Abstract: In the softswitch network based on packet switching, the concept of routing has changed a lot. By introducing routing servers and rationally planning the network structure, the efficiency of the network can be improved. This article describes the networking model of the softswitch network, and analyzes and discusses the application and related issues of the networking model at all stages of the softswitch network construction.
Keywords: network organization, routing server, stepless network, hierarchical network, application
1 Introduction
With the continuous development and maturity of IP network technology, the transfer of traditional telecommunications services to IP networks has formed an irreversible trend. The architecture of softswitch based on packet transmission network just meets the rapid development trend of IP network. The use of softswitch to build a next-generation network to provide voice / data / image integrated services has become the focus of telecom operators.
Softswitch has been widely used at home and abroad due to its simple terminal equipment deployment and rapid business development. How to use soft-switching equipment to quickly provide services that are currently difficult to implement on existing networks, and how soft-switching is organized in the network to adapt to the characteristics of data networks are topics that are widely discussed in the industry.
This paper makes technical research and discussion on the network organization in the softswitch network system.
2. Introduction of routing server (RS)
In the PSTN network, a hierarchical network architecture is adopted, and the switching equipment is divided into three levels of end office switches, tandem switches, and long-distance switches according to different locations. In a call, signaling and media are forwarded section by section. Tandem and long-distance switches simultaneously terminate signaling and media. Therefore, tandem and long-distance switches implement the functions of traffic aggregation and trunk resource sharing. There are direct routes and detour routes in routing. The maximum number of routes that can be selected for a target office is up to 5.
In the softswitch network system, the media bearing between the gateways is end-to-end, and the protocol messages between the softswitches can be end-to-end, or can be forwarded through a special tandem softswitch in the middle. However, in view of the characteristics of best effort of the packet network and unguaranteed quality of service, it should be considered to minimize the number of intermediate forwarding of protocol messages when networking.
Therefore, the concept of softswitch network routing is very different from the PSTN network. There is no longer a direct route and a detour route. There will be only one target office route for a call, that is, the next hop softswitch (may be the called The softswitch where it is located may also be an intermediate tandem softswitch). When the softswitch network reaches a certain scale, if the softswitches are connected in a mesh, the routing data will be very large, and it is difficult to refine the routing configuration through the softswitch itself. It is necessary to introduce a large-capacity, high-performance server dedicated to routing resolution. This article is collectively called a routing server (RS: Route Server), and its function is equivalent to the location server (LS: LocaTIon Server) in the TRIP (Telephony RouTIng over IP) protocol. ).
3. Softswitch network structure
3.1 Stepless network
All the softswitches of the network are located on the same plane, and the originating softswitch is directly routed to the receiving softswitch, and the softswitch is a mesh network structure. The routing information of the softswitch network is stored in the RS. The RS can be configured in different regions and hierarchies. The routing information of the routing information can be queried and dynamically synchronized between the RSs.
3.1.1 Network structure
RS is divided into two layers, among them, 1) The information stored by the provincial RS includes: the user information of the softswitch connected to it (such as SIP address, E.164 address), and the information of the softswitch address; the addresses of other provincial RS And user information. 2) The information stored by the national RS includes the address and user information of the provincial RS.
After the RS completes the route synchronization, user A of provincial A soft switch A needs to talk to user B of provincial B soft switch B. The specific process is as follows:
1) Provincial A soft switch A queries RS_A for location information of user B; 2) RS_A queries RS_B for location information of user B; 3) RS_B returns to RS_A the address information of soft switch B to which user B belongs; 4) soft switch A Send SIP signaling to Softswitch B, requesting call establishment.
3.1.2 Advantages and disadvantages:
Advantages: 1) The softswitch can be directly routed to the destination softswitch via RS, which avoids multiple processing and forwarding of call signaling messages in the IP network; 2) Centralized setting of routing data and unified management, when the routing information of a softswitch is updated , Can be broadcast to other RS ​​in time through TRIP and other protocols, which is convenient for configuration management of routing data. Shortcomings: 1) Need to be equipped with a series of RS, the network construction cost is relatively high, the RS and softswitch can be considered in the initial stage to reduce the construction cost; 2) All calls need to query the RS for routing data, and the processing efficiency of the softswitch system is certain Impact; 3) Due to differences in strategies and protocols adopted by different manufacturers, it is currently difficult for equipment to communicate.
3.2 Grading network
Call control protocol messages are transferred through multiple softswitches, and the media is connected end-to-end. Softswitch can be divided into two levels: local service softswitch and interprovincial tandem softswitch. The local service softswitch is responsible for providing rich services to users in the service area, including integrated services such as voice / data / image. Inter-provincial tandem softswitch is responsible for inter-provincial services of tandem softswitch, which is mainly responsible for routing and protocol transfer, and does not need to control the gateway device for media connection.
3.2.1 Network structure
The routing server has the following requirements: 1) The storage of routing data is responsible for providing end-to-end routing information between local softswitches in the province and routing information from local softswitch to interprovincial softswitch; 2) Local softswitch routing data changes It only needs to be synchronized with the RS of the province; when the inter-provincial softswitch data changes, it needs to be synchronized with the RS of other provinces. 3) For the same called address, different routing information can be returned according to the softswitch level that initiated the query request. For example, for an outbound call, the local softswitch query returns the IP address of the interprovincial softswitch, and the interprovincial softswitch returns the IP address information of the peer interprovincial softswitch.
After the RS completes the route synchronization, user A of provincial A soft switch A needs to talk to user B of provincial B soft switch B. The specific process is as follows:
1) Provincial A local softswitch A queries RS_A for location information of user B; 2) RS_A returns local softswitch A address information of interprovincial softswitch A '; 3) RS_A sends SIP messages to interprovincial softswitch A', Request call connection; 4) After receiving the SIP message, the inter-provincial softswitch A 'queries the RS_A and requests the routing information of user B. 5) RS_A returns the address information of interprovincial softswitch B 'to interprovincial softswitch A'; 6) interprovincial softswitch A 'sends a SIP message to interprovincial softswitch B' to request call connection; 7) interprovincial softswitch After receiving the SIP message, B 'queries RS_B and requests the routing information of user B; 8) RS_B returns the address information of local softswitch B to interprovincial softswitch B'; 9) Interprovincial softswitch B 'sends local softswitch B Send a SIP message to request call connection.
3.2.2 Advantages and disadvantages:
Advantages: 1) Only interprovincial softswitch can communicate with the external network, which can shield the network status of the softswitch in the province, and the security is better; 2) Using the RS mechanism, the routing information in the domain can be flexibly managed through the TRIP protocol and the like.
Shortcomings: 1) The protocol information of inter-provincial calls needs to be forwarded through multiple segments, which increases the reliability of the packet network; 2) It may have a certain impact on the service quality of the call connection time; 3) It needs to be considered when planning inter-provincial softswitch Related issues such as capacity and security backup.
3.3 Application suggestions for networking mode
3.3.1 Initial network construction
Business-driven network construction. At the initial stage of construction, the service volume provided by softswitch is relatively small, and the network scale is relatively small. Softswitch needs to set up points independently, and gradually expand the network capacity from point to surface.
In the case of coexistence of multiple networks and the PSTN network occupying an absolute advantage, softswitches are not spread out in large areas, and the number of softswitches that can be directly connected is limited. More users need to rely on circuit switching networks on SG and TG to solve. Therefore, the network construction at this stage basically adopts a stepless network, and the routing server and the softswitch are co-located.
At the same time, because the services provided by the softswitch need to cover multiple local networks, a softswitch device must be able to control the gateway devices placed on multiple local networks. The softswitch network provides services as a PSTN overlay network. In order to facilitate network expansion during subsequent business growth, it is advisable to initially adopt a separate application server and softswitch model. Value-added services are uniformly provided by the application server. Softswitch is only responsible for the function realization of basic services and the access and triggering of value-added services.
In terms of function, the following requirements must be added to the softswitch: (1) The softswitch needs not only the function of sub-authority management, but also the function of managing users, relays and other data by region; (2) due to the softswitch Equivalent to the long-distance / local phone / SSP integration of the existing PSTN network, providing a wealth of services, so it is necessary to be able to manage billing data by service on a divided domain basis; (3) Because the softswitch needs to communicate with multiple local networks The switch equipment of the company establishes signaling routes, and the point code allocation mechanism of each local network is different. Therefore, the soft switch is required to have the function of multiple signaling point codes.
3.3.2 Medium-term network construction
With the development of services, the demand for services has increased, the scale of the network has expanded, and the number of soft switching nodes in the network has gradually increased. When the user plane occupied by the packet-switched network controlled by the softswitch and the circuit-switched network is extremely close or even better, the original circuit-switched network gradually retreats to the edge, and the number of data network users continues to increase.
At this time, it is difficult to rely on the softswitch itself to refine the configuration of related routes. It may be considered to introduce a number of RSs to undertake the responsibility of route resolution. The emergence of RSs can begin to be individual, and each bears part of the routing information of the softswitch. RS is all at one level. When introducing RS, on the one hand, we must examine the support of softswitches for related protocols, and on the other hand, we must examine the impact of using RS routing on softswitch processing capabilities and other performance.
Because the pace of building softswitch networks in each region is different, at this stage, operators can implement the regions through inter-provincial softswitch or provincial RS according to the support of the equipment used by each region for the protocol Interworking between softswitch networks.
3.3.3 Late network construction
The size of the packet switching network controlled by softswitch continues to expand. When the number of RS increases to a certain degree, each RS will face the pressure of configuration and maintenance of routing data. At this time, the RS networking needs to be optimized. By disposing provincial RS and national RS to alleviate the difficulties of regional RS, the network gradually formed RS hierarchical and soft-switch flat networking mode during the evolution.
4 Other related issues
4.1 RS-related protocol capability requirements
1) Protocol capability requirements between softswitch and RS:
â— Retrieval of routing information;
RS retrieves routing information according to the request of the softswitch.
â— Add / delete / modify routing information;
When the user number of the softswitch changes or the routing information is changed due to network congestion, it should be able to notify the RS in a timely manner through relevant protocols. The RS updates the relevant routing information and broadcasts to notify other relevant RSs.
â— RS authentication for softswitch;
It should be able to authenticate the softswitch that initiated the request. Prevent illegal softswitches from stealing routing information.
â— Heartbeat mechanism.
There should be a heartbeat mechanism between the softswitch and the RS, which periodically checks the survival information of the other party. When the softswitch finds that the connection with the RS is interrupted, it can switch to the paired RS. Correspondingly, when the RS finds that the connection with a certain softswitch is interrupted, it should immediately update the routing status information to that softswitch and broadcast to inform the relevant RS.
2) Requirements of agreement between RS:
â— Exchange and synchronize routing information between RSs;
After the synchronization of the routing tables between RSs is completed, when the content of the routing tables changes, new routing information can be sent to the relevant RSs.
â— Route retrieval;
Retrieve routing information according to the request initiated by the next-level RS.
â— Prevent routing loop of addressing;
Prevent routing loops between RSs during addressing.
â— Authentication between RSs;
It should be able to authenticate the RS of the interactive information.
â— Heartbeat mechanism
The RS can periodically detect the survival information of the peer through the heartbeat mechanism.
4.2 Interoperability of softswitch networks between operators
Regardless of the networking method used by the operator's internal network, when implementing network interoperability between operators, due to problems related to interconnection fault location and cost settlement, it is generally considered to adopt the networking method of gateway softswitch and gateway gateway.
Set up several gateway softswitches in the network to be responsible for converging interoperability services between operators. On the one hand, due to network security considerations, it is necessary to shield the internal network structure of the operator; on the other hand, this structure can also facilitate the handling of interconnection and intercommunication failures. These gateway softswitches need to complete the transfer of the protocol and control the media stream. The gateway gateway is responsible for the aggregation of media streams across the network.
The gateway softswitch needs to implement related functions such as the black and white list, overload control, and billing of the relevant gateway. The gateway softswitch and the softswitch routing data of other operator's networks can be stored in the gateway softswitch and routed directly to the peer gateway gateway softswitch, or it can be routed through RS.
5. Conclusion
In summary, in the packet-switched network controlled by softswitch, the concept of routing has changed a lot. Using a routing server to route directly to the destination softswitch is a networking solution suitable for packet-switched networks. The introduction of the routing server should be based on a comprehensive consideration of network size, equipment support for protocols, and other issues, unified planning and deployment.
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