With the continuously increasing penetration of smartphones, tablets and other mobile devices (including M2M sensors), the data traffic on mobile networks has been continuously increasing and will continue to do so in the near foreseeable future. In the consumer space laptops are increasingly getting replaced by tablets for on-the-go content consumption as well as mild content creation (Even I am writing this blog post from my IPAD and not my desktop/laptop). I bet more tablets are flying off the retail shelves these days compared to laptops even in India. And i see more of this type of consumerization of IT in the enterprise space with many corporates encouraging the usage of tablets and smartphones (even BYOD in some cases) on their networks for employees to be always available 24x7. There exist use cases of dongles and a typical greenfield area where there is no fixed broadband available. There has also been a democratization of both the smartphone and tablet, with costs continuously going down as economies of scale are achieved. The connected devices (to mobile networks) are thus increasing in number. This is the space dimension problem.
The second point is what you do with the mobile device. It was plain voice earlier, followed by emails and basic browsing, but now it will increasingly cover social networking, video conferencing, video streaming & downloads, mobile application updates, VPN traffic, etc. So with the increasing capability of the mobile device, the data demand per user is also increasing rapidly. The content itself increasing in depth (for eg., video encoding standard quality to HD quality (720p, 1080p) and 4K in future, or increasing resolution of images usable on the net as the screens used to view them also increase in resolution). This is the time dimension problem.
So the traffic demand is increasing by a multiplication factor of time & space. To keep up this operators are gradually increasing investments in mobile broadband. Things have moved from GSM/EDGE (narrow band) to 3G/HSPA and now LTE. On the technology and standardization front, we are talking of LTE-Advanced with speeds of 100 Mbps - 1 Gbps (or almost equal to the LAN bandwidth !!!). However whether we will be able to keep the consumer pipe bandwidth up with ever increasing demands is anybody's guess.
Yet a very surprising challenge was thrown by the mobile broadband technologies. Traditionally 2G/3G voice was circuit switched. LTE is pure IP-based or packet switched network and was designed to simplify and flatten the overall network. It was assumed that by the time LTE is adopted, IMS would be mature and equally adopted the mobile operators. On ground, however, the increasing demand of mobile broadband has certainly pushed adoption of data plane LTE, but not the control and service plane IP-based IMS. Of the 222+ LTE deployments worldwide, only 2 have adopted IMS. Mobile operators have always seen (atleast in India), basic voice services has most fundamental demand. They have extensive investments in 2G and 3G voice services. They know that their consumers have similar investments in their mobile devices which are not yet past their usable lifetime and that LTE phones/tablets are not as common as 3G devices. Data has always being used as an additional source of revenue catering to a smaller fraction of subscription base (atleast here in India) and an additional nice-to-have service by a vast majority of subscribers. What makes matters further confusing for operators is that to offer new Multimedia services (data, video, etc) IMS is not the only option. And the users are also increasingly getting aware of this. Operators, however, implicity recognize the dangers of not offering services and just selling bandwidth (from one decreasing ARPU business of voice, they will head into another of data). But the decision making has been slow and therefore this chasm is created.
Anyways, lets look at technical options for resolving this (and there are six of them atleast):
(1) Simultaneous Voice and/over LTE (SVLTE) - In this type of technology the mobile station has to support both legacy 2G/3G and LTE simultaneously. For voice, the mobile station uses 2G/3G G circuiit switched network, while for data an LTE is used. The drawback ofcourse is the adverse impact on battery life of handset as it keeps two cellular radios on at the same time and beacuse of this most handset vendors do not support this technique. There is also no standardization for this feature, which is usually a prerequisite for carrier networks. The technology however is reasonably simple to implement and the handset state machine is also very straight forward. It also ensures that Voice traffic and Data traffic can work independently of each other and simultaneously. ZTE and Huawei are known to have handset solutions that can support this method for simultaneous CDMA and LTE networks.
(2) Circuit Switched Fallback (CDFB) - Standardized by 3GPP R8 (TS 23.272 ), it entails the method of switching the radio from LTE to 2G/3G to make or receive circuit switched calls on mobile handsets. This requires an upgrade to the MSC on the network side ( and no migration to IMS) but no extra support is required on the handset side. This makes it a very effective choice for deployment. However the downside is that beacuse of switchover, the call setup time is greatly increased and the handover scenarios are complex. Also data services are blocked when the voice service is being used which may not be acceptable in many deployments
(3) Voice Over LTE via GAN (VoLGA) - This method was once an industry forum (VoLGA forum) sponsored standard which utilizes 3GPP generic standard to allow Generic IP networks like WLAN or LTE to access 3G services. It is a short term solution like CSFB. It involves a special gateway element (VANC) which is connected to the PGW of LTE access network. VoLGA did not get sufficient support & traction from operators which did not forsee it as a solution moving forward and it was dropped in favour of CSFB in short term on account of investment required in new network elements as opposed to software upgrades of existing equipment in case of CSFB. It was thought to be in a retrogade direction considering LTE aims to simpliy network architecture by reducing NEs.
(4) MSC Server/SIP Adapter - This is a proprietary solution from NSN and is specific to NSN only. Not much is known in public domain about this (apart from Heavy Reading quoting this in its VoLTE market analysis report).
(5) VoLTE - This is long term and carrier multimedia and rich communication services (RCS) solution from mobile operators. It uses IMS for control plane architecture. Existing LTE enanled devices can have a new app (or even replace the dialer) to support IMS UE functionality whille the RAN has to be upgraded to IMS core. It is also possible that many operators can share an IMS core. While VoLTE looks logical the problem stems from the fact that IMS is not the only solution (or the madatory solution) for subscribers to avail rich communication & multimedia services. If a subscriber has invested/indulged in internet based services, he would ideally want the same service delivered on mobile networks to his mobile devices, not migrate to a new one unless their is a very compelling reason to do so. This puts a pig question mark on the success of the service bundles that IMS promises to bring to the operator table.
(6) OTT Services - If you look at WhatsApp, the amount of subscribers they have, the rich messaging that the user indulge in, and what it has done to the SMS market, then you would realize the danger that OTT Voice presents to operator's voice services. Imagine if whatsApp offers voice services tomorrow. Now consider that most communications happen when the subscriber is indoors in his residence, office, coffee shop, retail etc and if the fixed broadband infrastructure is extended to offer WiFi coverage in last 100 metres, then a lot of voice traffic can get offloaded to OTT Voice providers, dealing a body blow to service based voice revenues of the mobile operators. Another scenario is a large corporate offering proprietary VoIP/UC Client to all its employees who can keep in touch with each other while being mobile within and outside the office premises as oindividuals may not be always reachable on their office extensions. The biggest attraction of these services to the consumer is that they are virtually FREE. And for this reason they will keep coming back even if they face unreliability, outages, QoS problems, etc. Compare that with operator service, where everything comes for a price. The word "FREE" vs other Propaganda may cut with some operators, but will not with the average user. As long as users can get something for free vs paying for it, they are going to look very very hard at the first option before selecting the 2nd option. In effect, OTT applications have unbundled the Mobile operator network into connectivity bundle and services bundle, a fundamentally disruptive business trend.
There are also no fixed architectures or standards governing OTT Voice, messaging & other services. The focus is to create what subscribers would love and just increase this user base scaling your system all along the journey. Then this big community is fair game for targeting advertising but none of these revenue streams go to the mobile operator. Telco OEMs and Operators are traditionally very slow in innovation. They believe in a lengthy standardization process first and then roll out. The Internet guys move at light speed. The product that is successful becomes the standard. They cook up something even if its half baked and put it out to users for use. If users like it, the product is enhanced, otherwise it is killed. And we move on to the next big thing possibility.
To conclude, there are multiple ways to solve the Operator voice problem in LTE. Each having its own advantages and disadvantages. Its quite likely a lot of operators will adopt makeshift CS fallback or such temporary solution till they have more business clarity on how they will play in the non-voice services market. They may also play the ISP bandwidth seller game to test the market [Take Airtel In India for example. Their TD-LTE based LTE service (under the 4G marketing moniker) is typically working as a replacement of fixed broadband (dongle) or a solution limited to IPhone 5C/5S (which will drive the usage of facetime chat between apple device users]. Long term the choice is between VoLTE and OTT Voice. And its not a straightforward one. For standards voice the advantages frequently quoted are QoS, reliability, compatibility, etc. But many of these can be implemented in OTT solutions using clever solutions based on a user's device type, location, capability as well as always improving technologies like buffering etc. Not to mention the biggest advantage that most OTT service have is being "perceived" virtually free, even if user is paying for bandwidth (Mobile plans are always tiered not unlimited ...) atleast till now. I repeat, that as long as services are free, people are going to keep coming back.
Today many of us use Youtube, Skype, Viber on 3G networks and don't complain about quality. The Whatsapp/Hangout messaging was anyways superior to the SMS offering from telcos from day one. Its difficult to conceive the scenario that fragmented Telco services (one per operator) can compete with and beat the wow factor with such Internet based services. The game is no longer in the hand of telcos but in the hand of subscribers. And even though it looks like a zero sum game, one does not need to play it like that. Possibly we should look at WIN-WIN ways in which Telco operators could monetize these OTT services (and optimize their network usage efficiency) and these OTT service providers could benefit from partnering with operators by improving user experience even if they have to part with a share of their revenues. This is the situation that operators need to get into, not the subsitution of OTT services with their own. And if in the process, I am pronouncing the death of VoLTE or IMS or Telco services, so be it ...
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