| TCP - Transmission Control Protocol. A connection-oriented protocol used by most Internet applications to provide a reliable, full-duplex, byte stream for a user process. |
| UDP - User Datagram Protocol. A connectionless protocol for user processes. Also not reliable. |
| ICMP - Internet Control Message Protocol. Handles error and control information between gateways and hosts. |
| IP - Internet Protocol. Provides the packet delivery service for the upper layers. |
| ARP - Address Resolution Protocol. Maps an Internet address into a hardware address. |
| RARP - Reverse Address Resolution Protocol. |