Research progress in soft exchange technology standards
Shi Yumei
Summary Next Generation Network (NGN) contains a variety of transformations that are being happened. Soft exchange is the current research hotspot in various national telecommunications, will also be the development trend of telecommunications networks. Some countries are experimenting, and my country's relevant departments and operators have also launched softswitch tests. This paper mainly introduces the soft exchange architecture, the standard progress of soft exchange, the main functions of soft exchange, and several issues that need attention.
Key words next generation network softswitch network address conversion service quality
1 Softswitch network architecture
The main idea of softswitch network is the separation of business, control, transmission and access, and communicates with the standard protocol. The entire network is divided into four levels: business application and support layer, control layer, transfer layer and Access layer. The softswitch network architecture is shown in Figure 1. Soft switching is a control layer of the network, providing call control, connection, and partial business of various services. The Signaling Gateway (SG) is a device for connecting to the No.7 signaling network and the IP network, mainly completing the conversion function of the No. 7 signaling of PSTN / SDN and IP network signaling. In the access layer of the softswitch network, the relay media gateway (AG) is a gateway between the circuit switched network and the IP packet, providing media mapping and code conversion function; integrated access media gateway (AG) is used to connect user terminals And V5 access network equipment; Integrated Access Device (IAD) access user's voice, data, and video applications into a packet switched network, complete the corresponding function in a packet switched network; wireless access gateway (WAG) is completed Mobile users' access. User Intelligent Terminal As a user terminal device in a softswitch, the user terminal device has a local area network interface, directly accessing a soft switching device, and performs the transfer of the user's access, speech codec, and media stream. The soft terminal is a new user terminal in a softswitch network. It is a terminal software that runs on a user's PC or other device with similar functions, access soft switching devices, with other PC peripherals (headphones, microphones, cameras Wait, complete the user's access, voice codec, and transmission of media streams.
In the service application and support level of softswitch network, the application server provides a service execution environment, which is responsible for providing value-added intelligent services and various personalized services for users who access softswitch networks, including traditional intelligent network SCPs. (Business Control Point), SIP (Session Start Protocol) application server and third-party application server accessible through the PARLAY gateway; media server is a separate device for providing dedicated media resource functions in softswitch networks, in soft exchange or application servers Under the control, the media resources required by various services, including the acquisition and decoding of the DTMF signal, the generation and transmission of signal tones, the transmission, conference, conversion of the recording notification, the conversion between different codec algorithm, and communication and communication and Management maintenance function; network management system provides network management functions for all softswitch framework systems; billing and accounting systems provide all end users accounting, billing processing, bill generation and user interaction, bill generation, and user interaction, bill generation and user interaction; policy The server communicates with the various components of the COPS (Common Open Policy "protocol with the various components of the softswitch system, according to business requirements and feature allocation tags, control receiving, etc., can guarantee QoS for different business streams to meet user increasingly personal business. Demand; Location Server Records user information of all softswitch network users, including user location, attribute, etc., other devices such as soft exchange, application servers, etc. in soft switched networks; IADMS (integrated access device management system) as a network management system The agent between the integrated access device provides a network management function for a large number of IAD devices in a softswitch network.
The protocol interface of each component in the softswitch network given in Figure 1 is specifically described as follows:
SS interface: Interoperability interface between soft exchange and soft exchange, for SIP or BICC protocol.
SA Interface: Soft Switching and Signaling Gateway (SG) signaling transmission bearer interface, signaling transmission bearer protocols are SCTP, and M3ua, M2PA, M2ua, and Iua, etc., respectively. SB interface: Soft exchange and media gateway (TG / AG / WMG) control signaling interface, for H.248 or MGCP protocol.
SC Interface: Soft Switching and Integrated Access Device (IAD) control signaling interface, for H.248 or MGCP protocol, recommended to use H.248 protocol.
SD interface: Soft exchange and intelligent terminal, the control signaling interface between the SoftPhone terminal, which is SIP or H.323, H.248, MGCP protocol, respectively.
SE Interface: Soft Exchange and Policy Server (Policy Server) interface, specific protocols to be studied.
SF Interface: The interface between soft exchange and location server (Light WeightDirectory Protocol, TRIP (IP Network Transfer Call Agreement), etc., to be studied.
SG interface: The interface between soft exchanges and media servers is MGCP or H.248 protocol.
SH interface: Soft exchange and application server interface, for the INAP, SIP protocol or PARLAY API interface.
Si interface: The interface between soft exchange and billing and accounting system is an XML interface.
NA interface: The management interface between the network management system and IADMS is an XML interface.
NB interface: IADMS and softswitch network terminal management interface for SNMP protocols.
NC interface: management interface between network management systems and softswitch network devices for SNMP protocols.
2 Research on the standard of soft exchange system in my country
The research of softswitch network is current hotspot. In order to cooperate with softswitch networks in my country's gradual construction, China Communications Standardization Association has closely track the development process of international softswitch standards, and research on my country's softswitch-related standards, well A large amount of information and experience have been accumulated, and some achievements have been accumulated, and the development of my country's softswitch network, the evolution of the network, the development of equipment, and introduces the development phase.
2.1 Softswitch Network Overall Technology
It has begun to study softswitch network framework system, including the system model of determining softswitch network, softswitch network technology, business model, softswitch network performance and QoS, integrated network management, softswitch network addressing, network interoperability, and business interoperability , Softswitch network security requirements.
2.2 Networking equipment
The formulation of the following equipment specification:
· The overall technical requirements and revisions of softswitch equipment;
· Mobile softswitch equipment technical specifications;
· Softswitch equipment test specification;
· Media Gateway Technical Specification --ATM Relay Media Gateway;
· Media Gateway Technical Specification - IP Relay Media Gateway;
· Media Gateway Technical Specification - Comprehensive Access Media Gateway;
· Media Gateway Technical Specification - Supports Multimedia Business Parties;
· Media Gateway Technical Specification - Supports Mobile Business Parts;
· Media Gateway Test Specification --ATM Relay Media Gateway;
· Media Gateway Test Specification - IP Relay Media Gateway;
· Media Gateway Test Specification - Comprehensive Access Media Gateway;
· Media gateway controller technical specifications;
· Signaling gateway equipment technical specifications;
· Signaling gateway equipment test specification;
· Technical specifications based on soft exchange;
· Technical specifications based on soft exchange;
· Soft exchange-based access equipment (IAD) technical specifications;
· Integrated access equipment (IAD) test specification based on soft exchange.
The following equipment specifications are currently underway:
· IP intelligent terminal technical specifications and test specifications;
· Based on soft exchange where the location server test specification;
· Based on soft exchange application server testing specifications; · Media Net filial control pendulum test specification, etc.
2.3 Networking Agreement
The following protocol standards have been completed:
· Technical specifications based on H.248 media gateway control protocol;
· Technical specifications for call control (BICC) protocols with bearel;
· Flow Control Transfer Protocol (SCTP) technical specifications;
· Message Pass Section (MTP) Level 3 User Adaptation Layer (W3UA) Protocol Technical Specification;
· Technical specification for messaging part (MTP secondary user adaptation layer (M2UA) protocol;
· Media Gateway Control Protocol (MGCP) technical specifications;
· SIP and H.323 protocol interoperability;
· PARLAY protocol technical requirements;
· Message Pass section (MTP) secondary peer-to-peer adaptation layer (M2PA) protocol technical specification;
· ISDN User Adaises Layer Agreement (IUA) Technical Specification;
· V5 user adaptation layer protocol (V5UA) technical specifications.
The following agreement criteria is currently underway:
· IP network DIAMETER protocol technical specifications;
· Transfer Phone Calling Protocol (TRIP) technical specification on IP network;
· Call control technology specification based on session starting agreement (SIP);
· Technical specifications (revised) based on the H.248 media gateway control protocol;
· PARLAY X web server technical requirements;
· SIP protocol crossing NAT technical requirements;
· MGCP protocol crossing NAT technical requirements;
· H.323 agreement crossing NAT technical requirements;
· H.248 protocol crossing NAT technical requirements.
2.4 Network management
The following standards are currently underway:
· Comprehensive Access Equipment Management System (IADMS) technical requirements;
· Soft exchange-based integrated network management system (NMS) technical requirements.
2.5 business
The following standards are currently underway:
· Business system requirements based on soft exchange;
· Soft exchange - based business series specification: number display business technical specifications;
· Based on soft exchange, business series specification: call before the call;
Business Series Specification Based on Soft Exchange: Multi-Party Call Business Technical Specification;
· Based on softswitch business series specification: Click Dial Class Business Technical Specification;
· Soft exchange-based business series specification: video multimedia business technical specifications, etc.
3 functional requirements for soft switching system
Softswitch mainly completes the following features:
(1) Call control and processing functions
It provides control functions for basic services, multimedia business calls, including call processing, connection control, intelligent call trigger detection, and resource control.
(2) Agreement function
Softswate is an open, multi-protocol entity, so you must communicate with various media gateways, terminals, and networks, which must be adopted: H.248, SCTP, ISUP, TUP, INAP, H.323, RA-DIUS, SNMP, SIP, M2UA, M3UA, MGCP, BICC, ISDN, DSSL, V5.2, IUA, V5UA, DIAMETER, etc.
(3) Business provides function
Softswitch should be able to provide voice service, mobile business, multimedia business, including basic business and supplementary services; can provide existing intelligent networks with existing smart networks; can work with third parties to provide a variety of value-added services and intelligent services .
(4) Talking
The soft exchange enables the interoperability of the distribution network with the existing No.7 signaling network through the signaling gateway. Through the signaling gateway and the existing intelligent network, the H.323 protocol implements the IP telephone network with the existing H.323 system. Interoperability, using the SIP protocol to achieve interconnection with the SIP network system, using the SIP or BICC protocol to interconnect interconnection with other softswitch devices, provide interconnection between the IP network H.248 terminal, the SIP terminal, the H.323 terminal, and the MGCP terminal . (5) Resource management
Softswitch should provide resource management functions to centrally manage various resources in the system, such as resource allocation, release, and control, resource status detection, resource usage statistics, and set resource usage thresholds. Softswate can control the corresponding media stream width allocation according to the service type or the user service level property, control various media resources on the media server, provide the smart terminal / media gateway device to the carrying connection of the desired media resource, such as playing recording , Notice, voicemail, etc.
(6) billing function
Softswitch should have a collection of detailed documents and duplex, and can transfer the call to the corresponding billing center in accordance with the needs of the operator. When using a billing card, the soft exchange should have a real-time disconnection function.
(7) Certification and authorization function
Softswitch should support local authentication capabilities to authenticate and authorize users, media gateways in the jurisdiction area to prevent access to illegal users / devices. Softswitch should be able to connect to the certification center and send users, media gateway information within the jurisdiction to the certification center to prevent access to illegal users / devices.
(8) Address analysis
The soft switching device should be able to complete the conversion function of the E.164 address to the IP address, an alias address to the IP address, and can also complete the redirected function. For the number analysis and storage function, the softswitch supports the storage caller number 20 bit, the called number 24 bits, and can expand the ability of the 28-bit number, with the ability to analyze the 10-bit number and select the route, with any position increase Delete the ability to delete the number. The soft switching device has the ability to handle non-al alternate length numbers in the same area. Considering the use of the initial period of soft exchange, it is recommended that soft exchange has the ability to configure multiple area numbers. For multi-area business capabilities, soft exchange should support inter-independent business attributes between different area code, and should support functionality such as different zone numbers when the calling number is displayed.
(9) Voice handling function
Softswitch should control whether the media gateway uses voice compression, and provides the selected speech compression algorithm, and the algorithm should include at least G.729, G.723.1, optionally support G.726. Softswitch should control whether the media gateway uses echo cancellation technology and sets the size of the voicepin buffer.
(10) Overload control capability
Softswitch should be able to overload the system or network, with the ability to load the load control, such as a call, or the automatic step out of the ordinary user, or the like.
(11) Functions related to data / multimedia services
Softswitch should support interworking through the H.323 protocol and H.323 system, and can complete the conversion of the SIP protocol and H.323 protocol; it should be able to transparently transmit all information between terminals and servers, terminals and terminals, including text and voice Waiting; the media resources should be controlled to provide media services for the network terminal, including network recording notifications, calls, conference calls, etc., meeting calls, etc. The underlying control mechanism of the media type.
(12) Export filtration function using black and white list
Softswate should have a black and white list, which can prohibit / allow some calling users or calls from a certain call to some purposes to some purposes from the call user number or in the relay identification code.
(13) Call authentication function
Softswitch should be able to authenticate a call within the domain and other carrier networks to determine if the user has access to the business of this network. (14) Call interception function
Softswitch should be able to intercept and send corresponding recording notifications based on user attributes and user dial numbers.
4 need to pay attention to a few questions
4.1 Softswitch Network Technology Problem
After long-term operation accumulation, traditional telecommunications networks has been quite mature experience in network organizations; while soft exchange-based online organizations currently have no mature experience at home and abroad, is a full-plane structure based on soft exchange, or subregional selection Road structure, and addressing schemes, etc., there are further explorations in technology and practice.
4.1.1 Plane Routing Structure
As shown in FIG. 2, in this manner, the routing function is implemented in a soft exchange, each software is maintained in all users of all users, and the soft exchange is a logical network structure, and the resolution is parsed. You can be positioned to the called soft exchange.
4.1.2 Layered routing structure
(1) layered position server mode
As shown in FIG. 3, in this manner, the routing information is placed on the location server, and the position server can form a hierarchical structure, the soft exchange can be configured to configure one or more position servers, soft exchange to the position server sends an address resolution request, Address resolution is done on the location server. The sharing and interworking of routing information should be achieved between the location server, the softswitch and location servers should achieve the acquisition of routing information. In the mode of the layered position server structure, the number of layers of position servers depends on the capacity and construction scale of the actual network, and the operator can flexibly set according to the actual situation.
In this system, the soft exchange level is a logical mesh structure. It is different from the traditional telephone network, the concept, long distance, local and other concepts are weakened. Any soft switching device in the network can directly locate the soft exchange, there is no Call signaling is forwarded, but a routing service is provided by a centralized location server, and the location server can set a hierarchy in the network capacity to address large-scale networking issues.
Since the location server is not a standard entity defined by a softswitch network system, in order to solve a functional entity proposed by the large-scale networking of softswitch networks, its functions and features have not been uniformly recognized by the industry, and softswitch and location servers. And the communication procedures between the location servers, the industry has no unified standards, and the implementation of the manufacturers is also different, including TRIP, LDAP, etc.
From the way of acquiring from routing, the routing information of the location server can be static and dynamically generated, and the static configuration is similar to the existing H.323 VoIP phone network, that is, saves the number and gateway address in the gatekeeper. Correspondence. Dynamic routing discussing more technologies for TRIP, TRIP is proposed by IETF, which is a dynamic routing protocol driven by the policy, belongs to a domain positioning and routing protocol. TRIP-based routing considers many additional information, such as supported protocol, capacity, service quality, etc.
(2) Method of layered soft exchange structure
As shown in FIG. 4, in this manner, the terminal is used to interconnect between the soft exchange, and the soft exchange is used.
In the mode of layered soft exchange structure, the number of soft exchanges depends on the capacity and construction scale of the actual network, and the operator can flexibly set up according to the actual situation. This routing system draws on the hierarchical idea of the existing telephone network, divides the soft exchange into different levels, that is, the soft exchange level is not a logical mesh network structure, but increases the interconnection soft exchange. Interconnect Soft Exchange is responsible for interworking between softswitch networks in different domains, such as the route between inter-provincial routing or softswitch networks of different operators. When the routing data of the interconnected soft exchange, it will be soft. Exchange is divided into multi-level, such as provincial interconnects, large-level interconnects or national interconnections.
The routing information in this system is static, usually only the next hop softswitch can be configured, and for the interconnection between different operator networks, the other party can be configured. Soft exchange does not need to be understood its internal structure. The hierarchical softswitch routing system and location server scheme can solve the call routing problem when large-scale networking, where the hierarchical softswitching system is mature, and the technology is mature, and the softswitch can be maintained for each region softswitch network. And easy to expand, while interconnect soft exchange layers serve as a simple level, providing gateway features of external networks, avoiding too many interoperability, and ensures internal network structures and information security, but due to signaling Need to forward, each interconnected soft exchange of intermediates requires the call signaling, thereby bringing a large call delay.
Under the location server scheme, call signaling does not need to transfer, directly between start and destination software, but the current technology is not mature, and the communication procedures between position servers and soft exchanges and soft exchanges have no standards. And this structure is long,
Local concepts have been weakened and have a great impact on existing operations and management models. For static routing and dynamic routing, static routes simple, efficient, reliable, but data need to be manually updated, and can only support simple routing strategies; dynamic routing is relatively flexible, convenient, but the equipment is complex.
Due to the development of the network, different operators can choose different routing schemes according to their own network conditions, such as in the initial stage of network construction, can use softswitch full-interconnected planar structure, with the network size expand, use a layer of position server Provide routing services, in later, a hierarchical location server provides routing services for the whole network.
4.2 NAT penetration problem
In a softswitch network, a large number of IP intelligent terminals and integrated access devices (IAD) will be introduced. Since each terminal needs to take up an IP address, if large area applications, it will inevitably face the scarcity of IP called address. One of the methods to solve this problem is to allocate private IP addresses, and communicate between public-private address through NAT.
At present, the industry is very concerned about NAT penetration issues, and various solutions have also been proposed, including ALG (Application Level Gateway), Stun (Simple Traversal of Udp Through Nat), MIDCOM, etc. These solutions have their application. Which way is adopted to consider a comprehensive consideration from the following perspectives: 1 Upgrade requirements: What network elements need to be upgraded; 2 Network traffic: After using this solution, will it introduce new network overhead; 3 Voice quality: This solution Whether the program affects voice quality, increasing delay or packet loss rate? 4 Operator's investment: Does operators need to do a lot of investment? 5 Enterprise Investment: Does companies need to do a lot of investment? 6 Determine: This solution Whether the program can only take effect in a particular environment, whether you can support a variety of applications, whether you can cross the various NATs; 7 scalability: Whether this program supports large-scale applications. At present, my country is developing the corresponding NAT penetration standards.
5 full network QoS problem
The service real-time requirements of the softswitch network are high, so the QoS of the network is highly demanding, whether the QoS is the key to the future of the softswitch network, which depends to a large extent on softswitch network The packet bearer network is also required to implement the corresponding QoS control strategy from the network management. Therefore, there is a QoS solution for a whole network.
The QoS solution of the whole network is that the full network is to ensure that the entire network is to ensure that the entire network has been arranged in the full network. Perform in a controlled and manageable manner. QoS on softswitch network is currently being studied.
6 conclusion
Currently, softswitching needs to be gradually improved from signaling system to architecture. The API-related products are still exploring, but active trials and development soft exchange have become a major strategic trend in the current telecommunications industry.
