Links
[1] https://www.hootsgo.org/?q=node/6303
[2] http://www.tutorialspoint.com/data_communication_computer_network/transport_layer_introduction.htm
[3] http://www.tutorialspoint.com/data_communication_computer_network/transmission_control_protocol.htm
[4] http://www.tutorialspoint.com/data_communication_computer_network/user_datagram_protocol.htm