Analysis of a procedure for inserting steganographic data into VoIP   calls
  The paper concerns performance analysis of a steganographic method, dedicated primarily for VoIP, which was recently filed for patenting under the name LACK. The performance of the method depends on the procedure of inserting covert data into the stream of audio packets. After a brief presentation of the LACK method, the paper focuses on analysis of the dependence of the insertion procedure on the probability distribution of VoIP call duration. 
Wojciech Mazurczyk and Jozef Lubacz