# Networks

Four Layers of TCP/IP model.

{:.warning}

# TCP/IP

# Model

# TCP&UDP

Tips: HOST means Domain or IP address.

TCP(20bits) and UDP(8bits) could use a same port in a host without conflict.、

# FTP

FTP is often secured with SSL/TLS(FTPS) or SFTP.

FTP通信中使用两条TCP连接：

• 控制
• 数据传输

FTP uses multiple TCP connections:

• control channel(port 21)
• data channel(port 20)

# HTTP

# Request and Response

Request:

GET /hello.txt HTTP/1.1
Host: www.mysite.com
Accept-Language: en

Response:

# TCP socket

Code in Github

Note that if the client is the type of str, the encode() it:

message = "Current time is " + str(dt)
conn.send(message.encode())