Viewpoint: exploring the application and development of Softswitch Technology

The Softswitch technology is quite commonly used. So I studied the application and development of the Softswitch technology. I will share it with you here, hoping it will be useful to you. Compared with IMS, Softswitch is more suitable for implementing traditional narrowband voice services. Therefore, the subsequent development of softswitch should be aimed at inheriting and developing traditional voice services on the group switching network. On this basis, Softswitch can be applied to Public Switched Telephone Network (PSTN) Long-distance network and intelligent network transformation, at the same time, the general network architecture of softswitch will change with the development of business and the demand for improving service quality.

In the field of communication, the concept of the Next Generation Network (NGN) is gradually known as the rise of Softswitch technology. In the past, NGN was almost synonymous with the softswitch network. However, for various reasons, the softswitch network has not been rapidly popularized as people imagined, and the emergence of the new network technology, IP Multimedia Subsystem (IMS, make Softswitch no longer the whole of NGN. In the future, it is worth exploring how Softswitch locates and develops.

Positioning of Softswitch

As a matter of fact, the telecom industry has not yet formed a unified understanding of what kind of softswitch should follow. Compared with traditional circuit switching networks, Softswitch networks are more advanced in terms of IP-based networking, control and bearer layer separation. Practice has also proved that, with the same capacity, the softswitch network has lower O & M costs than the traditional network based on circuit switching, and the soft switch has a larger capacity than the traditional switch. The Softswitch technology has not been able to achieve large-scale development. The main reason is that people have doubts about the security and quality of service (QoS) assurance capabilities of grouping networks for voice services. With the popularization of various IP Voice (VoIP) applications, people's concerns about providing voice services based on group networks have been largely eliminated or gradually diluted, however, the rise of IMS technology makes the development prospects of softswitch confusing. So, can the Softswitch technology continue to develop in the IMS age and how should it develop? To clarify this problem, we must first conduct a comprehensive comparison and analysis on IMS and SoftSwitch.

From the perspective of the basic technology, SoftSwitch and IMS have a great similarity: both are based on IP-based networking, and both implement control and bearer separation; most of the protocol stacks are similar or identical; many gateway devices and terminal devices can even be common. The biggest difference between IMS and SoftSwitch lies in the following aspects:

◆ On the basis of softswitch control and bearer separation, IMS further isolates the call control layer and service control layer.

◆ IMS originated from mobile communication network applications. Therefore, it fully considers the support for mobility and adds an external database-Belonging user server (HSS) for user authentication and preservation of user service triggering rules.

◆ IMS uses Session Initiation Protocol (SIP) as call control and service control signaling. in softswitch, SIP is only one of multiple call control protocols, more use of Media Gateway Control Protocol (MGCP) and H.248 protocol.

In general, the difference between IMS and Softswitch is mainly in the network architecture. The network architecture of IMS is more advanced than that of softswitch, because IMS performs better network disaggregation than SoftSwitch. Continuous disaggregation at all levels of the network is the general trend of the development of the telecom network, from the traditional circuit switching network to the intelligent network, to the softswitch and IMS, all in line with this trend. Network disaggregation breaks the vertical business model and facilitates business development. In addition, the disaggregation of different types of networks creates conditions for network re-aggregation at different layers. This re-aggregation is the process of network convergence. It can be seen that the network architecture of IMS is more conducive to the convergence of fixed and mobile networks than that of SoftSwitch. However, it cannot be said that after the emergence of IMS, the softswitch can completely disappear. In terms of providing basic voice services, Softswitch still has advantages over IMS.

All IMS uses the SIP protocol, which has shown its advantages in multimedia applications. Although SIP can also achieve the most basic VoIP, it can be said that SIP is born for multimedia services. In contrast, the MGCP and H.248 protocols used in softswitch focus more on voice services and fully consider retaining some features of traditional telephone services when formulating these protocols. This makes it easier for MGCP and H.248 protocols to inherit traditional telephone services than SIP. Although SIP can enhance the telephone service capabilities through many extensions (for example, trigger and secondary dialing), first, this is not the original intention of developing SIP. Second, even if it is expanded, some services still cannot be implemented (such as hotline services ).

On the other hand, the traditional telephone business is very mature and there will be no more business expansion, which makes the IMS architecture unable to take advantage of the flexible service deployment. The existing IMS method for implementing traditional telephone services is to use dedicated traditional telephone service application servers. All calls must be forwarded through the call control layer, we also need to consider using SIP to adapt to various terminals and protocols, which will undoubtedly reduce the efficiency of business implementation. This does not take into account the cost advantage of softswitch over IMS. Another factor that cannot be ignored is that traditional Intelligent Network Resources are easily reused in the softswitch architecture, and it is difficult to implement it in the IMS architecture.

It can be seen that, in an environment where only traditional telephone services are required, Softswitch has some advantages over IMS. The future development of softswitch should mainly focus on traditional telephone services, that is, narrowband voice services. As long as the traditional voice business form does not disappear, the Softswitch technology has a reason for its existence.

Development and Application of Softswitch

Although the softswitch network architecture does not have a complete set of international standards, a relatively unified network architecture is gradually formed during the development of the Softswitch technology, this network architecture mainly includes soft switches, media gateways, signaling gateways, Media Servers, application servers, and other devices. The softswitch architecture is very mature and stable, but with the business development and the demand for service quality growth, people have put forward new requirements for this architecture. The introduction of business access control devices is one of the changes.

In the original softswitch architecture, the establishment of media streams between users is uncontrollable, and IP addresses are exposed between the communication parties and between users and core switching devices, this may cause a series of problems, such as illegal attacks, bandwidth theft, and illegal connection establishment. The Service Access Control Device (SAC) is mainly deployed between the softswitch core network and the access network, it mainly includes signaling stream proxy, media stream proxy, address translation, resource control, media stream monitoring and management, and other functions. After the SAC device is added, the IP address of the core Softswitch device is invisible to the end user, and the communication parties cannot see the IP address of the other Party. This effectively prevents illegal attacks and illegal connection establishment. In addition, all media streams must be forwarded through SAC, which can effectively control users' usage of bandwidth resources and monitor media streams.

The addition of SAC devices may lead to another change in the softswitch architecture. This means that the user authentication function is separated from the softswitch device to form an independent authentication, authentication, and billing (AAA) server. This is because the SAC device also needs to access the AAA Server and check the user's authentication information, which is difficult to meet in the softswitch device. The AAA Server stores the billing, authentication, and authentication information at the user access layer, distributes and manages keys, and stores information related to users with Softswitch, such as location information or IP address information. As a matter of fact, there is another point of contention, that is, whether the softswitch needs to support external user contract attribute centralized databases. This requirement comes from the Intelligent Transformation of fixed network. The centralized database of external user contract attributes is mainly used to trigger Intelligent Service. If a user signs a contract with an external Attribute Database and works with the AAA Server, the function positioning of this centralized database in the network is very similar to that in IMS, the difference is that the two networks adopt different Authentication and authentication algorithms, and The HSS stores the initial filtering rules suitable for SIP, the user-Signed attribute database stores the intelligent network trigger rules saved in the format of code number prefixes.

The introduction of SAC, AAA Server, external user contract attribute database, and other functional entities will undoubtedly improve the security and business flexibility of the softswitch network, which may be the development direction of the softswitch network architecture. However, as the development focus of telecom network equipment manufacturers has been migrated to the IMS network, it has a negative impact on the continued development of the softswitch network architecture. When Softswitch was just popular, people wanted it to support all foreseeable businesses, including voice services, video multimedia services, and data services. Over time and the emergence of IMS, people should treat the services supported by Softswitch more rationally.

The business of softswitch should first be positioned to inherit the traditional telephone business. These services include the traditional long-distance voice service, the traditional C5 local voice service, the supplementary services of various public switching telephone networks (PSTN), and the fax service and the Integrated Service Digital Network (ISDN) access, Modem access, and other basic narrowband data services. The Softswitch service can also be enhanced and expanded based on the traditional telephone service. For example, for pre-call-to-call services, more complex functions can be implemented on the softswitch. You only need to use the media server or the media resource processing board on the softswitch, it is easy to achieve audio mixing, so the Conference and telephone business is generally the standard configuration in the softswitch business.

Finally, some IP multimedia services can be introduced in the softswitch network, such as SIP-based point-to-point videophone. Although SIP-based services are implemented in IMS more often, it is very easy to provide some basic SIP services and the increased cost is not high for Softswitch that also supports SIP. With the development of softswitch over the years, many Softswitch applications have emerged on the Internet. In these applications, there are two types of applications that are very compatible with Softswitch and provide the positioning of traditional voice services based on group switching. These two types of applications are: Application of softswitch in the speech long-distance network and Application of softswitch in the intelligent transformation of the fixed network. In fact, there is another type of application, that is, the circuit domain (CS) application in the 3GPP system network structure. Because the CS control entity in the network structure of systems such as 3GPPR4 and R5-the mobile exchange center Server (MSCServer) adopts the mobile Softswitch technology.

The Application of softswitch in the speech long-distance network best reflects the technical advantages of SoftSwitch. Firstly, the application of softswitch in speech long-distance network has the following advantages over traditional circuit switching: (1) a larger system capacity makes the network structure simpler. (2) higher resource allocation efficiency. The call processing capability of a Softswitch device is greater than that of a traditional switch. Therefore, when deploying a speech long-distance network, you can set fewer switching nodes. The advantage of reducing switching nodes is obvious. The most direct advantage is that the network structure becomes simple and the routing configuration and maintenance become easier. Indirect Advantages include reducing the occupied area of the data center and the difficulty of configuring transmission resources. As the softswitch network is based on group switching and achieves control and load separation, resource redeployment is simpler and more efficient than circuit switching. When adjusting the bearer resources, the network structure and signaling routing do not need to be changed accordingly. Secondly, the application of softswitch in voice changtu network avoids the problems encountered by this technology in other scenarios. First, the long-distance network Softswitch does not carry end users, avoiding security attacks and user resource control issues. Second, long-distance networks do not involve man or access networks, and the bandwidth of backbone IP transmission networks is more easily guaranteed, therefore, QoS is not guaranteed. Based on the above reasons, Softswitch has been widely used in the transformation and expansion of the PSTN speech long-distance network.

The use of soft Switches during the smart transformation of the PSTN network is also a direction for Softswitch applications. In this application, a soft switch is mainly used to replace a PSTN board switch. Replacing the traditional exchange board switch with Softswitch can bring lower maintenance costs to the network. In addition, due to the advantages of large softswitch network capacity and convenient expansion, the future expansion of the domestic network requires sufficient resources, you only need to place more access gateways (AG) or relay gateways (TG) at the terminal layer, and add processing boards to Softswitch devices, which has no impact on the network architecture.

On the other hand, Softswitch's support for intelligent networks also makes it sufficient for this role. The support for the Intelligent Network Application Protocol (INAP) has become a required capability of softswitch devices, whether using an IP to carry INAP (INAPoverIP), or using a signaling gateway (SG) in the way of signaling transfer, Softswitch can easily achieve interconnection with traditional intelligent network devices, while Softswitch itself can also have the service exchange point (SSP) function. Of course, as mentioned in the previous section on the softswitch network architecture, when applying Softswitch to intelligent network transformation, it may need to support external centralized databases with user contract properties, because the use of external contracted attribute databases is the mainstream way to trigger smart network services.

Conclusion

In the future development, Softswitch should be mainly positioned to inherit the traditional voice services, while some basic IP multimedia services can be developed as appropriate. Based on this positioning, Softswitch can still be applied in many aspects such as PSTN long-distance network and intelligent network transformation. At the same time, based on the needs of business development and service quality improvement, the softswitch network architecture will continue to develop. In short, as long as people look at Softswitch rationally and use practicality as the principle, even today, where IMS is already widely used, Softswitch still has enough space for development.