Design And Implementation Of Signal System NO.7 Part Of PSTN Intercept And Control System

Recently, in the wake of the popularity of the PSTN and telephone,quantities of illegal contentsare spreading through the Public Switched Telephone Network (PSTN),which attracts great attention of the departments concerned.They wish to ensure national security and protect national interests with technical means.The deployment of the listening and call controlling system is an effective way,and monitoring the Signaling System Number 7(SSN7) isthe most important technology in this system.Firstly, by introducing the overall architecture of the PSTN listening and call controlling system and the function of each part,this paper analyzes the functions needed by the SSN7 part,then introduces standard, functional structure and basic formatting of the SSN7 and gives examples of the formatting of the ISUP which is frequently used in calling. These are the basic knowledge to design the SSN7 part, so understanding these is the necessary technical preparations for the design work of part.Secondly, this paper decomposes its function at multiple levels through the analysis of the basic functions of the SSN7 part, andthenproposes the partition method of the SSN7 and plansout the basic function of each module. Then, this paper introduces the signaling processes at all levels of SSN7 in sequence, focusing on the technique of error-correcting of the MTP2 layer. By studying the technology, this paper provides an effective way of thinking for the realization of transparent blocking. And this way has an important significance to solve the frequent ordinal number turnover of the MTP2 layer resulted from the line error.lt also provides a variety of intercept methods about the ISUP and the TUP based on signaling spoofing.The design of these methods will lay the foundation to stop the illegal information spreading by means of modification to the SSN7.Finally, this paper introduces the testing approach of the PSTN listening and call controlling system and this approach will prove the effectiveness of the SSN7 part and the reliability of the whole system by means of two access tests,four tests of signaling interception,five tests of call hijacking.