Page 131 - Handout Computer Network.

Computer Network 2026

• Dynamic Host Configuration Protocol (DHCP)
• Domain Name System (DNS)
6.2.3 TCP and UDP Port Numbers

Both TCP and UDP use port numbers to pass information to the upper layers. The
combination of an IP address and a port number is referred to as a socket.
Port numbers are used to keep track of different conversations crossing the network at
the same time. Application software developers agree to use well-known port numbers that are
controlled by the Internet Assigned Numbers Authority (IANA).

For example, any conversation bound for the FTP application uses the standard port
numbers 20 (for the data) and 21 (for control), as shown in Figure 6-5 shown a Port Numbers of
Applications.

Conversations that do not involve an application with a well-known port number are
assigned port numbers randomly from within a specific range above 1023. Some ports are
reserved in both TCP and UDP.

Figure 6-5 shown a Port Numbers of Applications

https://www.youtube.com/watch?v=9lSwHYgG6tU

6.3 TCP/IP Application Layer

The last layer of both the OSI and the TCP/IP model is referred to as the application layer.
The application layer is the closest to the end user when interacting with software applications
such as sending and receiving e-mail over a network.

You see how the application layer deals with data packets from client/server applications,
domain name services, and network applications by examining the following elements:

• Client/server

• Redirectors

• Domain Name System

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