Showing posts with label VoLTE. Show all posts
Showing posts with label VoLTE. Show all posts

Friday, 1 June 2012

On LTE Roaming ...

The IP eXchange (IPX) is used for data when the users roam between different networks. GPRS Roaming eXchange (GRX) is a service within IPX. One of the main areas of discussion within the LTE World Summit 2012 in the Signalling Focus day was roaming on LTE. Different vendors have different proposals and solutions; couple of them are as follows:



Interesting to see that iBasis has proposed LTE Signalling eXchange (LSX) as a way forward.

A presentation from Acme Packet (for an earlier conference) has interesting VoLTE roaming options proposal.

Finally, while everyone was focussing on LTE-LTE roaming, only Diametriq was looking at LTE-LTE/3G/2G Roaming. The relevant part of their presentation is embedded below.
Happy to hear more on this topic if anyone else wants to contribute. Please feel free to add comments.

Saturday, 19 May 2012

SPS and TTI Bundling Example

I have blogged about Semi-Persistent Scheduling (SPS) and Transmit Time Interval (TTI) Bundling feature before. They are both very important for VoIP and VoLTE to reduce the signalling overhead.



It should be noted that as per RRC Specs, SPS and TTI Bundling is mutually exclusive. The following from RRC specs:

TTI bundling can be enabled for FDD and for TDD only for configurations 0, 1 and 6. For TDD, E-UTRAN does not simultaneously enable TTI bundling and semi-persistent scheduling in this release of specification. Furthermore, E-UTRAN does not simultaneously configure TTI bundling and SCells with configured uplink.

Wednesday, 14 December 2011

ETSI INT IMS/EPC Interoperability Standardisation: Motivation, Roadmap & First Results

INT = IMS Network Testing. ETSI INT website here. More details below the presentation:

This was presented by Giulio Maggiore, Telecom Italia, ETSI TC INT Chairman in the 2nd FOKUS FUSECO Forum 2011, Berlin 17-18 Nov. 2011

From the ETSI leaflet (note that this is quite old information but still on the ETSI website here):

IMS interoperability is a key issue for boosting IMS (IP Multimedia Subsystem) roll-out and more specifically network interconnection between operators. Only through thorough testing in practical scenarios can operators ensure operational excellence in a multi-vendor and multi-provider environment.


IMS comprises a set of specifications designed to enable network operators to implement IP-based networks that can carry services for both fixed and mobile customers simultaneously.


IMS was developed originally in the mobile world (specifically in the specifications created by the 3rd Generation Partnership Project, 3GPP), and was adopted for fixed networks by ETSI’s TISPAN Technical Committee (Telecoms & Internet Converged Services & Protocols for Advanced Networks).


However this promise of advanced communications over the next generation network will only be delivered if those same networks can interconnect.


ETSI’s Technical Committee INT: IMS Network Testing


ETSI is bridging the existing gap between 3GPP IMS Core Network standards and the initial industry IMS implementations through the organization of IMS interoperability events in connection with ETSI’s Centre for Testing & Interoperability (CTI) and Plugtests™ interoperability testing service.


Our Technical Committee for IMS Network Testing (TC INT) is actively establishing close contact with a number of industry fora and organizations dealing with IMS interoperability, including 3GPP, GSMA, MSF (Multi Service Forum), IMS Forum and the ITU-T. TC INT develops IMS test specification according to conformance, network integration and interoperability testing methodologies. Other ongoing work includes development of tests for Supplementary Services based on regulatory requirements and IMS tests with legacy networks (e.g. SIP-I).


ETSI has already held two IMS interoperability events. The first examined interconnection aspects of 3GPP IMS Release 6, including such issues as basic call on the Mw interface. The second event had a wider scope that included the testing of 3GPP IMS Release 7 interworking, roaming, border control, and integration of application servers executing selected Multimedia Telephony supplementary services.


Future ETSI activities and events will go even deeper towards bridging 3GPP IMS standards and industry implementations. These will include the organization of further IMS interoperability events designed to boost the roll-out and take-off of IMS services and operators’ network interconnections.

Monday, 20 June 2011

Roaming with the IP eXchange (IPX)


From Wikipedia:

Traditionally, voice traffic interconnection between different operators has utilized the international SS7/TDM networks. However, lately the all-IP paradigm with VoIP is being rapidly introduced by different operators in various forms, such as IMS. In order to minimize the number of conversions between packet-switched voice and circuit-switched voice there is a clear need to deploy an IP based NNI (Network-to-Network Interface) and therefore an IP based interconnection network.

It is also evident that a large number of IP based services (such as Presence or IM) simply cannot be interconnected using a SS7/TDM network, further increasing the need for evolution into an IP based interconnection network.

Since the year 2000 GSM operators have been using GRX (GPRS Roaming Exchange) network for routing the IP based commercial roaming traffic between visited and home operators. Mainly 2.5G and 3G data roaming has been using GRX. GRX is a private IP network (separated from internet) consisting of multiple different GRX carriers that are connected to each other via peering points. However, GRX is limited only to GSM operator community and not all GRX's are capable of meeting the demands of real-time services.

Even though the GRX environment is not entirely suitable as a common IP network for interconnection and roaming, it offers a good starting point for the development of IPX. IPX development has been done in various GSM Association projects and working groups since 2004.


The following presentation is from LTE World Summit:

Friday, 27 May 2011

Dual Radio Solution for Voice in LTE

I did mention in the Twitter conversations post from LTE World Summit 2011 that there are now certain analysts and players in the market who think that it should be possible to have two radios. Here is a slide from ZTE that shows that they are thinking in this direction as well.


Click on the pic to enlarge.

Tri-SIM phones have been available for quite a while but now there are Quad-Sim Shanzhai phones that are available in China. I am sure there is a market for these kind of phones.

With the battery life and the mobile technology improving, these are no longer the concerns when talking about dual radio possibility in the devices. Another common argument is that there may be additional interference due to multiple radios simultaneously receiving/transmitting. I am sure these can be managed without much problem.

Another problem mentioned is we may need multiple SIM cards but the SIM cards used is actually a UICC. There can be multiple SIM applications and IMSI's on it. The network may need some very minor modifications but they should be able to manage this with no problems. In the good old days, we used to have mobiles with built in Fax. The mobile number used to be different from the Fax number. It was a similar kind of problem but managed without problem.

So there may still be time to keep LTE simple by standardising the dual-radio solution rather than having CSFB, VoLTE, SRVCC, VoLGA, etc.

Any thoughts?

Monday, 25 April 2011

Advanced Telephony Services for LTE

With LTE World Summit just round the corner, I was going through the last year's presentations and realised that we didn't talk of this one before.

The concept for the advanced telephony services has been around since the early days of IMS and this was one of the ways IMS was sold. Unfortunately IMS didn't take off as planned and only now with the standardisation of VoLTE, there is a possibility of the advanced services becoming a reality.

The following presentation summarises some of these advanced telephony services concepts.

Tuesday, 8 February 2011

VoLTE: Semi-Persistent Scheduling (SPS) and TTI Bundling

The following is from the recently released 4G Americas paper '4G Mobile Broadband Evolution: 3GPP Release-10 and beyond:

With the support of emergency and location services in Rel-9, interest in Voice over LTE (VoLTE) has increased. This is because the Rel-9 enhancements to support e911 were the last step to enable VoLTE (at least in countries that mandate e911) since the Rel-8 specifications already included the key LTE features required to support good coverage, high capacity/quality VoLTE. There are two main features in Rel-8 that focus on the coverage, capacity and quality of VoLTE: Semi-Persistent Scheduling (SPS) and TTI Bundling.

SPS is a feature that significantly reduces control channel overhead for applications that require persistent radio resource allocations such as VoIP. In LTE, both the DL and UL are fully scheduled since the DL and UL traffic channels are dynamically shared channels. This means that the physical DL control channel (PDCCH) must provide access grant information to indicate which users should decode the physical DL shared channel (PDSCH) in each subframe and which users are allowed to transmit on the physical UL shared channel (PUSCH) in each subframe. Without SPS, every DL or UL physical resource block (PRB) allocation must be granted via an access grant message on the PDCCH. This is sufficient for most bursty best effort types of applications which generally have large packet sizes and thus typically only a few users must be scheduled each subframe. However, for applications that require persistent allocations of small packets (i.e. VoIP), the access grant control channel overhead can be greatly reduced with SPS.

SPS therefore introduces a persistent PRB allocation that a user should expect on the DL or can transmit on the UL. There are many different ways in which SPS can setup persistent allocations, and Figure below shows one way appropriate for VoLTE. Note that speech codecs typically generate a speech packet every 20 ms. In LTE, the HARQ interlace time is 8 ms which means retransmissions of PRBs that have failed to be decoded can occur every 8 ms. Figure below shows an example where a maximum of five total transmissions (initial transmission plus four retransmissions) is assumed for each 20 ms speech packet with two parallel HARQ processes. This figure clearly shows that every 20 ms a new “first transmission” of a new speech packet is sent. This example does require an additional 20 ms of buffering in the receiver to allow for four retransmissions, but this is generally viewed as a good tradeoff to maximize capacity/coverage (compared to only sending a maximum of two retransmissions).

The example in Figure above can be applied to both the DL and UL and note that as long as there are speech packets arriving (i.e. a talk spurt) at the transmitter, the SPS PRBs would be dedicated to the user. Once speech packets stop arriving (i.e. silence period), these PRB resources can be re-assigned to other users. When the user begins talking again, a new SPS set of PRBs would be assigned for the duration of the new talkspurt. Note that dynamic scheduling of best effort data can occur on top of SPS, but the SPS allocations would take precedent over any scheduling conflicts.


TTI bundling is another feature in Rel-8 that optimizes the UL coverage for VoLTE. LTE defined 1 ms subframes as the Transmission Time Interval (TTI) which means scheduling occurs every 1 ms. Small TTIs are good for reducing round trip latency, but do introduce challenges for UL VoIP coverage. This is because on the UL, the maximum coverage is realized when a user sends a single PRB spanning 180 kHz of tones. By using a single 180 kHz wide PRB on the UL, the user transmit power/Hz is maximized. This is critical on the UL since the user transmit power is limited, so maximizing the power/Hz improves coverage. The issue is that since the HARQ interlace time is 8 ms, the subframe utilization is very low (1/8). In other words, 7/8 of the time the user is not transmitting. Therefore, users in poor coverage areas could be transmitting more power when a concept termed TTI bundling (explained in the next paragraph) is deployed.

While it’s true that one fix to the problem is to just initiate several parallel HARQ processes to fill in more of the 7/8 idle time, this approach adds significant IP overhead since each HARQ process requires its own IP header. Therefore, TTI bundling was introduced in Rel-8 which combined four subframes spanning 4 ms. This allowed for a single IP header over a bundled 4 ms TTI that greatly improved the subframe utilization (from 1/8 to 1/2) and thus the coverage (by more than 3 dB).

Martin Sauter puts it in a simpler way in his blog as follows: The purpose of TTI Bundling is to improve cell edge coverage and in-house reception for voice. When the base station detects that the mobile can't increase it's transmission power and reception is getting worse it can instruct the device to activate TTI bundling and send the same packet but with different error detection and correction bits in 2, 3 or even 4 consecutive transmit time intervals. The advantage over sending the packet in a single TTI and then detecting that it wasn't received correctly which in turn would lead to one or more retransmissions is that it saves a lot of signaling overhead. Latency is also reduced as no waiting time is required between the retransmissions. In case the bundle is not received correctly, it is repeated in the same way as an ordinary transmission of a packet. Holma and Toskala anticipate a 4dB cell edge gain for VoIP with this feature which is quite a lot. For details how the feature is implemented have a look at 3GPP TS 36.321.

A whitepaper explaining the concepts of TTI Bundling is available on Slideshare here.

Friday, 3 December 2010

Presentation: IMS for 3G Voice Services and Migration Strategies

Very interesting presentation from NTT DoCoMo in the IMS workshop I blogged about yesterday. It shows their strategy to move from legacy core network to an All IP Network (AIPN).


Thursday, 10 December 2009

VoLGA = 1, other VoLTE = 0


From Unstrung:

Deutsche Telekom Announced First Voice Calls over LTE with VoLGA. Deutsche Telekom announced today the world’s first voice call over LTE with excellent speech quality based on VoLGA (Voice over LTE via Generic Access) technology and two independent test environments.

Calls have been made between a test system, installed at Deutsche Telekom Headquarters in Bonn, Germany which is based on a VoLGA implementation of Kineto Wireless and a second totally independent system from Alcatel-Lucent, installed in their test center in Stuttgart, Germany. Both VoLGA-based Voice over LTE systems support inbound and outbound voice calling and SMS messaging between LTE-enabled devices and standard mobile and fixed telephones.

With this result Deutsche Telekom underlines the innovative leadership in the development of Next Generation Mobile Networks (NGMN), as it belongs to a series of tests through which the company consequently researches the capabilities of the potential NGMN technologies.

“Voice calling is an essential service for mobile operators. This demonstration is a key milestone towards establishing a future proof eco system and shows a cost efficient way for using voice over LTE”, stated Uwe Janssen, Senior Vice President of Core Networks. “The VoLGA test shows how operators could quickly and easily provide next generation voice services, re-using their existing core networks. At the same time this serves as a first step to prepare networks for the industry-agreed mid- and long-term solution for voice over LTE that will be based on IMS.”

In other related news from Fierce Wireless:

Ericsson has dropped its support for the VoLGA Forum, which promotes Voice over LTE via Generic Access, dealing a blow to the voice-over-LTE approach a little more than a month after the vendor signalled its enthusiasm for a different standard.

Erik Ekudden, Ericsson's vice president of technology and industry, said that when the VoLGA Forum was established earlier this year "we had the impression that VoLGA would become a global solution." However, "there are no signs that it [VoLGA] will be strongly supported" by mobile operators, he said in an interview with Unstrung.

Picture Source: Into Mobile

Friday, 6 November 2009

'One Voice Initiative': IMS Based approach adopted


AT&T*, Orange, Telefonica, TeliaSonera, Verizon, Vodafone, Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Nokia, Samsung Electronics Co. Ltd., and Sony Ericsson have defined the preferred way to ensure the smooth introduction and delivery of voice and SMS services on Long Term Evolution (LTE) networks worldwide.

The above telecommunications industry leaders have jointly developed a technical profile for LTE voice and SMS services, also known as the One Voice initiative. The profile defines an optimal set of existing 3GPP-specified functionalities that all industry stakeholders, including network vendors, service providers and handset manufacturers, can use to offer compatible LTE voice solutions.

Open collaborative discussions have concluded that the IP Multimedia Subsystem (IMS) based solution, as defined by 3GPP, is the most applicable approach to meeting the consumers’ expectations for service quality, reliability and availability when moving from existing circuit switched telephony services to IP-based LTE services. This approach will also open the path to service convergence, as IMS is able to simultaneously serve broadband wireline and LTE wireless networks.

By following the jointly defined technical profile, the industry can help guarantee international roaming and interoperability for LTE voice and SMS services, ensuring subscribers continuity of these vital services – all while offering service providers a smooth and well-defined path to LTE.

The objective of the initiative is to ensure the widest possible ecosystem for LTE and to avoid fragmentation of technical solutions. LTE will, with this initiative, not only serve as a broadband access for increasing data traffic, but also for continuing voice and SMS services. Network operators will be able to more quickly develop their customized LTE ecosystem in collaboration with both network equipment vendors and device manufacturers. In addition, the reassurance of global interoperability in an LTE voice landscape and the ability to offer both broadband access and telephony services over LTE will create strong foundations for future business.

The profile for the initial solution has been finalized and is available through the companies associated with this press release. The objective is to hand over the profile and continuing work to existing industry forums.

To view the technical profile, please visit http://news.vzw.com/OneVoiceProfile.pdf.

From Rethink Wireless:

One of the trickiest issues for early LTE deployers is uncertainty over how voice and SMS services - still the key cash cows for most operators - can be supported. Eventually, all these services will be carried over IP, using the IMS (IP Multimedia Subsystem) standard, but only a few carriers, like Verizon Wireless, are looking to deploy all-IP from day one. However, there is pressure to accelerate the process and reduce the cost and risk of LTE/IMS for carriers, and this is the objective of the new One Voice initiative.

Some operators believe they will initially deploy LTE as a data-only network, but most want to support voice and, even more importantly, SMS (which underpins many cellco processes and customer communications). Faced with the risk that large players might delay their plans until they have a strong route to voice, One Voice has defined a profile based on existing 3GPP standards for IMS-enabled voice.

The work has initially emerged from Nokia Siemens, which was previously trying to get wide industry support for its own interim voice over LTE solution, VoLTE (which only worked with its own softswitches). The company's convergent core marketing manager, Sandro Tavares, said One Voice should ease fears over how voice will be deployed by resolving roaming and interworking issues at an early stage. It is not creating a new standard, but aims to ensure compatibility between networks and devices by creating a common profile, which defines an optimal set of existing 3GPP functionalities for use by vendors and operators. "There is no new standard," added Tavares. "It's just using what is there already."

NSN is already producing LTE equipment that complies with the new profile, and so has a headstart in offering an important feature to early triallists - which could boost its so-far low profile in LTE tests, dominated by Ericsson and Huawei. However, the vendor will now hand its work to the 3GPP and GSM Association so that other companies can work on and adopt the profile. So far, it has signed support from most of the key operators that tend to wield influence over cellular standards, apart from DoCoMo and China Mobile - AT&T, Orange, Telefonica, TeliaSonera, Verizon Wireless and Vodafone are there, plus a strong line-up of vendors. These are Alcatel-Lucent and Ericsson on the infrastructure side and Nokia, Samsung and Sony Ericsson for devices. The group needs to get the Chinese vendors on board to complete the set, as well as Motorola.

The supporters of the initiative say this is their "preferred path" for voice over LTE, though for carriers that do not want to move to IMS at an early stage, there are other options available - namely open web-based voice; the stopgap solution of Circuit Switch Fallback (also enshrined in 3GPP standards), where the handset is forced off the LTE network onto 2G or 3G for voice calls; and variations on the theme of using circuit switch over packet techniques. There are two main approaches to this - MSC Voice, which is tied to a switch, with NSN's VoLTE the most prominent example; and VoLGA, which is architecture independent, and uses the UMA/GAN (Unlicensed Mobile Access/Generic Access Network) protocol. This Kineto originated technology was originally adopted for Wi-Fi/3G fixed-mobile convergence and as such did find its way into the 3GPP. VoLGA does not require modifications in the LTE RAN or core, or the MSC, but uses a separate gateway controller.

Some of the One Voice supporters are already involved in VoLGA (though its major carrier T-Mobile has not yet joined the new group). Steve Shaw, who heads up corporate marketing for Kineto and VoLGA, believes that IMS is the way that, ultimately, voice will be handled, but it has a long way to go before it is usable, and so there will still be a role for several years for approaches like VoLGA.

T-Mobile will I assume soon have to follow suit and fall in line otherwise they may have limited devices that are available and there will also be inter-operability issues.

Last week I attended a presentation by IET Berkshire on Voice Services over LTE, presented by Iain Sharp from Nortel. Even though this announcement came yesterday, Iain did say that IMS is the way forward for Voice over LTE. If interested you can see the presentation here.