Many mobile operators around the world are rolling out 4G LTE networks, but most are some way off providing voice over LTE (VoLTE) to their subscribers with 4G enabled devices.
Making that transition from circuit-switched 2G/3G networks to all-IP networks like 4G is complicated, however. US-based vendor Taqua has specifically targeted its range of products at helping operators make that transition smoothly and cost-effectively.
Headquartered in Richardson, Texas, Taqua is a supplier of next-generation fixed and mobile convergence switching, IP peering, backhaul systems, and enhanced applications.
John Hoadley, wireless CTO at Taqua tells Wireless: ‘Taqua was founded 15 years ago and has operated mainly in North America developing VoIP products on the wireless side. But four to five years ago we got involved in 3G/4G convergence after two local clients in the USA were looking for better coverage by using SIP-based small cells.
‘The question for us was: how could these small cells be integrated with carriers’ 3G core networks and then scaled- up to meet demand? The clients told us they wanted the calls to look the same to the customer in terms of how dialling and messages looked on the devices. They wanted it to just look like an ordinary call on the network.
The result was the development of femtocells, which have been widely deployed by US carriers Sprint and Cellcomm. ‘This is where our expertise in this field came from,’ says Hoadley, ‘providing 3G features that have become a springboard to voice over LTE (VoLTE) and voice over Wi-Fi (VoWi-Fi).
He points out that voice is no longer as important as it used to be in terms of a carrier’s financial results these days – it is declining at a slow rate of about 3%, as data grows at a rate of 20%. Data ARPU is eclipsing voice ARPU and the US is at this crossover point now, while in Japan the crossover occurred as early as 2011.
But voice remains very important to both carriers and especially their customers. Voice and data tariff offerings are now being sold as a package -even on pre-pay with some networks.
Hoadley says that OTT VoIP providers are targeting the prepaid market, so that prepaid non-bundled plans are driving the use of OTT voice. But he points out that these plans are punitive if a subscriber is a serious user of mobile broadband (e.g. 500MB per month).
Therefore, OTT mobile voice is a threat, but only for a very specific segment - prepaid subscribers who are not interested in large data packages. However, in making a successful transition from 3G to VoLTE the postpaid/high quality subscriber segment is critical, he argues.
Operators have a choice of three paths to follow if they are to fend off the OTT threat and ensure a smooth transition to LTE: become a pipe – access provider; become a key enabler – open APIs to their networks; or become an end-to-end digital solution provider, in which case integrating 3G and 4G is critical to providing full bundled solutions.
But VoLTE is challenging and several transition steps are needed to ensure service quality is maintained, according to Hoadley. The key challenges include:
- Affordable CSFB (circuit switched fallback) evolution with no call set up delay penalty
- Use of the best RF access for voice – Voice over Wi-Fi (VoWi-Fi) can have a role
- Service continuity across domains – 3G, 4G and Wi-Fi
- Service synchronisation and parity between legacy circuit switched networks and IMS core: use of existing investments in IN platforms; subscriber profile management; billing and IT transition costs and time to market.
Taqua has focused its recent development on providing solutions that enable the transition to VoLTE and VoWi-Fi, including:
- Centralised CSFB
- SCC-AS (session centralization and continuity application server) / SR-ACC (single radio voice call continuity)
- 3G-4G service parity
- Embedded VoWiFi.
Step 1 – CSFB (circuit switched fallback)
‘CSFB is the first step to integrating VoLTE into existing networks,’ says Hoadley. ‘3G networks are not that new now and only a small fraction of UMTS/HSPA switches have been upgraded to support the interface needed to integrate 4G.
‘Operators have two options. They can either upgrade every switch, but that is very time consuming and expensive to do, or they can deploy a centralised circuit switched fallback (CSFB) solution, which takes the burden out of all the software upgrades. We can install our CSFB offering on existing switching equipment.'
Hoadley notes that other vendors have come up with CSFB before, but the problem is it adds time to the call set up – anything from 6 to 10 seconds – as well as adding a high signalling burden. For some people, that could mean the call goes to voicemail before they even have a chance to answer it. This trade off has proved unacceptable to the carries and users.
‘We have solved that problem,’ says Hoadley, ‘so the call set up delay is the same as you’d get on any 2G/3G call from your mobile (c.5 seconds). Our CSFB offering takes over the communications with the 4G network and communicates with the 3G one. But we just look like one more element in the network. There is a lot of intellectual property and patents in enabling that and to avoid the added call set up times previous vendors have faced – this is where we are unique.'
Step 2 –SR-VCC and service parity solution
Once there is enough LTE coverage rolled out the task is to ensure the call hand-off between the LTE and 3G cells is done well, as mobile users move back and forth between the two. This is where Taqua’s SR-VCC (single radio voice call continuity) and 3G/4G VoLTE service parity solutions come in.
‘4G for voice is tricky to handle,’ says Hoadley, ‘so you can’t have extra latency built in. You need to provide a consistent quality to the call session, hence SR-VCC – this is a very important step to get right in migrating to VoLTE.’
Service parity between 3G and 4G is another vitally important step to get right. Moving the voice call off a switch-based 3G core to an all IMS (IP multimedia subsystem) 4G core isn’t easy. For the carriers this is an issue, because they have built a wide range of features on their 3G networks, especially their enterprise offerings and pre-paid systems.
‘They need to provide service parity, so that the network can access 3G features at the same time as accessing VoLTE,’ says Hoadley. ‘The carrier needs to be able to handle subscriber profile management issues: how does the carrier ensure that the billing system points at the 3G profile and the 4G profile, for example?’
Tying new offerings like VoLTE into existing billing and other back end IT systems is a big barrier to change for carriers, Hoadley says. But Taqua’s software solution now enables 4G devices to access 3G core features without the operator having to come up with a new billing system, for example.
Step 3 – Voice over Wi-Fi for capacity, coverage and cost reduction
This stage comes in when the operator’s network is extensive enough to provide VoLTE everywhere. ‘It will take a long time before we get there,’ says Hoadley. In the meantime, voice over Wi-Fi can play a role in the transition to 4G in a number of ways.’
For example, a VoWi-Fi solution can be embedded in Android mobile devices. An embedded client on the phone monitors the Wi-Fi and cellular signal and uses the strongest for the incoming and outgoing call.
‘This does not look like the kind of app you use to make a Skype call,’ says Hoadley. ‘There is no Skype-style interface required. It looks like a cellular call, but it’s an all-IP service over existing circuit switched 3G networks, once you are authenticated on the network. It is superior to OTT voice service like Skype, as you get integrated calling, messaging, notification...the kind of experience you have with current 2G/3G services.
‘One of the other things this does is provide better in-building coverage in homes or offices,’ he says. ‘The aim is to make use of the best RF for voice – Wi-Fi may be better than cellular in some situations. Most people use their mobile in the home or office. VoWi-Fi allows you to get coverage in your house or basement rather than using cellular.’
The other solution provided by VoWi-Fi is carrier offload – this is usually reserved for data, but operators can take voice traffic off the core cellular network too.
Backhaul for small cells
Small cells began life in the residential market with femtocells used to improve indoor coverage. ‘It is not a big market, but it is substantial,’ notes Hoadley. ‘Now networks are starting to address the indoor enterprise market and they are looking at outdoor small cells.
‘But if you can’t install enterprise small cells indoors, maybe you can do it from outside the office and push indoor coverage into the building. Okay, fine, but how do you get the traffic back to the network?’ he asks. ‘You may have access to fibre going to lampposts and so on, but you will probably have to find some wireless solutions.’
Taqua has developed a small point-to-multipoint cell for backhaul, which is non-line of sight capable. ‘There are obstructions everywhere in the cities,’ says Hoadley. ‘The small cell uses 2x2 MIMO, as you need two paths to scatter the signal around. We are using spectrum below 6GHz, as it propagates further and bounces around better – but you need some spare spectrum to be able to use this.’
Focus on the VoLTE evolution
‘There is a lot of opportunity for circuit switched fallback: maybe you don’t need this in somewhere like central London, but many areas do need it,’ argues Hoadley.
‘With VoWi-Fi, a lot of the carriers we talk to do think this is a decent proposition. We sell this software product sometimes through big OEMs and sometimes direct to carriers. OEMs are open to working with us, so they can offer the carriers a whole package. It is good for smaller vendors to get a leg up and our software is designed to fit on COTS equipment.
‘Small cell backhaul is our other key focus. All of our products will be available in Q1 2014 in Europe. They are already available in the US where they use slightly different standards to Europe, although they are converging,’ says Hoadley.
In conclusion, Hoadley says that the role of voice is changing but it remains critical and VoLTE is critical to that evolution. However, the service must be excellent to ensure a smooth transition between 3G and 4G and this is what Taqua’s CSFB, SR-VCC, service parity and embedded VoWi-Fi solutions are designed to provide.
Taqua core product portfolio
- T7000 Multimedia Gateway (T7000) for wireline and wireless switching/gateway applications
- T7100 Multimedia Controller (T7100) for media management, trunking, mobile core and peering
- T6100 Convergence Server (T6100) for mobile voice/messaging over 3G, 4G/LTE and WiFi
- W-Series NLOS Backhaul System for small cell non-line-of-sight wireless backhaul.