Application Layer
1. The only user-oriented layer provides users with frequently-used services 1) email 2) www 3) QQ ...... there are many more
2. common protocols: 1) Hypertext Transfer protocol HTTP 2) File Transfer Protocol FTP 3) Simple Mail Transfer Protocol SMTP 4) Domain Name System DNS 5) Remote logon protocol Telnet 6) simple Network Management Protocol (SNMP) 7) multi-purpose Mail Extension protocol (MIME)
3. Relationship between the application layer protocol and the underlying protocol:
4. customer/Server mode (C/S mode) and Web Service-based Browser/Server mode (B/S mode) of network application processes) the customer and the server respectively indicate that the two application processes that communicate with each other do not refer to computers.
5. Solutions for servers to process concurrent requests: Concurrent servers and duplicate servers
6. Concurrent Server: the concurrent server is called the master server. When the master server receives the request, it activates the corresponding sub-process, that is, the slave server.
7. duplicate server: it does not create a process from the server. Instead, it contains a request queue. After a customer requests arrive in the queue, they first enter the queue and serve them first.
Second Domain Name System 1. Domain Name-network host name represented by characters; IP address-number string, difficult to remember and understand; domain name-character, intuitive, easy to remember and understand;
IP Address: used for network layer address identification; Domain Name: used for Application Layer Address Identification; IP addresses and domain names are unique across the network and mapped to each other. 2. ing: ing between IP addresses and domain names: one IP Address can correspond to multiple domain names. For example, one domain name of a VM can also correspond to multiple IP addresses. Example: server Load balancer DNS round route 3.internet is divided into several hundred top-level domains, and each domain is divided into subdomains. 3-Character Domain: Organization Mode com Edu net org Mil
2-Character Domain: Geographic mode cn hk jp de UK Au top-level domain is divided:
Country (2 characters)
Other. Name. info. biz
Almost all American organizations are in the general domain, and non-American organizations are listed in the home domain of their country. 2. Authorized Domain Name Server: The Local Domain Name Server and the Root Domain Name Server are default servers. Each Domain Name Server knows the IP address of the Root Domain Name Server. 5. Two resolution methods; recursive resolution: only interact with one server
The domain name server is required to complete all "name-address" transformations at a time;
The task of recursive Parsing is mainly undertaken by the server software.
Repeated resolution: interacts with multiple servers in sequence
Each time a server is requested, if no other server can be requested;
The task of repeated resolution is mainly undertaken by the domain name parser software. 6. the Domain Name Server's cache Domain Name Server retains a domain name cache. Every time a new domain name is searched, the server places it in the cache;
When the host starts, it downloads all the databases of the domain name and address from the Domain Name Server, and maintains the cache that stores the domain name recently used, the Domain Name Server is used only when the domain name cannot be found from the cache. 3. Email Service 1. the core email server of the mail server system is responsible for receiving emails sent by users, sending them to the recipient's email server based on the recipient's address, and receiving emails sent from other email servers, and distribute it to the corresponding email address according to the recipient address; 2. common concepts: 1) Remote Access to Post Office Protocol POP3 2) Message Access Protocol IMAP 3) User proxy UA 4) message transmission proxy mta3.smtp: Use SMTP protocol to send mail messages between mail servers
Customer: email sending server
Server: receiving server 4. Mail reading and sending: When an email program sends an email to the mail server, it uses the Simple Mail transmission protocol SMTP;
When an email program reads a mail from the mail server, it can use the Post Office Protocol POP3 or interactive mail access protocol IMAP, depending on the protocol type supported by the mail server. 4. File Transfer 1. the file transfer service, also known as the FTP service, is one of the earliest service functions provided by the FTP application in the Internet, following the TCP/IP protocol 2. data Connection and control connection: ftp uses two TCP connections for file transmission:
1) control connection: the control connection is established on the client server. The server passively opens the well-known port (21) for FTP and waits for the customer's connection. The customer opens TCP port 21 in the active way.
Establish a connection.
2) data connection: each time a file is transmitted between the client and the server, a data connection is created. 3. Simple File Transfer Protocol: TFTP uses UDP datagram, does not support interaction, and does not have the column directory function. 50 thousand bytes 1. the World Wide Web (WWW), also known as web, is not a special computer network, but a mass, globally published HTML (hypertext makup language, a collection of documents or web pages. The functions implemented by the World Wide Web are called WWW (Web) applications. It provides users with a graphical interface that can be easily controlled.
Information resources on the Internet, known as hypermedia files, include text, graphics, sound, animation, databases, and a variety of software. 2. Browsers are Web client programs on users' computers. It displays the requested web page and provides many guidance and configuration information. The computer where the World Wide Web Document resides runs the server program, which provides the web page requested by the user. Therefore, this computer is also called the World Wide Web Server 3. Mosaic, the world's first browser. 4. Use the Uniform Resource Locator URL (Uniform Resource Locator) to mark various documents on the World Wide Web. Make each document have a unique identifier URL throughout the internet. The URL is equivalent to a file name in
Expand the network range. Therefore, a URL is a pointer to any accessible object on a machine connected to the Internet. General URL format: <protocol >://< host >:< port >/< path>, FTP-File Transfer Protocol FTP http-Hypertext Transfer protocol HTTP news-Usenet News host is the host's domain name 5. HTTP: the protocol used for interaction between the World Wide Web Client Program and the World Wide Web server program. It is the hypertext transfer protocol HTTP (Hypertext Transfer Protocol ). HTTP is an application layer protocol, which uses
TCP connection for reliable transmission. There are two types of HTTP packets: 1) request packets-Send request packets from the customer to the server. 2) Response Message-the answer from the server to the customer. A packet consists of three parts, that is, the start
Line, header line, and entity body. In the request message, the start line is the request line. 6. Cookies: Web sites use cookies to track users. Cookie indicates the status information transmitted between the HTTP server and the customer. The website server that uses cookies generates a unique identifier for the user. Use this knowledge
The website will be able to track the activities of the user on the website. 7. html: The markup in HTML indicates "set markup ". HTML defines many commands (TAGS) for typographical layout ). Only when the HTML document is suffixed with .htmlor .htm
8. Search Engine: The program used for searching in the World Wide Web is called a search engine. There are two types of search engines: 1) full-text search engine and 2) classification Directory Search Engine. 9. Full-text search engine principle: full-text search engine is a pure technical retrieval tool. It works by searching for software to collect information from various websites on the Internet. After finding a website, you can relink it to another website.
To another website. Then, a large online database is created according to certain rules for users to query. When querying, you only need to enter keywords to query the created index database (not in real time because
Information found on the IOT platform ). 10. classification Directory Search: The classification Directory Search engine does not collect any information about a website. Instead, it uses the keywords and website descriptions entered when each website submits website information to the search engine, after being manually reviewed and edited
To meet the website login conditions, enter the database in the category directory for online user query. Classification Directory Search is also called classification website search 6 Network Management 1. simple Network Management Protocol (SNMP): 2. 5 features of Network Management: 1) fault management 2) Configuration Management 3) billing management 4) Performance management 5) Security management 3. management Information Library (MIB) and management information structure (SMI ). MiB is a tree structure with 10 categories. Managed objects are all objects under these categories. See: http://wenku.baidu.com/view/9017d2c2aa00b52acfc7cadb.html? Edu_search = true ### http://wenku.baidu.com/view/6aab2a234b35eefdc8d33385.html? Edu_search = true ###
