OSI reference model

# Name use PDU protocols "address" (connectivity) devices / HW implemented by
7 Application app's gateway to network. supports net apps. "data"/"message" HTTP FTP Telnet DHCP DNS SNMP SMTP ... host name client/server, "gateway" app program
6 Presentation "translation of syntax" from app to network e.g. compression, encryption, file formats, coding (MIME, ASCII / EBCDIC e.g. SSL
5 Session establishes, maintains, ends sessions. "dialog control" e.g. duplex; checkpointing / recovery
4 Transport reliable end-to-end data transfer: error detection / correction, acknowledgement, flow control, segmentation segment TCP (connecton-oriented: guaranteed delivery, incl. flow control, congestion control, segmentation), UDP (connectionless) port O.S. TCP/IP stack
3 Network routing datagrams from one host to another. hierarchical logical addressing, fragmenting, routing (path determination in internetwork), delivery error reporting datagram / packet IP ARP ICMP, routing IP address; protocol field router O.S. TCP/IP stack
2 Data link move packet from one node to the next. framing, media access control, physical addressing, transmission error recovery frame Ethernet (802.3), WiFi (802.11), PPP, Frame Relay, CDP MAC; Type field NIC, switch, bridge, access point NIC firmware & driver
1 Physical move bits from one node to the next. medium, encoding, signaling voltages, data rates, transceiving (encoded / modulated bits) hub, repeater, media converter, "modem" (ISDN, T1, POTS, DSL, 802.11 PHY), cabling / connectors / topology NIC electronics / transceiver

please do not throw sausage pizza away
layers 1 to 3: "lower" layers
layers 4 to 7: "upper" layers
"8th layer" problem: your users

TCP/IP model lumps application, presentation, session layers into an Application layer. Transport layer also called Host-to-Host layer. Network layer also called Internet(working) layer. TCP and IP work as a team, complementing each other. There is only one IP protocol and all Internet components that have a network layer component must run it. IP is the glue that binds the Internet together.

OSI layers and corresponding TCP/IP layers and protocols:

Encapsulation of PDUs: