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Lesson 3 TCP/IP protocol suite
ObjectiveDescribe the use of the TCP/IP Protocol Stack
What is the TCP/IP protocol stack?
Transmission Control Protocol/Internet Protocol (TCP/IP) is a group of communication protocols developed to network dissimilar systems. Its structure follows the ISO Reference Model discussed earlier. While the ISO Model generically identifies the seven protocol layers used to achieve robust communications, the TCP/IP is a particular suite of protocols adopted as the global standard for Internet-based communications.
The illustration below shows that the TCP/IP suite (also called the TCP/IP stack) appears in the Network Layer of the OSI Model's protocol stack. Because of this, all network applications can be written to easily interface with the TCP/IP protocols without regard to a particular network software manufacturer or medium.
Protocol stack
What is TCP?
TCP is a connection-oriented protocol that guarantees delivery of data packets from a specific source to a specific destination. It provides reliable, end-to-end delivery.
What is IP?
IP routes packets around the Internet, and performs route discovery, fragmentation, and re-assembly of those packets. This means IP finds the fastest route to its destination, is able to determine the 'optimal' route moment by moment, and will re-order the packets into their proper sequence at the destination computer.

TCP/IP
Together, TCP and IP form the TCP/IP protocol stack (or "suite of protocols") that enables dissimilar computer systems to communicate.
TCP's cousin: UDP
UDP (User Datagram Protocol) is a connectionless protocol, considered the "poor cousin" of TCP. Whenever TCP sends a packet it numbers them sequentially, then queries the destination computer to see if they all arrived. UDP sends unnumbered packets (called datagrams) and never queries. UDP is faster than TCP because fewer bits are required per packet and no queries are sent. UDP is typically reserved for low-priority messages, such as scheduled server outage times to all users on a LAN.
In the next lesson, you will learn about TCP/IP addresses and how they are classified.