TCP's features - sequenced data, ITs reliable, connection oriented, aknowledgement is required, windowing flow control. UDP's features - unsequenced data, unreliable, connection less, no aknowledgement required, no windowing flow control, wireless media used. Vpn - vertual private networks used for connect the private network over the public network Ipsec - internet protocol security its L3 vpn because it worked on l3 info source ip add & destination ip add. It have 2 phase 1st for secure the session key & 2nd for secure the data it provide us vertual tunnel to connect the private networks over the public network. In ipsec we use authentication, hashing & encyption it encypts the L4 info of data packets it supports the authentication, encyption, encapsulation. We can use ipsec over gre for secure & encrypt the tunnel interface but it doen't support the encyption & authentication it only supports the encapsulation.

TCP vs UDP ... TCP is connection oriented and UDP is connectionlesss orientated. TCP provides acknowledgement where as in udp no provider