Similar to the convergence of fixed networks towards Next Generation Networks (NGN), mobile technologies are also undergoing convergence to meet mobile customer demands for bandwidth and service quality with the emergence of 2.5G, 3G mobile networks… The volume of transactions (voice/data) on mobile networks has rapidly increased in recent years and has exceeded the demand on wired lines since 1999. Research in Vietnam regarding mobile networks is still very limited and often theoretical, with few practical products. The underlying reason for this issue is that mobile networks encompass many complex techniques that are difficult to manage under the current conditions in Vietnam.
This article proposes a research development plan aimed at mastering the new generation mobile network suitable for Vietnam’s conditions.
1. Mobile Network Architecture
Similar to fixed networks, mobile networks consist of layers: user terminal layer, access layer, core network layer, and service provision layer, involving actors such as: customer-subscriber, service provider, and content provider.
Terminal Layer
The mobile terminal layer is responsible for interfacing with users and accessing services from the core network. Some functions included in the mobile terminal are: radio access protocols, service access protocols (call/data), end-to-end signaling, authentication (SIM), and frameworks for user services…
Access Layer
The access layer in mobile networks uses radio access instead of wired methods as in fixed networks.
Radio channel access protocols integrated within terminals and transceivers perform several basic functions: transmitting/receiving data over radio waves with acceptable reliability, encoding and decoding, controlling the transmission power of terminals, managing radio resources, and handover control…
The access layer is the gateway that imposes many limitations on enhancing the quality and bandwidth for services. Therefore, research addressing issues related to this layer is always a major focus in mobile network studies. Various research directions have led to the development of different access techniques: time division, frequency division, or code division. These methods serve as the basis for different types of mobile networks, such as TDM, GSM, CDMA… The most significant differences between mobile networks also lie within this layer.
Core Layer
The core layer of mobile networks performs functions such as: switching transaction sessions, mobile management, signaling for call establishment between the core network and terminals, inter-network signaling between core mobile networks, and signaling with legacy networks…
The core layer consists of components such as: Mobile Switching Center (MSC), subscriber management (HLR, VLR, EIR, UAC), and gateway mobile switching center (GMSC). Core layer components that manage subscribers, like EIR, HLR, and VLR, are often similar across mobile networks and generations as they are primarily part of database management unrelated to network technology. The switching components and gateway interfaces of GSM and CDMA networks are similar in principle but differ in protocols at specific interfaces.
Service Layer
The service layer provides services beyond basic subscriber services, defining the service and specific requirements for each service. The entities of this layer, along with other components of the mobile network, form a cohesive service provision system: SMSC, WAP Gateway (WAPGW), Multimedia Messaging Service Center (MMSC), Streaming server…
2. Development of Mobile Networks
In fixed networks, there is a convergence process of technology and services between telecommunications networks and the Internet based on IP packet switching techniques. The term NGN – Next Generation Network has been frequently mentioned in recent years. The Internet is also evolving daily, from low-speed modems to various high-speed and flexible access methods, among which Wireless-LAN presents a significant challenge to mobile networks, although its mobility capability remains limited.
Faced with the development of the Internet alongside the rich new services of fixed networks, mobile service providers cannot remain satisfied with the current 2G mobile networks, which only offer voice and SMS services. Many major telecommunications organizations and international standardization bodies are striving to propose a new mobile network architecture to flexibly adapt to the advancements in IP technology, capable of effectively meeting customer demands for new services. 3GPP is an open organization focused on standardizing next-generation mobile networks, researching and providing recommendations for mobile networks on the path towards convergence.
3GPP has conducted studies for various mobile networks, all aiming towards a common goal: the third generation mobile network (3G). A series of recommendations and proposals have also been accepted by the International Telecommunication Union (ITU) in the 3G standards (IMT-2000).
Some major companies have even announced the development of 4G networks, although there are no specific recommendations or definitions for 4G yet. It can be understood as a mobile network that converges 3G and Wireless-LAN, providing customers with very high bandwidth and global mobility based on IP technology.
Figure 2 highlights some milestones and fundamental characteristics in the development process of mobile-related technologies and the trend of future convergence in mobile networks.
Trends in Wireless Information Technology
The trend toward 3G is not a complete overhaul of technology but rather an effort to gradually upgrade existing networks to ensure compatibility while avoiding over-investment by operators.
In Vietnam, the process of moving toward the 3G mobile network generation is underway, involving theoretical research, the establishment of standards for network interfaces, proposals for experimental implementations of 3G in Vietnam, and narrow-range 3G trials on Mobifone and Vinaphone networks.
Current mobile network operators and some new mobile service providers (Viettel, SPT, ETC, etc.) are upgrading their networks or equipping them anew, following the roadmap from 2G to 2.5G and then to 3G, without any operator making direct investments in 3G at this time.
3. Current Status and Proposed Research Approaches in Vietnam
Current Research Evaluation
Research in Vietnam regarding mobile networks in the past has primarily focused on theoretical issues and technology implementation rather than product development. This limitation, alongside the general constraints of Vietnam in telecommunications research, is exacerbated by the concentration of the most complex technologies in mobile network engineering, which are beyond our reach.
In recent years, some entities in Vietnam have invested in research directed toward product development in mobile networks, and for the first time, these research products have participated or have the potential to participate in the network structure and service provision for 2G and 2.5G mobile networks in Vietnam. Notable examples include CDIT with products such as: Short Message Service Center (SMSC), Missed Call Notification Service, Roaming Subscriber Notification System (2G), Multimedia Messaging Service Center (MMSC), WAP 2.0 Service Provision System, and Video Streaming Service System (2.5G).
Overall, these research products focus primarily on the service provision layer, while research on core networks, access networks, and terminal ends remains scant.
Here, the author proposes a research approach to mobile networks in the near future, aiming to gradually master this technology entirely in the not-too-distant future.
Proposal
Implementing a complete 3G mobile network is currently not feasible for Vietnam. While popular technologies are encroaching on specialized technologies, a full replacement has not yet occurred, especially for technologies used at the terminal and radio access layers. Wireless LAN is a trend, but many limitations are still being addressed in the future.
The most appropriate approach in the Vietnamese context will be to develop network components starting from the service layer, moving through the core layer, and part of the access network. The service layer has nearly been mastered by Vietnamese researchers, while the core layer and part of the access layer are the focus of this paper. This mastery is to be achieved through the model of a virtual mobile network.
In fact, the concept of a virtual mobile network has not been mentioned for the first time; several proposals have been introduced online, but these proposals only cover narrow scopes (for example, only for SMS services). The virtual mobile network referred to here has a broader meaning, resembling an actual mobile network but with a few limited features that will be clarified in the solutions below.
4. Virtual Mobile Network
A virtual mobile network is understood as a mobile network with relatively complete functionality compared to a real mobile network, but the components of the radio access layer are replaced by various methods. There are two solutions for the virtual mobile network corresponding to the implementation of the radio access layer:
– Solution 1: The mobile terminal uses pure IP terminals (IP terminal)
– Solution 2: Reuse the existing radio infrastructure of service providers
Solutions for the virtual mobile network here apply to both GSM and CDMA networks and undergo similar processes to transition to 3G as with a real mobile network. In CDMA and GSM mobile networks, the differences are focused on radio access techniques, while core network entities are similar; thus, this paper will focus on solving core network research by analyzing the transition to 3G from the GSM network, with proposals and approaches that can be similarly applied.
The radio access part of the mobile network is currently temporarily approached through theoretical research and will have more specific proposals during the implementation of the virtual mobile network.
Structure of Virtual Mobile Network According to Solution 1
Structure of Virtual Mobile Network According to Solution 1
In this solution, the terminals are IP terminals (IP terminal) and take the form of VoIP phones on the Internet. The radio parts: BTS, BSC are replaced by IP-based access techniques through VoIP signaling protocols; the interfaces between these elements over IP are not as clear-cut as defined in mobile networks. However, these IP terminals can be located anywhere on the Internet, and the core and access network components ensure full functionalities for searching/calling, locating, and registering just like real mobile devices. In this model, there is currently no possibility for roaming among subscribers of different networks.
With this solution, compatibility only needs to be at the interface with current networks, while the IP side entirely depends on subjective design, such as subscriber location, searching, handover, etc.
Structure of Virtual Mobile Network According to Solution 2
This solution leases the radio infrastructure of existing network operators for the access layer, with all signaling routed to the virtual network. This means that actual mobile terminals are aggregated within a number range and are managed by the virtual mobile network. The virtual mobile network here will consist of components from the core and service layers but will not include the radio access layer.
Solution 2
The virtual network elements according to this solution are also based on IP, but the interfaces are defined clearly as in real mobile networks. With this solution, the virtual network elements are more similar to actual networks than in Solution 1, but implementation and practical deployment are more challenging than in Solution 1 due to the lack of a business model for leasing radio infrastructure in Vietnam. This issue could be mitigated by investing in a few radio stations during the testing phase. The compatibility of the virtual network elements requires a higher standard since they actually control mobile terminals like current mobile networks.
Virtual Mobile Network to 3G
The network elements of a 3G network will be similar to a 2.5G network while ultimately aiming for an All-IP version, where channel switching elements like MSC, interconnect gateways in the core layer, and BSC in the access layer will be replaced with elements that have similar functionalities: SGSN, GGSN, MG (media-gateway), and Softswitch.
Research on virtual mobile networks has both practical and theoretical significance in that it is feasible for implementation and creates a testing environment when we lack control over access technology but still aims for a mobile network with all necessary features, aligning with global research trends.
The most fundamental elements of the virtual mobile system with the most basic services such as: HLR, VLR, can be developed immediately with limited initial capacity, and the signaling protocols surrounding these elements, initially MAP and IS41, can be supplemented with relative ease. The crux of these two elements is reliability and real-time data processing, with localized research on each of these aspects having been conducted recently in several telecommunications products: Calling card systems, SMSC systems, and real-time billing systems.
The MSC, the call-switching part of the virtual mobile network, can be implemented based on using IP-based call servers such as SIP servers, Softswitches, etc. The trend of using Softswitches for call processing in mobile networks is a global trend that has been applied worldwide. SIP servers or Softswitches have also been in the research phase or recently completed in Vietnam.
5. Conclusion
Many network elements of 3G are also the same as those of the virtual mobile network mentioned above. Therefore, researching and developing the virtual mobile network is an appropriate and feasible approach under current conditions. After this period, we will have a higher degree of autonomy concerning mobile network generations 3G, 4G, and especially train a specialized research team in mobile technology, bridging the gap between Vietnam and other countries regarding mobile technology, which Vietnam has lagged significantly behind in recent decades.
Nguyễn Trung Kiên (Excerpt from VNPT)
