While VoLGA supporters still maintain that VOLGA will fulfil a useful role, the weight behind the One Voice initiative seems set to dictate the future direction to ensure voice over LTE interworking and roaming using 3GPP specifications for IMS. The specification includes E-UTRAN, evolved packet core, user equipment and IMS core features that the group considers essential to interoperable IMS voice. In the long run, support of voice and messaging in LTE over IMS remains the major target.
VOLGA supporters argue that there are numerous shortcomings with CSFB as an interim voice over LTE solution. CSFB requires modifications to existing elements within the network (MSCs) as well as specific support on new devices. The MSC modifications are also required for the SMS-over-SGs functionality as well as voice. Exact timing on the availability of these upgrades across the whole pool of current MSC implementations is unclear although SMS support is vital from day 1 for operational reasons even for data devices. The other shortcoming with CSFB is call set up latency which is a major factor in determining quality of experience when making a phone call. The concept of falling back to 2G or 3G from LTE has an obvious pre-requisite that there needs to be a suitable network with coverage available. In some cases this might not be case, for example operators that do not have 2G/3G networks. Another problem with CSFB is that is that it will likely drop any running LTE data connection when running concurrently with a CSFB call. There are also limitations in supporting SMS. There are costs associated with implementing CSFB. The costs are associated with both the network and handset even though there are also costs associated with other alternative approaches of voice over LTE. There is a problematic integration with CSFB and LTE femtocells. An LTE device connected to a femto would either need to fallback to 2G / 3G in the femto itself, or look for a macro cell-site instead. Adding 2G into femtos is very complex, while adding 3G increases cost, complexity and time-to-market.
As expected the supporters of CSFB have a different view from that of VOLGA supporters regarding CSFB. According to the supporteers of CSFB , CSFB is considered the preferred solution for the early stages of LTE network deployment as it represents a low-cost, low-risk approach. From the user perspective, it minimizes call establishment delay and supports smooth handoffs. For operators, the solution enables them to make full use of their existing networks to protect investments. The operators are able to re-use MSC interconnect, roaming agreements, charging and settlement processes. On 13 January 2011, ¬Huawei announced that they have successfully completed a CSFB voice call with an unnamed 3rd-party handset provider. “Conducted at Huawei's LTE and Evolved Packet Core (EPC) Interoperability Testing Lab in Shanghai, the call demonstrate that operators using LTE/EPC to provide pure data services will still be able to leverage its existing CS network to provide voice services”.
Moreover, VOLGA supporters are of the view that VOLGA should be the preferred interim solution for voice over LTE. They argue that 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 MSC 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 use of SMS services over LTE without any modifications in the network. On the mobile device side, the protocol stack initially developed for GAN can also be re-used 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.When supported by the visited network VOLGA enables a smooth introduction of global LTE roaming, all services can be delivered via the VoLGA circuit to packet gateway and the MSC in the visited network. In case where VoLGA is not supported, the VoLGA gateway and the Mobile Switching Centers in the home network may be used instead.
It seems there is a battle between VOLGA and CSFB on who will win the race as being the interim solution for voice over LTE. At the moment it is not clear as to which standard will be adopted between the two as the global standard. Considering that the skeptics of CSFB are of the view that CSFB in a sub- standard technically speaking based on the arguments discussed above and that the supporters of VOLGA are of the view that VOLGA is superior to CSFB. Then it should make sense that operators will adopt VOLGA. However, there are always politics and some decisions are taken on corridors during these standard development processes meetings. There are commercial issues at play and also limits on what can be discussed to avoid breaching competition laws. Sometimes, it is not about the technical superiority of the standard but it is about who backing the standard. According to GSA 56 % of LTE deployments will implement CSFB as their interim voice over LTE solution. So, I think CSFB will be the most successful interim solution for voice over LTE in that most operators will implement it. This is based on the fact that the major operators and equipment manufacturers are supporting CSFB. I think the long term solution for voice over LTE will be IMS. According to GSMA 94 % of LTE deployments will deploy IMS as their long term solution.
References
http://www.3gpp.org
http://www.volga-forum.com
http://www.cellular-news.com
http://www.gsa.com
http://www.gsmworld.com
http://www.disruptive-analysis.com
Wednesday, 8 June 2011
Monday, 6 June 2011
Why are these standards developed by different organizations?
LTE standards are developed by 3GPP. 3GPP is a partnership project between different standardization organizations ( known as organizational partners) in the field of telecommunications, which was established in 1998 to formulate technical specifications and technical reports for a 3G mobile system based on evolved GSM core networks and the radio access technologies that support (Universal Terrestrial Radio Access (UTRA) both FDD and TDD modes. Subsequently, the work of 3GPP was extended to include the maintenance and development of the Global System for Mobile communication (GSM) technical specifications and technical reports including evolved radio access technologies namely General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE).
The organizational partners (OG) of 3GPP are the following:
• The Association of Radio Industries and Businesses (ARIB)-Japan
• Alliance for telecommunications Industry Solutions ( ATIS) –North America
• China Communications Standards Association ( CCSA) –China
• The European Telecommunications Standards Institute ( ETSI) Europe
• Telecommunications Technology Association (TTA) Korea
• Telecommunication Technology Committee ( Japan)
The main role of the OGs is to determine the general policy and strategy of 3GPP. The OGs may invite Market Representation Partners( MPR) as they deem fit to take part in the work of 3GPP and offer market advice and to bring to the latter a consensus view of market requirements.
The technical specifications within 3GPP are developed by Technical Specification Groups (TSGs). Each TSG is responsible for preparing, approving and maintaining specifications in terms of its terms of reference. The TSG may organize their work in Working Groups(WG) and liaise with other groups as appropriate. The TSGs report to the Project Coordination Group ( PCG), which is the highest decision making body in 3GPP.
When LTE was first conceived , 3GPP made a decision that LTE would be the first technology in the GSM family not to support circuit-switched connections
The reason for this decision was that a single IP-based transport system is key to ensuring that LTE networks are efficient enough to carry large volumes of traffic cost-effectively. Unfortunately this decision came with a price that LTE would not support voice services. As such there was there was an assumption that operators would provide voice services using an IP Multimedia Subsystem (IMS) and the related Multimedia Telephony Service (MMtel) standard.
However, when IMS/MMtel was conceived in 2006, many operators were not enthusiastic in their support for IMS and there was some pressure to define an alternative means of implementing voice services on LTE networks. Consequently, 3GGP began with the process of defining CSFB approach as an interim solution, that could be used by operators until they were ready to adopt IMS. This opened the door to other approaches and 3GPP began to define another interim approach namely circuit-switched over packet-switched system (CS over PS). The emergence of these different solution raised some questions as to whether these interim approaches would end up being used for a long time. Another issue that was raised was that the GSM principle of interoperability might be put at risk. Would it be possible for devices supporting these solution to roam on each other networks. As a result, 3GPP decided to halt the CS over PS work. 3GPP decision to halt the CS over PS work was based on the grounds that they did not want to be perceived as endorsing the third option.
Consequently, in March 2009 the VoLGA Forum was established to continue with the definition of CS over PS outside of 3GPP. The VoLGA Forum has 19 member companies, including Alcatel-Lucent, Cisco, Deutsche Telekom, Ditech Networks, GENBAND, HTC, Huawei, Kineto Wireless, LG Electronics, Mavenir, Motorola, Samsung, Sonus, SPA, Tecore Networks, Ulticom, Vitendo, WiChorus and ZTE. Ericsson was originally a member of the VOLGA Forum but revoked their membership in December 2009 citing that when VOLGA was established they were under the impression that VOLGA would become a global solution however it seemed that VOLGA would not be supported by mobile operators. In September 2009, the VoLGA Forum published the first complete set of approved specifications for delivering mobile voice and SMS messaging services over LTE access networks.
VoLGA will enable mobile operators to do the following:
• Bring voice and SMS services over LTE radio access networks and femtocells.
• Support new revenue-generating applications over LTE, such as IMS combinational services and the Rich Communications Suite (RCS).
• Provide an improved overall user experience capitalizing on the performance advantages of LTE.
• Navigate a smooth transition to IMS telephony.
• Launch data-only LTE devices leveraging the existing SMS-based customer care applications such as remote device management, configuration updates and SMS-based service announcements.
In July 2010, the VoLGA Forum released an updated set of specifications for delivering mobile voice and SMS services over LTE. This latest release adds key new features and capabilities to facilitate rapid deployment, including the following:
• The use of VOLGA over HSPA
• Support for SIM-less emergency calling
• Optimized voicee-bearer routing
The One Voice Initiative was a collaboration between AT&T, Orange, Telefónica, TeliaSonera, Verizon Wireless, Vodafone, Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Nokia, Samsung and Sony Ericsson that used current open standards to define the minimum mandatory set of functionality for interoperable IMS-based voice and SMS over LTE. A powerful group of more than 40 organizations including major operators and equipment manufacturers behind this initiative. T-Mobile was not a member of One Voice as they are a member of VOLGA. The goals of One Vice Initiative included the following:
• Define a common approach to implement voice and SMS in LTE
• Speed up commercial deployment of IMS voice over LTE
• Pave the way to true multimedia architecture by building an LTE voice ecosystem based on IMS
• Avoid fragmentation caused by alternative market options
The intention of this initiative was to convince the GSMA and 3GPP to formally recommend its adoption and it succeeded in doing that. Version 1 of One Voice, Voice over IMS profile was published in November 2009 and this was announced in a press release at LTE Americas in Texas, USA.
The GSMA adopted the technical profile developed by the One Voice Initiative and established the Voice over LTE ( VOLTE) initiative. The GSMA VoLTE initiative was formally announced on 15 February 2010 in a press release stating that: “In establishing the VoLTE initiative, GSMA has adopted the work of the One Voice Initiative* as the basis of the work to lead the global mobile industry towards a standard way of delivering voice and messaging services for Long-Term Evolution (LTE). Using IP Multimedia Subsystem specifications developed by 3GPP as its basis, GSMA have expanded upon the original scope of One Voice work to address the entire end-to-end voice and SMS ecosystem by also focusing on Roaming and Interconnect interfaces, in addition the interface between customer and network”.
In September 2010, the GSMA published the IREG Permanent Reference Document IR.92, which outlines the specifications for migrating 2G & 3G mobile voice, video and messaging services to 4G mobile broadband networks including LTE. The requirements in the specification are compliant with 3GPP Release 8 and there are some additional requirements from 3GPP Release 9 in support of packet switched emergency calls.
The requirements in this specification comprise IMS features, media requirements, bearer management features, LTE radio requirements.
The VoLTE profile uses a subset of general IMS features and of the MMTel service. The subset is selected to provide an IP telephony service with a similar user experience as the CS service of 2G and 3G networks. The aim of the profile is to provide a minimal set of features that can serve as a starting point. The profile must still be open to functional growth in networks and devices to reach the full 3GPP specifications for IMS and MMTel, for example, using multimedia, supporting users with multiple devices. Considerable efforts have therefore been made to ensure that user equipment(UE) that supports the VoLTE feature set can be used even in networks that provide all 3GPP IMS and MMTel features. The baseline profile mandates the use of different options for the IMS feature. For example, SIP registration; authentication; addressing; basic call handling; forking; and signaling compression. With regard to authentication, the baseline profile supports both MSISDN and SIP-URI based addressing. The baseline profile supports a single handheld device scenario.
The media handling in the VoLTE baseline profile have a set of requirements that provide voice services with the same quality as that of legacy circuit-switched service. In spite of the additional delay introduced by de-jittering, the end-to-end delay of MMTel terminals and LTE networks is on par with or even better than that of 2G/3G circuit-switched telephony.
When there are frame error rates, LTE voice bearers add erroneous transmission repair. As a result, most packets are sent successfully over the LTE air interface, and the residual frame error rate for voice media is low. The addition of solutions for codec rate adaptation, which is specified in the MMTel specification, can further enhance media transport.
In terms of this profile, LTE EPC systems must be equipped with policy and charging control (PCC).PCC has a set of Rx and Gx interfaces that connect EPC with the IMS domain. In addition, the PCC architecture introduces a policy and charging rules function (PCRF) that encompasses policy decision and flow-based charging control functions. With PCC implemented, IMS can start a network initiated process to set up suitable 3GPP EPS bearers for telephony service.
To support roaming services, the profile uses a roaming model where the IMS P-CSCF is located in the visited network and uses local breakout from the packet core network . As a result IMS voice services for roaming users require new IMS-based roaming agreements between the network service providers. If there are no such agreements in place, the UE is required to use CSFB for voice calls while roaming if LTE is used in the visited network.
The VOLTE profile, also has a specification for IMS emergency calls. This is according to the 3GPP Rel-9 which, added the functions in EPC to enable IMS emergency calls over packet switched access. Release 9 also includes support for SIM-less emergency calls , user and control plane location services, and enhancements to the air interface to improve over the air time difference of arrival (OTDOA) accuracy.
References
http://www.3gpp.org
http://www.volga-forum.com
http://www.cellular-news.com
http://www.gsa.com
Lennart Norell, Eric Parsons and Per Synnergren. 2010. Telephony services over LTE and to end. Ericsson review.
The organizational partners (OG) of 3GPP are the following:
• The Association of Radio Industries and Businesses (ARIB)-Japan
• Alliance for telecommunications Industry Solutions ( ATIS) –North America
• China Communications Standards Association ( CCSA) –China
• The European Telecommunications Standards Institute ( ETSI) Europe
• Telecommunications Technology Association (TTA) Korea
• Telecommunication Technology Committee ( Japan)
The main role of the OGs is to determine the general policy and strategy of 3GPP. The OGs may invite Market Representation Partners( MPR) as they deem fit to take part in the work of 3GPP and offer market advice and to bring to the latter a consensus view of market requirements.
The technical specifications within 3GPP are developed by Technical Specification Groups (TSGs). Each TSG is responsible for preparing, approving and maintaining specifications in terms of its terms of reference. The TSG may organize their work in Working Groups(WG) and liaise with other groups as appropriate. The TSGs report to the Project Coordination Group ( PCG), which is the highest decision making body in 3GPP.
When LTE was first conceived , 3GPP made a decision that LTE would be the first technology in the GSM family not to support circuit-switched connections
The reason for this decision was that a single IP-based transport system is key to ensuring that LTE networks are efficient enough to carry large volumes of traffic cost-effectively. Unfortunately this decision came with a price that LTE would not support voice services. As such there was there was an assumption that operators would provide voice services using an IP Multimedia Subsystem (IMS) and the related Multimedia Telephony Service (MMtel) standard.
However, when IMS/MMtel was conceived in 2006, many operators were not enthusiastic in their support for IMS and there was some pressure to define an alternative means of implementing voice services on LTE networks. Consequently, 3GGP began with the process of defining CSFB approach as an interim solution, that could be used by operators until they were ready to adopt IMS. This opened the door to other approaches and 3GPP began to define another interim approach namely circuit-switched over packet-switched system (CS over PS). The emergence of these different solution raised some questions as to whether these interim approaches would end up being used for a long time. Another issue that was raised was that the GSM principle of interoperability might be put at risk. Would it be possible for devices supporting these solution to roam on each other networks. As a result, 3GPP decided to halt the CS over PS work. 3GPP decision to halt the CS over PS work was based on the grounds that they did not want to be perceived as endorsing the third option.
Consequently, in March 2009 the VoLGA Forum was established to continue with the definition of CS over PS outside of 3GPP. The VoLGA Forum has 19 member companies, including Alcatel-Lucent, Cisco, Deutsche Telekom, Ditech Networks, GENBAND, HTC, Huawei, Kineto Wireless, LG Electronics, Mavenir, Motorola, Samsung, Sonus, SPA, Tecore Networks, Ulticom, Vitendo, WiChorus and ZTE. Ericsson was originally a member of the VOLGA Forum but revoked their membership in December 2009 citing that when VOLGA was established they were under the impression that VOLGA would become a global solution however it seemed that VOLGA would not be supported by mobile operators. In September 2009, the VoLGA Forum published the first complete set of approved specifications for delivering mobile voice and SMS messaging services over LTE access networks.
VoLGA will enable mobile operators to do the following:
• Bring voice and SMS services over LTE radio access networks and femtocells.
• Support new revenue-generating applications over LTE, such as IMS combinational services and the Rich Communications Suite (RCS).
• Provide an improved overall user experience capitalizing on the performance advantages of LTE.
• Navigate a smooth transition to IMS telephony.
• Launch data-only LTE devices leveraging the existing SMS-based customer care applications such as remote device management, configuration updates and SMS-based service announcements.
In July 2010, the VoLGA Forum released an updated set of specifications for delivering mobile voice and SMS services over LTE. This latest release adds key new features and capabilities to facilitate rapid deployment, including the following:
• The use of VOLGA over HSPA
• Support for SIM-less emergency calling
• Optimized voicee-bearer routing
The One Voice Initiative was a collaboration between AT&T, Orange, Telefónica, TeliaSonera, Verizon Wireless, Vodafone, Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Nokia, Samsung and Sony Ericsson that used current open standards to define the minimum mandatory set of functionality for interoperable IMS-based voice and SMS over LTE. A powerful group of more than 40 organizations including major operators and equipment manufacturers behind this initiative. T-Mobile was not a member of One Voice as they are a member of VOLGA. The goals of One Vice Initiative included the following:
• Define a common approach to implement voice and SMS in LTE
• Speed up commercial deployment of IMS voice over LTE
• Pave the way to true multimedia architecture by building an LTE voice ecosystem based on IMS
• Avoid fragmentation caused by alternative market options
The intention of this initiative was to convince the GSMA and 3GPP to formally recommend its adoption and it succeeded in doing that. Version 1 of One Voice, Voice over IMS profile was published in November 2009 and this was announced in a press release at LTE Americas in Texas, USA.
The GSMA adopted the technical profile developed by the One Voice Initiative and established the Voice over LTE ( VOLTE) initiative. The GSMA VoLTE initiative was formally announced on 15 February 2010 in a press release stating that: “In establishing the VoLTE initiative, GSMA has adopted the work of the One Voice Initiative* as the basis of the work to lead the global mobile industry towards a standard way of delivering voice and messaging services for Long-Term Evolution (LTE). Using IP Multimedia Subsystem specifications developed by 3GPP as its basis, GSMA have expanded upon the original scope of One Voice work to address the entire end-to-end voice and SMS ecosystem by also focusing on Roaming and Interconnect interfaces, in addition the interface between customer and network”.
In September 2010, the GSMA published the IREG Permanent Reference Document IR.92, which outlines the specifications for migrating 2G & 3G mobile voice, video and messaging services to 4G mobile broadband networks including LTE. The requirements in the specification are compliant with 3GPP Release 8 and there are some additional requirements from 3GPP Release 9 in support of packet switched emergency calls.
The requirements in this specification comprise IMS features, media requirements, bearer management features, LTE radio requirements.
The VoLTE profile uses a subset of general IMS features and of the MMTel service. The subset is selected to provide an IP telephony service with a similar user experience as the CS service of 2G and 3G networks. The aim of the profile is to provide a minimal set of features that can serve as a starting point. The profile must still be open to functional growth in networks and devices to reach the full 3GPP specifications for IMS and MMTel, for example, using multimedia, supporting users with multiple devices. Considerable efforts have therefore been made to ensure that user equipment(UE) that supports the VoLTE feature set can be used even in networks that provide all 3GPP IMS and MMTel features. The baseline profile mandates the use of different options for the IMS feature. For example, SIP registration; authentication; addressing; basic call handling; forking; and signaling compression. With regard to authentication, the baseline profile supports both MSISDN and SIP-URI based addressing. The baseline profile supports a single handheld device scenario.
The media handling in the VoLTE baseline profile have a set of requirements that provide voice services with the same quality as that of legacy circuit-switched service. In spite of the additional delay introduced by de-jittering, the end-to-end delay of MMTel terminals and LTE networks is on par with or even better than that of 2G/3G circuit-switched telephony.
When there are frame error rates, LTE voice bearers add erroneous transmission repair. As a result, most packets are sent successfully over the LTE air interface, and the residual frame error rate for voice media is low. The addition of solutions for codec rate adaptation, which is specified in the MMTel specification, can further enhance media transport.
In terms of this profile, LTE EPC systems must be equipped with policy and charging control (PCC).PCC has a set of Rx and Gx interfaces that connect EPC with the IMS domain. In addition, the PCC architecture introduces a policy and charging rules function (PCRF) that encompasses policy decision and flow-based charging control functions. With PCC implemented, IMS can start a network initiated process to set up suitable 3GPP EPS bearers for telephony service.
To support roaming services, the profile uses a roaming model where the IMS P-CSCF is located in the visited network and uses local breakout from the packet core network . As a result IMS voice services for roaming users require new IMS-based roaming agreements between the network service providers. If there are no such agreements in place, the UE is required to use CSFB for voice calls while roaming if LTE is used in the visited network.
The VOLTE profile, also has a specification for IMS emergency calls. This is according to the 3GPP Rel-9 which, added the functions in EPC to enable IMS emergency calls over packet switched access. Release 9 also includes support for SIM-less emergency calls , user and control plane location services, and enhancements to the air interface to improve over the air time difference of arrival (OTDOA) accuracy.
References
http://www.3gpp.org
http://www.volga-forum.com
http://www.cellular-news.com
http://www.gsa.com
Lennart Norell, Eric Parsons and Per Synnergren. 2010. Telephony services over LTE and to end. Ericsson review.
Sunday, 5 June 2011
Different techniques to support the provision of voice over LTE
LTE is the new cellular system developed by the 3GPP. The systems is composed of a radio part , called evolved UTRAN (eUTRAN) and the core network part called the Evolved Packet Core. The system composed of these two parts is called the Evolved packet System (EPS). The core network supports GERAN and UTRAN radio access and it also supports interworking with the legacy circuit switched domain. The non 3GPP networks are also supported. LTE is a 4G technology which precedes UMTS and HSPA, and it is adheres to the requirements of the IMT advanced standard as prescribed by the ITU. However, EPS does not have a circuit switched domain to handle voice calls in the traditional way as in 2G And 3G. In 2G and 3G voice has been separated from the data by utilizing circuit switched and packet switched domain respectively. According to GSMA, voice revenue will still account for 61 % of all mobile service revenue in 2013. So it critical for the mobile industry had to come up with a solution for LTE to be able to handle voice calls. There are different techniques that can be used to support voice over LTE and they all will be based on voice over IP (VOIP). This blog does cover all the proposed alternative techniques. It will only cover the four main techniques that have been identified.
• Circuit Switched Fallback ( CSFB) to 2G/3G Circuit Switched-3GPP
• Circuit Switched over packet Switched-voice over LTE via Generic Access( VOLGA)
• Over the top (OTT)
• IMS based 3GPP Multimedia Subsystem (IMS) Multimedia Telephony(MMTel)
Circuit Switched Callback
CSFB is a 3GPP interim standard solution for early deployments stages of LTE where IMS is not available. During the early stages of LTE deployment it may take some time before IMS and VOIP services can be provided. 3GPP decided on a phased approach for the provision on voice services on LTE. Since CSFB only provides support for voice and sms , it is considered as an interim solution in the evolution towards into a fully fledged multimedia communication service.
3GPP CSFB standards work specifies the architecture enhancements for functionality to enable Fallback from E-UTRAN access to 2G/3G CS domain access. Using this functionality enables the provision voice and other CS-domain services (e.g. CS UDI video / SMS/ LCS / USSD) by reuse of CS infrastructure. The specifications documents overall CS Fallback architecture and stage 2 level specifications for the 3GPP components. Roaming aspects are documented as well. CT1 and CT4 specifies Stage3 capabilities and functionalities according to SA2 Stage 2 in TS 23.272 as follows:
• combined EPS/IMSI attach and tracking area update procedures based on similar mechanisms as those used by the combined GPRS attach and routing area update procedures from 3GPP TS 24.008, in order to register the UE to the CS domain for future Fallback from E-UTRAN access to 2G/3G CS domain access;
• IMSI or combined EPS/IMSI detach procedure, both UE and network initiated, based on similar mechanisms as those used by the GPRS detach procedure from 3GPP TS 24.008;
• CS fallback related capability for the UE to receive the CS paging request via EPS and respond to this paging via the GERAN/UTRAN, or to request a CS call in E-UTRAN and establish the call in GERAN/UTRAN;
• procedures for supporting Mobile originating and Mobile terminating SMS in EPS;
• procedures required for the support of CS fallback to 1xRTT;
• procedures on the SGs interface between the MME and the MSC, based on the Gs interface procedures.
Figure 1:CS fallback in EPS architecture
The CS fallback in EPS function is realized by reusing the Gs interface mechanism between the MSC Server and the MME. Gs is an interface for exchanging information between MSC/VLR and SGSN. MME is a logical node accommodating a base station (eNodeB) and providing mobility management and other functions.
If you have a mobile LTE terminal, a call arrives at the terminal from the existing CS domain via EPC. The mobile terminal receives a paging message and recognises that the network is calling for a CS based voice and therefore switches to 2G/3G . The response confirming the call acceptance will be sent to from the mobile terminal to the 2G/3G Cs system and from that point on all call control for the voice service will be performed on the 2G/3G side.
The CS callback consists of a function that notifies a mobile terminal about a call request from the CS domain and combined mobility management functions between CS domain and the EPC for that purpose.
Circuit Switched over packet Switched-voice over LTE via Generic Access ( VOLGA)
VOLGA is positioned as the interim alternative to address the provision of voice services on LTE prior to IMS LTE deployments. VOLGA is not standardized by 3GPP. The main idea of the VOLGA solution is to adapt Universal Mobile Access/Generic Access Network (UMA/GAN) for LTE and reuse 3GPP Single Radio Voice Call Continuity (SRVCC) mechanism for handover from LTE to 2G/3G CS. Using the 3GPP GAN standard as the basis for voice and SMS service delivery over LTE has a number of advantages.
This solution is recommended and developed by the VOLGA Forum. The forum is working to develop VoLGA specifications, based on the existing 3GPP GAN standard, which are designed to provide voice, SMS (and other circuit-switched) services as they transition between GSM, UMTS and LTE access networks. It is expected that the VoLGA specifications will be presented to the 3GPP for consideration as a recognized standard. The concept is to connect the already existing Mobile Switching Centers ( MSC) to the LTE network via a gateway. As no fallback to a legacy network is required, call setup times are not increased and the user's quality of experience is similar to that of the 2G or 3G voice environment.
Over the top (OTT)
Some network operators could decide to offer voice services over LTE with external partners such as Skype and Google talk. However, the challenge to this solution is that external voice service providers have no control over quality of service in the wireless network, as such they cannot ensure a good quality of experience to the user. This could be solved by installing logic in the network to ensure quality of service for data streams that are recognized to belong to an external voice service the user has subscribed to. Another challenge with OTT is that calls cannot be handed over to a circuit switched 2G or 3G network when a user leaves the LTE coverage area.
IMS based 3GPP Multimedia Subsystem (IMS) Multimedia Telephony(MMTel)
3GPP IMS Multimedia Telephony based on IMS is the standardized long term solution to offer voice services over LTE. IMS is an access system that works towards different access types including fixed networks, UMTS, GSM, LTE and WLAN. It is composed of a service layer with interfaces towards application servers or service platforms and a session control layer dealing with integration towards underlying access networks. IMS Centralized Services (ICS) and Single Radio Voice Call continuity (SRVCC) are essential features for the use of IMS for VOIP. SRVCC handles handover from packet based access to Circuit switched for calls that are anchored in the IMS. The SRVCC uses IMS for call control and requires support of ICS. ICS enables connections to be incorporated in IMS sessions in a consistent way. ICS is also needed to support supplementary services such as call hold and call wait.
IMS based solution has many advantages, it can support all standard voice call service features such as call waiting, call hold and call barring, and is capable of serving large numbers of subscribers. IMS can also be used to integrate voice calls with enhanced, rich features such as presence, instant messaging and video content, across networks run by different mobile operators. The One Voice group was formed to work on an IMS-based solution. The work of One Voice group is used as the basis of the GSMA’s Voice over LTE initiative (VoLTE), which is aiming to accelerate the launch of IMS-based voice services as the long term solution for voice over LTE.
References
Ericsson white paper .December 2010. Voice over LTE.
Kjuus, Hakon, E. and Nordvik, AnneMari. 2010. Handling of Voice and Data Services in the Evolved Packet Core.
Tanaka Itsuma, Koshimizi Takashi, Nishida Katsutoshi. CS Fallback Function for Combined LTE and 3G Circuit Switched Services. NTT Docomo Technical Journal Vol.11 No.3
Martin Sauter. August 2009. VOLGA – A Whitepaper.
http://www.3gpp.org
• Circuit Switched Fallback ( CSFB) to 2G/3G Circuit Switched-3GPP
• Circuit Switched over packet Switched-voice over LTE via Generic Access( VOLGA)
• Over the top (OTT)
• IMS based 3GPP Multimedia Subsystem (IMS) Multimedia Telephony(MMTel)
Circuit Switched Callback
CSFB is a 3GPP interim standard solution for early deployments stages of LTE where IMS is not available. During the early stages of LTE deployment it may take some time before IMS and VOIP services can be provided. 3GPP decided on a phased approach for the provision on voice services on LTE. Since CSFB only provides support for voice and sms , it is considered as an interim solution in the evolution towards into a fully fledged multimedia communication service.
3GPP CSFB standards work specifies the architecture enhancements for functionality to enable Fallback from E-UTRAN access to 2G/3G CS domain access. Using this functionality enables the provision voice and other CS-domain services (e.g. CS UDI video / SMS/ LCS / USSD) by reuse of CS infrastructure. The specifications documents overall CS Fallback architecture and stage 2 level specifications for the 3GPP components. Roaming aspects are documented as well. CT1 and CT4 specifies Stage3 capabilities and functionalities according to SA2 Stage 2 in TS 23.272 as follows:
• combined EPS/IMSI attach and tracking area update procedures based on similar mechanisms as those used by the combined GPRS attach and routing area update procedures from 3GPP TS 24.008, in order to register the UE to the CS domain for future Fallback from E-UTRAN access to 2G/3G CS domain access;
• IMSI or combined EPS/IMSI detach procedure, both UE and network initiated, based on similar mechanisms as those used by the GPRS detach procedure from 3GPP TS 24.008;
• CS fallback related capability for the UE to receive the CS paging request via EPS and respond to this paging via the GERAN/UTRAN, or to request a CS call in E-UTRAN and establish the call in GERAN/UTRAN;
• procedures for supporting Mobile originating and Mobile terminating SMS in EPS;
• procedures required for the support of CS fallback to 1xRTT;
• procedures on the SGs interface between the MME and the MSC, based on the Gs interface procedures.
Figure 1:CS fallback in EPS architecture
The CS fallback in EPS function is realized by reusing the Gs interface mechanism between the MSC Server and the MME. Gs is an interface for exchanging information between MSC/VLR and SGSN. MME is a logical node accommodating a base station (eNodeB) and providing mobility management and other functions.
If you have a mobile LTE terminal, a call arrives at the terminal from the existing CS domain via EPC. The mobile terminal receives a paging message and recognises that the network is calling for a CS based voice and therefore switches to 2G/3G . The response confirming the call acceptance will be sent to from the mobile terminal to the 2G/3G Cs system and from that point on all call control for the voice service will be performed on the 2G/3G side.
The CS callback consists of a function that notifies a mobile terminal about a call request from the CS domain and combined mobility management functions between CS domain and the EPC for that purpose.
Circuit Switched over packet Switched-voice over LTE via Generic Access ( VOLGA)
VOLGA is positioned as the interim alternative to address the provision of voice services on LTE prior to IMS LTE deployments. VOLGA is not standardized by 3GPP. The main idea of the VOLGA solution is to adapt Universal Mobile Access/Generic Access Network (UMA/GAN) for LTE and reuse 3GPP Single Radio Voice Call Continuity (SRVCC) mechanism for handover from LTE to 2G/3G CS. Using the 3GPP GAN standard as the basis for voice and SMS service delivery over LTE has a number of advantages.
This solution is recommended and developed by the VOLGA Forum. The forum is working to develop VoLGA specifications, based on the existing 3GPP GAN standard, which are designed to provide voice, SMS (and other circuit-switched) services as they transition between GSM, UMTS and LTE access networks. It is expected that the VoLGA specifications will be presented to the 3GPP for consideration as a recognized standard. The concept is to connect the already existing Mobile Switching Centers ( MSC) to the LTE network via a gateway. As no fallback to a legacy network is required, call setup times are not increased and the user's quality of experience is similar to that of the 2G or 3G voice environment.
Over the top (OTT)
Some network operators could decide to offer voice services over LTE with external partners such as Skype and Google talk. However, the challenge to this solution is that external voice service providers have no control over quality of service in the wireless network, as such they cannot ensure a good quality of experience to the user. This could be solved by installing logic in the network to ensure quality of service for data streams that are recognized to belong to an external voice service the user has subscribed to. Another challenge with OTT is that calls cannot be handed over to a circuit switched 2G or 3G network when a user leaves the LTE coverage area.
IMS based 3GPP Multimedia Subsystem (IMS) Multimedia Telephony(MMTel)
3GPP IMS Multimedia Telephony based on IMS is the standardized long term solution to offer voice services over LTE. IMS is an access system that works towards different access types including fixed networks, UMTS, GSM, LTE and WLAN. It is composed of a service layer with interfaces towards application servers or service platforms and a session control layer dealing with integration towards underlying access networks. IMS Centralized Services (ICS) and Single Radio Voice Call continuity (SRVCC) are essential features for the use of IMS for VOIP. SRVCC handles handover from packet based access to Circuit switched for calls that are anchored in the IMS. The SRVCC uses IMS for call control and requires support of ICS. ICS enables connections to be incorporated in IMS sessions in a consistent way. ICS is also needed to support supplementary services such as call hold and call wait.
IMS based solution has many advantages, it can support all standard voice call service features such as call waiting, call hold and call barring, and is capable of serving large numbers of subscribers. IMS can also be used to integrate voice calls with enhanced, rich features such as presence, instant messaging and video content, across networks run by different mobile operators. The One Voice group was formed to work on an IMS-based solution. The work of One Voice group is used as the basis of the GSMA’s Voice over LTE initiative (VoLTE), which is aiming to accelerate the launch of IMS-based voice services as the long term solution for voice over LTE.
References
Ericsson white paper .December 2010. Voice over LTE.
Kjuus, Hakon, E. and Nordvik, AnneMari. 2010. Handling of Voice and Data Services in the Evolved Packet Core.
Tanaka Itsuma, Koshimizi Takashi, Nishida Katsutoshi. CS Fallback Function for Combined LTE and 3G Circuit Switched Services. NTT Docomo Technical Journal Vol.11 No.3
Martin Sauter. August 2009. VOLGA – A Whitepaper.
http://www.3gpp.org
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