Chapter 5. Fundamentals of TCP/IP Transport and Applications

any TCP/IP transport layer protocols are considered Layer ___ protocols.

4

Multiplexing relies on a concept called a socket. A socket consists of three things:

An IP address A transport protocol A port number

Many protocols operate under these same concepts, so the terms connection-oriented and connectionless are used to refer to the general idea of each. More formally, these terms can be defined as follows:

Connection-oriented protocol: A protocol that requires an exchange of messages before data transfer begins, or that has a required pre-established correlation between two endpoints. Connectionless protocol: A protocol that does not require an exchange of messages and that does not require a pre-established correlation between two endpoints.

Applications that provide a service, such as FTP, Telnet, and web servers, open a socket using a well-known port and listen for connection requests. Because these connection requests from clients are required to include both the source and destination port numbers, the port numbers used by the servers must be well-known.

Popular Applications and Their Well-Known Port Numbers

Flow Control Using Windowing

TCP implements flow control by using a window concept that is applied to the amount of data that can be outstanding and awaiting acknowledgment at any one point in time. The window concept lets the receiving host tell the sender how much data it can receive right now, giving the receiving host a way to make the sending host slow down or speed up. The receiver can slide the window size up and down—called a sliding window or dynamic window—to change how much data the sending host can send.

The key difference between TCP and UDP is that:

TCP provides retransmission (error recovery) and helps to avoid congestion (flow control), whereas UDP does not.

The OSI transport layer (Layer 4) defines several functions, the most important of which are:

error recovery and flow control.

hosts typically allocate dynamic port numbers starting at 1024 because the ports below 1024 are reserved for well-known applications.

hosts typically allocate dynamic port numbers starting at 1024 because the ports below 1024 are reserved for well-known applications.

The message created by TCP that begins with the TCP header, followed by any application data, is called

is called a TCP segment. Alternatively, the more generic term Layer 4 PDU, or L4PDU, can also be used.

TCP (Transmission Control Protocol)

is directed toward providing services for the applications that sit at the endpoint computers. Regardless of whether two computers are on the same Ethernet, or are separated by the entire Internet, TCP performs its functions the same way.

TCP connection establishment occurs before any of the other TCP features can begin their work. Connection establishment refers to:

the process of initializing Sequence and Acknowledgment fields and agreeing on the port numbers used.