Role of VoIP in VoWLAN

In traditional speech, we all communicate in Wired form. The first time was a analog signal, followed by a digital signal. Now, our voice communication methods can be implemented through network IP addresses. This leads to today's topic-VoIP and VoWLAN.

VoWLAN Overview

VoWLAN is one of the emerging applications of WLAN. VoIP transmits voice signals through a data network; WLAN), and uses wireless access points for wireless Internet access. VoWLAN can be said to be an organic combination of the two, it can use the existing WLAN Network to achieve wireless VoIP call capabilities, enterprise employees can use VoWLAN to communicate with each other, access E-mail and other connected network resources at any time outside the office, this improves the utilization of network resources and reduces the call cost, thus saving the overall IT cost of enterprises. Residential users can also use VoIP phones connected to a broadband 802.11 Wireless Network to reduce their calls. The Data Flow of the VoWLAN system is as follows: the voice signal is transmitted to the VoIP gateway through the Access Point AP (AccessPoint). The Gateway can be the original wired VoIP gateway, so that the voice data is stored in the IP network and the PBX switch). This method enables the functions of traditional wired office phones and residential telephones to be implemented in VoWLAN. operators only need to add devices such as voice gateways and billing systems to provide VoWLAN applications for their WLAN hotspots, efficient combination of data communication and voice communication.

SIP Overview

Currently, three basic communication protocols are involved in VoIP: H323, SIP, and MGCP. SIP is called the Session Initiation Protocol SessionInitiationProtocol). It is a protocol proposed by the Internet Engineering Task Group IETF. Compared with the H.323 protocol, the SIP Protocol focuses on using IP phones as an application on the Internet. Compared with actual applications such as FTP and E-mail, it adds the requirements for signaling and QoS, they support basically the same business and all use RTP as the media transmission protocol. SIP is a text-based protocol, similar to HTTP. Text-based encoding means that the meaning of the header domain is clear at a glance, such as From, To, Subject and other domain names. This distributed standard style that requires almost no complex documentation, its superiority has been proven in the past. SMTP is a popular mail protocol ). The message body of the SIP is described using SDP. The format of each item in the SDP is '=', which is also relatively simple. The SIP can easily supplement services or intelligent services, you only need to make full use of the defined header domain of the SIP and perform simple extension on the SIP to implement these services. For example, for call transfer, you only need to add the Contact Header domain to the BYE request message and add the third-party address to be transferred. For some intelligent services that are difficult to implement by extending the header domain, you can add business agents in the architecture to provide some supplementary services or interfaces with intelligent network devices; the SIP protocol draws on the design ideas of other Internet standards and protocols and follows the principles of simplicity, openness, compatibility, and scalability that the Internet has always adhered.

System Hardware Design

Central controller

The central controller MCU uses UBICOM's IP2022 network processor. It is a microprocessor designed for Internet-edge. Its main features: software is used to process the protocol, rather than hardware logic to implement the Protocol, which reduces the complexity of chip. For packet arriving, memory-to-memory operations are used, without the need for large capacity, expensive on-chip caches (high-speed buffer storage), and packet buffers; the simple design of the real-time operating system, without memory-hungry requirement; designer can implement various Internet-edge applications by designing software. The Memory of IP2022 is divided into two parts: on-chip and off-chip, using the Harvard architecture, separated data and code memories; 4 k bytes on-chip data memory, 64 k bytes on-chip flash memory, 16 k The on-chip PRAM of tes, external memory, and extra flash memory are used to put more code. For example, the code of the embedded web server can be stored in the external flash, it also includes some dll functions. And online firmware upgrades. SRAM is used to expand PRAM space. For example, buffer packets can be used in SRAM.

Speech Module

This module uses TLV320AIC10. TLV320AIC10 is A new 16-bit A/D and D/A audio interface AIC chip with low power consumption, which has been released by TI in recent years. It is controlled by five control registers. Among them, control register 1: Software reset, DAC 16-bit or 15 + 1-Bit mode selection and anti-aliasing filter, sampling filter, interpolation filter enabling/bypass selection. Control register 2: determines the working mode and sampling rate. Low-power mode control. The frequency-division register control determines the clock frequency and sampling period of the filter ). Control register 3: Software power-off, analog and digital signal feedback and Event Control Mode Selection; ADC 16-bit or 15 + 1-Bit mode selection. Control Register 4: Input/Output gain control is achieved by controlling the input and output Programmable Gain amplifiers ). AIC initialization mainly sets the four register parameters. The interface between the device and the single-chip microcomputer is easy to implement, and it is easier to develop and use. It is particularly suitable for various VoIP, cable modem, voice and telephone fields, such as voice transmission, recognition, and synthesis of low bit rate and high performance intensive devices.