Address Resolution Protocol (ARP) When 2 computers try to communicate, an ARP request is initiated. If the IP address is on the local network, the source host checks its ARP cache to see if it already has the hardware address(MAC address) of the receiving host.
Internet Protocol (IP) IP is a connectionless protocol, which means that a session is not created before sending data. IP is responsible for addressing and routing of packets between computers.
Transmission Control Protocol (TCP) As opposed to IP, TCP is connection oriented and assures reliable delivery of packets. When the destination host receives a segment it sends back an acknowledgement (ACK).
User Datagram Protocol (UDP) UDP is a connectionless service that sends small amounts of data at one time and does not guarantee delivery. It is commonly used with applications such as NETSTAT, TFTP, SNMP, NETBIOS name service and NETBIOS datagram service.
