There is no such thing as TCP/IP. TCP over IP is really many other things, such as HTTP, DHCP, POP, and about 500 more terms over TCP, plus UDP and ICMP over IP.
In networking, any single communication between a computer and another computer is called a session. When you open a web page or call your buddy using internet you create a session. All sessions must being and eventually end.
Transmission Control Protocol (TCP) enables connection-oriented communication in networks that use the TCP/IP protocol suite. This protocol designed to check for errors.
User Datagram Protocol (UDP) is perfect for the types of sessions that don’t require the overhead of all that connection-oriented stuff. These include sessions that use important protocols such as DNS, DHCP, NTP/SNTP, and TFTP.
Internet Control Message Protocol (ICMP) works at Layer 3 to handle low-level housekeeping tasks such as host unreachable messages and router advertisements.
Internet Group Management Protocol (IGMP) enables routers to communicate with hosts and switches to determine a “group” membership. multicast traffic (called an IGMP group) is assigned to an address in the Class D range, and those who wish to receive this multicast must tell their upstream router or switch that they wish to receive it. To do so, they join the IGMP group.
Port numbers is critical to protect your network, make routers work better, and address a zillion other issues.