Design And Research Of VoIP Communication System Based On WI-FI Technology

At present,the majority of domestic oil,coal,chemical and other industrial and mining enterprises adopt PSTN network or VoIP network as the communication system.The wired access way makes these enterprises difficult to lay cable in the complex and difficult construction area.The above disadvantage is more serious,especially in areas involving workers.These enterprises often use independent operation of the computer network,telephone communication network and program-controlled scheduling and other network systems,resulting in a large number of equipment costs,line charges and maintenance costs in the process of network construction and operation,which increases expenses of the enterprises.The maximum transmission rate of the computer local area network is up to 1000Mbps,but its abundant bandwidth resources are not fully utilized,which results in resources waste.At the same time,these communication systems still have the shortcoming of single calling mode,so they can't realize flexible and convenient scheduling for different regions.In this thesis,the design of the network telephone communication system based on WI-FI technology is put forward in order to solve the above problems.Based on the deep research of MGCP protocol,the efficient and simple O_MGCP protocol is proposed.It embeds the RQNT command in the CRCX command and achieves MDCX command function in the CRCX command;adds the SDP protocol;supports for single call,and group call and full-range function,achieving flexible switching between the voice call and general voice communication;eliminates the design of EPCF commands.The hardware design part of the thesis includes four subsystems:wireless user terminal,access point,media gateway controller and trunk gateway.In the function modules of the subsystems,the wireless user terminal has the same main control module,power module,storage unit module and CPLD module as the media gateway controller,and also has WI-FI transmission module and MSP430F149 single-chip keyboard scanning and LCD module.Access point as a data forwarding center,mainly includes WI-FI transmission module and low-level driver module.Trunk gateway for connecting the PSTN network and packet networks,is mainly composed of main control module,trunk interface module,audio decoding module,DTMF forwarding module and busy tone detection module.The software design includes WI-FI terminal program,access poin t program,O_MGCP pro tocol,Trunk Gateway programand UDPF/IP protocol stack.The programs of WI-FI terminal,O_MGCP protocol,TG and UDP/IP protocol stack are realized on CCS3.3 development platform.On the Keil 4.12 platform,the access point program is designed.On the IAR4.10 platform,the keyboard scanning and LCD display subroutine design of the MSP430F149 MCU are realized.On the platform of Quartus II 8.0,the logic control function of programmable complex logic device(CPLD)is realized by VHDL language.The network telephone system with simple maintenance,convenient networking and flexible use of features,has the functions of amplifying call and telephone intercom function,as well as single call,group call and gerneral calling.It can also establish a connection with PSTN users,saving a lot of equipment costs,line larges and engineering costs for construction of telephone network and improving the utilization ratio of the network resources of the industrial and mining enterprises with significant economic and socail benefits.