M. Edwards, “IP telephony ready to explode into corpo-rate world,” Communications News, Vol. 38(5), pp. 96-97, 2001.
 W. Mazurczyk, and K. Szczypiorski, “Steganography of VoIP Streams,” Federated Conferences and Workshops Int Symp Information Security (IS'08), pp. 1001–103, Mexico, Nov 9–14, 2008.
 D. Gruhl, W. Bender, and A. Lu, "Echo hiding," in Information Hiding: 1st Int. Workshop (Lecture Notes in Computer Science), Vol. 1174, pp. 295-315, R. J. Anderson, Ed. Berlin, Germany: Springer-Verlag, 1996.
 Y. Erfani, and S. Siahpoush, “Robust audio watermark-ing using improved TS echo hiding”, Digital Signal Processing, Vol. 19, pp. 809-814, 2009.
 O. Chen, and W. Wu, “Highly robust, secure, and per-ceptual-quality echo hiding scheme,” IEEE, Vol. 16(3), pp.1558-7916, 2008.
 H. J. Kim, Y. H. Choi, “A novel echo hiding scheme with backward and forward kernels”, IEEE transactions on circuits and systems for video technology, Vol. 13(8), pp.885-889, 2003.
 A. Delforouzi, and M. Pooyan, “Increasing payload of echo hiding scheme using dual backward and forward delay kernels,” IEEE International Symposium on Sig-nal Processing and Information Technolog, 2007.
 H. Oh, J. Seok, J. Hong, and D. Yount, “New echo em-bedding technique for robust and imperceptible audio watermarking”, Proceedings of 2001 IEEE Interna-tional Conference on the Acoustics, Speech and Signal Processing, Vol. 3, pp. 1341-1344, 2001.
 W. Wu, and O. Chen, “Analysis-by-Synthesis echo hid-ing scheme using mirrored kernels”, Acoustics, Speech and Signal Processing, Vol. 2, pp. 325-328, 2006.
 I.Ruid,”Real-Time steganography with RTP,” Technical Report, September, Retrived from URL: http://www.uninformed.org/?v=8&a=3&t=pdf.
 C. Wang, and W. Wu, “Information hiding in real-time VoIP Streams”, Ninth IEEE International Symposium on Multimedia, Taichung, pp. 255 – 262, Taiwan, 10-12 December 2007.
 H. Tian, K. Zhou, H. Jiang, J. Liu, Y. Huang, and D. Feng, “An M-Sequence Based Steganography Model for Voice over IP”, IEEE International Conference on Communications (ICC 2009), pp. 1-5, Dresden, Germa-ny, 14-18 June, 2009.
 R. Miao and Y. Huang, “An approach of covert com-munication based on the adaptive steganography scheme on voice over IP”, IEEE International Confer-ence on (ICC 2011), 2011.
 H. Tian, H. Jiang, K. Zhou, and D. Feng, “Adaptive partial-matching steganography for voice over IP using triple M sequences”, Computer Communication, Vol. 34, pp. 2236–2247, 2011.
 H. Tian, J. Qin, G. Shuting, Y. Huang, J. Liu, T, Wang, Y. Chen, and Y. Cai, “Improved adaptive partial-matching steganography for Voice over IP”, Computer Communication,Vol. 70(3), pp. 1-14, 2015.
 W. Mazurczyk, and Z. Kotulski, “New security and control protocol for VoIP based on steganography and digital watermarking”, In Proc. of 5th International Conference on Computer Science-Research and Appli-cations (IBIZA2006), Poland, Kazimierz Dolny, pp. 9-11 February 2006.
 W. Mazurczyk and S. Szczypiorski, “Covert Channels in SIP for VoIP signalling”, ICGeS 2008 - Communica-tions in Computer and Information Science(CCIS), Vol. 12, pp.65-70, United Kingdom, 23-25 June 2008.
 L. Y. Bai, Y. Huang, G. Hou, and B. Xiao, “Covert channels based on jitter field of the RTCP header”, In-ternational Conference on Intelligent Information Hid-ing and Multimedia Signal Processing, 2008.
 R. Christopher and A. Forbes, New Covert Channel over RTP, MSc thesis, Rochester Institute of Technolo-gy, 2009, retrieved from URL:https://ritdml.rit.edu/bitstream/handle/1850/12883/CForbesThesis8-212009.pdf?sequence=1 .
 G. Shah, and M. Blaze, “Covert channels through ex-ternal interference”, Proceedings of the USENIX con-ference on Offensive technologies, Montreal, Canada, August 10, 2009.
 W. Mazurczyk, P. Szaga, K. Szczypiorski, “Using trans-coding for hidden communication in IP telephony,” Computing Research Repository (CoRR), Cornell Uni-versity, Ithaca, NY (USA), Nov 4. 2011, URL: http://arxiv.org/abs/1111.1250.
 B. Chen and G. Wornell, “Quantization index modula-tion,” a class of provably good methods for digital wa-termarking and information embedding, Vol. 47(4), pp.1423–1443, 2001.
 M. Nutzinger, and J. Wurzer, “A novel phase coding technique for steganography in auditive media,” Pro-ceedings of the IEEE International Conference on Availability, pp. 91–98, August 2011.
 I. Cox, J. Kilian, F. Leighton, and T. Shamoon, “Secure spread spectrum watermarking for multimedia,” IEEE Transactions on Image Processing, Vol. 6(12), pp. 1673–1687, 1997.
 J. Yijing, L. Zhang, and S. Tang, “Real time Covert VoIP Communications over Smart Grids by Using AES-Based Audio Steganography”, IEEE International Con-ference on Green Computing and Communications (GreenCom), 2013 IEEE and Internet of Things (iTh-ings/CPSCom), and IEEE Cyber, Physical and Social Computing, pp. 2102-2107.
 G. Zhanzhan, and T. Guangming, "A further study of optimal matrix construction for matrix embedding ste-ganography," Journal of Internet Technology, Vol. 20(1), pp. 205-217, 2019.
 F. Li, B. Li, L. Peng, W. Chen, L. Zheng, K. Xu, “A Ste-ganographic Method Based on High Bit Rates Speech Codec of G.723.1”, Cloud Computing and Security, Vol. 11068, pp. 312-322, ICCCS 2018.
 T. Takahashi and W. Lee, “An assessment of VoIP cov-ert channel threats,” Proceedings of the International conference on Security and Privacy in Communication Networks, pp. 371–380, September 2007.
 R. Kazemi, R. Rezaei, M. A. Akhaee, and F. Behnia, “Covert communications through mobile voice chan-nels,” IET Information Security, Vol. 10( 3), pp. 156-164, 2015.
 A. Valizade and Z. J. Wang, “An improved multiplica-tive spread spectrum embedding scheme for data hid-ing”, IEEE transaction on information forensics and Security, Vol. 7, No.4, pp. 1127-1143, 2012.
 M. Akhaee, and F. Marvasti, “A survey on digital data hiding schemes: principals, algorithms, and applica-tions,” ISeCure, Vol. 5, No. 1, pp. 1-32, 2013.
 P. P. Francis-Cobley, and A. A. Coward "Voice over IP versus voice of frame relay," International Journal of Network Management, Vol. 14, pp. 223-230, 2004.
 J. S. Garofolo, L. F. Lamel, W. M. Fisher, J. G. Fiscus, and D. S. Pallett, “DARPA TIMIT acoustic-phonetic continous speech corpus CD-ROM. NIST speech disc 1-1.1,” NASA STI/Recon Technical Report N, Vol. 93, 1993.
 C. Kraetzer, and J. Dittmann, “Mel-cepstrum based steganalysis for VoIP-Steganography,” pp. 650505–650517, February, 2007.