Referring to the ARPA protocol suite that provides the basis for what has evolved into the Internet and, therefore, often is referred to as the Internet protocol suite. This is a four-layer protocol suite that maps into the OSI Reference Model that followed a few years later.Table T-2 includes the major protocols that comprise the TCP/IP protocol suite as they relate to the ARPA and OSI models.

Table T-2: TCP/IP Protocol Suite

OSI Layer	ARPA Layer	Protocol
7 Application	Process/ Application	FTP File Transfer Protocol	SMTP Simple Mail Transfer Protocol	SNMP Simple Network Management Protocol	TELNET Telecommunications Network
6 Presentation
5 Session
4 Transport	Host-to-Host	TCP Transmission Control Protocol		UDP User Datagram Protocol
3 Network	Internet	ARP Address Resolution Protocol		ICMP Internet Control Message Protocol	IP Internet Protocol
2 Data Link	Network Interface	LAN, MAN, WAN Network Interface Card (NIC)
1 Physical		Transmission Media

See also ARP, ARPA, FTP, ICMP, Internet, IP, LAN, MAN, NIC, OSI Reference Model, protocol, SMTP, SNMP, TCP, TELNET, transmission media, UDP, and WAN.