There are lots of publications and reports are written on Voice over LTE lately about amplified bandwidth advantages of Long Time Evaluation and Communication Service Providers (Communication Service Providers) approach to install this is also in research to improve this technology as the 4G foundation. Many Communication Service Providers have been declared their LTE plans and from those some of them already have even begun limited LTE data trials. In next generation For sure there's an approaching wave of network improvements and new handsets devices that will definitely renovate mobile broadband.

Communication Service Providers taking into consideration the transition to LTE data are faced with the assessment of whether to also put forward LTE voice services consecutively to improved utilization of the latest network infrastructure, or install LTE data-only set-up. Fundamentally, it seems that the requirement is there to transition to LTE voice faster slightly than presently. This approach provides sense as LTE need completely new radio access equipment, from transmitter to base station regulator upgrades, and maintaining two radio contact networks very much amplify OPEX which may be finest extend across a wider sector of contributions.

It is the 'how' to deal out LTE voice services that has produced uncertainty. When LTE was formerly envision the conservative thinking was that the COMMUNICATION SERVICE PROVIDER's networks would have transitioned to IMS architectures by then and consequently voice on LTE would obviously be based on VoIP. The actuality is that as of this writing, there are extremely a small number of true IMS production networks in place and so Communication Service Providers have to settle how to rapidly install LTE with the certainty of network alteration timelines and resources.

Certainly there are alternative on how to advance with voice delivery structure. The conditions of which is the ordinary agreement that present 2G and 3G systems will be in set for some time for the future, and consequently Communication Service Providers have to take into consideration not only how their systems network will develop, but how to sustain roaming and give up across numerous Communication Service Providers. Besides, the prospect is that existing 2G / 3G subscribers will be to drift to 4G as Communication Service Providers make possible upgrade incentive, which puts extra burden of facilitating quality and service similarity as part the improve as subscribers will be expecting their present call feature set to act the same once they promoted.

Options for voice delivery are:

  • Dual Mode Handsets:

o Support both GSM and UMTS means that users are capable of roam in-out through national and international networks and make certain service stability when LTE networks up to now not fully built up.

  • 3GPP IMS:

o The upgrading of the core network to IMS architecture opportunity might take by the COMMUNICATION SERVICE PROVIDER. Installation of IMS-based LTE voice has been documented since IMS Release 8. Moving to IMS has the obvious advantage of commoditizing a large portion of the network, bringing with it all the benefits discussed for several years now.

  • Voice over LTE Generic Access:

o One more option that has been put onward is Voice over LTE Generic Access (VoLGA), sustain by a newly-formed industry group known as the VoLGA discussion. VoLGA suggests utilizing the IMS-based LTE radio access network, but preserving the circuit-switched network either GSM or CDMA-based by initiate a network element known as the VANC "VoLGA Access Network Controller". The VANC is accountable for concerning the packet switched LTE access network to the present circuit switched core network, make sure that offered MSC are not altered. Certainly this ensures that there's nominal disturbance to existing switching essentials and present voice appliance may be distributed.

  • Circuit Switched Fallback:

o These handsets generally operates in 4G (LTE) method when accessing data services are idle, but switches to a 2G or 3G radio when an incoming call is informed to the system, or an outgoing call is emerged. A mechanism to notify the handset via 4G-IP data path that a call is inbound and no need to be formalized.

  • Proprietary Solutions:

o There is no other option exist, like upgradable IP-enabled MSCs, but those be inclined to be attached to definite vendor structural design. To be clear, these architecture choices deal with how to maintain the packet switched LTE radio network with the service operator core network for the principle of delivering voice.

The Move to Packet Switched Wireless Networks

With the quickly rising utilization of mobile telecommunication networks for broadband Internet access, network operators and telecommunication vendors decided that it was time to define and implement next generation network technologies to keep up with the demand. The most widely adopted next generation typical is referred to as LTE, or Long Term Evolution. LTE is a project of the Third Generation Partnership Project (3GPP1) and offers an upgrade path for all major third generation wireless network technologies. Based on the Internet Protocol (IP), it fully leverages the flexibility of packet switching and follows the path taken in fixed line networks with DSL, cable and fiber to the home deployments.

No Native Voice and SMS in LTE

While packet switched wireless networks have many benefits, there is also a major disadvantage: Voice calls and SMS messaging, the main revenue generators of mobile network operators, are no longer available in LTE, as they are based on a circuit switched radio and core network infrastructure. To counter this issue, 3GPP has so far adopted two different approaches:

Fallback to 2G or 3G for Voice

The first solution, designed to be available early on, is referred to as Circuit Switched Fallback (CSFB). As the name implies it allows mobile devices to fall back to 2G or 3G networks for circuit switched services such as voice calls. The main problems with this approach are longer call setup times which result in a significant degradation of the customer experience and the necessity for software upgrades on circuit switched network nodes such as the Mobile Switching Centers (MSCs).

IMS as a Potential Solution for the Mid and Long Term

A solution envisaged for the mid and long term is to introduce network operator based voice services in LTE with the IP Multimedia Subsystem (IMS). Development of this fully IP based platform for rich media communication including voice calls begun many years ago for UMTS. Recently, enhancements have been specified for handing-over ongoing IMS based voice calls to circuit switched networks such as GSM when the customer leaves the UMTS or LTE coverage area during a call. Due to the significant complexity of the system, however, it is likely that it will still take several years before large scale commercial IMS deployments will be undertaken.


Launched in March, 2009, the Voice over LTE via Generic Access, or VoLGA Forum ( was initiated to specify and promote an approach for extending traditional voice and SMS services over LTE access networks.

The group is working to develop VoLGA specifications, based on the existing 3GPP GAN typical, which are designed to Facilitate users a consistent set of voice, SMS (and other circuit-switched) services as they transition among GSM, UMTS and LTE access networks.

VoLGA will support all existing circuit services as well as IMS RCS and other combinational services providing mobile operators a viable roadmap towards new revenue generating services. In time, it is expected that the VoLGA specifications will be presented to the 3GPP for consideration as a recognized typical.


Considering the overall transition to a full LTE environment, VoLGA offers a long-term telephony approach. It is clear that any LTE telephony service or handset must support the 2G/3G as a fall back for service delivery. The utilization of VoLGA for telephony simply reuses the existing telephony client which is already required to be present in any LTE handset.

Even in a full IMS telephony Installation, the 2G/3G telephony client will be present in the handset. Similar to the RCS model today, operators can invest in IMS for non-telephony services while continuing to leverage their existing 2G/3G telephony networks for LTE with VoLGA.

An operator specifying voice over LTE has a fundamental requirement to facilitate the same service experience - capabilities, functions and quality - which are supported in today's mobile networks. The existing R4 MCS service core offers a natural platform for delivering these services. The implication is that mobile networks will support 2G/3G telephony services for many years to come.

Voice over LTE via GAN

A third solution, which this paper will focus on, is Voice over LTE via Generic Access Network, or VoLGA for short, which is defined by the VoLGA meeting. Here, the concept is to connect the already existing Mobile Switching Centers to the LTE network via a gateway. As no fallback to a legacy network is required, call setup times are not increased and the customer's quality of experience is consistent with that of the 2G or 3G voice environment. VoLGA is based on the existing 3GPP Generic Access Network (GAN) typical, which is deployed for example by T-Mobile in the US and Orange in France. The principle of GAN is to extend mobile services over a generic IP access network. One of the popular applications of GAN is with Wi-Fi-enabled phones. With GAN-based dual-mode mobile phones, all services are either available over their GSM networks as usual, or over Wi-Fi at home or in public places. Moving among the two network technologies is fully transparent to the customer.

On the network side, VoLGA only requires software enhancements to the circuit to packet gateways which already exist for GAN. No modifications are required on the Mobile Switching Centers or the LTE core and access network nodes. This enables a rapid development and market introduction, especially in multi-vendor MSC network environments. Furthermore, VoLGA enables the utilization of all other circuit switched services over LTE without any modifications in the network. One of these applications is the short message service (SMS), which is not only a significant revenue generator but also an important tool for mobile device provisioning over the air and a requirement of the European Union for informing users about voice and data charges while they are roaming in another country.

On the mobile device side, the protocol stack initially developed for GAN can also be re-utilized in large parts. The two main software additions required are to include the LTE access technology as a radio bearer together with a modified handover procedure, as the VoLGA approach allows for a smooth handover of ongoing voice calls to GSM or UMTS when the subscriber leaves the LTE coverage area.

VoLGA also enables a smooth introduction of global LTE roaming. If supported by the visited network, all services can be delivered via the VoLGA circuit to packet gateway and the Mobile Switching Centers in the visited network. In case VoLGA is not supported, the VoLGA gateway and the Mobile Switching Centers in the home network may be utilized instead, although this is currently not described in the specification. While the benifits for the customer are noticeable, this flexibility is also very useful from the network operator's point of view as it allows delivery of crucial services such as mandatory data on roaming charges via SMS while roaming.

The following chapters will now go into more details and show how VoLGA will work in practice from a technical point of view.

VoLGA Overview Origins

The roots of 'Voice over LTE via GAN' (VoLGA) are the 3GPP Generic Access Network (GAN) specifications which add Wi-Fi as an access technology to 3GPP based networks such as GSM and UMTS. GAN requires dual mode mobile devices which have both a GSM/UMTS radio interface and a Wi-Fi radio interface. Such mobile devices are available today from a number of manufacturers including Samsung, Nokia, Sagem, LG, HTC3, Motorola4, Sony-Ericsson and RIM (Blackberry)5. When these dual-mode devices detect the availability of a suitable Wi-Fi network, e.g. at home or a public hotspot, they connect to the Wi-Fi access point and register with the GSM/UMTS core network over the Wi-Fi link and the Internet. A GAN gateway securely connects a subscriber to the infrastructure of a network operator and voice calls and other circuit switched services such as SMS are then securely transported among the mobile device and the Gateway over the intermediate Wi-Fi link and Internet access network.

VoLGA re-uses this principle by replacing the Wi-Fi access with LTE. From a mobile device point of view there is not much difference among the two access methods because both networks are based on IP. This re-utilization of GAN was initially explored in the 3GPP Technical Report 23.8796 and at the beginning of 2009, the VoLGA Forum was founded to foster the creation of detailed specification documents and subsequent development of the solution.


Evolution to LTE:

The road to the mobile broadband future has several paths and each mobile operator will have different timetables and reasons for taking one path over another. But seemingly all agree on the ultimate goal - an efficient all-IP wireless network capable of supporting voice, video and data services. Choosing the air interface best suited to meet the needs of tomorrow's IP-based services is the key to reaching that goal. In addition to impacting their access and core networks, the choice they make also impacts the simultaneous evolution of the entire wireless ecosystem including devices, applications and services.

For many years now a true world cellular typical has been one of the industry's targets. GSM dominated the second generation (2G) technologies but there was still fragmentation with CDMA and TDMA as well as iDEN. With the move to third generation (3G), nearly all TDMA operators migrated to the GSM technology path. Yet the historical division among GSM and CDMA remained.

It is with the next step of technology evolution that the opportunity has arisen for a global typical technology. Many mobile operators have converged on the technology they believe will offer them and their customers the most benefits.

That technology is Long Term Evolution (LTE). For the first time in the world, a future technology typical has spanned the U.S., Asia and Europe with commitments from leading operators on their planned Installation of LTE and a global consensus that LTE will become the dominant technology for the next generation of mobile broadband.

In June of 2008, the Next Generation Mobile Networks Alliance (NGMN) selected LTE as the first technology that matched its requirements successfully. The GSMA, UMTS Forum, 3G Americas and other global organizations have reiterated their support of the 3GPP evolution to LTE. Additionally, the LTE/SAE Trial Initiative (LSTI) has afford support through early co-development and testing of the entire ecosystem from chipset, device and infrastructure vendors. LTE is in the early stages of its evolution, but several of the world's largest mobile.

LTE: A Key Next Step in Mobile Network Evolution

The next-generation, all-IP access network is on the minds of all mobile industry leaders. Installation of a Long Term Evolution (LTE) access network has quickly emerged as an important next step in mobile network evolution. With very high data transfer rates and exceptionally low latency, LTE promises to Facilitate users with a true mobile broadband experience.

At the same time, the tremendous success of 3G/HSPA data solutions over the past year has demonstrated strong consumer demand for mobile Internet access services. The GSM Association (GSMA) recently reported that 3G data has become the fastest growing broadband service in the world, with millions of new subscriptions monthly.

As LTE enables operators to offer an even higher performance mobile broadband service at a significantly lower cost structure than their 3G/HSPA networks, they are looking to leverage the technology to capitalize on this proven consumer demand for a true 'mobile Internet.'

To meet this demand, a number of major mobile operators are now targeting LTE market trials as early as the second half of 2009. ABI Research Analyst Nadine Manjaro was recently quoted saying, "some operators may choose to bypass 3G and move directly to LTE, putting increased pressure on equipment vendors to meet accelerated timelines."

The Operator Imperative: Voice over LTE

As mobile operators plan for this next generation of mobile Internet, they are keen to avoid mistakes made by many fixed-line operators. The Installation of high-speed broadband networks left many fixed operators delivering a 'dumb pipe,' ideal for 'over-the-top' service delivery. Alternative service providers were able to quickly flourish by delivering voice over the top of fixed broadband networks, because the fixed operators themselves were slow to bring out their own competitive VoIP offers.

The mantra for mobile operators is to be 'smart-pipe' providers. This approach acknowledges consumer demand for a mobile broadband pipe providing straight forward Internet access. But rather than leaving it solely to over-the-top competitors to deliver voice services over these pipes, there is an imperative for mobile operators to seamlessly weave their own voice services into the broadband connection. Consumers can, and likely will, still subscribe to alternative VoIP providers, but a mobile operator's goal should be to put their own voice service front and center.

In this presumed approach, an operator would continue to leverage their existing circuit-based core voice networks to service users when connected to the operators' 2G/GSM or 3G/UMTS access network. However, to service users when connected to LTE, the operator would leverage a new IMS-based core network, upon which all of their current services would have been replicated.

VoLGA in the Network

Figure 2 provides an overview of the basic network setup for VoLGA in the home network as described in the Voice over LTE via Generic Access Stage 2 specification7. For an easy start, the optional interfaces that enable explicit quality of service in the LTE network and those required for handing over ongoing voice calls to a circuit switched network are not represented. These are discussed separately further down in the document. The only new network element introduced is the VoLGA Access Network Controller (VANC), represented in green in the figure below. All other network elements and the interfaces among them already exist and are reused without any modifications.

VoLGA from the LTE Network Point of View

On the LTE side, the VANC connects to the Packet Data Network Gateway (P-GW) via the typical SGi interface. Both signaling and customer data traffic (i.e. the voice packets) are transported over this interface. From an LTE core network point of view the VANC looks like any other IP based external node and IP packets exchanged among a wireless device and the VANC are transparently forwarded through the Evolved Packet Core (EPC) network.

VoLGA from the Circuit Switched Network Point of View

On the circuit switched network side the A-interface is utilized to connect the VANC to a GSM Mobile Switching Center (MSC). The Iu-interface is utilized to connect the VANC to the UMTS MSC. The VANC thus looks like a GSM Base Station Controller (BSC) to a GSM MSC and like a UMTS Radio Network Controller (RNC) to a UMTS Mobile Switching Center. Which interface is utilized in practice depends on the requirements of the network operator. As the Aand Iu interfaces are utilized without any enhancements, the MSCs are not aware that the mobiles are not directly connected via their respective radio networks but instead are connected over LTE. Consequently, no changes are required on these network nodes to support voice, SMS and other services over the LTE network.

Registering to the Network

When a mobile device is switched on and detects an LTE network it first registers with the Mobility Management Entity (MME) over the LTE access network. The MME uses the S6 a interface to the Home Location Register / Home Subscriber Server (HLR/HSS) to retrieve the subscriber data required for authenticating and managing the customer.

After registering with the LTE network, the mobile then establishes a connection to the VANC. How this is done depends on the VoLGA specific configuration data stored in the mobile device. First, a suitable IP connection needs to be in place. In the home network the default bearer might be utilized. It is also possible to utilization a separate bearer and IP address for the principle. The host name or IP address of the VANC can be pre-provisioned in the mobile device or can be acquired by querying a Dynamic Host Configuration Protocol (DHCP) server in the network over the bearer that was established for VoLGA in the previous step. Once the IP address of the VANC is known, the mobile establishes a secure IPSec tunnel to it over the LTE radio network through the LTE core network and over the SGi interface. During the process the VANC authenticates the customer with the help of authentication data stored in the HLR/HSS, which it contacts over the D' interface.

Next, the mobile device schedule to the MSC during the secure tunnel and the VANC. The Direct Transfer Application Part (DTAP) protocol is utilized for this principle, which is already recognized from GSM and UMTS. Messages are tunneled transparently among the mobile device and the MSC by all network components involved. Merely the VANC adds data such as a cell-id (2G) or the service area identifier (3G) to the initial registration message as defined in the GSM and UMTS standards respectively.

Outgoing Voice Calls over LTE

Figure 3 represents the signaling exchange to establish a mobile originated voice call over LTE. All signaling and control plane messages among the UE and the VANC are transported over the established IPSec tunnel. In a first step, the mobile device sends a message to the VANC to change the connection from idle to dedicated state. Afterwards, a typical GSM/UMTS CM Service Request message is sent to establish a connection to the MSC. When the VANC receives the message it creates a dedicated signaling connection to the MSC over the A- or Iu interface for this customer and forwards the message. The MSC then usually authenticates the customer and activates ciphering (step 4 and 5 in the figure). Then, the mobile device sends a Setup message in step 6, which contains among other things, the phone number of the person that is to be called. The MSC acknowledges the request with a Call Proceeding message in step 7.

As the MSC thinks of the VANC as a GSM Base Station Controller or UMTS Radio Network Controller, it then sends an Assignment Request message to the VANC to request the establishment of a circuit switched bearer channel. The VANC translates this message into an Activate Channel message to the mobile device in step 9 to prepare it for the exchange of IP packets containing voice data. Optionally, quality of service for the voice packets can be ensured by activating a second bearer in the LTE network (step 11). This is further discussed below. Once the mobile device is prepared for the voice data stream, an Assignment Response message is sent back to the MSC in step 13 to signal to it the successful 'pseudo' establishment of a circuit switched channel in the radio network. Once the call has been established with the other party, the MSC sends Alerting and Connect Messages (step 14 and15) which the mobile device acknowledges. The voice path is then established and the voice conversation can begin.

The voice signal is either transmitted in a 64 kbit/s TDM timeslot on the A-interface in the case of a GSM MSC or via an ATM or IP based data flow in the case of a UMTS MSC. The VANC translates this data stream into IP packets for transmission over the LTE network and vice versa. The standardized Real-time Transfer Protocol (RTP) is utilized for this principle and this is the same RTP protocol that is also utilized by many other voices over IP solutions such as those utilizing SIP and IMS.

Incoming Voice Calls over LTE

Incoming voice calls work in a similar way. As from the MSC point of view no connection is currently established to the mobile device, a typical paging message is sent to the VANC as if it were the BSC or RNC. As the VANC has an established IPSec tunnel to the mobile device it can forward the paging message directly to the mobile. All of this is transparent to the LTE network, i.e. the paging message sent through the IPSec tunnel is not seen and also not needed by the LTE network to find the mobile device.

From the LTE network point of view, the paging message is not visible as it is transported inside an IPSec data packet. If the mobile device's state in the LTE network is 'active', the IP packet is delivered immediately without delay. It could also be that the mobile device has been inactive for some time. As a consequence the physical connection among the network and the mobile device has been released. The device's IP address has been preserved, however, and thus it is still logically present for the network in or around the area of the base station that was last utilized to communicate with it. This area is referred to as the tracking area.

The MME can then re-establish contact to the mobile device by sending an LTE paging message via all base stations of the device's last known tracking area. When the LTE paging message is received by the mobile device it re-establishes radio contact. Afterwards, the IPSec encapsulated packet containing the paging message is delivered to the mobile and the call establishment signaling can commence. The time required for the LTE paging is similar to the time required to page the mobile device in a circuit switched wireless network. Therefore, the call establishment time for a voice call over LTE is similar to that of a GSM or UMTS network.


A very important functionality of VoLGA is its ability to hand over ongoing calls from the LTE network to a GSM or UMTS network when the customer leaves the LTE coverage area. In fact, this is one of the most valuable differentiators that network operator supplied voice services have compared to over-the-top VoIP services. Services such as Skype cannot fall back to a circuit switched channel as they are purely based on IP and thus have no means to interact with the radio network.

Figure 4: The Sv interface utilized by VoLGA for circuit switched handovers

For VoLGA, handover mechanisms are utilized which have been initially specified for IMS Single Radio Voice Call Continuity (SR-VCC) in 3GPP TS 23.2168. The basic handover steps are as follows:

When the mobile registers with the LTE network it signals its SR-VCC capability to the MME. The network is thus aware that this procedure needs to be executed when the mobile device is about to leave the LTE coverage area while a bearer is active.

When the base station (the eNodeB) detects that the mobile device could be better served by a 2G or 3G cell it can instruct the mobile device to measure the signal strength of such neighboring cells. Based on these measurement results or based on pre-configured values, the eNodeB then informs the MME that a handover to a 2G or 3G cell is required.

The MME in turn informs the VANC about the handover which is about to be made. The message includes data such as the target cell-id and the id of the subscriber for which the handover is to be made. For this principle, the MME uses the SR-VCC interface Sv as represented in Figure 2.3. In case the message is sent to the VANC for a subscriber that uses IMS instead of VoLGA, it's possible to forward this message unaltered to the MSC. For clarity, this interface is not represented in Figure 4.

In the next step the VANC uses the data it has received from the MME to create a typical GSM or UMTS handover message to the indicated target cell. If the target cell is connected to the same MSC as the VANC, the target cell is prepared for the handover locally and the handover is executed as soon as the cell is ready. From an MSC point of view the handover looks no different from a typical GSM or UTMS handover. In case the target cell is connected to a different MSC, a typical Inter-MSC handover procedure is initiated.

For VoLGA, the MSC does not have to support the new interface as it is terminated in the VANC. Therefore, no modifications are required on the MSC for VoLGA handovers.

Quality of Service

Another important VoLGA feature that sets it apart from over the top VoIP applications is the ability to activate network based quality of service measures to ensure that the required bandwidth for the call is reserved throughout the wireless network and especially among the base station and the mobile device. Again, mechanisms and network nodes that have originally been specified for IMS are reused. In a 3GPP wireless network, the Policy Charging Rule Function (PCRF) entity is responsible for approving and distributing quality of service requests from applications hosted in the network to the underlying transport network nodes such as the P-GW, S-GW and the eNodeB (the base station). Figure 5 shows how the VANC can request QoS by connecting to the PCRF via the standardized Rx interface.

To activate QoS for a call the VANC contacts the PCRF during step 11 in the call establishment process as represented in Figure 2.2 and requests that packets to and from certain IP addresses and UDP ports be given a higher priority in the network. Based on the subscription profile of the customer in the HLR/HSS, the request is granted or denied. If granted, the PCRF establishes a secondary bearer throughout the LTE network and also informs the mobile device. Packets matching the criteria set above are then given a preferential treatment by all network components and also the mobile device as uplink capacity might also be limited.

International Roaming

When a subscriber roams to a foreign LTE network the VoLGA specification allows for two options:

Local Breakout:

The first and preferred scenario is that VoLGA is natively supported in the roaming network. In this case, the mobile uses a VANC and MSC in the visited network. To get the subscriber's subscription data from the HLR / HSS in the home network, interfaces that already exist today for typical international GSM and UMTS roaming are utilized. For billing, the typical international billing procedure is utilized.

In a default setup today, a roaming subscriber always contacts a 2G or 3G Gateway GPRS support node (GGSN) in the home network. This is convenient for the customer as he doesn't have to change the configuration of his device while roaming. However, this scheme requires that all IP traffic is routed to the subscriber's home network. This is not only very uneconomical but it is also impossible to contact network nodes in the visited network such as a local VANC. For LTE, it is likely that the same scheme is utilized for many purposes. In this case the gateway node is the home P-GW.

To reach the VANC in the visited network a feature referred to as 'local breakout' is utilized. It was standardized already in the early UMTS specifications but to this day is utilized only very little if at all. Local breakout allows the utilization of a GGSN (in case of GSM and UMTS) or a PGW (in case of LTE) in the visited network and is controlled by using a visited network specific Access Point Name (APN) which has to be configured in the mobile device. The VoLGA specification mandates a list of networks and associated APNs in the mobile device for that principle. In addition, a default APN is specified which is utilized if the foreign network is not in the list.

Once the mobile device has established an IP connection to the P-GW in the visited network, the typical procedures described earlier (e.g. a DHCP lookup) are utilized to determine the IP address of the VANC in the visited network. For the software of the mobile device this procedure is the same as if the P-GW was in the home network. By using local breakout it is thus very simple to enable international VoLGA roaming. SMS messages for roaming users are forwarded to the MSC in the visited network to which the subscriber is attached and from there via the VANC to the mobile device. Again, this is a typical roaming procedure. Subscriber originated SMS messages follow the same route in the opposite direction.

Home Network Routing:

In case the visited network does not support VoLGA natively it is possible to utilization an APN that establishes a connection to the P-GW in the home network of the subscriber. This is currently not described specifically but the typical would allow for this. As described above, this is what happens today for a typical IP connection for most roamers anyway. There are several disadvantages however:

The voice packets need to be routed back to the home network. For calls into the home country of the subscriber this is not much of an inconvenience but for calls to the visiting country a loop from the visited country to the home country and back is introduced in the speech path.

The VANC in the home network and the MME in the visited network might not be able to communicate with each other. As a consequence, handovers among the visited LTE network and a GSM or UMTS network in the foreign country are not possible.

Emergency calls are not possible in this setup, as a home network MSC is utilized that can't connect the call to an emergency center in the visited country. It is therefore essential that an automatic fallback is performed to a GSM or UMTS network in the visited network before an emergency call is attempted. This is discussed in more detail in the next section.

Despite these disadvantages it might still be favorable to Facilitate VoLGA services from the home network in visited networks that do not support it natively. This way, it is possible for example to ensure delivery of SMS messages, for example for roaming tariff data or EU mandated bill-shock warning.

Emergency Calls:

Emergency calls to police, fire departments and medical services are an important feature of wireless networks. In practice the customer dials a standardized short code such as 100, 102, etc. in india. A special call setup procedure is then utilized to ensure that room is made for this call in case the network is overloaded. In some countries, the identity of the cell from which the emergency call was established is forwarded to the emergency center to help locate the person requiring emergency assistance.

VoLGA supports emergency calls as follows:

As the messaging among the mobile device and the MSC is exchanged transparently, emergency calls work the same way over VoLGA as in a 2G or 3G network, i.e. the same messages for call setup are being utilized. As LTE cell-id can't be processed by a 2G or 3G MSC, the VANC has to ensure that a proper virtual cell-id representing the LTE macro cell is appended to the initial call setup message.

If a PCRF is utilized for quality of service in the network, the VANC signals a different priority to it during the emergency call establishment to ensure all IP packets for this call get the highest priority in the network and especially on the radio link. The VANC itself is aware of the emergency situation because the mobile device indicates this through the IPSec tunnel before the actual call establishment messaging. In addition, the VANC can monitor the call setup messaging and despite not altering it, thus becomes aware of the emergency situation.

The VoLGA system can also be configured to instruct the mobile device during initial registration that a fallback to a 2G or 3G network should be made for emergency calls. Some operators might prefer this method, as no extra datafill is required in the network for the localization of the call.

Present and Future Alternatives:

VoLGA is not the only system designed to deliver voice and SMS services over LTE networks. This chapter quickly summarizes a number of other options, their benifits and their disadvantages compared to VoLGA.

CS Fallback (CSFB):

The approach favored by many 3GPP members as an initial solution for delivering voice and SMS services over LTE is 'circuit switched fallback', which is specified in Time Stamp 23.27210. The idea behind this solution is to utilization a 2G or 3G network for incoming and outgoing calls, i.e. the mobile has to leave the LTE network for making or accepting voice calls. A more detailed introduction can be found at Wireless Moves, there are a number of disadvantages to CSFB:

Changing to another network takes time, which has an adverse effect on call setup times. Already today, users perceive mobile call setup times as too long. It is estimated that even in the best case scenario, both mobile originating and mobile terminating call establishment times would increase by at least 1.5 seconds. In many scenarios, it might even be more.

From a network point of view a new MSC and SGSN interface is required to signal incoming calls and SMS messages to the MME. This interface, referred to as SGs in the standards, is based on IP and therefore requires new software on network nodes that are delivering the main services today. Some network operators see this as a critical point as they are hesitant to introduce a new and unproven feature on critical infrastructure without an intense testing effort. Also, many network operators have bought MSCs and SGSNs from different vendors, further increasing cost and interoperability testing.

On the positive side, no fallback to a 2G or 3G network is required for delivering SMS messages. However, there currently seem to be a number of open issues, especially around roaming availability and standardization gaps concerning concatenated SMS delivery as indicated in 3GPP discussion paper SP-09042912.


A solution, long in the making, is the IP Multimedia Subsystem, or IMS for short. It's core is based on the popular Session Initiation Protocol (SIP) which is widely utilized in fixed line IP based networks for Voice over IP. For wireless networks, many additions were specified like for example features to handle wireless specific issues such as unreliable radio connections, application servers for external application development, international roaming, scalability, security, etc.

While standardization on IMS has started many years ago, few if any commercial deployments have been undertaken so far due to, among other things, its significant complexity. Given the current state, it is unlikely that an IMS solution is available in the first years of LTE to serve as a voice platform. Therefore, IMS will not be an immediate alternative to VoLGA. An introduction to IMS is given in Chapter 6 of 13 and for a very detailed introduction to IMS, 14 is recommended.

The initial concept of IMS was to be an IP platform only, i.e. no ties were specified for services to roam among an IP network and a circuit switched legacy network. Over time, it was recognized that this approach is not suitable for a practical Installation and extensions have been standardized to enable ongoing voice sessions to be handed over among an IP based wireless access network and a circuit switched access network. The latest of these features is Single Radio Voice Call Continuity (SRVCC). As the somewhat long name of the feature implies that only a single radio in the mobile device has to be active on at any one time, even during a handover. This simplifies mobile device development.

3GPP had the foresight to specify SRVCC in an IMS independent manner. Therefore, the VoLGA forum decided to utilization it as the means to handover VoLGA calls from LTE to GSM or UMTS. As a result, no VoLGA specific features are required in the MSC or SGSN for VoLGA, which is a great plus for Installation in a running network.

Over-the-Top VoIP

Some network operators might also decide to go an entirely different way and offer voice services over LTE with external partners. UK network operator '3', for example, has partnered with Skype15 to deliver voice services in addition to their own circuit switched services. While their Skype client also uses circuit switched resources for the time being this could change quickly in the future.

There are two technical disadvantages of partnering with external voice service providers, however. The first one is that external voice service providers have no control over quality of service in the wireless network and thus they can't ensure a good quality of experience under all load situations. A potential solution to this issue could be to install logic in the network to ensure quality of service for data streams that are recognized to belong to an external voice service the customer has subscribed to. PCRF functionality could be utilized for this as described earlier but there is no standardized way to offer this yet.

The second problem with Over-the-Top VoIP is that calls can't be handed over to a circuit switched 2G or 3G network when a customer leaves the LTE coverage area. Like before, this is because external applications can't be tied into the wireless network infrastructure easily. This is a serious disadvantage, as LTE networks will have an inferior network coverage compared to GSM for many years to come.

Service Brokering:

Regardless of the architecture chosen, Communication Service Providers will be faced with application delivery challenges created by the transition in LTE to packet based voice. Today's voice services are predominantly delivered via Service Control Points (SCP) or Intelligent Network (IN) Application Servers connected via IN protocols such as INAP and CAMEL.

Those services tend to be highly stable and profitable but also highly customized, and therefore not easily moved to SIP-based application servers. Communication Service Providers will need to deliver these same services (down to feature sets and even quirky behavior) on LTE users to ensure migrated users have the same level of service and experience. As Communication Service Providers evolve their networks for LTE and other networks, the resulting networks present tremendous challenges in voice services and application delivery. Realizing this, the industry has come forward with a principle-built network element: the Service Broker, a solution specifically designed to overcome network architecture challenges and ensure voice service delivery from any network domain to any other network domain. Service Brokers are placed among the application layer and the control layer, and assume and deliver a number of roles as needed: the IMS IM-SSF, SCIM, and reverse IM-SSF, Media Resource Broker (MRB), IN trigger management and subscriber data management. All these roles have the common principle of delivering and extending the reach of applications to all network domains of the COMMUNICATION SERVICE PROVIDER. Let's take a look at how Service Broker might fit within two of the most popular network proposals, IMS and VoLGA.

LTE Voice over IMS:

Service Brokers Facilitate the capability of extending current voice services by providing seamless call / session interworking among the packet switched LTE access network, and circuit-switched 3G applications without requiring changes to either. For those Communication Service Providers that have fixed line networks as well, they are also able to reutilize voice services which may have been only offered in that network domain to new wireless LTE users..

In the figure above, LTE clients are able to access all applications they previously utilized, such as PrePaid, CRBT, Voice VPN, Find Me / Follow Me, etc, and therefore are not required to change their subscribed services. From a network perspective, the Service Broker enables the IMS network to "see" the existing applications as new SIP-based applications, by providing the interworking required. As far as the IMS network is concerned, the Service Broker is the SIP server, while to the existing SCPs the Service Broker is an existing 3G MSC.

LTE Voice over VoLGA

Those Communication Service Providers that choose to follow an architecture based on the VoLGA forum proposals, the Service Broker provides the inverse benefit: allowing next-gen SIPbased applications to be utilized by the existing 3G network. It also becomes possible to bring forward those applications residing on the fixed line network as well, further enhancing the service delivery options.

Service Broker Functions

Service Brokers Facilitate other functionality that, once deployed, can be of added benefit to the COMMUNICATION SERVICE PROVIDER. Among the most often delivered features are:

  • IMS SCIM (now renamed the IMS Service Broker)
  • IN-IN Trigger Management
  • Real-Time Charging
  • Protocol/Call Flow Management
  • Subscriber Data Management Interaction
  • Media Resource Brokering
  • Service Orchestration

The Service Broker's ability of performing orchestration and combination of discrete voice applications and services into new combined offerings (voice mash-ups) is particularly exciting. With this capability Communication Service Providers are able to create new revenue producing offers to users where they previously were not available: CRBT and PrePaid, Find Me / Follow Me combined with Voice VPNs, etc. Service Brokers also Facilitate the capability of generating Real Time Charging events, either programmatically (via an API) or automatically as part of service delivery. The challenge facing CPSs is delivering new, innovative services that seamlessly integrate into existing billing platforms. Doing so often means normalizing charging events or even transforming charging events from one technology to another, as is the case in IN to IMS migration. Because the Service Broker is responsible for orchestrating and delivering combinational services, it is often then the responsibility of the Service Broker to generate a charging event upon successful start / completion of those enhanced services.

Literature Review:

The Solution: Voice over LTE via GAN

As a result of these changes in the IMS market, a number of operators are now looking for an alternative approach for delivering their mainstream voice services out over LTE. These operators are keen to identify a method for voice service delivery over LTE that enables them to leverage their proven, installed voice core networks. The concept is to 'elevate' an operator's existing core voice network to act as a packet service delivered over the LTE access network. Rather than attempting to recreate core telephony services in IMS, simply make the existing telephony infrastructure a packet service delivered over IP via LTE. The existing 3GPP Generic Access Network (GAN) typical has quickly emerged as a favored approach for realizing this concept (Figure 2).

The 3GPP GAN typical, also commonly referred to as the UMA typical, is the technology behind a number of 'home zone' services deployed by leading operators worldwide. The premise behind GAN has always been to extend existing mobile services over any generic broadband access network. Originally applied to fixed broadband networks like DSL and cable, it quickly became clear that GAN also applies directly to mobile broadband networks, such as LTE.

The UMA/GAN typical, initially introduced in 3GPP Release 6, has been vetted and proven in commercial deployments worldwide with millions of users today. The GAN specification was extended in Release 8 in 2008 to also include support for 3G core network interfaces (Iu), in addition to 2G (A/Gb) interfaces. Leveraging the 3GPP GAN typical as the basis for voice and SMS service delivery over LTE has a number of benifits:

Investment protection

Clearly, basing LTE telephony services on an existing (expansive) voice core network protects a substantial capital investment..

Proven service core

The existing, expanding and evolving voice core network is a proven, reliable resource at the heart of mobile networks worldwide.

Low-operational disruption

Expansive operation support systems (OSS) and business support systems (BSS) have been developed and integrated with the existing voice core network. These network services can be extended to the LTE environment.

3GPP standards-based delivery

3GPP GAN typical has proven an effective and robust method for extending mobile voice services over broadband packet access networks. With only minor modifications, the existing GAN typical can be utilized to deliver voice over LTE today.

Minimal impact to handset manufacturers

A key lesson learned from 3G network deployments was the importance of encouraging early handset development. With 3G networks deployed, operators waited years for viable handsets to begin loading networks. Any confusion over the telephony client will undoubtedly delay the availability of LTE devices. Defining LTE voice to be identical to the existing voice services of the 3G and 2G networks immediately de-risks a large portion of the handset development.

Supported by all major handset vendors

Today every major handset manufacturer, including Nokia, Samsung, LGE, Sony-Ericsson, RIM, Motorola and HTC, has developed GAN handsets. This too aids in de-risking LTE device development. These considerations have made GAN the leading approach for delivering telephony services over LTE.

Busting the backhaul bottleneck

LTE will increasingly expose mobile backhaul infrastructure based on leased line and TDM architecture as a bottleneck to consumers' growing appetite for data on-the-go. Such legacy backhaul systems cannot be scaled up cost-effectively to meet the transport requirements of next-generation networks. Instead, Communication Service Providers are looking to migrate their transport from TDM to IP/Ethernet.

To help, Nokia Siemens Networks has launched its Carrier Ethernet Transport (CET) solution, to simplify backhaul across the entire network, or to migrate data traffic to Ethernet and keep voice on existing transport infrastructure. The solution is tailored to individual transport infrastructure needs and the existing architecture situation, but typically can achieve:

up to 30 percent lower transport costs through Multi-Layer Optimization

simplified operations with centralized management

up to 25 percent site cost savings by eliminating shelter equipment, and reducing space and power consumption

efficient migration to full packet for an enriched customer experience

CET is a new way to build mobile backhaul, offering economical Installation and operation, as well as features to meet the changing needs of the industry.

Software-defined radio helps make more of spectrum

Spectrum is a scarce resource for most Communication Service Providers facing the challenge of rapidly rising traffic volumes in their networks. It's an issue addressed by the Nokia Siemens Networks Single RAN solution, which provides Communication Service Providers a highly cost-effective way to increase spectral efficiency without increasing network complexity.

The solution combines software-defined radio with advanced baseband and radio capabilities that can concurrently run more than one radio access technology in the same band and at the same time. Furthermore, the energy savings are significant with only one base station needed to run several radio technologies, instead of individual base stations for each technology.

This makes it possible to evolve to new base station and transport capabilities without the need for any new hardware. Through software upgrades alone, Flexi BTS sites can be upgraded from High Speed Packet Access (HSPA) technology to Long Term Evolution (LTE). Not only does this enable a COMMUNICATION SERVICE PROVIDER to maximize its spectrum utilization, but it also helps to keep operational costs low, while speeding up the time to market for new technologies.

Business beyond flat rates

The widespread introduction of flat-rate tariffs has been a key development that has helped to create the explosion in mobile broadband utilization. Promising consumers simplicity and no unexpected shocks in their monthly bills, these tariffs can challenge COMMUNICATION SERVICE PROVIDER profitability. Communication Service Providers need to anticipate and model how consumers are going to utilization flat rate and then monitor this usage continually to adjust the offering.

To meet the challenges effectively demands a solution that combines charging with the right measures of policy control to support the differing needs of customers.

The innovative Nokia Siemens Networks Flexi Intelligent Service Node (ISN) lies at the heart of such a solution. Flexi ISN is able to distinguish the type of traffic, such as HTTP browsing, WAP browsing, MMS, streaming, and content download, to enable different charging models based on the type of data service utilized.

This enables Communication Service Providers to open up new service opportunities and maximize data revenues with differentiated charging and flexible data subscriptions, building their business beyond flat rates.

The fast track to Voice over LTE

Nokia Siemens Networks has launched a smart approach for providing voice services over LTE networks, needing only simple and cost-effective software and hardware upgrades to existing circuit-switched core networks. The award winning 'Fast Track VoLTE' provides a cost-effective way to offer Voice over LTE (VoLTE) in any mobile network.

Communication Service Providers can utilization their existing mobile soft switching and Nokia Siemens Networks' Mobile VoIP Server (NVS) infrastructure to manage voice traffic over the LTE network, a function that will eventually be handled by IP Multimedia Subsystem (IMS). This provides Communication Service Providers an important time-to-market advantage.

Fast Track VoLTE provides a transitional step among traditional networks and the all-IP world of LTE. The solution allows Communication Service Providers to exploit their existing circuit-switched mobile core network investments, while providing next-generation service. Investments in Fast Track VoLTE are fully re-usable when upgrading network architecture to IMS, thus reducing capital expenditure (CAPEX) in the long term.

Evolved Packet Core supports LTE transition

A key part of the end-to-end Nokia Siemens Networks LTE solution is the Evolved Packet Core (EPC). The system enables communications service providers (COMMUNICATION SERVICE PROVIDER) to upgrade their core networks to cater for the new LTE radio access, as well as support existing mobile technologies, ranging from 2G to 3G/HSPA, CDMA, Wi-Fi and WiMAX.

EPC is specified by 3GPP under its Service Architecture Evolution (SAE) banner, and provides connectivity among the radio network and the content and service networks. Furthermore, because all traffic flows through the EPC gateway it can act as the policy and charging enforcement point, enabling Communication Service Providers to stay in control of the utilization of network resources.

Nokia Siemens Networks' EPC is built on our leadership in flat network architecture and our driving role in 3GPP standardization. It offers smooth migration paths for Communication Service Providers moving to LTE/SAE, as well as supporting a smooth evolution alternative to upgrade our current SGSN and Flexi ISN elements to 3GPP R8 through a simple software upgrade.

LTE Laptop USB Modem

An LTE 'dongle,' or USB modem, is likely to be the first alternative afford for consumers of LTE network services. The dongle is a well-known tool for delivering mobile broad­band services.

With today's 3G dongle services, mobile operators don't typically facilitate their own branded VoIP service; thus, consumers have a high-speed IP network that invites VoIP competitors.

Today, it is possible to utilization UMA/GAN technology to facilitate a softmobile VoIP client, which derives service from the existing mobile voice core. Orange recently launched Unix PC in France, which is a perfect example of this service. The softmobile application resides on a USB key and is a self-contained application that runs on the subscriber's laptop.

For LTE, it makes sense to bundle a VoLGA-based softmobile client into the LTE dongle to deliver integrated broadband and telephony services to users from the start.

LTE Broadband Router

LTE is viewed as a replacement technology for today's fixed-line broadband connections into the home. With VoLGA, the LTE router can be utilized to replace the fixed home phone as well.

The fixed-line service is delivered via a VoLGA client in the broadband router with RJ-11 ports providing dial tone in the home; thus enabling the mobile operator to deliver broadband data, as well as fixed and mobile voice service, through a single, branded LTE connection. T-Mobile's extremely successful fixed-line VoIP service, @Home, has demonstrated that mobile operators can capture fixed-line revenues with UMA/GAN today.

LTE MIDs (Mobile Internet Devices)

Operators are envisioning a new class of devices that will enable them to capitalize on the LTE network -- mobile internet devices (MID). MIDs are a cross among a mobile phone and laptop, specifically designed to deliver a media-rich mobile Internet experi­ence beyond what a traditional handset can support, but without the overhead of a lap­top. The MID would have an embedded LTE radio and be afford as part of a mobile broadband service.

LTE MIDs will likely facilitate an embedded (or downloadable) softmobile client to offset potential VoIP competition. Using an existing VoLGA-based softmobile client, operators can embed telephony directly into an LTE MID as part of a technology launch.

LTE Handsets

Handset manufacturers will develop LTE devices only when there is a clear mandate for telephony from operators. Any hesitation, confusion or delay in telephony or the approach for delivering telephony will serve to delay the handset market.

For the major device manufacturers, leveraging the existing R4 service components for telephony and utilizing the UMA/GAN engine for packetizing traffic over LTE is relatively straightforward. This approach relies on software elements already proven in the field. The effect of standardizing on VoLGA for voice over LTE is to de-risk the development of LTE devices and enable manufacturers to focus on the complexities of a new radio resource.

However, several key trends in the communications market have emerged over the last few years that have caused significant changes in the IMS Installation plans of many mobile operators. For example, with the success of Internet-based search, commerce, music and Web 2.0 services, some operators are now rethinking their overall mobile data service approach. Rather than putting effort into conceptualizing, developing and delivering their own mobile data services, many operators are now focusing on doing a better job at working with, and mobilizing, successful Internet-based services.

The success of Release 4 soft-switch MSCs is also having an impact on operator IMS plans. These new voice switches are providing all the feature richness of legacy MSCs, while providing the capital and operational cost benefits of all-IP systems. Still in the early stages of Installation, these systems face many years of depreciation. And unlike moving to an IMS-based telephony core network, soft MSCs enable operators to continue to leverage all their existing (and expansive) operational support systems (billing, provisioning, services, customer care...).

As a result of these trends, the market is now starting to see several categories of mobile operators emerge when it comes to IMS. For some, the plan of record remains an eventual migration of all services to an IMS-based core network, albeit more slowly than originally anticipated. However, for a growing number of other operators, while they may still plan to install IMS, they are looking to focus those efforts on the introduction of new services rather than the recreation of existing services (e.g. telephony) in the IMS domain. The IMS Rich Communication Suite (RCS) effort within the GSMA is a good example of this new focus (see sidebar, p. 4).

Developed profile for LTE voice and SMS services:

A series of leading companies from the telecommunications industry have recently announced that they managed to define a preferred manner in which voice and SMS services on Long Time Evolution (LTE) should be easily introduced on upcoming networks all around the world. Industry leaders developed a technical profile for LTE voice and SMS services, which is known as the One Voice initiative.

The new, jointly developed profile describes "an optimal set of existing 3GPP-specified functionalities that all industry stakeholders, including network vendors, service providers, and handset manufacturers, can utilization to offer compatible LTE voice solutions." According to the involved companies, the technical profile is also meant to ensure that international roaming and interoperability for LTE voice and SMS services will be available.

"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 wire line and LTE wireless networks," the team also noted.

The goal of the initiative is to guarantee that LTE will enjoy a wide ecosystem, and that fragmentation of technical solutions won't surface. The 4G typical will not be utilized only for broadband access and increasing data traffic, but for the availability of voice and SMS services, too. Carriers will have the opportunity to develop their LTE ecosystems faster, while collaborating both with infrastructure providers and with mobile phone makers. Moreover, the profile will also make sure that there is global interoperability when it comes to LTE voice and other services on the upcoming 4G networks.

The industry names that participated at this initiative include AT&T, Orange, Telephonic, TeliaSonera, Verizon, Vodafone, Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Nokia, Samsung Electronics Co. Ltd., and Sony Ericsson. The jointly developed profile for the initial solution is available through the companies mentioned above.

Summary and Acknowledgments Benefits

This paper has represented that VoLGA has a number of significant benefits over other Voice over IP solutions for LTE. On the network side, VoLGA does not require updating any of the existing network components, thus ensuring a very quick and smooth market introduction. Instead, all development is concentrated in the VoLGA Access Network Controller (VANC). In addition, VoLGA enables other circuit switched services from day one without any additional development. One of those is SMS for person to person messaging, a significant revenue generator for mobile network operators. In addition, SMS is also utilized for updating the configuration of mobile devices and for transmitting mandatory roaming data messages in Europe, both essential services when networks are launched. On the mobile devices side it is also likely that VoLGA can be developed very quickly, as the already exisisting GAN protocol stack can be mostly re-utilized. The only major change in the software is handover handling, as the network based Single Radio Voice Call Continuity (SRVCC) feature will be utilized.

And finally, VoLGA can also ensure a smooth introduction of global roaming. In case it is supported in the visited network, local breakout allows using the VANC and MSCs in the visited network. For network operators launching LTE as a data only network or only with voice options not supported by a mobile device, it is also possible to utilization the VANC and the MSCs of the home network.


The main disadvantages of VoLGA at this point are as follows:

First, it is not fully standardized yet as the stage 3 specifications has not yet been finalized. This is expected shortly, however. As it is likely that the stage 3 specification will be based on the equivalent GAN stage 3 specifications, vendors can already develop products without waiting for a final stage 3 specifications being published by the VoLGA forum.

Second, VoLGA is currently not a work item in 3GPP. There are probably several motivation for this, one being that the various features for Release was already high and most members wanted to ensure the tight completion deadline was met which would have been more difficult with an extended project scope. Some opposition for the work item has also been met from 3GPP participants who favor other Voice over LTE solutions. The situation is thus similar to the situation during the early times of GAN, which was also first developed outside 3GPP before it was included as a specification later-on.


Leveraging the 3GPP GAN representative to widen voice services as of an accessible core voice network above LTE propose the lowest risk, best path to LTE telephony. The improvement of a set of VoLGA terms presents a performance path to transport voice over LTE via GAN. For all operators grapple with approach for distribute voice over LTE, VoLGA afford long-term asset fortification, in addition to short-term service speed up considered to deliver profitable telephony services today.

Operators around the world are finding to accelerate LTE deployments. Relatively the deliver of an undifferentiated broadband link, lots of of these operators are concentrated on being 'smart pipe' providers by weaving their existing telephony services into the offer.

Communications Service Providers are at present spending much time and energy succeeding LTE radio access network skill, which will make certain exist deployments preserve or exceed existing mobile consistency. The next quite a few quarters will confirm attractive as Communication Service Providers decide LTE voice delivery architectures, a lot of it predisposed by time and their individual network design's necessities. Cautious deliberation of voice services and function will make sure high-value consumers (early LTE adopters) are capable to benefit from the same voice features and services they are at present utilized to, make sure they are permanent change. Service Brokers will participate a serious role in ensuring Communication Service Providers are able to immediate transfer present voice proceeds platforms for those early on LTE customers.

Even for mobile service providers looking to ultimately transfer all services, together with mobile telephony, to IMS, the VoLGA-based approach propose a good mid-term clarification for voice over LTE.

From a complexity point of view, VoLGA makes it very simple to leverage existing 2G and 3G circuit switched equipment in live networks for LTE. This is especially because no software enhancements are required on existing network nodes. Due to this and other benifits of VoLGA described above, the author of this paper believes that VoLGA has the chance to become a widespread Voice over LTE solution and will ensure that two of the main revenue generators for network operators, voice calls and SMS, will be available in LTE networks very early on.

List of Abbreviations for Easy Reference:


2G  2nd generation wireless networks; refers to GSM networks in this paper.

3G  3rd generation wireless networks; refers to UMTS networks in this paper.

3GPP 3rd Generation Partnership Project; refers to the organization in charge of GSM, UMTS and LTE standards

APN Access Point Name; An identifier given to the network when a packet session is started so the network can contact the desired gateway node to establish an Internet connection

BSC     Base Station Controller; A radio network element in 2G networks that controls a number of base stations.

CSFB    Circuit Switched Fallback; A method to fall back from LTE to a 2G or 3G network for voice calls.

DHCP    Dynamic Host Configuration Protocol; Utilized in IP networks to assign an IP address, default gateway IP address and other network based parameters to a device when it connects to the network.

GAN     Generic Access Network; A method to utilize a GSM or UMTS core network over Wi-Fi (WLAN) access.

HLR/HSS Home Location Register / Home Subscriber Server; The database in the mobile core network where subscriber data is stored

IMS     IP Multimedia Subsystem; Supporting structure for next generation multimedia applications in fixed a wireless networks.

LTE     Long Term Evolution; Commonly utilized acronym utilized for network beyond 3G. Technically the utilization of this term, however, is not quite correct as it was only a placeholder for a new radio network acronym.

QoS     Quality of Service; Mechanisms to ensure that IP packets for applications are delivered in a timely manner for applications such as VoIP which are very intolerant to packet delay and jitter.

TDM     Time Division Multiplexing; Legacy method still widely utilized today in wireless networks to transport voice calls.

VoIP    Voice over IP; Methods to transport voice calls over IP networks.

VoLGA   Voice over LTE via Generic Access.


The Third Generation Partnership Project -

The VoLGA Forum -

HTC Shadow II -

The Motorola Morrison -

GAN device manufacturers: (version from 30 July 2009)

3GPP TR 23.879 - Study on Circuit Switched (CS) domain services over evolved Packet Switched (PS) access; Stage 2, 3GPP Release 8

Voice over LTE via Generic Access; Stage 2 Specification; Phase 1 - Available at the VoLGA Forum website

3GPP TS 23.216 - Single Radio Voice Call Continuity (SRVCC); Stage 2

Bill Shock Warning by March 2010 -

3GPP TS 23.272 - Circuit Switched (CS) fallback in Evolved Packet System (EPS);

Introduction to CS Fallback-

3GPP discussion paper SP-090429-