Review of soft switches and next-generation networks

Over the past few years, with the rapid popularization and maturity of domestic IP phone technology and successful market operation practices, people have been paying more attention to and enthusiastic about China Telecom's next-generation network. Few people raise objections to IP technology as the basic backbone service platform of the next-generation Telecom Network of telecom operators. However, when people talk about the next generation network, they often concentrate on the soft switch technology. It seems that the soft switch technology is all discussed in the next generation network technology. However, the soft switch technology itself can only provide very limited "network" Concepts and functions, let alone provide the overall network architecture of the Next Generation Network. This makes the thinking and Discussion on the Next Generation Network Limited to the local structure and scope of the soft switch technology. At the same time, this also makes the practice and goal of the Next Generation Network appear blind and confused for technology. Logical conflicts in some basic concepts have caused many people to be still confused about the relationship between the soft switch technology, IP phone technology and the Next Generation Network; some people also regard the IP telephone technology and the soft switch technology as isolated and opposite. Therefore, the author believes that it is necessary to review the concepts of soft switch technology and IP phone technology and their roles in the Next Generation Network.

Concept of soft switches in the Next Generation Network
Although Softswitch is currently a hot topic in the Next Generation Network, the concept of Softswitch is still somewhat plausible. So what is the concept of a device? System Concept? System Concept? Or technical architecture? What is the relationship between a vswitch and an IP address and the Next Generation Network?
According to the definition of isc in the international Softswitch Forum, Softswitch is a device and system that uses program-controlled software to provide call control functions based on the sub-network. According to this definition, we can clearly see that Softswitch is a typical technical practice method designed for the speech purpose of the sub-networking. It focuses more on the devices and systems of call control functions. It cannot constitute a special overall networking technical mechanism and network architecture. But why is such a simple concept confusing? One of the reasons for this problem may be that many people in China translate Softswitch into "Softswitch ". The term "Softswitch" is not clear enough to give it a logical illusion. From a literal perspective, it is difficult to distinguish whether it is a device system concept or a system concept. China's telecom industry has always translated switch as switch, while switching as "switch ". So why are we making an exception here? Even more troublesome, it is difficult to identify the differences between "softswitching" and "softswitch" in Chinese. Therefore, the author believes that for the seriousness of academic research, we should translate Softswitch into soft switch more accurately. In the formal written language, "Softswitch" should be avoided as a short name for soft switches.
There have been a lot of discussions about vswitches, and people have basically agreed on the technical characteristics of vswitches. Vswitches use MGCP/H.248 media control protocol technology to separate call control from media bearer. Therefore, some foreign scholars refer to soft switches as call proxy CA or media gateway controller MGC. The concept of a soft switch not only makes the voice service function of the Next Generation Network completely transparent and compatible with the switch function of the traditional PSTN network, but also fundamentally ensures that the IP phone technology can completely replace the PSTN network. Vswitches are basically designed to implement the functionality of the PSTN vswitch on the IP network. In traditional PSTN networks, switches are vertical, closed, and private system structures. Soft switches are standard and open system structures separated by call control and media. In addition, the soft switch and the PSTN "hard" switch have some common features. For example, they are system devices that are relatively centrally controlled and managed, and all user-oriented data and call status information are stored in the system. This makes the soft switch very important to telecom operators, because only in this way can it meet telecom operation requirements, implement effective call service control and O & M management for IP point network endpoint access and PSTN interconnection.
It is particularly worth mentioning that, in order to support multimedia smart endpoint access, soft switches may also support the H.323 protocol and the SIP protocol to control and manage H.323 and SIP endpoints. In this way, the soft switch itself cannot completely implement call control and media bearer separation for all the endpoints under its control and management. In addition, the soft switch must also support H.323 and SIP protocols in the "inter-office" to connect to the H.323 network, the SIP network, and other soft switches. However, MGCP/H.248 media control protocol technology is always the basic feature of vswitches. If a call control device system does not support MGCP or H.248 media control protocols, it cannot be called a soft switch. Call control devices that are characterized by H.323 protocol are usually referred to as the Gatekeeper keeper), and call control devices that are characterized by SIP protocol are called the proxy server ProxyServer ).
Therefore, judging from the telephone services provided by soft switches and their technical features, soft switches are an important part of the next generation network system, but do not provide any fundamental innovation in network architecture.
A soft switch is an implementation method of the Next Generation Network IP phone technology.
Some may say that the IP phone technology is H.323, and the soft switch technology is the next generation network technology. They are not the same thing.
So what are the fundamental challenges of the next generation network?
The goal of the next-generation network is to gradually integrate voice, data, and video services and integrate multiple services on the IP network. Voice is the most popular, basic, and important service for carriers. Its market covers the widest range, and its business income has a greater impact than other businesses. After nearly a hundred years of development, the traditional PSTN technology and TDM network provide mature business models and quality standards for carrier speech services. Data IP networks were originally designed for data services, while voice is a time-sensitive service, the IP telephone technology that provides large-scale voice services in data IP networks is the primary challenge for any operator in the transition to the next generation network.
The IP telephone technology demonstrates that the traditional PSTN service can evolve into a group IP network. It is useless for any next-generation network architecture to better adapt to the IP phone service. At the same time, the call control architecture of IP phones is also the basis of any multimedia business. Therefore, the research and practice of the IP telephone architecture system naturally become the core and fundamental research in the next generation network architecture system.

Any tests on the next generation network will become meaningless if there is no IP phone, and the small-scale or laboratory tests on the next generation network have very limited significance. Because the small network test mode is not necessarily suitable for the big network of IP Telecom, the test results of the small network test in the laboratory do not necessarily fully explain the problems of the big network of IP Telecom. Therefore, only the test results of IP Phone applications in large production networks can fundamentally Promote the Development of the Next Generation Network.
There is no doubt that the IP phone technology is always closely related to the technology and development of the next generation network. The IP phone technology that provides the Call Control Function in the Next Generation Network will play an extremely important role.
In the discussion of the next-generation network architecture system, there have always been two very different strategies. One is to emphasize smart endpoints and edges and simple network facilities. Because the driving force of end-to-end multimedia converged services comes from endpoints and edges, the flourishing innovation and prosperity of next-generation network services are dependent on this. The success of the Internet also proves the importance of this idea to multimedia services. Another idea is to propose simple endpoints and edges, and smart network facilities. This is because only uniform endpoints and edge devices are conducive to the management and control of large-scale business. The speech service provided by the PSTN network has verified the reliability of this business practice. ITU-H.323 protocol and IETF-SIP Protocol are the technical system that reflects the first strategic thinking to some extent. The soft switch characterized by IETF/ITU-MGCP/H.248 protocol is the implementation means of the second strategy. As mentioned above, in order to achieve the telecom operation goal of end-to-end IP phones to a greater extent, people have designed a soft switch technology mechanism for telecom operators. The IP telephone voice service is the most important and fundamental service function in the soft switch. It is worth mentioning that the soft switch itself does not directly provide IP data services. Vswitches support video and multimedia endpoint services through call control mode and Function Extension. Vswitches still need to collaborate with other key technologies and devices to provide more comprehensive video and multimedia services.
Obviously, the true meaning of the next generation network requires both the innovation and prosperity of smart endpoint businesses and the scale-up management of its systems. The difficulties discussed in the next-generation network architecture system are how to comprehensively balance multiple technologies. I think that the current technology maturity and development, based on the ITU-H.323 protocol, IETF-SIP protocol and MGCP/H.248 protocol of soft switches are IP and next generation network implementation means. These three technologies have their own differences and expertise and need to complement each other. The best strategy is to adopt a network architecture system and implementation means that integrate the three technologies. The access and aggregation nodes of the most popular and basic IP phone service in the next generation network rely mainly on the soft switch technology characterized by MGCP/H248 protocol; the integration of multimedia and end-to-end services in the next generation network may depend mainly on the ITU-H.323 protocol and IETF-SIP protocol technology. The next generation network architecture is determined by the H.323 and SIP network systems. As a matter of fact, as many scholars have already pointed out, soft switches can also be seen as the results of smart gateway decomposition under the H.323 and SIP systems. In this way, the network architecture of the three technologies may be more clear.
Large-scale implementation of the IP telephone network with the architecture characteristics of the Next Generation Network System and its scalability, reliability and operability are an important part of the evolution towards the next generation network. Not only does the next-generation network require business practices that integrate the three technologies, including soft switch technology, H.323 technology, and SIP technology, many other problems related to the Operation Management of the Next Generation Network also need to be verified through the operation implementation of the IP telephone network. Therefore, domestic telecom operators should first build an IP telephone network with a distributed structure according to business and market needs, and actively carry out IP telephone services to verify the operability and manageability of the Next Generation Network. Practice has proved that the efforts and contributions made by domestic telecom operators in exploring and operating various IP phone technologies over the past few years are the most significant milestones in the evolution towards the next generation network goal.
The concept of "Softswitch is the core of the Next Generation Network" needs to be elaborated and discussed.
Another popular term in the discussion on next-generation networks is "Softswitch is the core of next-generation networks ". I think it is worth further consideration. To sum up, the soft switch technology is one of the most important and critical speech service aggregation node technologies in the Next Generation Network. There is no doubt that we should pay special attention and attention to it. However, the technical features of vswitches do not provide the only and direct core network technology.
In addition, in terms of concept, "Softswitch is the core of the Next Generation Network" will bring about confusion in some basic propositions and logical confusions. The core technologies of the Next Generation Network should fundamentally include various network technology systems that support voice, data, and video services. The soft switch itself is only a local device system and does not have the characteristics of a comprehensive network architecture. Although the soft switch supports the access of smart endpoints, video endpoints, and multimedia endpoints, it does not mean that all voice, data, and video services must be centrally implemented on the softswitch machine. In theory, even if there is a possibility of such a device, there is absolutely no need to do so. This system does not have any advantages but has a series of overall architecture defects. The soft switch technology does not directly provide IP data services. The soft switch can support the video endpoint call service, but generally does not regard it as the core device that focuses on the video conferencing service control. The soft switch technology is mainly designed for centralized call control functions. The next generation network will also rely on a series of other existing IP technologies and other application technologies to support voice, data, video, and other services.
In terms of policy, the phrase "Softswitch is the core of next-generation networks" often makes it easy to think that the soft switch technology is equivalent to the next-generation network technology, in this way, the focus of research and practice is only on the scope of a single soft switch technology and its surrounding areas, and the future investment is only on the equipment and systems related to the soft switch.
Technically, the term "Softswitch is the core of the Next Generation Network" tends to make everyone expect the next generation network to be on soft switch devices, next Generation Networks are constructed with soft switches as the core, so that the discussion and practices on next-generation networks remain at the conceptual level of basic, local, small-scale, and individual device system technologies for a long time, as a result, the local structure of the soft switch is the overall network architecture of the Next Generation Network.
In practice, it is easy to ignore the practice and discussion of other next-generation network technologies by testing and exploring the Networking Mode of soft switches as the core, this limits that the next generation network can only be a "no-network" mode in which soft switches are connected to each other ". Obviously, the "no-network" next-generation network architecture can only support one or several soft switches, which is not suitable for telecom operators to operate on a large scale. This phenomenon is called the "island phenomenon" of the soft switch technology practice ".
In terms of network structure, "Softswitch is the core of next-generation networks" cannot answer questions such as the need for next-generation networks without core network technologies. If not, how to avoid the "island" Phenomenon of soft switches, how to solve coordination and interconnection between soft switches, and how to carry out full-network services of the next-generation network, what is the core network technology of the Next Generation Network.
As a next-generation network covering the whole country, we should first consider the operational nature of the network. The operational nature includes the scalability and manageability of the network. That is to say, the next-generation network architecture and networking are very important. We believe that the architecture of the next-generation network system should comprehensively consider the network structure of the entire voice service network from both the horizontal and vertical aspects.
The system of the Next Generation Network should be composed of the core network and the local switches located at the next generation network access and edge locations. The core network of the Next Generation Network is a backbone communication network covering the service scope of operators. The core network of the Next Generation Network implements interconnection and communication between soft switches, multiple operators, and different networks to implement traffic control and scheduling across the network; shared centralized database retrieval services across the network, shared business creation environment, and network management across the network.
The core network of the Next Generation Network provides networking methods, routing policies, traffic control, network-wide service creation and management, and network-wide maintenance and management. To achieve unlimited scalability and telecom-level manageability of the Next Generation Network, the core network of the Next Generation Network should adopt a layered call signaling system and a flat voice stream structure. The main purpose of adopting this architecture is smooth speech stream transmission, which avoids the consumption of circuit resources in the traditional circuit switching network by the speech channel level-by-level convergence mode, and gives full play to the superiority of the sub-network; the hierarchical call signaling system is mainly used to meet the unlimited scalability of network operations. It avoids the scalability limitations caused by the point-to-point direct connection call establishment mode and simplifies the system configuration, unified resource servers or databases.
Obviously, in the next generation of IP telephone implementation of the three main technologies, ITU-H.323 protocol network technology, IETF-SIP protocol network technology will play a major role in the core network. Therefore, in the true sense, the core network of the next generation network does not necessarily need to use a soft switch, because the control function of the bearer media is mainly in the access of the endpoint and the edge of the PSTN switching network. The core network of the Next Generation Network is located in the center of the services and applications of the IP network, and its function structure must be more distributed and independent. Its system equipment must be more open and universal, and its operation and management must be more flexible and mobile. Many telecom operators in the world have used H.323's Internet guard or SIP proxy servers and other network application servers for networking, networking, and network-wide business and O & M. Recently, the emergence of some new core network technologies such as ITU-T's Q. GTD1, Q. GTD2), more to illustrate this. Therefore, the term "Softswitch is the core of the Next Generation Network" is not accurate.
This does not mean denying the importance and critical position of the soft switch technology in the Next Generation Network. In fact, the true soft switch should be a general-purpose classless) soft switch, which undertakes the responsibility of regional or local system platforms in the Next Generation Network, it is capable of simultaneously controlling network access traffic and controlling edge interconnected traffic of the PSTN network. Regional general-purpose soft switches and National Core backbone networks can build a complete next-generation network communication system.
Practice policies on vswitches in the Next Generation Network
At present, there are two completely different attitudes towards the next development direction of China Telecom's voice network practices. One is to focus on gradually replacing the network elements of the PSTN network with the network elements of the Next Generation Network. The idea is to use Softswitch devices to replace the original PSTN devices in a category-by-category manner. This solution emphasizes future-oriented and technology-oriented research, but faces great challenges in practice. If the PSTN device is replaced by class-by-class as the next-generation network evolution strategy and primary goal, it is easy to make the next-generation network practices lose its practical significance and market value. Another idea is to use new technologies as new tools and means to drive new business models and create new market mechanisms. This concept emphasizes the effectiveness of resources and enables technologies to serve telecom operators' business needs and motivations. It emphasizes using new technical means to flexibly implement effective service functions of the PSTN, so that telecom operators can provide Differentiated Services. Obviously, the latter is more practical and vital, and more protective for operators' investment.
The fundamental business-oriented approach of the Next Generation Network is that the technical mechanisms and implementation methods must be market-oriented. The maximum drive of the commercial next-generation network business will come from the network edge and endpoint. The business convergence of the Next Generation Network must also begin with the edge and endpoint of the network. The soft switch technology is only constantly integrated with the endpoint and edge IP access technology, the most accurate requirements on new technologies can be reflected only when operators fully consider the various challenges they may encounter during operation and make them more effective in solving such problems as QoS, security, firewall, and IP address, in order to better display the characteristics of the Next Generation Network. This "out-of-the-box" power will be an important factor in determining the success of the next generation network.