for mobile operators. All too often the answer—particularly in the case of ‘tromboning’ calls all the way back to the home network—has been inelegant and costly. LTE data sessions can be broken out locally, negating the need for convoluted routing solutions. But in a VoIMS environment all of the intelligence that decides how to route the call resides in the home network, meaning that the call still has to be routed back.

The industry’s solution to this issue is Roaming Architecture for Voice over LTE with Local Breakout (RAVEL). Currently in the midst of standardisation at 3GPP, RAVEL is intended to enable the home network to decide, where appropriate, for the VoIMS call to be broken out locally. 

Three quarters of respondents to the survey said they support an industry-wide move to RAVEL for VoLTE roaming. This is emphatic in its enthusiasm but 25 per cent remains a significant share of respondents still to be convinced. Just over half of respondents said they plan to support VoIMS for LTE roaming using the RAVEL architecture, while 12.3 per cent said they would support it, but not using RAVEL.

Until RAVEL is available, 27.4 per cent of respondents said they plan to use home-routing for all VoLTE traffic, while just under one fifth said they would use a non-standard VoLTE roaming solution.

Well, the solution was standardised in 3GPP Release-11. NTT Docomo has an excellent whitepaper (embedded below) explaining the issue and the proposed solution.

In 3GPP Release 11, the VoLTE roaming and interconnection architecture was standardized in cooperation with the GSMA Association. The new architecture is able to implement voice call charging in the same way as circuit-switched voice roaming and interconnection models by routing both C-Plane messages and voice data on the same path. This was not possible with the earlier VoLTE roaming and interconnection architecture.

Anyway, here is the complete whitepaper

NTT Docomo: VoLTE Roaming and Interconnection Standard Technology from Zahid Ghadialy