Chapter 16 - TCP: Software For Reliable Communication

Introduction
A Packet Switching System Can Be Overrun (merging highways)
TCP Helps IP Guarantee Delivery
Although IP software allows a computer to send and receive datagrams, IP does not handle all the problems that can arise. A computer using the Internet also needs TCP software to provide error-free communication.
TCP Provides A Connection Between Computer Programs (uses port numbers to identify session)
TCP software makes it possible for two computer programs to communicate across the Internet in a manner similar to the way humans use a telephone. Once the programs establish a connection, they can exchange arbitrary amounts of data and then terminate communication.
The Magic Of Recovering Lost Datagrams - TTL
TCP Retransmission Is Automatic
TCP and IP Work Together
A computer connected to the Internet needs both TCP and IP software. IP provides a way to transfer a packet from its source to its destination, but does not handle problems like datagram loss or delivery out of order. TCP handles the problems that IP does not. Together, they provide a reliable way to send data across the Internet.
TCP is connection-oriented vs. UDP (User Datagram Protocol) which is connectionless [TCP used by most applications (e.g. e-mail, web, etc.) that require that data must get there, UDP uses by applications that don't care, e.g. games]