Early engraving of Joseph Merrick But Joseph Merrick lived on, firmly believing that his mother's experience with the fairground elephant was the root of his problems. Mary Merrick became a Sunday School
TCP/IP Protocol Architecture. TCP/IP protocols map to a four-layer conceptual model known as the DARPA model , named after the U.S. government agency that initially developed TCP/IP. The four layers of the DARPA model are: Application, Transport, Internet, and Network Interface. Each layer in the DARPA model corresponds to one or more layers of the seven-layer Open Systems Interconnection (OSI) model. Figure 1.1 shows the TCP/IP protocol architecture. Figure 1.1 TCP/IP Protocol Architecture. Network Interface Layer
Layer 4 should be protocols that have their own protocol number in the IP header e.g.: TCP(6), UDP(17), ICMP(1), IGMP, ESP, IPIP, GRE. L2TP is over IP, and PPTP uses a TCP connection (port 1720) for control channel and GRE for data tunnel, so most definitely isn't at the Data Link Layer below IP.