The TCP/IP is a popular network model created by DARPA in the 1970s. TCP/IP is an informal name (named after the first two protocols created); the formal name is the Internet Protocol Suite. The TCP/IP model is simpler than the OSI model, as shown above.
While TCP and IP receive top billing, TCP/IP is actually a suite of protocols including UDP (user datagram protocol) and ICMP (internet control message protocol), among many others.
Network access layer
The network access layer of the TCP/IP model combines layers 1 (physical) and 2 (data link) of the OSI model. It describes layer 1 issues such as energy, bits, and the medium used to carry them (copper, fiber, wireless, etc.). It also describes layer 2 issues like converting bits into protocol units such as Ethernet frames, MAC addresses,
and network interface cards (NICs).
Internet layer
The Internet layer of the TCP/IP model aligns with the layer 3 (network) layer of the OSI model. This is where IP addresses and routing live. When data is transmitted from a node on one LAN to a node on a different LAN, the Internet layer is used. IPv4, IPv6, ICMP, and routing protocols (among others) are Internet layer TCP/IP
protocols.
Host-to-host transport layer
The Host-to-Host Transport layer is sometimes called either “Host-to-Host” or, more commonly, “Transport”; this book will use “Transport.” It connects the Internet layer to the application-layer. It is where applications are addressed on a network via ports. TCP and UDP are the two transport layer protocols of TCP/IP.
Application-layer
The TCP/IP application-layer combines layers 5–7 (session, presentation, and application) of the OSI model. Most of these protocols use a client-server architecture, where a client (eg, ssh) connects to a listening server (called a daemon on UNIX systems), such as sshd. The clients and servers use either TCP or UDP (and sometimes both) as a transport layer protocol. TCP/IP application-layer protocols include secure shell (SSH), Telnet, and FTP, among many others.
