^IETF (1999), RFC 2661, Layer Two Tunneling Protocol "L2TP"
^"Point-to-Point Tunneling Protocol (PPTP)". TheNetworkEncyclopedia.com. 2013. Retrieved 2014-07-28. Point-to-Point Tunneling Protocol (PPTP) [:] A data-link layer protocol for wide area networks (WANs) based on the Point-to-Point Protocol (PPP) and developed by Microsoft that enables network traffic to be encapsulated and routed over an unsecured public network such as the Internet.[permanent dead link]
^Honda, Osamu; Ohsaki, Hiroyuki; Imase, Makoto; Ishizuka, Mika; Murayama, Junichi (October 2005). "Understanding TCP over TCP: effects of TCP tunneling on end-to-end throughput and latency". In Atiquzzaman, Mohammed; Balandin, Sergey I (eds.). Performance, Quality of Service, and Control of Next-Generation Communication and Sensor Networks III. Vol. 6011. Bibcode:2005SPIE.6011..138H. CiteSeerX10.1.1.78.5815. doi:10.1117/12.630496. S2CID8945952.
^Honda, Osamu; Ohsaki, Hiroyuki; Imase, Makoto; Ishizuka, Mika; Murayama, Junichi (October 2005). "Understanding TCP over TCP: effects of TCP tunneling on end-to-end throughput and latency". In Atiquzzaman, Mohammed; Balandin, Sergey I (eds.). Performance, Quality of Service, and Control of Next-Generation Communication and Sensor Networks III. Vol. 6011. p. 60110H. Bibcode:2005SPIE.6011..138H. doi:10.1117/12.630496. S2CID8945952.
^Honda, Osamu; Ohsaki, Hiroyuki; Imase, Makoto; Ishizuka, Mika; Murayama, Junichi (October 2005). "Understanding TCP over TCP: effects of TCP tunneling on end-to-end throughput and latency". In Atiquzzaman, Mohammed; Balandin, Sergey I. (eds.). Performance, Quality of Service, and Control of Next-Generation Communication and Sensor Networks III. Vol. 6011. Bibcode:2005SPIE.6011..138H. CiteSeerX10.1.1.78.5815. doi:10.1117/12.630496. S2CID8945952.