Computer Network Study Notes (6) --- Application Layer

1. Domain Name System DNS

Domain Name System (DNS) is a naming system used by the Internet to convert the names of machines that are easy to use into IP addresses. It is designed as an online distributed database system and uses a client server.

Domain name structure:

Top-level domain names include (1) national top-level domain names (2) Communication top-level domain names (3) Infrastructure domain names

Second-level domain names include (1) category Domain Names (2) administrative domain names

Domain Name Server:

The DNS server is not governed by the "Domain", but by the "zone ".

Domain Name Server types include (1) Root Domain Name Server (2) top-level domain name server (3) Permission Domain Name Server (4) Local Domain Name Server

Domain name resolution process includes (1) recursive query (2) iterative Query

Ii. File Transfer Protocol

File sharing protocol:

1. Copy the entire file

(1) TCP-based FTP

(2) UDP-based TFTP

2. Online Access

FTP server process:

1. Main process: receives new requests

2. Subordinate process: processes a single request.

(1) Process Control

(2) data transmission process

Iii. Remote Terminal protocol TELNET

TELNET uses the network virtual terminal NVT format:

 

4. WWW

WWW is not a special computer network. It is a large-scale online information storage system and a distributed hypermedia system (extension of hypertext system)

Uniform Resource Locator URL:

URL = <protocol>; //

Hypertext Transfer protocol HTTP:

The HTTP protocol is stateless. the operation procedure is shown in Figure 6-9.

The proxy server is a network entity, also known as the high-speed cache of the World Wide Web. Its function is as follows:

HTTP packets include:

(1) Request Message

(2) Response Message

The structure is shown in the following figure:

World Wide Web documentation:

1. Static World Wide Web documents (HTML)

2. Dynamic World Wide Web documentation

3. event Web documentation (server push technology and event documentation technology)

Information Retrieval System for the World Wide Web:

Full-text search engine and classified Directory Search Engine

V. Email

The main components of email include user proxy, email server, mail sending protocol (such as SMTP), and mail reading protocol (such as POP3 and IMAP)

World Wide Web-based email:

Vi. Dynamic Host Configuration Protocol DHCP

In order to make the Protocol Software generic and easy to transplant, the protocol software parameters can be assigned a value (Protocol configuration)

DHCP process:

VII. Simple Network Management Protocol

The main components of network management include:

1. Management site

2. Managed Devices

3. Network Management Protocol

The three components of network management include:

1. SNMP itself

2. Manage SMI

3. Manage the information library MIB

When SMI establishes rules, MIB describe the variables, and SNMP completes the action of the network management.