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IP电话是1999年最受关注的电信业务之一.中国电信、中国联通、中国吉通3家公司在全国25个城市进行了IP电话的商用试验,IP电话已经成为对传统电信业务的挑战.IP电话技术的核心是话音压缩,传统电话网上的电话技术一般为32KbpsADPCM或64KbpsPCM,而IP电话技术的标准采用8KbpsCS-ACELP,再加上静噪抑制和带宽共享与动态分配技术,平均每路电话实际占用带宽仅为4～6Kbps,若使用率为25%,则统计意义上每路电话占用带宽仅为1～1.5Kbps.由此可见,从技术上讲IP电话技术具备传统电话技术无法比拟的优势,但大规模开展IP电话服务还将涉及许多问题.其中话音时延和抖动等影响通话质量的技术问题必须首先得到解决.IP电话的基本原理是:由专门设备或软件将呼叫方的话音/传真信号采样并数字化,压缩,打包,经过IP网络传输到对方,对方的专门设备或软件接收到话音包后,解压缩,还原成模拟信号送给电话听筒或传真机.由此可见,IP电话技术的基础是话音压缩和解压缩技术.TTU(国际电联)批准了G.729作为新的话音压缩标准,除G.729压缩标准外,其他的话音压缩技术还有几种,采用较多的是G.723/G.723.1.当网络上的话音延时(加上声音采样、数字化压缩、延时)超过200ms时,通话双方一般就愿意倾向采用半双工的通话方式.一方说完后另一方再说.?
IP telephony was one of the most watched telecommunications services in 1999. Three companies, China Telecom, China Unicom and China Jitong, conducted commercial trials of IP telephony in 25 cities nationwide, and IP telephony has become a challenge to traditional telecom services.IP Telephone technology is the core of voice compression, the traditional telephone network telephone technology is generally 32KbpsADPCM or 64KbpsPCM, while the standard IP phone technology using 8KbpsCS-ACELP, together with the noise suppression and bandwidth sharing and dynamic allocation of technology, the actual number of each phone actually The occupied bandwidth is only 4 ~ 6Kbps, if the usage rate is 25%, the statistical bandwidth occupied by each phone is only 1 ~ 1.5Kbps. This shows that from the technical point of view, IP telephony technology with the traditional telephone technology incomparable advantages , But the large-scale development of IP telephony services will also involve many problems, including voice delay and jitter and other technical problems affecting the quality of the call must first be resolved.IP telephony basic principle is: the specialized equipment or software will be the caller’s voice / Fax signal sampling and digitization, compression, packaging, transmission to each other through the IP network, the other party’s special equipment or software to receive voice packets, unzip, restore Analog signals are sent to telephone handsets or fax machines, so that the basis of IP telephony technology is voice compression and decompression technology.TTU (ITU) has approved G.729 as the new voice compression standard, with the exception of the G.729 compression standard In addition, there are several other voice compression technologies that use more G.723 / G.723.1. When the voice delay on the network (plus voice sampling, digital compression, delay) exceeds 200ms, both parties to the call In general, we are willing to adopt the half-duplex calling method.