Shulou(Shulou.com)06/03 Report--

Transport layer protocol, application layer protocol

I. Transport layer protocol

1. Overview of the transport layer

(1) the role of the transport layer

The IP layer provides point-to-point connectivity

The transport layer provides end-to-end connectivity

(2) Transport layer protocol

TCP (Transmission Control Protocol) Transmission Control Protocol

Reliable, connection-oriented protocol; low transmission efficiency

UDP (User Datagram Protocol) user Datagram Protocol

Unreliable, connectionless service

High transmission efficiency

2. TCP protocol (reliably)

0-1023 is a commonly used port number, which has been occupied. The custom port number is more than 1024, and the maximum value is 65535.

(1) encapsulation format of TCP

(2) connection and disconnection of TCP

TCP connection-three-way handshake

Disconnection of TCP-four disconnections

(3) flow control and error control of TCP

Flow Control Mechanism of TCP-- sliding window

Flow Control Mechanism of TCP-congestion Control

Three ways of error Control in TCP

-- checksum

-- confirm

-- timeout

(4) timer of TCP

① TCP retransmission timer-to control lost segments

② TCP persistence timer-to prevent zero window deadlock

③ TCP's keep-alive timer-prevents long periods of idle between two TCP connections

Time waiting timer for ④ TCP-used during connection termination, when the last ACK is sent, the connection is not closed immediately

Instead, wait for a period of time to ensure that duplicate FIN segments are received.

(5) the application of TCP

Port number protocol function

21 FTP File transfer Protocol for file upload and download

23 Telnet is used for remote login by connecting to this port of the target computer

After verification, the target computer can be remotely controlled and managed.

25 SMTP simple Mail transfer Protocol for sending messages

53 DNS domain name service, when the user enters the name of the website, DNS is responsible for resolving him to the IP address

80 HTTP hypertext transfer protocol, through HTTP to achieve the transmission of hypertext on the network

3. UDP protocol

(1) encapsulation format of UDP

(2) Application of UDP

Port number protocol description

53 DNS Domain name Service

69 TFTP simple File transfer Protocol

123NTP Network time Protocol

111RPC remote procedure call

(3) flow control and error control of UDP

UDP has no flow control mechanism.

UDP only has checksum to provide error control.

-upper layer protocols are required to provide error control: for example, TFTP protocol

Overview of the application layer

1. The role of the application layer

Work with applications to exchange application-specific data using the basic network

2. Common application layer protocols

-DNS

-SMTP and POP3

-HTTP and HTTPS

-Telnet

-FTP and TFTP

III. Detailed presentation of application layer protocols

1. DNS (Domain Name System) domain name system

Function: used to complete the mapping between domain name and IP address

Port number: Port 53 of TCP or UDP

Distributed, hierarchical

Domain name spatial structure

-- Root domain

-- Top level domain

-- second-level domain name

FQDN = hostname + .DNS suffix

Universal domain

2. SMTP and POP3

-SMTP (Simple Mail Transfer Protocol) simple Mail transfer Protocol

Function: for sending and receiving mail

The port number is 25.

-POP3 (Post Office Protocol V3) Post Office Protocol version 3

Function: for clients to receive mail

The port number is 110

3. HTTP and HTTPS

-HTTP (Hyper Text Transfer Protocol) Hypertext transfer Protocol

Function: used to transmit data such as normal version, hypertext, audio and video used by Internet browser

The port number is 80 of TCP

-HTTPS secure Hypertext transfer Protocol

Role: based on HTTP development, provide encryption, can ensure the privacy and integrity of messages

The port number is 443

4. FTP and TFTP

-FTP (File Transfer Protocol) File transfer Protocol

The most widely used file transfer application

Ports 20 and 21 with port numbers of TCP

-TFTP (Trivial File Transfer Protocol) simple File transfer Protocol

Used to transfer some trivial small files

Port 69 with port number UDP

5. The working principle of FTP

-- Control connection: TCP 21, used to send FTP command information

-- data connection: TCP 20 for uploading and downloading data

-types of data connection establishment: active mode and passive mode

6. The working principle of TFTP

-- data transmission occurs between connection establishment and termination

-- the file is divided into several blocks

Each block is 512 bytes

The last piece must be between 0 and 511.

-- guarantee the reliability of file transfer

Flow control and error control are provided by TFTP itself

7. Telnet (Terminal Network) terminal network application

Remotely manage a computer or router / switch via text

The port number is 23 of TCP

8. Telnet configuration command

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