“IP telephony can be implemented not only on the Internet or Intranet, but also on the local area network. The LAN IP phone can not only unify the internal data network and voice network, but also greatly reduce the cost of the telephone system. At present, the highway communication network is becoming a dedicated multimedia transmission system with multiple services and long transmission distances. However, most highway emergency calls, command calls, and business calls are generally implemented by program-controlled telephone exchange systems, with high call costs and single services. .
Authors: Bai Ruqing, Wang Wei, Yuan Qingyun
IP telephony can be implemented not only on the Internet or Intranet, but also on the local area network. The LAN IP phone can not only unify the internal data network and voice network, but also greatly reduce the cost of the telephone system. At present, the highway communication network is becoming a dedicated multimedia transmission system with multiple services and long transmission distances. However, most highway emergency calls, command calls, and business calls are generally implemented by program-controlled telephone exchange systems, with high call costs and single services. . If the voice service and data service can be integrated on the basis of the existing data transmission network, the construction cost of the telephone network can be reduced, and the network can be flexible. At the same time, using softswitch as the digital voice control platform can realize a wide range of intelligent voice services and services. Development and implementation are very convenient.
The Realization Basis of VoIP in Expressway Communication Network
The realization of new technologies such as Gigabit Ethernet, dense wavelength division multiplexing and Packet over SDH in the LAN, MAN and WAN environments allows for more bandwidth for data networks at a lower price. Therefore, it is very effective to realize Internet telephony based on expressway communication network VoIP. While meeting the daily administrative business telephone communication in expressway jurisdiction, it enables IP voice to more effectively intervene in expressway toll business, making IP dedicated The utilization efficiency of the Internet is higher, and the quality of fee-based services is better, which highlights the application value and development prospects of VoIP technology.
VoIP uses the IP packet switching network as the transmission platform to compress and pack the analog voice signal through a series of special processing, so that it can be transmitted using the connectionless UDP protocol. In order to transmit voice signals on an IP network, several elements and functions are required. The simplest form of a network consists of two or more VoIP-enabled devices connected through an IP network. The basic structure of the VoIP model is shown in Figure 1. It can be seen from the figure that VoIP equipment converts voice signals into IP data streams and forwards these data streams to IP destinations, which then convert them back to voice multiples. The network between the two must support IP transmission and can be any combination of IP routers and network links.
Figure 1 VoIP model structure
The expressway communication system is the support system for modern expressway operation and management. It must realize the accurate and timely transmission of information such as data, voice and images of the monitoring system and the toll system, and maintain the smooth communication of business contacts between expressway management departments. And it is necessary to establish necessary connections between various departments within the expressway and the outside world. Due to the needs of network charging and network monitoring, especially the interaction of video image data, the highway communication system adopts a multi-level IP network based on the IP data network. The modern communication network has a hierarchical structure, which functionally divides the network into a service network, a transmission network and a support network, which is a good integration of the VoIP model structure.
The highway communication network segmentation is based on actual physical connections, and can be divided into user networks, access networks, and core networks (or local area networks, access networks, and backbone networks). According to this, the expressway communication private network is divided into a three-layer network structure, as shown in Figure 2.
Figure 2 Highway communication hierarchical structure
The highway backbone network mainly provides high-speed information channels for upload services and cross-local network services. It has the characteristics of large transmission capacity, large distance span, high circuit quality requirements, and strong importance. The existing backbone network is mainly based on synchronous digital sequence (SDH) Technology. The highway communication system access network is an extension of the SDH backbone network and a communication platform for road sections, suitable for the multi-service access of the highway communication network. Located at the lower level is a computer local area network using the common Ethernet method, which is composed of computers, servers, and routers at various toll stations. The access network accounts for more than 50% of the investment in the construction of the entire highway communication network, and the access network directly faces a large number of users and various application systems, and can complete integrated services such as voice, data, and images. At present, the access network basically adopts the OLT-ONU access method. OLT is installed in the communication sub-center of the road section, and ONU is configured in each toll station and service area. Various data of the charging and monitoring system are connected to the nearby ONU and integrated and transmitted to the OLT of the sub-center. The OLT is connected to the ADM interface and connected to the SDH backbone network. This access method has rich interfaces. Although the 2M digital interface is the basic unit, it is divided into 2/4-wire audio voice interface, sub-rate interface, ISDN 2B+D, ISDN 30B+ through various internal interface boards. D interface with fixed rate.
The application of the IP-based Ethernet access method has greater advantages. It sets up Ethernet switches and EOS (Ethernet Over SDH) equipment in the communication sub-centers of the road section, and configures Ethernet switches in various toll stations and service areas. Ethernet access directly provides a computer network platform, which is convenient for calling various related software. , Sturdy and reliable, convenient for network interconnection. The various information of the charging and monitoring system is connected to the nearby Ethernet switch to realize the whole process of IP access to the network. These are well compatible with the requirements of the VoIP network voice communication access technology.
Realization of Expressway VoIP System
The expressway adopts VoIP technology, and the concrete realization structure of the system is shown in Figure 3. The realization method can realize toll lane intercom and external communication, inter-departmental business telephone communication, and IP telephone network communication with external public telephones.
Figure 3 System structure
First of all, it is necessary to install hardware equipment. In order to make full use of the existing computers in the toll lanes and realize the toll lane intercom and external communication, there are two options: one is to use the lane computer to achieve voice transmission by sound cards, microphones and speakers. This solution is easy to implement and low in cost. However, voice quality needs to be improved; second, PC plug-in or external products can be used to develop special voice processing products. The use of DSP technology can achieve echo cancellation, and the voice quality is better. Secondly, install the intercom software on the toll station computer. The software is used to provide an intercom control interface and Display user icons. If you need to know the toll lane conditions, click on the user icon, and then select the “intercom” or “monitor” mode; if you need to make a broadcast call, select the user you want to call and the group call mode. At the toll booth, the toll collector presses the “intercom” button to request an intercom to the station monitoring room, and the station can speak after responding. The intercom level and mutual relationship between users are set by the software according to management requirements.
Based on the realization of toll lane intercom and external communication, this method also realizes business calls between departments. The business telephone system can be connected with an IP telephone gateway combined with a PBX, and the existing telephone equipment and IP telephone gateway can be used to access the computer network. After connecting the department’s business phone to the PBX, it then connects to the WAN through the gateway. The main functions of the gateway are signaling processing, voice encoding and decoding, and routing protocol processing, and provide an interface for IP network connection. When the telephone user dials, the IP telephone gateway responds, accepts the input of the other party’s telephone number, and based on this telephone number, queries the “gatekeeper” for the IP address of the IP telephone gateway as the destination of the packet. After knowing the IP address, the IP telephone gateway completes the connection between it and the other party’s IP telephone gateway through the call control protocol. This call control protocol specifies the operation process when exchanging phone number information and line setting information between IP telephone gateways, and the operation process required when exchanging information with the gatekeeper. After establishing the connection, between the IP telephone gateway of the other party, start to use RTP to transmit the actual voice data.
This method not only realizes toll lane intercom and external communication, inter-departmental business telephone communication, it can also interconnect the IP telephone network and the existing PSTN public telephone network. In order to realize the intercommunication with public telephones, the IP telephone gateway needs to be connected to the telephone company’s subscriber switch trunk line interface, and at the same time connected to the No.7 common-channel signaling network, the IP telephone gateway can be connected to existing long-distance telephones. The company’s trunk switch works the same. As long as the phone user dials the identification number before the phone number of the other party and dials the identification number before the phone number of the public network, the call setting information such as the phone number of the other party can be transmitted to the IP telephone gateway via the No.7 common-channel signaling network to perform IP The communication between the telephone and ordinary PSTN users is shown in Figure 4.
Figure 4 Schematic diagram of IP telephone network and external telephone communication
This implementation scheme mainly considers the use of existing network lines to achieve voice transmission, fully utilizes existing network resources, can save communication resources and use the network to achieve multi-level intercom that was previously impossible, such as sub-centers that can directly communicate with lanes. The communication situation improves the management level; it is more economical and practical for the management system of the ordinary expressway that has not established a dedicated communication network and has poor communication conditions, which can greatly increase the utilization rate of the network and reduce the telephone bill.
Application of VoIP phone in charging system
In order to ensure the business order and service quality of various management stations and toll crossings, it is necessary to have reasonable communication technology and equipment to carry out remote and real-time service quality and traffic safety monitoring and management of the entire service management area, including very important communication monitoring manage. Although the regional headquarters has already set up a control center platform and is equipped with a video monitoring system, it still needs to be equipped with a voice communication monitoring system. This voice communication monitoring system is implemented by VoIP technology. Through the use of VoIP technology using IP packet switching, the control center can monitor the on-site voice communication at various toll crossings in real time and intervene through voice, or perform full-way monitoring, recording and post-inquiries; the toll management station can participate in monitoring, broadcasting and Recording, directly participating in the intervention of emergency emergencies and the coordination of daily business; the staff at the toll crossing can accept the monitoring and management from the control center and the management station in the daily service.
VoIP Internet phone provides advantages such as low cost, high flexibility, high productivity, and enhanced application efficiency. Expressway communication network integrates the structure and access requirements of VoIP network. Therefore, it is very important to realize VoIP Internet phone based on expressway communication network. Effective. While meeting the daily administrative business telephone communication in the expressway jurisdiction, it enables IP voice to more effectively intervene in the expressway toll business, making the use of IP private network more efficient, and the quality of tolling services is better. The application value and development prospects of VoIP technology.