3.2: Application-Level Protocols
There are a number of application protocols available, but only three have been included in your textbook: Domain Name System (DNS), Electronic Mail (SMTP and POP3), and HyperText Transfer Protocol (HTTP). The DNS protocol allows you to easily reference resources outside of your network. E-mail protocols allow you to reach out and communicate with friends and family, and HTTP is the popular protocol for accessing webpages on other systems.
In addition to the three application protocols covered in your textbook you will also take a look at the SNMP and SSH protocols. These two protocols are being used more and more in Internet applications. In particular, the SNMP protocol allows the administrators to manage a large network in a more efficient way, and the SSH protocol allows us to design virtual private networks over public networks.
As you read through these subunits, think about your own social networking activities. How does each of these protocols allow you to communicate using a variety of media, equipment, and file types/software?
3.2.1: Domain Name System (DNS)
Read section 3.2.1, "The Domain Name System," on pages 32-37.
In order to access a website, you need to know the website's IP address. IP addresses can be somewhat cumbersome and difficult to remember, since they are simply four numbers separated by periods (e.g., 120.755.3.9). The Domain Name System (DNS) is the application that has solved this problem by allowing us to use "human readable" names for websites. What is the domain name for your home page on your work, school, or home LAN? What is the IP address for each one? Which would you rather use - the IP address or the domain name?
Read this article. The Domain Name System is a networking protocol. It converts domain names to the IP addresses, which are needed to locate and identify computer services and devices with the underlying network protocols.
3.2.2: Electronic Mail (SMTP and POP3)
Read Section 3.2.2, "Electronic mail," on pages 37-46. In this section you will look at the e-mail application and explore two of the more popular protocols: SMTP and POP3. How does e-mail work? How long does it take for a message to reach its destination? Then what happens?
3.2.3: HyperText Transfer Protocol (HTTP)
Read Section 3.2.3, "HyperText Transfer Protocol," on pages 46-55. HTTP is a text-based protocol, in which the client sends a request and the server returns a response. In this section link across the World Wide Web via your textbook to see how this is accomplished.
3.2.4: Simple Network Management Protocol (SNMP)
Read this article. As you read, pay special attention to the definitions of managed devices, agent, and network management system (NMS). At the same time, try to explain what kind of message flows are defined in NMS.
3.2.5: The Secure Shell (SSH) Protocol Architecture
Read this article. As you read, pay attention to how SSH protocol is defined and the difference between FTP and SSH-based Secure FTP.