The speech processing module can be divided into two parts , the first part includes speech compression , voice activity detection and echo cancellation module , which improve speech quality ; the other part includes dtmf and cpt module , which generate and detect some necessary telephony signal in the communication . this thesis is organized as follows 该语音处理模块由两部分组成,一方面是对语音的处理,包括语音压缩模块、静音处理模块和回声消除模块,主要为了提高voip的语音质量;另一方面是对电话通信的控制和处理,包括双音多频模块和呼叫进程音模块,主要为了产生和检测ip电话通信中一些必须的电话信号。
Every field has its own special computer network , however they still use the switching network of programming control which is provided by the post telephone and telegraph system . the cost of the telephone is a large part in the spending of every department . instructing the switching network to realize the telephone communication needs much of equipment charges , lines charges , protection charges , project charges and time 虽然各行业都有自己的专用计算机网络，但是各行业仍利用邮电系统提供的程控交换电话网络通信，需支付大量的电话费，占用了各部门的很大一部分开销；建立程控交换电话网络实现电话通信需要大量的设备费、线路费、维护费和工程费等费用，并且需要一定的施工工期。
People require more and more advanced telecommunicated mode . that is , people want to telephone the others not only in office or home but also in any places , and that they also wish to communicate with others while they are walking or driving . therefore mobile telephone gets a high - speed development and a extensive application 随着现代通信技术的飞速发展，人们对电话通信方式的要求越来越高，不仅要求能在办公室、住宅等固定场所打电话，而且希望能在任何场所随时拨叫或接听电话，还要能在走路或行车时进行通话，因此移动电话得到了高速的发展和广泛的应用。
Comparing to two - copper - pair fix rate of hdsl transmission system , the msdsl multi - rate symmetrical dsl can transport a variety of speed over one pair of copper wire . for n 64 kbps broadband data service , the msdsl has the benefit of cost saving and longer transmission distance 是一款msdsl multi - rate symmetrical dsl ，多速率对称数字环路，它是数据通信和电话通信的综合型设备，此设备使用多速率的dsl技术，以一对双绞线为介质，可传输64kb s到2 . 048mb s的数字信号。
