Networks (GAN), Voice over LTE via Generic Access. (VoLGA), 3G, LTE, 3GPP,
IMS. I. INTRODUCTION. Generic Access Technology is a 3rd generation term in.
International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012)
Evolution from 3rd Generation Generic Access Networks to Voice over LTE via Generic Access (VoLGA) Farzeen Qureshi1, Muhammad Usama bin Aftab2 Department of Telecommunications Engineering, NED University of Engineering and Technology, Karachi, Pakistan 1
[email protected] [email protected]
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A. Requirements at early stage Question may arise, what is the need of the Generic Access network? For the answer, we need to first focus on history of wireless communication. When the world switched from 2nd generation (GSM) to 3rd Generation, a rapid change from Circuit Switched network towards packet switched network was experienced.
Abstract—The paper gives a theoretical overview and comparison of 3rd Generation Generic Access Networks with LTE’s VoLGA. Migration towards Packet Switched Technology brought significant changes on Voice and Text services because of their circuit switched nature. The Problem was identified and solution was introduced under 3rd Generation Partnership project. VoLGA is more likely to be adopted in the initial stage of LTE, but IMS can be the long term solution.
This transition brought up a huge problem i.e. the voice and SMS (small message service), the two revenue generator services for service providers are not native in Packet switched networks as they purely belong to the circuit switched network architecture.
Keywords—Wireless Communications, Generic Access Networks (GAN), Voice over LTE via Generic Access (VoLGA), 3G, LTE, 3GPP, IMS.
The Solution can be categorized in three major portions [12]:
I. INTRODUCTION Generic Access Technology is a 3rd generation term in wireless communications, where it helps to move voice and text (the conventional mobile-telephony services) to IPNetwork. It enables user to experience a vertical handoff between two competent technologies GSM/UMTS and IEEE standard 802.11 (Wi-Fi), in order to securely transmit mobile traffic. [6]
Drop back to 2G for Voice/Text IMS (IP Multi-Media Subsystem) as separate entity Generic Access Network as Intermediate Solution
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A simple solution can be that we switch back towards the 2G circuit switched network for voice and text. This switching back to 2G is obviously not a long term solution as the technology is changing day by day. And also a big disadvantage exists i.e. we need to make software based changes in MSC for providing this backward compatibility support to 3rd Generation network. The second and the most complicated of the solutions can be, that we completely separate out this task to a different entity named as IMS (IP Multimedia Subsystem). The work on this has already been started years back, a recent development is that now an ongoing call can be switched from IMS to circuit switched network. This solution has significant complexity and has not been finalized yet.
As the name suggests Generic Access given by IEEE standard of Wi-Fi’s on unlicensed frequency spectrum, therefore it is commercially known as UMA (Unlicensed Mobile Access). The Major component added in the Core network for providing Generic Access is GAN-C. 2.
II. GENERIC ACCESS NETWORK (GAN) Generic Access Network, in simple words is the system that enables users to switch to an IP-Network over Wi-Fi. When a mobile discover that it is in the range of a Wi-Fi access point/Wi-Fi public hotspot, it establishes a secure IP-Connection to the GAN Controller present in the Core network (Figure 1). The GAN-C present in the core network simple act as a stand-alone base station, so mobile station can now experiences that it is simply in some other base station. 28
International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012) Now the Intermediate solution, which is somewhat acceptable, is that user get connected to the already existing Mobile Switching System of a 3rd generation packet switched network via a Gateway. This is achieved by not doing any software enhancement in MSC of 2nd generation network or the Core network in 3 rd generation technology rather the main software up gradation will be carried out on the Gateway which is to be developed once and can be used in any 3GPP enhancements in future. This solution brought up the concept of Generic Access network (GAN) which we will be discussed in more detail further in this paper.
Here we can device that, the use of 802.11 implies low and affordable rates, better coverage at homes, also low roaming charges outside ones network. Another Advantage is that, the GAN allows use of just one number, Mobile Station/Handset, a set of services and phone directory for all calls combining GSM and 802.11 that’s why one can say that GAN can migrate between IP and cellular coverage smoothly. D. Disadvantages of GAN One main disadvantage [4] is that the user must have Wi-Fi/UMA (GAN) enabled Mobile phones to gain access to the services. Calls become more prone to disconnect in lieu of transitions from Wi-Fi to the wireless service and vice versa. Also UMA (GAN) uses different frequency (s) that may be more prone to interference. Also, there may be some Authentication set up being provided before user gain access to the network services. The Mobile phones that support both Wi-Fi/UMA may be costly. Using GAN/UMA enabled Mobile Phones, it requires Wi-Fi to be enabled, which will drain the battery faster, this reduces both the talk time and standby time when compared to disabling GAN/UMA (and in turn Wi-Fi). III. WORLD BEYOND 3RD GENERATION GENERIC ACCESS NETWORKS Generic Access Network itself has tremendous advantages because it is one of the intermediate solutions that lead to a packet switched network architecture to carry voice and text. In a long run, 4th generation networks are based on packet switched architecture and the IMS is not that much mature enough to be deployed completely. So the solution lies in the hand of Generic Access networks. In 4th Generation or to be more specific in “LTE”, VoLGA (Voice over LTE via Generic Access) was introduced, working on the same generic access methods.
Figure 1 GAN Architecture
B. Early GAN was dual-mode While understanding the main phenomenon of the GAN, the best example is ―Dual Mode Handset‖. Supposing a situation where there is a mobile user who resides within the range of a Wi-Fi access point, his handset will vertical handoff the technology from GSM/UMTS to IP-Network over Wi-Fi link. This process is transparent to the user. The behavior is known as the Dual mode where a cell phone support two technologies and provide adaptive switching between both of them accordingly.
IV. VOICE OVER LTE VIA GENERIC ACCESS (VOLGA) VoLGA is basically the solution for LTE networks to adopt typical circuit switched facilities over IP-based network with no changes in the fundamental architecture of LTE [7]. It is one and the only additional component that is introduced is VAN-C (VoLGA Access Network Controller). This enables multi-vendor support, irrespective of any changes in their equipment. The software modification is done in the VAN-C which is also previously built for Generic Access Network in 3 rd Generation.
C. Advantages of GAN GAN provides advantages [4] with that of the Carrier and the Subscribers; one main advantage is that, rather than setting up costly sites in areas where coverage cannot be provided i.e. the Dead Zone, GAN supports coverage through low power 802.11 AP (Access Points).
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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012)
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For the MSCs, VAN-C is simply acting as a the mobile base station, this leaves an important concept that there is no need to upgrade anything in the existing circuit switched architecture because the MSCs are seeing VAN-C as a simple base station for the mobile. The other concept is the need of VoLGA which is fulfilled, now for the LTE network. A voice call or the text message can be routed through VAN-C with ease and transparency.
C. Handovers One of the most important features of VoLGA is the ability to handover voice call when the user leaves the coverage area of any LTE network. This enables a user to make an uninterrupted call even in the absence of LTE network, because the VAN-C will direct the call to the circuit switched network. If we see the procedure of Skype calls, it is impossible to be directed over circuit switched network and it is compulsory for them to remain in packet switched network as it is based on IP-Network completely, but on the other hand in VoLGA architecture it has an option to direct the call to the circuit switched network, hence it gives more flexible way of communication.
Figure 1 VoLGA Architecture
A. VoLGA Architecture In VoLGA architecture, the basic element is VAN-C which links different standards in order to facilitate voice and text services to the LTE user transparently. From LTE side, VAN-C is connected to the S-GW/P-GW through SGi interface. Taking into account, that both signaling and packets are transferred on the same link (Figure2). For EPC (Evolved Packet Core) of LTE, VAN-C acts as a simple IP based external node on which packets will be send and received. The HLR/HSS is connected to the VAN-C directly so that fall back technologies can access the databases of the 4th Generation users when the reverse flow of voice and text from GSM/UMTS is active.
V. CONCLUSION AND FUTURE ENHANCEMENTS Most verily it is possible in future that the packet switched network will be transferred completely to the IMS based services. As discussed before the complexity of IMS led it not to be deployed completely yet. Another modification can be of CSFB (Circuit Switched Fall Back) [9], that for every voice call or text message, LTE will fall back towards the services of circuit switched network but again, it is not a long run procedure for any vendor. The last modification can be that the operator will shift directly towards the Over-the-Top VoIP service provider like Skype to route calls for LTE.
The Architectural behavior can be understood easily by taking a practical example. When a handset is turned on and detects an LTE network, MME registers it to the HLR/HSS (Home Location Register/Home Subscriber Server) over S6a interface. Then a secured IP Connection is provided by the VAN-C to the LTE handset (for IP assignment DHCP can be used). Once connection is established the transfer of voice and text on the fall back technologies can be done easily over SGi interface as discussed before.
References [1] M. Sauter, ―VoLGA – A Whitepaper‖ 2009. [2] Wireless Moves -- http://www.wirelessmoves.com [3] The VoLGA Forum – http://www.volga-forum.com [4] Wikipedia – http://www.wikipedia.com [5] Oleg Stepaniuk, ―Voice over LTE via Generic Access (VoLGA) as a
B. Circuit Switched end of VoLGA In Figure, the VAN-C is connected with the MSC of a GSM Network and also with the MSC of UMTS Network. It gives two important understandings of the VoLGA Architecture:
possible solution of mobile network transformation‖ – IEEE.
[6] 3GPP Generic Access Network: 3GPP TS43.318, ―Mobile Broadcasting with Wimax‖; Amitabh Kumar, 2009.
[7] VoLGA: Voice Over LTE via Generic Access, ―Kineto Wireless – A Whitepaper‖; March 2009.
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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 3, March 2012) [8] Voice over LTE via Generic Access (VoLGA), LTE World; http://www.lteworld.com
[9] Stefan Constantinescu, ―LTE: In support of VoLGA over CSBF and IMS‖; 2009, http://www.intomobile.com/ [10] Event Helix, ―Voice of LTE Generic Access (VoLGA)‖ ‖http://www.eventhelix.com/lte/lte-tutorials.htm
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