With the rapid development of communication network technology, people's requirements for broadband and business are also growing rapidly. In order to provide users with more flexible and diverse existing businesses and new businesses, providing more personalized services to users, and proposing the concept of next-generation networks. At present, major telecom operators have begun to experiment with next-generation communication networks. As one of the focuses of next-generation communication network solutions, Softswitch has become a hot topic in the industry in recent years. China's network and exchange standards research group has completed the overall technical requirements framework for the softswitch system, and plan 863 has also set up research projects for the softswitch system in multimedia and mobile communication systems.
1. Proposal and definition of Softswitch
The concept of softswitch originated first in the United States. At that time, in the enterprise network environment, users used Ethernet-based phones to implement the ip pbx function through a Call Manager and Call Server based on PC servers ). For such a set of equipment, the system does not need to separately lay the network, but can achieve unified management and maintenance only through sharing with the LAN, the overall cost is much lower than the traditional PBX. Because the enterprise network environment does not have high requirements on device reliability, billing, and management, it is mainly used to meet communication requirements and has a low device threshold. Many equipment vendors can provide such solutions, therefore, the ip pbx application has achieved great success. Inspired by the success of ip pbx, in order to improve the comprehensive operation efficiency of the network, the network development tends to be more reasonable and open, and better serve users. The industry has put forward the idea that the traditional switching device components are divided into call control and Media Processing, and standard protocols MGCP and H248 are used between the two, as a result, SoftSwitch technology came into being.
The concept of SoftSwitch was quickly recognized and valued by the industry. The establishment of ISCInternational SoftSwitch Consortium further accelerates the pace of development of SoftSwitch technology, the standards and protocols related to Softswitch have received the attention of IETF, ITU-T and other international standardization organizations.
According to the definition of isc in the international Softswitch Forum, Softswitch is a device and system that uses program-controlled software to provide the call control function and separate media processing. Therefore, the basic meaning of Softswitch is to separate the call control function from the media gateway transport layer, and implement the basic call control function through software, thus realizing the separation of call transmission and call control, establish a separate plane for control, switching, and software programmable functions. Softswitch provides Connection Control, translation and routing, Gateway management, call control, bandwidth management, signaling, security, and call details. At the same time, Softswitch also encapsulates network resources and network capabilities, and connects to the application layer through standard open business interfaces, allowing you to quickly provide new services on the network.
2. Network Structure Based on Softswitch Technology
As one of the core devices of the next-generation network, Softswitch must be considered for intercommunication with other networks when establishing a network structure based on Softswitch technology. In the next generation network, there should be a unified network system structure. The network structure 1 Based on the Softswitch technology is shown in.
As shown in the figure, Softswitch is located at the network control layer, which effectively achieves the separation of Call Control and media processing functions based on the sub-networking using program-controlled software.
Interfaces between the softswitch and the application/service layer provide interfaces for accessing various databases, third-party application platforms, and functional servers to support value-added services, management services, and third-party applications. Among them: interfaces between SoftSwitch and application servers can adopt SIP and APIs, such as Parlay, to provide support for third-party applications and value-added services; interfaces between the softswitch and the policy server dynamically intervene in the work of network devices. COPS protocols can be used. interfaces between the softswitch and the gateway center implement network management and adopt SNMP; the interface between SoftSwitch and intelligent network SCP supports existing intelligent network services and uses the INAP protocol.
Through the interaction between the core branch network and the gateway at the media layer, the gateway receives call-related information during processing and instructs the gateway to complete the call. Its main task is to establish a relationship between each point. These relationships can be simple calls or complicated handling. Softswitch is mainly used to process real-time services, such as voice services, video services, and multimedia services.
Interfaces between Softswitch are used to implement interaction between different switches. You can use the SIP-T, H.323, or BICC protocols.
3. Design Principles and objectives of Softswitch Technology
Softswitch is a distributed software system that provides seamless interoperability between networks based on different technologies, protocols, and devices, the basic design principle is to create a distributed software system with good scalability, interface standards, and business openness. It is independent of the specific underlying hardware/operating system, it can well process the synchronization communication protocols required by various businesses, and push the architecture to the Moore's curve track in an ideal position. And it should be able to support the following basic requirements:
1) are calls independent of protocols and devices? Development of call processing and/Synchronous meeting management applications for smoke equipment.
2) the softswitch network can safely execute multiple third-party applications without any harmful effects caused by malicious or erroneous applications.
3) third-party hardware vendors can increase support for new devices and protocols.
4) business and application providers can add policies that support the entire system without compromising their performance and security.
5) ability to implement synchronous communication control to support various post-business office systems including billing, network management and other operation support systems.
6) supports running time bundling or dynamic topology of synchronization communication control networks that help improve the structure.
7) small to large network scalability and support for complete fault recovery.
The realization goal of Softswitch is to implement Protocol Conversion for various media streams through computer software programming with the cooperation of media devices and media gateways, and based on the group network IP address/ATM) to provide devices with the same functions as circuit switches and facilitate value-added services and flexible scaling.
The Reference Model 2 of the softswitch system.
4 main protocols used by Softswitch
The softswitch system involves many protocols, including H.248, SCTP, ISUP, TUP, INAP, H.323, RADIUS, SNMP, SIP, M3UA, MGCP, BICC, PRI, and BRI. International organizations, such as IETF, ITU-T, and SoftSwitch Org, have been actively leading the research on SoftSwitch and protocols. Many key protocols have been developed or tend to be completed. These protocols will regulate the entire research and development of softswitch, and enable product intercommunication between products from the phase of using proprietary protocols of various manufacturers to the phase of using common standard protocols in the industry, the original intention of realizing Softswitch is to provide a standard and open system structure, and various network components can develop independently. In terms of research progress of softswitch, China is at the level of global synchronization. In the second half of 1999, the "Network and exchange standards research group" of the Ministry of Information Industry started the research on the softswitch project, and has completed the "General Technical Requirements for Softswitch Equipment". In addition, the "IP standard research group" is developing technical specifications for devices such as relay media gateway TG, signaling gateway SG, Access Gateway AG, and integrated access device IAD.
Below is a brief introduction to several major protocols.
1. H.248/MEGACO
Both H.248 and MEGACO protocols are called media gateway control protocols and are applied between media gateway and H.248/MEGACO and SoftSwitch devices. The content of the two Protocols is basically the same, but H.248 was proposed by ITU, while MEGACO was proposed by IEFT and jointly recommended by both parties. They introduce two abstract concepts: Termination terminal) and Context Association. In the Termination terminal), the media stream parameters, MODEM, and bearer capacity parameters are encapsulated, while Context Association) indicates the connection between some Termination terminals. H.248/MEGACO uses eight commands, including Add, Modify, Subtract, and Move, to establish and release the call between the Termination terminal and Context.
2. Media Gateway Control Protocol MGCP)
Media Gateway Control Protocol (MGCP) is a combination of simple Gateway Control Protocol (SGCP) and IP Device Control Protocol (IPDC) proposed by IEFT. The MEGACO Protocol is further improved, improved, and improved for the MGCP protocol. The MGCP protocol can be said to be a relatively mature protocol, and its content is similar to that of the MEGACO Protocol. At present, many devices in the softswitch system support this protocol, and its shortcomings are gradually manifested. In the future, it may be replaced by the H.248/MEGACO Protocol.
In the softswitch system, the MGCP protocol is the same as the H.248/MEGACO Protocol and is used between the media gateway and MGCP terminal and the softswitch device, this protocol is used to control the connection, establishment, and release of the Media/control flow on the media gateway and MGCP terminal.
3. Session Initiation Protocol (SIP)
Session Initiation Protocol (SIP) is an application layer control protocol proposed by IETF for multimedia communication over IP networks. Based on the Internet protocol HTTP), follow the Internet design principles, and work in peer-to-peer mode. Using SIP, you can connect, establish, and release sessions, and support unicast, multicast, and mobility. In addition, if SIP is used with SDP, You can dynamically adjust and modify session attributes, such as call bandwidth, transmitted media type, and CODEC format. For details, see ietf rfc 2543bis.
In the softswitch system, the SIP protocol is mainly used between the softswitch and the SIP terminal. Some manufacturers also apply the SIP protocol to the softswitch and the application server to provide value-added services based on the SIP protocol. In general, the SIP protocol is mainly used for voice and data-based businesses, as well as call establishment and release between multimedia businesses. In particular, because of its simplicity and flexibility, the 3GPP, which serves as the mobile communication Standardization Organization, has decided to establish a full IP network for the third-generation mobile communication on its basis, in addition, it is required that 3G terminals support the SIP protocol in the future.
4. SCTP Protocol
SCTP is a traffic control transfer protocol proposed by IETF. PSTN signaling information is transmitted over a connectionless network. This protocol can provide reliable data transmission over the IP network. SCTP can transmit user data without errors and duplication in the confirmation mode, and segment user data according to MTU restrictions of the path; ensure that user messages are delivered sequentially in multiple streams, and copy the messages of multiple users to the data block of SCTP. Use the SCTP even connection mechanism to ensure self-handling of some faults at the network level. SCTP also avoids congestion and prevents flooding and anonymous attacks.
The SCTP protocol is the main carrier of the control protocol in Softswitch.
5 main features and functions of Softswitch Technology
1. The main features of Softswitch technology are shown in the following aspects:
1) supports programmable call processing systems for various networks, such as PSTN, ATM, and IP protocols.
2) It can be conveniently run on various commercial computers and operating systems.
3) high efficiency and flexibility. For example:
· The addition of a relay gateway in Softswitch is an alternative to a long-distance/exchange switch C4 switch. It provides VoIP or VTOA functions in the backbone network.
· The addition of an Access Gateway in Softswitch is an alternative to a voice Virtual Private Network VPN)/private small switch PBX, which provides the VoIP function in the backbone network.
· With the addition of a RAS in softswitch, public bearer relay can be used to provide the managed MODEM service.
· The addition of a relay gateway and a local performance server in Softswitch is an alternative to the C5 switch of a local switch. It provides VoIP or VTOA functions in the backbone network.
4) Open IN intelligent network services can be reused through an open and flexible number book interface. For example, it provides a number Book Embedding mechanism with access to the relational database management system, lightweight number book access protocol, and transaction capability Application Part Of The number book.
5) provides open application programming interface APIs for third-party developers to create next-generation businesses ).
6) It has the programmable rear office features. For example, programmable event detail records and detailed call events are written to a collection event device of a business provider.
7) advanced management of all software components based on policy servers. It includes Simple Network Management Protocol interfaces, Policy Description Language exposed to all components, and a system for compiling and executing customer policies.
2. softswitch is a collection of multiple logical functions. It provides comprehensive call control, connection, and some business functions, it is the core device for calling, controlling, and providing services for the next generation telecommunication network Voice/Data/video services. The main menu is as follows:
1) Call Control and handling Provide control functions for the establishment, maintenance and release of basic calls.
2) protocol functions support the corresponding standard protocols, including H.248, SCTP, H.323, SNMP, and SIP.
3) The business provision function provides a variety of general or personalized businesses.
4) Business Exchange Function
5) Intercommunication functions can be achieved through various gateways and response devices.
6) The resource management function centrally manages various resources in the system, such as resource allocation, release, and control.
7) the billing function transfers the ticket to the billing Center Based on the operation requirements.
8) the authentication/authorization function can be used for authentication and authorization to prevent access by illegal users or devices.
9) Address Resolution and voice processing functions.
6. Application Based on Softswitch
With the continuous development of communication network technology and the formulation and supplement of various Softswitch standards, many manufacturers have launched Softswitch solutions, and operators are actively conducting relevant experiments. At present, many domestic and foreign telecom equipment manufacturers, such as Siemens, Alcatel, Ericsson, Nortel, and ZTE, are actively developing new switch transition platforms, and propose solutions for Softswitch in the Next Generation Network. The Application of softswitch in VoIP is briefly introduced here. Figure 3 shows the structure of the VoIP network based on Softswitch technology.
It can be seen that its function is very similar to the exchange/long-distance network between the current circuit exchange transmission system, C4 switch is replaced by the combination of the softswitch system and a group of relay gateways. The relay gateway itself is controlled by the Softswitch technology using the master/called protocol, this protocol is a MGCP/IPDC protocol related to a specified time slot of a circuit switch with a specified source/destination RTP/UDP/IP stream.
As a part of call processing, the Softswitch technology identifies the most likely egress gateway to end the call and uses this information to command the relay gateway to execute the specified function, that is, the Softswitch technology can complete each call by selecting a minimum-cost route, so that the selected egress gateway is closest to the target phone. Therefore, the call operation function of the original circuit switching network is completed.
The Access Gateway can terminate the PRI of ISDN or the CAS signaling from the enterprise PBX. This Access Gateway can be controlled by Softswitch in multiple ways based on the group Telephone Protocol. For a gateway based on the H.323 protocol, the softswitch can act like an H.323 gateway. If the gateway is connected to the PRIQ.931 tunnel) or CAS signaling is returned to the softswitch, the softswitch can also use protocols like MGCP/IPDC to better control the Access Gateway. This also demonstrates the capability of the Softswitch technology to process access gateways.
The Softswitch technology is connected to the cable network through the SIP Protocol to support the enterprise's ip pbx and IP Phone. It can also access SCP through the TCP/IP protocol or through the TCP/SCCP protocol to access the SS7 network, making seamless interconnection possible.
7 main issues that need to be paid attention to in the Next Generation Network Based on Softswitch
Although the next-generation network based on Softswitch is a complete network solution that can be applied in various communication fields, most of the current solutions are in the experimental stage due to its new technology, large-scale applications have not yet been formed, and many problems still need to be concerned, such as QOS, gateway, security, service provision methods, and organic integration with existing networks.
1. QOS Problems
QOS is a very important issue for any network. Basically, Softswitch itself does not solve the QOS problem, but relies on its bearer network to ensure service quality. The bearer network can be either ATM or IP address. For an ATM bearer network, it has a strong QOS mechanism. However, for the IP bearer network, how can we solve the QOS problem. The Next Generation Network Based on Softswitch is a very critical issue, because from the current Device Development Situation of manufacturers and the general trend of network development, IP-based bearer networks should be the trend of the times.
2. Management of Softswitch networks
According to the current implementation of softswitch, most of the requests use SNMP as the Network Management Protocol of the softswitch system. However, the SNMP network management system has some limitations, it is impossible to comprehensively manage the changes in different business needs. Because SNMP uses UDP-based bearer mode, it cannot ensure reliable transmission of network management information. At the same time, the next generation network based on Softswitch provides real-time services, and the network management system must have certain QOS management capabilities. However, at present, the softswitch-based network management system has poor processing capabilities. Further Improvement and improvement are required to meet the service quality requirements of users.
3. The protocols involved in softswitch still need to be improved
Each network interface of the softswitch network uses an open protocol for communication. However, at present, the interface standardization is not complete, both in the formulation of the Protocol and the development of various manufacturers, and most of the protocols are still in the expansion and improvement phase. Therefore, it may take some time before the final open network.
To sum up, although Softswitch has great development potential, it is still in its infancy. The communication system with Softswitch as the core will provide service openness and meet the development trend of the three-in-one network. It will provide voice, data, video, and multimedia integrated services, it meets the development goals of personalized communication, mobile communication, and information retrieval anytime and anywhere.
