References:
1. S.K.Ganiev, M.M.Karimov va K.A. Toshev, “Axborot xavfsizligi,” Toshkent, 2008.
2. "Different Types of VPNs and When to Use Them," VPN Mentor. Retrieved October 16, 2020.
3. R.Younglove, "Virtual Private Networks - How They Work," Journal of Computational Control Engineering, ISSN 0956-3385, 11 (6),2000,pp. 260–262. doi:10.1049/cce: 20000602.