1. Briefly describe the osi seven-layer model and the TCP/IP five-layer model
(1) OSI seven layer model
: from the top down to
the application layer
the application layer (Application Layer) provides for the application software set of interfaces to set up communication between the application and another. For example: HTTP, HTTPS, FTP, TELNET, SSH, SMTP, POP3, MySQL, etc.
Presentation layer
function: convert data into a format compatible with the receiver's system format and suitable for transmission.
Session layer
function: communication management, responsible for establishing and disconnecting communication connections.
Transport layer
function: Manage data transmission between two nodes, responsible for reliable transmission (to ensure reliable data transmission to the target address). Data transmission unit: segment
network layer
function: address management and routing, addressing by IP address. Data transmission unit: message (packet)
data link layer
function: responsible for network addressing, error detection and correction, and realize the conversion between data frame and bit stream. It is divided into two sub-layers: logical link control (logical link control). Link control, LLC) sublayer and media access control (Media access control, MAC) sublayer. Addressing by MAC address, data unit: frame
physical layer:
function: to realize the conversion of the signal of the communication medium to the digital signal, responsible for the connection of the physical device, with 0 and 1 representing the voltage level, defining the specifications of the connector and the network cable, Data unit: 0101 bit stream
(2) The five-layer TCP/IP model from
top to bottom is:
Application layer,
Transport layer,
Interent layer,
Data link layer,
Physical layer
(3) Comparison of OSI seven-layer model and TCP/IP five-layer model
2. Summarize and describe TCP three-way handshake and four waved hands
(1) Three-way handshake
client ---> server message: SYN=1, seq=x
server ---> client message: SYN=1, ACK=1, seq=y, ack=x+1
client End--->Server message: ACK=1, seq=x+1, ack=Y+1
(2) Wave the
active party four times --->Passive message FIN=1 seq=m, ack=n
passive Party ---> Active Party Message ACK=1 seq=n, ack=m+1
Passive Party ---> Active Party Message FIN=1, ACK=1 seq=n, ack=m+1
Actively Release--- >Passive party message ACK=1,seq=m+1,ack=n+1
Both the server and the client can be the active party, whoever disconnects actively is the active party
3. Describe the difference between TCP and UDP
